The fructose survival hypothesis for obesity

The Hepatic Axis Fructose-Methylglyoxal-AMPK: Starring or Secondary Role in Chronic Metabolic Disease?

Biochemical alterations linked to metabolic syndrome (MetS), type 2 diabetes (T2DM), and metabolic dysfunction-associated steatotic liver disease (MASLD) may be brought on by the Western diet. Based on research conducted over the past decade, fructose is one of the main culprits. Over 80% of ingested fructose is metabolized by the liver at first pass, where it stimulates de novo lipogenesis (DNL) to drive hepatic triglyceride (TG) synthesis, which contributes to MASLD, hepatic insulin resistance (IR), and dyslipidemia. Fructose reduction produces quick and significant amelioration in these metabolic disturbances. We hereby propose potential overarching processes that can link these pathways to signaling disruption by the critical metabolic sensor AMP-activated protein kinase (AMPK). We proffer that when large amounts of fructose and glucose enter the liver, triose fluxes may be sufficient to produce transient increases in methylglyoxal (MG), allowing steady-state concentrations between its production and catabolism by glyoxalases to be high enough to modify AMPK-sensitive functional amino acid residues. These reactions would transiently interfere with AMPK activation by both AMP and aldolase. Such a sequence of events would boost the well-documented lipogenic impact of fructose. Given that MG adducts are irreversible, modified AMPK molecules would be less effective in metabolite sensing until they were replaced by synthesis. If proven, this mechanism provides another avenue of possibilities to tackle the problem of fructose in our diet. We additionally discuss potential multimodal treatments and future research avenues for this apparent hepatic AMPK malfunction.

Exploring Glyoxalase Strategies for Managing Sugar-Induced Chronic Diseases

The liver's crucial role in methylglyoxal (MG) metabolism is frequently overlooked in the literature. We present a perspective that enhances the current understanding of the role of methylglyoxal (MG) and the glyoxalase cycle in the pathogenesis of insulin resistance and obesity, ultimately leading to type 2 diabetes mellitus (DM) and cardiovascular disease (CVD). Fructose may be a significant substrate contributing, particularly in contemporary times, to the flux of trioses in the liver, accounting for a substantial portion of MG production. The steady-state concentration of MG-and the subsequent modification of proteins-would then be determined by the flux of trioses, their utilization in lipogenesis, and their decomposition into MG, which is further converted into D-lactate by glyoxalase enzymes GLO1 and GLO2. Consequently, enhancing the activity and/or expression of GLO1 could potentially mitigate the adverse effects of fructose in the liver. Additional research and validation are required to confirm these biological pathways. These arguments are in favor of further research into safe and efficient ways to activate the glyoxalase pathway to lessen the negative effects of fructose metabolism that lead to insulin resistance (IR) and its related repercussions.

Fructose activates a stress response shared by methylglyoxal and hydrogen peroxide in Streptococcus mutans

Fructose catabolism by Streptococcus mutans is initiated by three phosphotransferase (PTS) transporters yielding fructose-1-phosphate (F-1-P) or fructose-6-phosphate. Deletion of one such F-1-P-generating PTS, fruI, was shown to reduce the cariogenicity of S. mutans in rats fed a high-sucrose diet. Moreover, a recent study linked fructose metabolism in S. mutans to a reactive electrophile species methylglyoxal. Here, we conducted a comparative transcriptomic analysis of S. mutans treated briefly with 50 mM fructose, 50 mM glucose, 5 mM methylglyoxal, or 0.5 mM hydrogen peroxide (H2O2). The results revealed a striking overlap between the fructose and methylglyoxal transcriptomes, totaling 176 genes, 61 of which were also shared with the H2O2 transcriptome. This core of 61 genes encompassed many of the same pathways affected by exposure to low pH or zinc intoxication. Consistent with these findings, fructose negatively impacted the metal homeostasis of a mutant deficient in zinc expulsion and the growth of a mutant of the major oxidative stress regulator SpxA1. Importantly, fructose metabolism lowered culture pH at a faster pace, allowed better survival under acidic and nutrient-depleted conditions, and enhanced the competitiveness of S. mutans against Streptococcus sanguinis, although a moderated level of F-1-P might further boost some of these benefits. Conversely, several commensal streptococcal species displayed a greater sensitivity to fructose that may negatively affect their persistence and competitiveness in dental biofilm. In conclusion, fructose metabolism is integrated into the stress core of S. mutans and regulates critical functions required for survival and its ability to induce dysbiosis in the oral cavity.IMPORTANCEFructose is a common monosaccharide in the biosphere, yet its overconsumption has been linked to various health problems in humans including insulin resistance, obesity, diabetes, non-alcoholic liver diseases, and even cancer. These effects are in large part attributable to the unique biochemical characteristics and metabolic responses associated with the degradation of fructose. Yet, an understanding of the effects of fructose on the physiology of bacteria and its implications for the human microbiome is severely lacking. Here, we performed a series of analyses on the gene regulation of a dental pathogen Streptococcus mutans by exposing it to fructose and other important stress agents. Further supported by growth, persistence, and competition assays, our findings revealed the ability of fructose to activate a set of stress-related functions that may prove critical to the ability of the bacterium to persist and cause diseases both within and without the oral cavity.

