13C tracer recovery in human stools after digestion of a fat-rich meal labelled with [1,1,1-13C3]tripalmitin and [1,1,1-13C3]triolein

Bridging the Gap from Enterotypes to Personalized Dietary Recommendations: A Metabolomics Perspective on Microbiome Research

Advances in high-throughput DNA sequencing have propelled research into the human microbiome and its link to metabolic health. We explore microbiome analysis methods, specifically emphasizing metabolomics, how dietary choices impact the production of microbial metabolites, providing an overview of studies examining the connection between enterotypes and diet, and thus, improvement of personalized dietary recommendations. Acetate, propionate, and butyrate constitute more than 95% of the collective pool of short-chain fatty acids. Conflicting data on acetate's effects may result from its dynamic signaling, which can vary depending on physiological conditions and metabolic phenotypes. Human studies suggest that propionate has overall anti-obesity effects due to its well-documented chemistry, cellular signaling mechanisms, and various clinical benefits. Butyrate, similar to propionate, has the ability to reduce obesity by stimulating the release of appetite-suppressing hormones and promoting the synthesis of leptin. Tryptophan affects systemic hormone secretion, with indole stimulating the release of GLP-1, which impacts insulin secretion, appetite suppression, and gastric emptying. Bile acids, synthesized from cholesterol in the liver and subsequently modified by gut bacteria, play an essential role in the digestion and absorption of dietary fats and fat-soluble vitamins, but they also interact directly with intestinal microbiota and their metabolites. One study using statistical methods identified primarily two groupings of enterotypes Bacteroides and Ruminococcus. The Prevotella-dominated enterotype, P-type, in humans correlates with vegetarians, high-fiber and carbohydrate-rich diets, and traditional diets. Conversely, individuals who consume diets rich in animal fats and proteins, typical in Western-style diets, often exhibit the Bacteroides-dominated, B-type, enterotype. The P-type showcases efficient hydrolytic enzymes for plant fiber degradation but has limited lipid and protein fermentation capacity. Conversely, the B-type features specialized enzymes tailored for the degradation of animal-derived carbohydrates and proteins, showcasing an enhanced saccharolytic and proteolytic potential. Generally, models excel at predictions but often struggle to fully elucidate why certain substances yield varied responses. These studies provide valuable insights into the potential for personalized dietary recommendations based on enterotypes.

The Effects of the Mediterranean Diet on Health and Gut Microbiota

The Mediterranean Diet (MD) is plant-based and consists of multiple daily portions of vegetables, fruit, cereals, and olive oil. Although there are challenges with isolating the MD from the typical Mediterranean lifestyle and culture (including prolonged 'social' meals and siestas), much evidence supports the health benefits of the MD that include improved longevity, reduced metabolic risk of Diabetes Mellitus, obesity, and Metabolic Syndrome, reduced risk of malignancy and cardiovascular disease, and improved cognitive function. The MD is also associated with characteristic modifications to gut microbiota, mediated through its constituent parts (primarily dietary fibres, extra virgin olive oil, and polyunsaturated fatty acids [including ω-3]). These include enhanced growth of species that produce short-chain fatty acids (butyrate), such as Clostridium leptum and Eubacterium rectale, enhanced growth of Bifidobacteria, Bacteroides, and Faecalibacterium prausnitzii species, and reduced growth of Firmicutes and Blautia species. Such changes in gut microbiota are known to be associated favourably with inflammatory and oxidative status, propensity for malignancy and overall metabolic health. A key challenge for the future is to explore the extent to which the health benefits of the MD are mediated by such changes to gut microbiota. The MD confers both health and environmental benefits. Adoption of the MD should perhaps be encouraged and facilitated more generally and not just restricted to populations from Mediterranean regions. However, there are key challenges to this approach that include limited perennial availability of the constituent parts of the MD in some non-Mediterranean regions, intolerability of a high-fibre diet for some people, and potential cultural disconnects that juxtapose some traditional (including Western) diets with the MD.

Vitamin A Deficiency during the Perinatal Period and First Weeks of Life Modifies Vitamin A and Lipid Postprandial Metabolism in Both Female and Male Young Rats

SCOPE

The effect of vitamin A deficiency on vitamin A and lipid postprandial metabolism in young rats is addressed, considering the effect of sex.

METHODS AND RESULTS

Sprague-Dawley rats are fed either 400 UI.kg^-1 vitamin A diet (vitamin A-deficient (VAD) diet) or 2300 UI.kg^-1 vitamin A (control diet), before being mated. Mothers receive the same VAD or control diet during gestation and lactation. Offspring receive the same diet than mothers until 8 weeks of age. VAD diet-fed female and male offspring display a severe vitamin A deficiency with no body weight or glucose tolerance defects. Fasting plasma triglyceride concentrations are decreased in VAD diet-fed animals compared to controls (p < 0.05). Retinyl ester postprandial responses after vitamin A gavage, expressed as area under the curves, are not different in VAD diet-fed and control animals, although retinyl ester postprandial peak is significantly delayed (p < 0.05) in VAD diet-fed rats. Lipids also accumulate in the distal part of the intestine after gavage and [1-¹³ C]-oleate postprandial response is decreased in VAD diet-fed males.

CONCLUSION

Vitamin A deficiency modulates both vitamin A absorption rate and lipid postprandial metabolism, which can partly explain the altered fasting lipid status observed in VAD diet-fed offspring.