FRUCTOSE ACTIVATES A STRESS RESPONSE SHARED BY METHYLGLYOXAL AND HYDROGEN PEROXIDE IN STREPTOCOCCUS MUTANS

Fructose catabolism by Streptococcus mutans is initiated by three PTS transporters yielding either fructose-1-phoshate (F-1-P) or fructose-6-phosphate (F-6-P). Deletion of one such F-1-P-generating PTS, fruI, has been shown to reduce the cariogenicity of S. mutans in rats fed a high-sucrose diet. Moreover, a recent study linked fructose metabolism in S. mutans to a reactive electrophile species (RES) methylglyoxal. Here, we conducted a comparative transcriptomic analysis of exponentially grown S. mutans shocked with 50 mM fructose, 50 mM glucose, 5 mM methylglyoxal, or 0.5 mM hydrogen peroxide (H2O2). The results revealed a striking overlap between the fructose and methylglyoxal transcriptomes, totaling 176 genes, 61 of which were also shared with the H2O2 transcriptome. This core of 61 genes encompassed many of the same pathways affected by exposure to low pH or zinc intoxication. Consistent with these findings, fructose negatively impacted metal homeostasis of a mutant deficient in zinc expulsion and the growth of a mutant of the major oxidative stress regulator SpxA1. We further demonstrated the induction of the superoxide dismutase (sodA) and the fruRKI operon by different levels of fructose. Finally, fructose metabolism lowered culture pH at a faster pace, allowed better survival under acidic and nutrient-depleted conditions, and enhanced the competitiveness of S. mutans against Streptococcus sanguinis, although a moderated level of F-1-P might further boost some of these benefits. In conclusion, fructose metabolism is integrated into the stress core of S. mutans and regulates critical functions required for survival in both the oral cavity and during systemic infections. Importance. Fructose is a common monosaccharide in the biosphere, yet its overconsumption has been linked to various health problems in humans including insulin resistance, obesity, diabetes, and non-alcoholic liver diseases. These effects are in large part attributed to the unique biochemical characteristics and metabolic responses associated with the degradation of fructose. Yet, an understanding of the effects of fructose on the physiology of bacteria and its implications to the human microbiome is severely lacking. Here we performed a series of analyses on the gene regulation of a dental pathogen Streptococcus mutans by exposing it to fructose and other important stress agents. Further supported by growth, persistence, and competition assays, our findings revealed the ability of fructose to activate a set of cellular functions that may prove critical to the ability of the bacterium to persist and cause diseases both within and without of the oral cavity.

A Comprehensive Review of Metabolic Dysfunction-Associated Steatotic Liver Disease: Its Mechanistic Development Focusing on Methylglyoxal and Counterbalancing Treatment Strategies

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial disorder characterized by excessive lipid accumulation in the liver which dysregulates the organ's function. The key contributor to MASLD development is insulin resistance (IR) which affects many organs (including adipose tissue, skeletal muscles, and the liver), whereas the molecular background is associated with oxidative, nitrosative, and carbonyl stress. Among molecules responsible for carbonyl stress effects, methylglyoxal (MGO) seems to play a major pathological function. MGO-a by-product of glycolysis, fructolysis, and lipolysis (from glycerol and fatty acids-derived ketone bodies)-is implicated in hyperglycemia, hyperlipidemia, obesity, type 2 diabetes, hypertension, and cardiovascular diseases. Its causative effect in the stimulation of prooxidative and proinflammatory pathways has been well documented. Since metabolic dysregulation leading to these pathologies promotes MASLD, the role of MGO in MASLD is addressed in this review. Potential MGO participation in the mechanism of MASLD development is discussed in regard to its role in different signaling routes leading to pathological events accelerating the disorder. Moreover, treatment strategies including approved and potential therapies in MASLD are overviewed and discussed in this review. Among them, medications aimed at attenuating MGO-induced pathological processes are addressed.

The Rhesus Macaque as an Animal Model for Human Nutrition: An Ecological-Evolutionary Perspective

Nutrition is a complex and contested area in biomedicine, which requires diverse evidence sources. Nonhuman primate models are considered an important biomedical research tool because of their biological similarities to humans, but they are typically used with little explicit consideration of their ecology and evolution. Using the rhesus macaque (RM), we consider the potential of nutritional ecology for enriching the use of primates as models for human nutrition. We introduce some relevant aspects of RM evolutionary and social ecology and discuss two examples where they have been used in biomedical research: obesity and aging. We next consider how insights from nutritional ecology can help inform and direct the use of RM as a biomedical model. We conclude by illustrating how conceptual tools might inform the use of RM as a model for human nutrition and extracting insights from RM that might be relevant to broader theoretical considerations around animal model systems.

Macronutrient interactions and models of obesity: Insights from nutritional geometry

The global obesity epidemic results from a complex interplay of genetic and environmental factors, with diet being a prominent modifiable element driving weight gain and adiposity. Although excess intake of energetic macronutrients is implicated in causing obesity, ongoing debate centers on whether sugar or fat or both are driving the rising obesity rates. This has led to competing models of obesity such as the "Carbohydrate Insulin Model", the "Energy Balance Model", and the "Fructose Survival Hypothesis". Conflicting evidence from studies designed to focus on individual energetic macronutrients or energy rather than macronutrient mixtures underlies this disagreement. Recent research in humans and animals employing the nutritional geometry framework (NGF) emphasizes the importance of considering interactions among dietary components. Protein interacts with carbohydrates, fats, and dietary energy density to influence both calorie intake ("protein leverage") and, directly and indirectly, metabolic physiology and adiposity. Consideration of these interactions can help to reconcile different models of obesity, and potentially cast new light on obesity interventions.

Inter-organ metabolic interaction networks in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multisystem metabolic disorder, marked by abnormal lipid accumulation and intricate inter-organ interactions, which contribute to systemic metabolic imbalances. NAFLD may progress through several stages, including simple steatosis (NAFL), non-alcoholic steatohepatitis (NASH), cirrhosis, and potentially liver cancer. This disease is closely associated with metabolic disorders driven by overnutrition, with key pathological processes including lipid dysregulation, impaired lipid autophagy, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and local inflammation. While hepatic lipid metabolism in NAFLD is well-documented, further research into inter-organ communication mechanisms is crucial for a deeper understanding of NAFLD progression. This review delves into intrahepatic networks and tissue-specific signaling mediators involved in NAFLD pathogenesis, emphasizing their impact on distal organs.

Pacific Islands Families Study: Serum Uric Acid in Pacific Youth and the Associations with Free-Sugar Intake and Appendicular Skeletal Muscle Mass

BACKGROUND

Fructose (50% of sucrose/sugar) is one component of free-sugars and is metabolized to uric acid, which is a known risk factor for gout and metabolic syndrome. Pacific peoples in New Zealand experience a higher prevalence of gout, type 2 diabetes, and overweight/obesity than other ethnic groups. Interestingly, despite having a similar body mass index (BMI), they tend to have a higher proportion of appendicular skeletal muscle mass (ASMM) and less fat than other ethnic groups. Given this context, this study aimed to evaluate the associations between serum uric acid (SUA), free-sugar intake, and ASMM.