Human intestinal lipid storage through sequential meals reveals faster dinner appearance is associated with hyperlipidemia

Background

It is increasingly recognized that intestinal cells can store lipids after a meal, yet the effect of this phenomenon on lipid absorption patterns in insulin resistance remains unknown.

Methods

The kinetics of meal fat appearance were measured in insulin-sensitive (IS, n = 8) and insulin-resistant (IR, n = 8) subjects after sequential, isotopically labeled lunch and dinner meals. Plasma dynamics on triacylglycerol-rich (TAG-rich) lipoproteins and plasma hormones were analyzed using a nonlinear, non–steady state kinetic model.

Results

At the onset of dinner, IS subjects showed an abrupt plasma appearance of lunch lipid consistent with the “second-meal effect,” followed by slower appearance of dinner fat in plasma, resulting in reduced accumulation of dinner TAG of 48% compared with lunch. By contrast, IR subjects exhibited faster meal TAG appearance rates after both lunch and dinner. This effect of lower enterocyte storage between meals was associated with greater nocturnal and next-morning hyperlipidemia. The biochemical data and the kinetic analysis of second-meal effect dynamics are consistent with rapid secretion of stored TAG bypassing lipolysis and resynthesis. In addition, the data are consistent with a role for the diurnal pattern of plasma leptin in regulating the processing of dietary lipid.

Conclusion

These data support the concept that intestinal lipid storage may be physiologically beneficial in IS subjects.

Trial registration

ClinicalTrials.gov NCT02020343.

Funding

This study was supported by a grant from the American Diabetes Association (grant 1-13-TS-12).

The link among microbiota, epigenetics, and disease development

The microbiome is a community of various microorganisms that inhabit or live on the skin of humans/animals, sharing the body space with their hosts. It is a sort of complex ecosystem of trillions of commensals, symbiotic, and pathogenic microorganisms, including trillions of bacteria, archaea, protozoa, fungi, and viruses. The microbiota plays a role in the health and disease status of the host. Their number, species dominance, and viability are dynamic. Their long-term disturbance is usually accompanied by serious diseases such as metabolic disorders, cardiovascular diseases, or even cancer. While epigenetics is a term that refers to different stimuli that induce modifications in gene expression patterns without structural changes in the inherited DNA sequence, these changes can be reversible or even persist for several generations. Epigenetics can be described as cell memory that stores experience against internal and external factors. Results from multiple institutions have contributed to the role and close interaction of both microbiota and epigenetics in disease induction. Understanding the mechanisms of both players enables a better understanding of disease induction and development and also opens the horizon to revolutionary therapeutic approaches. The present review illustrates the roles of diet, microbiome, and epigenetics in the induction of several chronic diseases. In addition, it discusses the application of epigenetic data to develop diagnostic biomarkers and therapeutics and evaluate their safety for patients. Understanding the interaction among all these elements enables the development of innovative preventive/therapeutic approaches for disease control.

High-throughput LC-MS method to investigate postprandial lipemia: considerations for future precision nutrition research

Elevated postprandial lipemia is an independent risk factor for cardiovascular disease, yet methods to quantitate postmeal handling of dietary lipids in humans are limited. This study tested a new method to track dietary lipid appearance using a stable isotope tracer (²H₁₁-oleate) in liquid meals containing three levels of fat [low fat (LF), 15 g; moderate fat (MF), 30 g; high fat (HF), 60 g]. Meals were fed to 12 healthy men [means ± SD, age 31.3 ± 9.2 yr, body mass index (BMI) 24.5 ± 1.9 kg/m²] during four randomized study visits; the HF meal was administered twice for reproducibility. Blood was collected over 8 h postprandially, triglyceride (TG)-rich lipoproteins (TRL), and particles with a Svedberg flotation rate >400 (S_f > 400, n = 8) were isolated by ultracentrifugation, and labeling of two TG species (54:3 and 52:2) was quantified by LC-MS. Total plasma TRL-TG concentrations were threefold greater than S_f > 400-TG. Both S_f > 400- and TRL-TG 54:3 were present at higher concentrations than 52:2, and singly labeled TG concentrations were higher than doubly labeled. Furthermore, TG 54:3 and the singly labeled molecules demonstrated higher plasma absolute entry rates differing significantly across fat levels within a single TG species (P < 0.01). Calculation of fractional entry showed no significant differences in label handling supporting the utility of either TG species for appearance rate calculations. These data demonstrate the utility of labeling research meals with stable isotopes to investigate human postprandial lipemia while simultaneously highlighting the importance of examining individual responses. Meal type and timing, control of prestudy activities, and effects of sex on outcomes should match the research goals. The method, optimized here, will be beneficial to conduct basic science research in precision nutrition and clinical drug development.NEW & NOTEWORTHY A novel method to test human intestinal lipid handling using stable isotope labeling is presented and, for the first time, plasma appearance and lipid turnover were quantified in 12 healthy men following meals with varying amounts of fat. The method can be applied to studies in precision nutrition characterizing individual response to support basic science research or drug development. This report discusses key questions for consideration in precision nutrition that were highlighted by the data.