METHODS

In a nested sub-study from the Pacific Islands Families birth-cohort study, 101 boys and 99 girls (all aged 14 and 15 years) self-reported how often they had consumed foods containing sugar in the past month. Anthropometry, body fatness, and ASMM by dual-energy X-ray absorptiometry and metabolic risk factors, including SUA were measured.

RESULTS

Overall, 43% of girls and 57% of boys consumed 'sugary drinks' twice or more a day. When analyzed by group, ASMM was positively related to SUA for both boys and girls (r = 0.593, p < 0.0001). The effect of the intake of 'sugary drinks' on SUA (r = 0.176, p = 0.013) was reduced when ASMM was considered in the relationships.

CONCLUSIONS

This study shows high SUA levels in Pacific adolescents, with a positive association between ASMM and SUA in both genders. Sugary drink intake was positively associated with SUA in both boys and girls. High ASMM in Pacific people and an increased risk for raised SUA make it important to work with Pacific communities to reduce added sugar intake and adopt integrated, family-based, culturally centered, and life-course approaches to prevent chronic diseases, including gout.

High glucose combined with lipopolysaccharide stimulation inhibits cell proliferation and migration of human HaCaT keratinocytes by impacting redox homeostasis and activating the polyol pathway

BACKGROUND

High glucose level and chronic inflammation are characteristic features of diabetic cutaneous wounds. Keratinocytes make up the epidermis and play an important role in skin repair. However, metabolomic changes of keratinocytes in chronic diabetic ulcers have not been fully studied.

METHODS AND RESULTS

This study used high levels of glucose combined with lipopolysaccharide to treat human HaCaT keratinocytes. Untargeted metabolomic combined with colorimetric assays were used to explore the changes of keratinocyte metabolites and related metabolic pathways caused by high glucose and lipopolysaccharide. Results demonstrated that high glucose combined with lipopolysaccharide treatment increased intracellular reactive oxygen species and impaired proliferation and migration of keratinocytes. Untargeted metabolomics analysis identified a total of 273 differential metabolites. Redox metabolism associated metabolites were largely altered. Reduced nicotinamide adenine dinucleotide, gamma-glutamylcysteine, superoxide dismutase activity and SOD2 gene expression were significantly upregulated while nicotinamide adenine dinucleotide, glutathione, glutathione peroxidase, several types of lysophosphatidylcholine, lysophosphatidylinositol, and GPR55 gene expression were downregulated. Alterations of glutathione and nicotinamide adenine dinucleotide were verified by colorimetric assays. For the first time, high glucose and LPS were observed to boost the levels of fructose, aldose reductase and sorbitol dehydrogenase of the polyol pathway in HaCaT cells. Further treatment of HaCaT with fructose leading to inhibition of cell proliferation and migration.

CONCLUSIONS

Our data suggest high glucose combined with lipopolysaccharide significantly altered redox homeostasis associated metabolites and activate the polyol pathway in keratinocytes to impact cell proliferation and migration, providing new strategies for the treatment of chronic diabetic ulcers.

Trigger Warning: How Modern Diet, Lifestyle, and Environment Pull the Trigger on Autosomal Dominant Polycystic Kidney Disease Progression

Understanding chronic kidney disease (CKD) through the lens of evolutionary biology highlights the mismatch between our Paleolithic-optimized genes and modern diets, which led to the dramatically increased prevalence of CKD in modern societies. In particular, the Standard American Diet (SAD), high in carbohydrates and ultra-processed foods, causes conditions like type 2 diabetes (T2D), chronic inflammation, and hypertension, leading to CKD. Autosomal dominant polycystic kidney disease (ADPKD), a genetic form of CKD, is characterized by progressive renal cystogenesis that leads to renal failure. This review challenges the fatalistic view of ADPKD as solely a genetic disease. We argue that, just like non-genetic CKD, modern dietary practices, lifestyle, and environmental exposures initiate and accelerate ADPKD progression. Evidence shows that carbohydrate overconsumption, hyperglycemia, and insulin resistance significantly impact renal health. Additionally, factors like dehydration, electrolyte imbalances, nephrotoxin exposure, gastrointestinal dysbiosis, and renal microcrystal formation exacerbate ADPKD. Conversely, carbohydrate restriction, ketogenic metabolic therapy (KMT), and antagonizing the lithogenic risk show promise in slowing ADPKD progression. Addressing disease triggers through dietary modifications and lifestyle changes offers a conservative, non-pharmacological strategy for disease modification in ADPKD. This comprehensive review underscores the urgency of integrating diet and lifestyle factors into the clinical management of ADPKD to mitigate disease progression, improve patient outcomes, and offer therapeutic choices that can be implemented worldwide at low or no cost to healthcare payers and patients.

Dietary fructose: from uric acid to a metabolic switch in pediatric metabolic dysfunction-associated steatotic liver disease

Fructose consumption in pediatric subjects is rising, as the prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). Despite increasing evidence supporting the detrimental effects of fructose in the development of Metabolic Syndrome (MetS) and its related comorbidities, the association between fructose intake and liver disease remains unclear, mainly in youths. The current narrative review aims to illustrate the correlation between fructose metabolism and liver functions besides its impact on obesity and MASLD in pediatrics. Fructose metabolism is involved in the liver through the classical lipogenic pathway via de novo lipogenesis (DNL) or in the alternative pathway via uric acid accumulation. Hyperuricemia is one of the main features of MALSD patients, underlining how uric acid is growing interest as a new marker of disease. Observational and interventional studies conducted in children and adolescents, who consumed large amounts of fructose and glucose in their diet, were included. Most of these studies emphasized the association between high fructose intake and weight gain, dyslipidemia, insulin resistance, and MASLD/MASH, even in normal-weight children. Conversely, reducing fructose intake ameliorates liver fat accumulation, lipid profile, and weight. In conclusion, fructose seems a potent inducer of both insulin resistance and hepatic fat accumulation.

Beneficial Effects of the Ketogenic Diet on Nonalcoholic Fatty Liver Disease (NAFLD/MAFLD)

The prevalence of nonalcoholic fatty liver disease (NAFLD) is likely to be approaching 38% of the world's population. It is predicted to become worse and is the main cause of morbidity and mortality due to hepatic pathologies. It is particularly worrying that NAFLD is increasingly diagnosed in children and is closely related, among other conditions, to insulin resistance and metabolic syndrome. Against this background is the concern that the awareness of patients with NAFLD is low; in one study, almost 96% of adult patients with NAFLD in the USA were not aware of their disease. Thus, studies on the therapeutic tools used to treat NAFLD are extremely important. One promising treatment is a well-formulated ketogenic diet (KD). The aim of this paper is to present a review of the available publications and the current state of knowledge of the effect of the KD on NAFLD. This paper includes characteristics of the key factors (from the point of view of NAFLD regression), on which ketogenic diet exerts its effects, i.e., reduction in insulin resistance and body weight, elimination of fructose and monosaccharides, limitation of the total carbohydrate intake, anti-inflammatory ketosis state, or modulation of gut microbiome and metabolome. In the context of the evidence for the effectiveness of the KD in the regression of NAFLD, this paper also suggests the important role of taking responsibility for one's own health through increasing self-monitoring and self-education.

Uncovering the Links Between Dietary Sugar and Cancer: A Narrative Review Exploring the Impact of Dietary Sugar and Fasting on Cancer Risk and Prevention

Over the last several years, the scientific community has grown concerned about the relationship between dietary sugar intake and cancer development. The main causes of concern are the increasing intake of processed foods rich in sugar and the rising incidence of cancer cases. This study aims to uncover the complex relationship between sugar consumption and cancer development and its progression, with a particular focus on investigating whether fasting can protect against this condition. Our review provides a detailed discussion of the molecular aspects of the sugar-cancer relationship and an analysis of the existing literature. It explains how sugar affects cell signaling, inflammation, and hormonal pathways associated with the development of cancer. We also explored the new role of fasting in the prevention of cancer and its impact on cancer patients. This encompasses fasting-triggered autophagy, metabolic alterations, and possible health benefits, which form the major concern of this paper. Thus, by deepening the knowledge of these relations and providing the results of the analysis accompanied by concise and meaningful illustrations to facilitate the understanding of the data, we open the door to the further development of ideas to minimize the rates of cancer and improve overall well-being.