High-Fat Diets Led to OTU-Level Shifts in Fecal Samples of Healthy Adult Dogs

High fat diets have been reported to negatively affect the microbiota in both mice and humans. However, there is a lack of studies in canine models. The variation among the gastrointestinal (GI) tract anatomy/physiology and typical diet compositions of these animal species may lead to vastly different results. Due to the large inclusion rate of dietary fat in pet food, it is critical to understand its effects in a canine model. Therefore, the study objective was to report the effects of high fat, low carbohydrate diets on the fecal microbiota in healthy adult dogs. Eight adult beagles were randomly assigned to one of four dietary treatments within each 15-day period of a replicated 4x4 Latin Square design. Diets contained 32% (T1), 37% (T2), 42% (T3), and 47% (T4) fat. T2, T3, and T4 were created by adding increasing levels of canola oil to T1, a commercially manufactured canned canine diet, which served as the control diet. Fresh fecal samples were collected during the last 5 days of each period for microbial analysis. DNA was extracted from fecal samples and paired-end 16S rRNA gene amplicon sequencing was performed using the Illumina MiSeq platform. When comparing whole microbial communities using PERMANOVA, no significant differences were observed among treatments (P = 0.735). Individual OTUs were analyzed using the GLIMMIX procedure of SAS with fixed effects of diet and room, and the random effects of period and animal. Out of the 100 most abundant individual OTUs, 36 showed significant differences in abundance based on treatment (q < 0.05). Overall, OTUs assigned to genera related to fat digestion increased while OTUs assigned to genera involved in carbohydrate digestion decreased. In conclusion, the microbial community adapted to dietary intervention without jeopardizing the health of the animals, evaluated by body condition score, fecal characteristics, and blood parameters.

Effect of the ingestion of vegetable oils associated with energy-restricted normofat diet on intestinal microbiota and permeability in overweight women

Previous studies suggest that the type of dietary fatty acid may modulate the intestinal bacterial ecosystem. However, this effect is still inconclusive. Thus, the aim of this study was to investigate the effect of the intake of vegetable oils rich in different types of fatty acids, associated with energy-restricted normofat diets, on the composition of intestinal microbiota and permeability, on LPS concentrations, and fecal short chain fatty acids and pH. This was a 9 consecutive weeks (±5 days), randomized, parallel, double-blind clinical trial. Overweight women received daily breakfast containing 25 mL of one of the test oils: soybean oil (n = 17), extra virgin olive oil (n = 19) or coconut oil (n = 16). Blood, fecal and urine samples were collected on the first and last day of the experiment for the analysis of the variables of interest. The consumption of the three oils did not affect the diversity and relative abundance of intestinal bacteria. We observed an increase in bacterial richness estimated by the Chao 1 index, and a reduction in the concentration of isovaleric fatty acid in the group that ingested soybean oil. Paracellular and transcellular permeability increased after the ingestion of extra virgin olive oil and coconut oil. However, LPS concentrations remained unchanged. The intake of different types of fatty acids associated with the energy-restricted normofat diet modestly affected the intestinal microbiota and permeability, without resulting in metabolic endotoxemia in overweight women.

Probiotic from human breast milk, Lactobacillus fermentum, promotes growth in animal model of chronic malnutrition

BACKGROUND

Chronic undernutrition leads to growth hormone resistance and poor growth in children, which has been shown to be modulated by microbiota. We studied whether Lactobacillus fermentum CECT5716 (Lf ^CECT5716), isolated from mother's breast milk, could promote juvenile growth through the modulation of lipid absorption in a model of starvation.

METHODS

Germ-free (GF) Drosophila melanogaster larvae were inoculated with Lf ^CECT5716 in conditions of undernutrition with and without infant formula. The impact of Lf ^CECT5716 on larval growth was assessed 7 days after egg laying (AED) by measuring the larval size and on maturation by measuring the emergence of pupae during 21 days AED. For lipid absorption test, Caco2/TC7 intestinal cells were incubated with Lf ^CECT5716 and challenged with mixed lipid micelles.

RESULTS

The mono-associated larvae with Lf ^CECT5716 were significantly longer than GF larvae (3.7 vs 2.5 mm; p < 0.0001). The effect was maintained when Lf ^CECT5716 was added to the infant formula. The maturation time of larvae was accelerated by Lf ^CECT5716 (12 vs 13.2 days; p = 0.01). Lf ^CECT5716 did not have significant impact on lipid absorption in Caco2/TC7 cells.

CONCLUSIONS

Lf ^CECT5716 is a growth-promoting strain upon undernutrition in Drosophila, with a maintained effect when added to an infant formula but without effect on lipid absorption in vitro.

Microbiota and Lifestyle: A Special Focus on Diet

It is widely known that a good balance and healthy function for bacteria groups in the colon are necessary to maintain homeostasis and preserve health. However, the lack of consensus on what defines a healthy gut microbiota and the multitude of factors that influence human gut microbiota composition complicate the development of appropriate dietary recommendations for our gut microbiota. Furthermore, the varied response to the intake of probiotics and prebiotics observed in healthy adults suggests the existence of potential inter- and intra-individual factors, which might account for gut microbiota changes to a greater extent than diet. The changing dietary habits worldwide involving consumption of processed foods containing artificial ingredients, such as sweeteners; the coincident rise in emotional disorders; and the worsening of other lifestyle habits, such as smoking habits, drug consumption, and sleep, can together contribute to gut dysbiosis and health impairment, as well as the development of chronic diseases. This review summarizes the current literature on the effects of specific dietary ingredients (probiotics, prebiotics, alcohol, refined sugars and sweeteners, fats) in the gut microbiota of healthy adults and the potential inter- and intra-individual factors involved, as well as the influence of other potential lifestyle factors that are dramatically increasing nowadays.

Linoleic acid inhibits Lactobacillus activity by destroying cell membrane and affecting normal metabolism

BACKGROUND

The reason why dietary polyunsaturated fatty acids (PUFAs) affect the activity of Lactobacillus remains unclear. In this study, linoleic acid was used to study the mechanism underlying its inhibition function against Lactobacillus activity.

RESULTS

The growth curve of Lactobacillus rhamnosus LGG and the metabolite content in bacterial liquid were determined at varying linoleic acid concentration. The degree of cell membrane damage of L. rhamnosus LGG was determined by flow cytometry and fluorescence microscopy, and the cell structure was observed by scanning electron microscopy and transmission electron microscopy. The effect of linoleic acid on Lactobacillus activity was assessed in a simulated gut environment. Results showed that L. rhamnosus LGG grew slowly, cell metabolites leaked into the liquid, cell membrane was damaged, and the cell structure changed at a linoleic acid concentration of 50 μg mL^-1 .

CONCLUSION

The mechanism of action of linoleic acid on Lactobacillus showed that that linoleic acid destroyed the cell membrane of bacteria, thereby affecting the normal metabolism of the bacteria and ultimately leading to their death. © 2019 Society of Chemical Industry.

Docosahexaenoic Acid (DHA) Bioavailability in Humans after Oral Intake of DHA-Containing Triacylglycerol or the Structured Phospholipid AceDoPC®

AceDoPC^® is a structured glycerophospholipid that targets the brain with docosahexaenoic acid (DHA) and is neuroprotective in the experimental ischemic stroke. AceDoPC^® is a stabilized form of the physiological 2-DHA-LysoPC with an acetyl group at the sn1 position; preventing the migration of DHA from the sn2 to sn1 position. In this study we aimed to know the bioavailability of ¹³C-labeled DHA after oral intake of a single dose of ¹³C-AceDoPC^®, in comparison with ¹³C-DHA in triglycerides (TAG), using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) to assess the ¹³C enrichment of DHA-containing lipids. ¹³C-DHA enrichment in plasma phospholipids was significantly higher after intake of AceDoPC^® compared with TAG-DHA, peaking after 24 h in both cases. In red cells, ¹³C-DHA enrichment in choline phospholipids was comparable from both sources of DHA, with a maximum after 72 h, whereas the ¹³C-DHA enrichment in ethanolamine phospholipids was higher from AceDoPC^® compared to TAG-DHA, and continued to increase after 144 h. Overall, our study indicates that DHA from AceDoPC^® is more efficient than from TAG-DHA for a sustained accumulation in red cell ethanolamine phospholipids, which has been associated with increased brain accretion.

In vitro digestion of complex foods: How microstructure influences food disintegration and micronutrient bioaccessibility

Digestion is a mechanical and chemical process that is only partly understood, and even less so for complex foods. In particular, the issue of the impact of food structure on the digestion process is still unresolved. In this study, the fate of four micronutrient-enriched foods with identical compositions but different microstructures (Custard, Pudding, Sponge cake, Biscuit) was investigated using the 3-phase in vitro model of human digestion developed by the INFOGEST network. Matrix disintegration and hydrolysis of macronutrients (proteins, lipids and carbohydrates) were monitored during the three phases of digestion using biochemical techniques, size-exclusion chromatography, thin-layer chromatography and gas chromatography. Micronutrient release (vitamin B9 and lutein) was monitored using reverse-phase chromatography. Food structure did not greatly influence macronutrient hydrolysis, except for lipolysis that was four-times higher for Biscuit compared to Custard. However, the bioaccessibility of both micronutrients depended on the food structure and on the micronutrient. Vitamin B9 release was faster for Biscuit and Sponge cake during the gastric phase, whereas lutein release was higher for Custard during the intestinal step. Extensive statistical analysis highlighted the impact of food structure on the digestion process, with different digestion pathways depending on the food matrix. It also made it possible to characterise the gastric step as a predominantly macronutrient solubilisation phase, and the intestinal step as a predominantly hydrolysis phase.

Neuroactive compounds in foods: Occurrence, mechanism and potential health effects

Neuroactive compounds are synthesized by certain plants and microorganisms by undertaking different tasks, especially as a stress response. Most common neuroactive compounds in foods are gamma-aminobutyric acid (GABA), serotonin, melatonin, kynurenine, kynurenic acid, dopamine, norepinephrine, histamine, tryptamine, tyramine and β-phenylethylamine. Fermented foods contain some of these compounds, which can affect human health and mood. Moreover, food processing such as roasting and malting alter amount and profile of neuroactive compounds in foods. In addition to plant-origin and microbially-formed neuroactive compounds in foods, these substances are also formed by gut microbiota, which is the most attractive subject to assess the interaction between gut microbiota and mental health. The discovery of microbiota-gut-brain axis calls for the investigation of the effects of diet on the formation of neuroactive compounds in the gut. Furthermore, probiotics and prebiotics are indispensable elements for the understanding of the food-mood relationship. The focus of this comprehensive review is to investigate the neuroactive compounds found naturally in foods or formed during fermentation. Their formation pathways in humans, plants and microorganisms, potential health effects, effects of diet on the formation of microbial metabolites including neuroactive compounds in the gut are discussed throughout this review. Furthermore, the importance of gut-brain axis, probiotics and prebiotics are discussed.