Sex Differences Affect the NRF2 Signaling Pathway in the Early Phase of Liver Steatosis: A High-Fat-Diet-Fed Rat Model Supplemented with Liquid Fructose

Sex differences may play a role in the etiopathogenesis and severity of metabolic dysfunction-associated steatotic liver disease (MASLD), a disorder characterized by excessive fat accumulation associated with increased inflammation and oxidative stress. We previously observed the development of steatosis specifically in female rats fed a high-fat diet enriched with liquid fructose (HFHFr) for 12 weeks. The aim of this study was to better characterize the observed sex differences by focusing on the antioxidant and cytoprotective pathways related to the KEAP1/NRF2 axis. The KEAP1/NRF2 signaling pathway, autophagy process (LC3B and LAMP2), and endoplasmic reticulum stress response (XBP1) were analyzed in liver homogenates in male and female rats that were fed a 12-week HFHFr diet. In females, the HFHFr diet resulted in the initial activation of the KEAP1/NRF2 pathway, which was not followed by the modulation of downstream molecular targets; this was possibly due to the increase in KEAP1 levels preventing the nuclear translocation of NRF2 despite its cytosolic increase. Interestingly, while in both sexes the HFHFr diet resulted in an increase in the levels of LC3BII/LC3BI, a marker of autophagosome formation, only males showed a significant upregulation of LAMP2 and XBP1s; this did not occur in females, suggesting impaired autophagic flux in this sex. Overall, our results suggest that males are characterized by a greater ability to cope with an HFHFr metabolic stimulus mainly through an autophagic-mediated proteostatic process while in females, this is impaired. This might depend at least in part upon the fine modulation of the cytoprotective and antioxidant KEAP1/NRF2 pathway resulting in sex differences in the occurrence and severity of MASLD. These results should be considered to design effective therapeutics for MASLD.

The association between SII and aging: evidence from NHANES 1999-2018

Background

The study aimed to examine the association between the systemic immune-inflammation index (SII), a contemporary metric of systemic inflammatory response, and biological aging, which are closely interconnected processes.

Methods

This cross-sectional study utilized 10 cycles of data from the NHANES database spanning from 1990 to 2018. The study examined the relationship between the SII index, calculated as P * N/L, where P represents preoperative peripheral platelet count, N represents neutrophil count, and L represents lymphocyte count, and biological aging. Biological aging was assessed through various methods, such as phenotypic age, phenotypic age acceleration (PhenoAgeAccel), biological age, and biological age acceleration (BioAgeAccel). Correlations were analyzed using weighted linear regression and subgroup analysis.

Results

Among the 7,491 participants analyzed, the average age was 45.26 ± 0.34 years, with 52.16% being female. The average phenotypic and biological ages were 40.06 ± 0.36 and 45.89 ± 0.32 years, respectively. Following adjustment for potential confounders, elevated SII scores were linked to increased phenotypic age, biological age, Phenotypic age acceleration, and Biological age acceleration. Positive correlations were observed between health behavior and health factor scores and biological aging, with stronger associations seen for health factors. In health factor-specific analyses, the β coefficient was notably higher for high BMI. The robust positive associations between SII scores and both phenotypic age and biological age in the stratified analyses were consistently observed across all strata.

Conclusion

The evidence from the NHANES data indicate that SII may serve as a valuable marker for assessing different facets of aging and health outcomes, such as mortality and the aging process. Additional research is warranted to comprehensively elucidate the implications of SII in the aging process and its utility as a clinical instrument for evaluating and addressing age-related ailments.

Could Insulin Be a Better Regulator of Appetite/Satiety Balance and Body Weight Maintenance in Response to Glucose Exposure Compared to Sucrose Substitutes? Unraveling Current Knowledge and Searching for More Appropriate Choices

BACKGROUND

Insulin exerts a crucial impact on glucose control, cellular growing, function, and metabolism. It is partially modulated by nutrients, especially as a response to the intake of foods, including carbohydrates. Moreover, insulin can exert an anorexigenic effect when inserted into the hypothalamus of the brain, in which a complex network of an appetite/hunger control system occurs. The current literature review aims at thoroughly summarizing and scrutinizing whether insulin release in response to glucose exposure may be a better choice to control body weight gain and related diseases compared to the use of sucrose substitutes (SSs) in combination with a long-term, well-balanced diet.