Homogeneous triacylglycerol tracers have an impact on the thermal and structural properties of dietary fat and its lipolysis rate under simulated physiological conditions

Dietary fats are present in the diet under different types of structures, such as spread vs emulsions (notably in processed foods and enteral formula), and interest is growing regarding their digestion and intestinal absorption. In clinical trials, there is often a need to add stable isotope-labeled triacylglycerols (TAGs) as tracers to the ingested fat in order to track its intestinal absorption and further metabolic fate. Because most TAG tracers contain saturated fatty acids, they may modify the physicochemical properties of the ingested labeled fat and thereby its digestion. However, the actual impact of tracer addition on fat crystalline properties and lipolysis by digestive lipases still deserves to be explored. In this context, we monitored the thermal and polymorphic behavior of anhydrous milk fat (AMF) enriched in homogeneous TAGs tracers and further compared it with the native AMF using differential scanning calorimetry and power X-ray diffraction. As tracers, we used a mixture of tripalmitin, triolein and tricaprylin at 2 different concentrations (1.5 and 5.7 wt%, which have been used in clinical trials). The addition of TAG tracers modified the AMF melting profile, especially at the highest tested concentration (5.7 wt%). Both AMF and AMF enriched with 1.5 wt% tracers were completely melted around 37 °C, i.e. close to the body temperature, while the AMF enriched with 5.7 wt% tracers remained partially crystallized at this temperature. Similar trends were observed in both bulk and emulsified systems. Moreover, the kinetics of AMF polymorphic transformation was modified in the presence of tracers. While only β' form was observed in the native AMF, the β-form was clearly detected in the AMF containing 5.7 wt% tracers. We further tested the impact of tracers on the lipolysis of AMF in bulk using a static in vitro model of duodenal digestion. Lipolysis of AMF enriched with 5.7 wt% tracers was delayed compared with that of AMF and AMF enriched with 1.5 wt% tracers. Therefore, low amounts of TAG tracers including tripalmitin do not have a high impact on fat digestion, but one has to be cautious when using higher amounts of these tracers.

Impact of a Healthy Dietary Pattern on Gut Microbiota and Systemic Inflammation in Humans

Gut microbiota have recently been suggested to play a part in low-grade systemic inflammation, which is considered a key risk factor for cardiometabolic disorders. Diet is known to affect gut microbiota; however, the effects of diet and dietary components on gut microbiota and inflammation are not fully understood. In the present review, we summarize recent research on human dietary intervention studies, investigating the effects of healthy diets or dietary components on gut microbiota and systemic inflammation. We included 18 studies that reported how different dietary components altered gut microbiota composition, short-chain fatty acid levels, and/or inflammatory markers. However, the heterogeneity among the intervention studies makes it difficult to conclude whether diets or dietary components affect gut microbiota homeostasis and inflammation. More appropriately designed studies are needed to better understand the effects of diet on the gut microbiota, systemic inflammation, and risk of cardiometabolic disorders.

3D Chemical Shift-Encoded MRI for Volume and Composition Quantification of Abdominal Adipose Tissue During an Overfeeding Protocol in Healthy Volunteers

BACKGROUND

Overweight and obesity are major worldwide health concerns characterized by an abnormal accumulation of fat in adipose tissue (AT) and liver.

PURPOSE

To evaluate the volume and the fatty acid (FA) composition of the subcutaneous adipose tissue (SAT) and the visceral adipose tissue (VAT) and the fat content in the liver from 3D chemical-shift-encoded (CSE)-MRI acquisition, before and after a 31-day overfeeding protocol.

STUDY TYPE

Prospective and longitudinal study.

SUBJECTS

Twenty-one nonobese healthy male volunteers.

FIELD STRENGTH/SEQUENCE

A 3D spoiled-gradient multiple echo sequence and STEAM sequence were performed at 3T.

ASSESSMENT

AT volume was automatically segmented on CSE-MRI between L2 to L4 lumbar vertebrae and compared to the dual-energy X-ray absorptiometry (DEXA) measurement. CSE-MRI and MR spectroscopy (MRS) data were analyzed to assess the proton density fat fraction (PDFF) in the liver and the FA composition in SAT and VAT. Gas chromatography-mass spectrometry (GC-MS) analyses were performed on 13 SAT samples as a FA composition countermeasure.

STATISTICAL TESTS

Paired t-test, Pearson's correlation coefficient, and Bland-Altman plots were used to compare measurements.

RESULTS

SAT and VAT volumes significantly increased (P < 0.001). CSE-MRI and DEXA measurements were strongly correlated (r = 0.98, P < 0.001). PDFF significantly increased in the liver (+1.35, P = 0.002 for CSE-MRI, + 1.74, P = 0.002 for MRS). FA composition of SAT and VAT appeared to be consistent between localized-MRS and CSE-MRI (on whole segmented volume) measurements. A significant difference between SAT and VAT FA composition was found (P < 0.001 for CSE-MRI, P = 0.001 for MRS). MRS and CSE-MRI measurements of the FA composition were correlated with the GC-MS results (for ndb: r_MRS/GC-MS  = 0.83 P < 0.001, r_{CSE-MRI/GC-MS}  = 0.84, P = 0.001; for nmidb: r_MRS/GC-MS  = 0.74, P = 0.006, r_{CSE-MRI/GC-MS}  = 0.66, P = 0.020) DATA CONCLUSION: The follow-up of liver PDFF, volume, and FA composition of AT during an overfeeding diet was demonstrated through different methods. The CSE-MRI sequence associated with a dedicated postprocessing was found reliable for such quantification.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1587-1599.

Impact of dietary compounds on cancer-related gut microbiota and microRNA

Cancer is one of the most common causes of death worldwide. Extensive research has been conducted on cancer; regardless, the link between cancer and diet remains undetermined. Recent studies have emphasized the importance of miRNAs in cancer-associated pathways from the perspective of dietary modulation. We highlighted the recent data on dietary modulation of gut microbiota and miRNAs related to cancer on the basis of recently published results. The targets of miRNAs are oncogenes or tumor suppressors that mediate the progression and initiation of carcinogenesis. Different miRNAs display complex expression profiles in response to dietary manipulation. Various dietary components, such as fatty acids, resveratrol, isothiocyanate, and curcumin, have been effectively used in cancer prevention and treatment. This potency is attributed to the capability of these components to alter miRNA expression, thereby modulating the vital pathways involved in metastasis, invasion, apoptosis, tumor growth, and cell proliferation.

Diet, the intestinal microbiota, and immune health in aging

Many countries are facing aging populations, with those over 65 years of age likely to represent the largest population over the next 10-20 years. Living longer often comes with poor health and, in particular, a decline in the immune function characterized by poor vaccine responses and increased risk of infection and certain cancers. Aging and diet represent major intrinsic and extrinsic factors that influence the makeup and activity of resident intestinal microbes, the microbiota, the efficient functioning of which is essential for sustaining overall health and the effectiveness of the immune system. The provision of elderly specific dietary recommendations appears to be lacking but is necessary since this population has an altered microbiota and immune response and may not respond in the same way as their healthy and younger counterparts. We have reviewed the evidence supporting the role of diet and, in particular, dietary carbohydrate, protein, and fat in influencing the microbiota and its generation of key metabolites that influence the efficient functioning of immune cells during aging, and how dietary intervention might be of benefit in improving the intestinal health and immune status in the elderly.

Impact of dietary fat on gut microbiota and low-grade systemic inflammation: mechanisms and clinical implications on obesity

Dietary fat strongly affects human health by modulating gut microbiota composition and low-grade systemic inflammation. High-fat diets have been implicated in reduced gut microbiota richness, increased Firmicutes to Bacteroidetes ratio, and several changes at family, genus and species levels. Saturated (SFA), monounsaturated (MUFA), polyunsaturated (PUFA) and conjugated linolenic fatty acids share important pathways of immune system activation/inhibition with gut microbes, modulating obesogenic and proinflammatory profiles. Mechanisms that link dietary fat, gut microbiota and obesity are mediated by increased intestinal permeability, systemic endotoxemia, and the activity of the endocannabinoid system. Although the probiotic therapy could be a complementary strategy to improve gut microbiota composition, it did not show permanent effects to treat fat-induced dysbiosis. Based upon evidence to date, we believe that high-fat diets and SFA consumption should be avoided, and MUFA and omega-3 PUFA intake should be encouraged in order to regulate gut microbiota and inflammation, promoting body weight/fat control.

Foodomics as part of the host-microbiota-exposome interplay

The functional complexity of human gut microbiota and its relationship with host physiology and environmental modulating factors, offers the opportunity to investigate (i) the host and microbiota role in organism-environment relationship; (ii) the individual functional diversity and response to environmental stimuli (exposome); (iii) the host genome and microbiota metagenomes' modifications by diet-mediated epigenomic controls (nutriepigenomics); and (iv) the genotype-phenotype "trajectories" under physiological and disease constraints. Systems biology-based approaches aim at integrating biological data at cellular, tissue and organ organization levels, using computational modeling to interpret diseases' physiopathological mechanisms (i.e., onset and progression). Proteomics improves the existing gene models by profiling molecular phenotypes at protein abundance level, by analyzing post-translational modifications and protein-protein interactions and providing specific pathway information, hence contributing to functional molecular networks. Transcriptomics and metabolomics may determine host ad microbiota changes induced by food ingredients at molecular level, complementing functional genomics and proteomics data. Since foodomics is an -omic wide methodology may feed back all integrative data to foster the omics-based systems medicine field. Hence, coupled to ecological genomics of gut microbial communities, foodomics may highlight health benefits from nutrients, dissecting diet-induced gut microbiota eubiosis mechanisms and significantly contributing to understand and prevent complex disease phenotypes.

BIOLOGICAL SIGNIFICANCE

Besides transcriptomics and proteomics there is a growing interest in applying metabolic profiling to food science for the development of functional foods. Indeed, one of the biggest challenges of modern nutrition is to propose a healthy diet to populations worldwide, intrinsically respecting the high inter-individual variability, driven by complex host/nutrients/microbiota/environment interactions. Therefore, metabolic profiling can assist at various levels for the development of functional foods, starting from screening for food composition to identification of new biomarkers to trace food intake. This current approach can support diet intervention strategies, epidemiological studies, and controlling of metabolic disorders worldwide spreading, hence ensuring healthy aging. With high-throughput molecular technologies driving foodomics, studying bidirectional interactions of host-microbial co-metabolism, innate immune development, dysfunctional nutrient absorption and processing, complex signaling pathways involved in nutritional metabolism, is now likely. In all cases, as microbiome pipeline efforts continue, it is possible that enhanced standardized protocols can be developed, which may lead to new testable biological and clinical hypotheses. This Review provides a comprehensive update on the current state-of-the-art of the integrated -omics route in food, microbiota and host co-metabolism studies, which may revolutionize the design of new dietary intervention strategies.