METHODS

This is a comprehensive literature review, which was performed through searching in-depth for the most accurate scientific databases and applying effective and relevant keywords.

RESULTS

The insulin action can be inserted into the hypothalamic orexigenic/anorexigenic complex system, activating several anorexigenic peptides, increasing the hedonic aspect of food intake, and effectively controlling the human body weight. In contrast, SSs appear not to affect the orexigenic/anorexigenic complex system, resulting in more cases of uncontrolled body weight maintenance while also increasing the risk of developing related diseases.

CONCLUSIONS

Most evidence, mainly derived from in vitro and in vivo animal studies, has reinforced the insulin anorexigenic action in the hypothalamus of the brain. Simultaneously, most available clinical studies showed that SSs during a well-balanced diet either maintain or even increase body weight, which may indirectly be ascribed to the fact that they cannot cover the hedonic aspect of food intake. However, there is a strong demand for long-term longitudinal surveys to effectively specify the impact of SSs on human metabolic health.

Nicotinamide Mononucleotide (NMN) Works in Type 2 Diabetes through Unexpected Effects in Adipose Tissue, Not by Mitochondrial Biogenesis

Nicotinamide mononucleotide (NMN) has emerged as a promising therapeutic intervention for age-related disorders, including type 2 diabetes. In this study, we confirmed the previously observed effects of NMN treatment on glucose uptake and investigated its underlying mechanisms in various tissues and cell lines. Through the most comprehensive proteomic analysis to date, we discovered a series of novel organ-specific effects responsible for glucose uptake as measured by the IPGTT: adipose tissue growing (suggested by increased protein synthesis and degradation and mTOR proliferation signaling upregulation). Notably, we observed the upregulation of thermogenic UCP1, promoting enhanced glucose conversion to heat in intermuscular adipose tissue while showing a surprising repressive effect on mitochondrial biogenesis in muscle and the brain. Additionally, liver and muscle cells displayed a unique response, characterized by spliceosome downregulation and concurrent upregulation of chaperones, proteasomes, and ribosomes, leading to mildly impaired and energy-inefficient protein synthesis machinery. Furthermore, our findings revealed remarkable metabolic rewiring in the brain. This involved increased production of ketone bodies, downregulation of mitochondrial OXPHOS and TCA cycle components, as well as the induction of well-known fasting-associated effects. Collectively, our data elucidate the multifaceted nature of NMN action, highlighting its organ-specific effects and their role in improving glucose uptake. These findings deepen our understanding of NMN's therapeutic potential and pave the way for novel strategies in managing metabolic disorders.

The fructose survival hypothesis as a mechanism for unifying the various obesity hypotheses

The pathogenesis of obesity remains contested. Although genetics is important, the rapid rise in obesity with Western culture and diet suggests an environmental component. Today, some of the major hypotheses for obesity include the energy balance hypothesis, the carbohydrate-insulin model, the protein-leverage hypothesis, and the seed oil hypothesis. Each hypothesis has its own support, creating controversy over their respective roles in driving obesity. Here we propose that all hypotheses are largely correct and can be unified by another dietary hypothesis, the fructose survival hypothesis. Fructose is unique in resetting ATP levels to a lower level in the cell as a consequence of suppressing mitochondrial function, while blocking the replacement of ATP from fat. The low intracellular ATP levels result in carbohydrate-dependent hunger, impaired satiety (leptin resistance), and metabolic effects that result in the increased intake of energy-dense fats. This hypothesis emphasizes the unique role of carbohydrates in stimulating intake while fat provides the main source of energy. Thus, obesity is a disorder of energy metabolism, in which there is low usable energy (ATP) in the setting of elevated total energy. This leads to metabolic effects independent of excess energy while the excess energy drives weight gain.