Dietary emulsifiers from milk and soybean differently impact adiposity and inflammation in association with modulation of colonic goblet cells in high-fat fed mice

SCOPE

Enhanced adiposity and metabolic inflammation are major features of obesity that could be impacted by dietary emulsifiers. We investigated in high-fat fed mice the effects of using a new polar lipid (PL) emulsifier from milk (MPL) instead of soybean lecithin (soybean PL [SPL]) on adipose tissue and intestinal mucosa function.

METHODS AND RESULTS

Four groups of C57BL6 mice received for 8 wks a low-fat (LF) diet or a high-fat diet devoid of PLs or an high-fat diet including MPL (high-fat-MPL) or SPL (high-fat-SPL). Compared with high-fat diet, high-fat-SPL diet increased white adipose tissue (WAT) mass (p < 0.05), with larger adipocytes (p < 0.05) and increased expression of tumor necrosis factor alpha, monochemoattractant protein-1, LPS-binding protein, and leptin (p < 0.05). This was not observed with high-fat-MPL diet despite similar dietary intakes and increased expression of fatty acid transport protein 4 and microsomal TG transfer protein, involved in lipid absorption, in upper intestine (p < 0.05). High-fat-MPL mice had a lower expression in WAT of cluster of differentiation 68, marker of macrophage infiltration, versus high-fat and high-fat-SPL mice (p < 0.05), and more goblet cells in the colon (p < 0.05).

CONCLUSIONS

Unlike SPL, MPL in the high-fat diet did not induce WAT hypertrophy and inflammation but increased colonic goblet cells. This supports further clinical exploration of different sources of dietary emulsifiers in the frame of obesity outbreak.

Association between the gut microbiota and diet: Fetal life, early childhood, and further life

Gut microbiota establishment and further microbiota shifts are very important for maintaining host health throughout life. There are some factors, including genetics, the mother's health and diet, delivery mode, breast or formula feeding, that may influence the gut microbiota. By the end of approximately the first 3 y of life, the gut microbiota becomes an adult-like stable system. Once established, 60 to 70% of the microbiota composition remains stable throughout life, but 30 to 40% can be altered by changes in the diet and other factors such as physical activity, lifestyle, bacterial infections, and antibiotic or surgical treatment. Diet-related factors that influence the gut microbiota in people of all ages are of great interest. Nutrition may have therapeutic success in gut microbiota correction. This review describes current evidence concerning the links between gut microbiota composition and dietary patterns throughout life.

Diet, the gut microbiome, and epigenetics

Increasingly, the gut microbiome is implicated in the etiology of cancer, not only as an infectious agent but also by altering exposure to dietary compounds that influence disease risk. Whereas the composition and metabolism of the gut microbiome is influenced by diet, the gut microbiome can also modify dietary exposures in ways that are beneficial or detrimental to the human host. The colonic bacteria metabolize macronutrients, either as specialists or in consortia of bacteria, in a variety of diverse metabolic pathways. Microbial metabolites of diet can also be epigenetic activators of gene expression that may influence cancer risk in humans. Epigenetics involves heritable changes in gene expression via post-translational and post-transcriptional modifications. Microbial metabolites can influence epigenetics by altering the pool of compounds used for modification or by directly inhibiting enzymes involved in epigenetic pathways. Colonic epithelium is immediately exposed to these metabolites, although some metabolites are also found in systemic circulation. In this review, we discuss the role of the gut microbiome in dietary metabolism and how microbial metabolites may influence gene expression linked to colon cancer risk.

Evidence for greater production of colonic short-chain fatty acids in overweight than lean humans

BACKGROUND

Short-chain fatty acids (SCFA) are produced by colonic microbiota from dietary carbohydrates and proteins that reach the colon. It has been suggested that SCFA may promote obesity via increased colonic energy availability. Recent studies suggest obese humans have higher faecal SCFA than lean, but it is unclear whether this difference is due to increased SCFA production or reduced absorption.

OBJECTIVES

To compare rectal SCFA absorption, dietary intake and faecal microbial profile in lean (LN) versus overweight and obese (OWO) individuals.

DESIGN

Eleven LN and eleven OWO individuals completed a 3-day diet record, provided a fresh faecal sample and had SCFA absorption measured using the rectal dialysis bag method. The procedures were repeated after 2 weeks.

RESULTS

Age-adjusted faecal SCFA concentration was significantly higher in OWO than LN individuals (81.3±7.4 vs 64.1±10.4 mmol kg(-1), P=0.023). SCFA absorption (24.4±0.8% vs 24.7±1.2%, respectively, P=0.787) and dietary intakes were similar between the groups, except for a higher fat intake in OWO individuals. However, fat intake did not correlate with SCFAs or bacterial abundance. OWO individuals had higher relative Firmicutes abundance (83.1±4.1 vs 69.5±5.8%, respectively, P=0.008) and a higher Firmicutes:Bacteriodetes ratio (P=0.023) than LN individuals. There was a positive correlation between Firmicutes and faecal SCFA within the whole group (r=0.507, P=0.044), with a stronger correlation after adjusting for available carbohydrate (r=0.615, P=0.005).

CONCLUSIONS

The higher faecal SCFA in OWO individuals is not because of differences in SCFA absorption or diet. Our results are consistent with the hypothesis that OWO individuals produce more colonic SCFA than LN individuals because of differences in colonic microbiota. However, further studies are needed to prove this.

Elucidating the interactions between the human gut microbiota and its host through metabolic modeling

Increased understanding of the interactions between the gut microbiota, diet and environmental effects may allow us to design efficient treatment strategies for addressing global health problems. Existence of symbiotic microorganisms in the human gut provides different functions for the host such as conversion of nutrients, training of the immune system, and resistance to pathogens. The gut microbiome also plays an influential role in maintaining human health, and it is a potential target for prevention and treatment of common disorders including obesity, type 2 diabetes, and atherosclerosis. Due to the extreme complexity of such disorders, it is necessary to develop mathematical models for deciphering the role of its individual elements as well as the entire system and such models may assist in better understanding of the interactions between the bacteria in the human gut and the host by use of genome-scale metabolic models (GEMs). Recently, GEMs have been employed to explore the interactions between predominant bacteria in the gut ecosystems. Additionally, these models enabled analysis of the contribution of each species to the overall metabolism of the microbiota through the integration of omics data. The outcome of these studies can be used for proposing optimal conditions for desired microbiome phenotypes. Here, we review the recent progress and challenges for elucidating the interactions between the human gut microbiota and host through metabolic modeling. We discuss how these models may provide scaffolds for analyzing high-throughput data, developing probiotics and prebiotics, evaluating the effects of probiotics and prebiotics and eventually designing clinical interventions.

Beneficial modulation of the gut microbiota

The human gut microbiota comprises approximately 100 trillion microbial cells and has a significant effect on many aspects of human physiology including metabolism, nutrient absorption and immune function. Disruption of this population has been implicated in many conditions and diseases, including examples such as obesity, inflammatory bowel disease and colorectal cancer that are highlighted in this review. A logical extension of these observations suggests that the manipulation of the gut microbiota can be employed to prevent or treat these conditions. Thus, here we highlight a variety of options, including the use of changes in diet (including the use of prebiotics), antimicrobial-based intervention, probiotics and faecal microbiota transplantation, and discuss their relative merits with respect to modulating the intestinal community in a beneficial way.

Modulating absorption and postprandial handling of dietary fatty acids by structuring fat in the meal: a randomized crossover clinical trial

BACKGROUND

Prolonged postprandial hypertriglyceridemia is a potential risk factor for cardiovascular diseases. In the context of obesity, this is associated with a chronic imbalance of lipid partitioning oriented toward storage and not toward β-oxidation.

OBJECTIVE

We tested the hypothesis that the physical structure of fat in a meal can modify the absorption, chylomicron transport, and further metabolic handling of dietary fatty acids.

DESIGN

Nine normal-weight and 9 obese subjects were fed 40 g milk fat (+[(13)C]triacylglycerols), either emulsified or nonemulsified, in breakfasts of identical composition. We measured the postprandial triacylglycerol content and size of the chylomicron-rich fraction, plasma kinetics of [(13)C]fatty acids, exogenous lipid oxidation with breath-test/indirect calorimetry, and fecal excretion.

RESULTS

The emulsified fat resulted in earlier (>1 h) and sharper chylomicron and [(13)C]fatty acid peaks in plasma than in spread fat in both groups (P < 0.0001). After 2 h, the emulsified fat resulted in greater apolipoprotein B-48 concentrations (9.7 ± 0.7 compared with 7.1 ± 0.9 mg/L; P < 0.05) in the normal-weight subjects than did the spread fat. In the obese subjects, emulsified fat resulted in a 3-fold greater chylomicron size (218 ± 24 nm) compared with the spread fat (P < 0.05). The emulsified fat induced higher dietary fatty acid spillover in plasma and a sharper (13)CO(2) appearance, which provoked increased exogenous lipid oxidation in each group: from 45% to 52% in normal-weight subjects (P < 0.05) and from 40% to 57% in obese subjects (P < 0.01).

CONCLUSION

This study supports a new concept of "slow vs fast fat," whereby intestinal absorption can be modulated by structuring dietary fat to modulate postprandial lipemia and lipid β-oxidation in humans with different BMIs. This trial was registered at clinicaltrials.gov as NCT01249378.

The influence of diet on the gut microbiota

Diet is a major factor driving the composition and metabolism of the colonic microbiota. The amount, type and balance of the main dietary macronutrients (carbohydrates, proteins and fats) have a great impact on the large intestinal microbiota. The human colon contains a dense population of bacterial cells that outnumber host cells 10-fold. Bacteroidetes, Firmicutes and Actinobacteria are the three major phyla that inhabit the human large intestine and these bacteria possess a fascinating array of enzymes that can degrade complex dietary substrates. Certain colonic bacteria are able to metabolise a remarkable variety of substrates whilst other species carry out more specialised activities, including primary degradation of plant cell walls. Microbial metabolism of dietary carbohydrates results mainly in the formation of short chain fatty acids and gases. The major bacterial fermentation products are acetate, propionate and butyrate; and the production of these tends to lower the colonic pH. These weak acids influence the microbial composition and directly affect host health, with butyrate the preferred energy source for the colonocytes. Certain bacterial species in the colon survive by cross-feeding, using either the breakdown products of complex carbohydrate degradation or fermentation products such as lactic acid for growth. Microbial protein metabolism results in additional fermentation products, some of which are potentially harmful to host health. The current 'omic era promises rapid progress towards understanding how diet can be used to modulate the composition and metabolism of the gut microbiota, allowing researchers to provide informed advice, that should improve long-term health status.