Dietary Phospholipids Alleviate Diet-Induced Obesity in Mice: Which Fatty Acids and Which Polar Head

The weight loss effects of dietary phospholipids have been extensively studied. However, little attention has been paid to the influence of phospholipids (PLs) with different fatty acids and polar headgroups on the development of obesity. High-fat-diet-fed mice were administrated with different kinds of PLs (2%, w/w) with specific fatty acids and headgroups, including EPA-enriched phosphatidylcholine/phosphatidylethanolamine/phosphatidylserine (EPA-PC/PE/PS), DHA-PC/PE/PS, Egg-PC/PE/PS, and Soy-PC/PE/PS for eight weeks. Body weight, white adipose tissue weight, and the levels of serum lipid and inflammatory markers were measured. The expression of genes related to lipid metabolism in the liver were determined. The results showed that PLs decreased body weight, fat storage, and circulating lipid levels, and EPA-PLs had the best efficiency. Serum TNF-α, MCP-1 levels were significantly reduced via treatment with DHA-PLs and PS groups. Mechanistic investigation revealed that PLs, especially EPA-PLs and PSs, reduced fat accumulation through enhancing the expression of genes involved in fatty acid β-oxidation (Cpt1a, Cpt2, Cd36, and Acaa1a) and downregulating lipogenesis gene (Srebp1c, Scd1, Fas, and Acc) expression. These data suggest that EPA-PS exhibits the best effects among other PLs in terms of ameliorating obesity, which might be attributed to the fatty acid composition of phospholipids, as well as their headgroup.

Quantity and Variety of Fruit and Vegetable Intake with Changes in Measures of Adiposity among Community-Dwelling Chinese Older Adults

BACKGROUND

The association between fruit and vegetable intake, considering both quantity and variety, and weight change among older adults remains controversial. We aimed to investigate the association between fruit and vegetable intake, variety, and changes in adiposity measures among community-dwelling Chinese older adults.

METHODS

A total of 2944 participants aged ≥65 years from Hong Kong communities were included. Fruit and vegetable intake was estimated by a locally validated food frequency questionnaire. Adiposity measures (weight, body mass index (BMI), waist circumference, fat and lean mass) were assessed at baseline and the year four follow-up. Restricted cubic spline and logistic models were performed to estimate the associations between fruit and vegetable intake, variety, and changes in adiposity measures.

RESULTS

A nonlinear association between vegetable intake and weight change was found, following a J-shape curve. Increased vegetable intake was associated with less increases in weight, BMI, and fat mass among those below median intakes. However, these associations became insignificant at higher intakes (all P-nonlinearity < 0.05). The ORs (95% CIs) for weight gain across the quartiles of vegetable intake were as follows: 1.00 (reference), 0.81 (0.56, 1.17), 0.55 (0.36, 0.83), and 0.88 (0.58, 1.33). Similar patterns were observed in overweight and normal weight participants, but not in those with low body weight. No associations with weight change were found for fruit intake or fruit and vegetable variety.

CONCLUSIONS

Moderate vegetable intake was associated with less weight gain among community-dwelling Chinese older adults, but not in those with low body weight. No association was observed between fruit intake or variety with weight change.

Breaking down silos: the multifaceted nature of obesity and the future of weight management

The continued global increase in the prevalence of obesity prompted a meeting at the Royal Society of London investigating causal mechanisms of the disease, 'Causes of obesity: theories, conjectures, and evidence' in October 2022. Evidence presented indicates areas of obesity science where there have been advancements, including an increased understanding of biological and physiological processes of weight gain and maintenance, yet it is clear there is still debate on the relative contribution of plausible causes of the modern obesity epidemic. Consensus was reached that obesity is not a reflection of diminished willpower, but rather the confluence of multiple, complex factors. As such, addressing obesity requires multifactorial prevention and treatment strategies. The accumulated evidence suggests that a continued focus primarily on individual-level contributors will be suboptimal in promoting weight management at the population level. Here, we consider individual biological and physiological processes within the broader context of sociodemographic and sociocultural exposures as well as environmental changes to optimize research priorities and public health efforts. This requires a consideration of a systems-level approach that efficiently addresses both systemic and group-specific environmental determinants, including psychosocial factors, that often serve as a barrier to otherwise efficacious prevention and treatment options. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.