Mechanisms of increase in plasma triacylglycerol concentrations as a result of high carbohydrate intakes in patients with non-insulin-dependent diabetes mellitus

Association between adherence to a low carbohydrate dietary (LCD) pattern with breast milk characteristics and oxidative markers in infants' urine: a cross-sectional study

BACKGROUND

Breast milk (BM) is a dynamic fluid that varies over time and between women. The variations in BM components are most likely associated with maternal diet quality. This study aimed to assess adherence to a low carbohydrate dietary (LCD) pattern with oxidative stress markers of BM characteristics and infants' urine.

MATERIALS AND METHODS

In this cross-sectional study 350 breastfeeding mothers and their infants were recruited. BM samples were collected from mothers, and urine specimens were obtained from each infant. To evaluate LCD scores, subjects were divided into 10 deciles according to the percent of energy obtained from carbohydrates, proteins, and fats. Determination of total antioxidant activity was conducted using the ferric reducing antioxidant power (FRAP), 2, 2'-diphenyl-1-picrylhydrazyl (DPPH), thiobarbituric acid reactive substances (TBARs), and Ellman's assay. Biochemical assays of samples including calcium, total protein, and triglyceride level were also performed using commercial kits.

RESULTS

Participants with the greatest LCD pattern adherence were placed into the last quartile (Q4), and those with the minimum LCD were in the first quartile (Q1). Individuals in the highest LCD quartile had significantly higher levels of milk FRAP, thiol, and protein, as well as infant urinary FRAP and lower milk MDA levels than those in the lowest quartile. Multivariate linear regression analyses indicated that higher score of the LCD pattern was associated with a higher level of milk thiol, protein, and lower level of milk MDA (p < 0.05).

CONCLUSION

Our findings show that adherence to a LCD, as defined by a low level of carbohydrates in daily food intake, is linked with improved BM quality and markers of oxidative stress in infant urine.

The association between meal specific low carbohydrate diet score and cardiometabolic risk factors: A cross-sectional study of Iranian adults

BACKGROUND AND AIM

Since evidence regarding low-CHO diet and cardiometabolic risk factors is controversial, this study aimed to assess the relation between low-CHO diet score and metabolic syndrome (MetS) and cardiometabolic risk factors among a group of Iranian adults.

METHODS

This cross-sectional study was conducted with 840 subjects with the age range of 20-65 years. Dietary intakes were assessed by completing three 24-hour recalls. Total, animal- and vegetable-based low-CHO diet score were calculated. We used logistic regression with different models to determine whether there were relationships between low-CHO diet score and MetS and MetS components.

RESULTS

We found that there was no significant association between low-CHO diet, animal-based and vegetable-based low-CHO diet scores and risk of MetS in three meals. Except for the animal-based low-CHO diet score, which was significantly associated with general obesity at lunch meal (OR: 1.17, 95% CI: 0.76-1.82, P = .03). There were a significant association between low-CHO diet and high-density lipoprotein cholesterol (HDL-C) levels in lunch meal (OR: 1.50, 95% CI: 1.06-2.14, P = .03). Vegetable-based low-CHO diet score was associated with a lower risk of elevated TG in lunch meal in the fully adjusted model (OR: 0.59, 95% CI: 0.39-0.90, P = .04).

CONCLUSION

Diets with lower amounts of carbohydrate and higher contents of fat and protein were not significantly associated with the risk for MetS in Iranian adults. Only animal-based low-CHO diet score was significantly associated with general obesity at lunch meal.

The association between low-carbohydrate diet score and metabolic syndrome among Iranian adults

OBJECTIVE

Assessing the relationship between low-carbohydrate diet (LCD) score and metabolic syndrome (Mets) in Iranian adults.

DESIGN

Cross-sectional study.

SETTING

Yazd Health Study and Taghzieh Mardom-e-Yazd study.

PARTICIPANTS

Data of 2074 participants were used. Dietary intakes were assessed by a validated semi-quantitative FFQ. LCD score was calculated for each person by summing up the assigned scores to deciles of energy percentages from macronutrients. Mets was evaluated using National Cholesterol Education Program Adult Treatment Panel III. Eventually, association between LCD score and Mets was examined using logistic regression.

RESULTS

Total Mets prevalence was approximately 40·5 %. After adjustment for confounders, subjects in the higher quartile of LCD score had a significant lower chance of Mets than lower quartile among all participants (Q4 v. Q1: OR: 0·68, 95 % CI (0·50, 0·92)) and separately in men (Q4 v. Q1: OR: 0·54, 95 % CI (0·34, 0·86)) and women (Q2 v. Q1: OR: 0·53, 95 % CI (0·34, 0·82)). Furthermore, more LCD adherence in men reduced abdominal obesity by 47 % (Q3 v. Q1: OR: 0·53, 95 % CI (0·28, 0·99)). A significant inverse relation was also observed between low HDL cholesterol and LCD score in all participants (Q4 versus Q1 OR: 0·74, 95% CI: 0·56-0·99) and separately in men (Q4 versus Q1 OR: 0·63, 95% CI: 0·40-0·98).

CONCLUSIONS

More adherence to LCD might be related to lower chance of Mets and some of its components such as low HDL-cholesterol and abdominal obesity specially in men. Further studies are required to confirm the findings.

Dietary Impact on Postprandial Lipemia

Abnormalities in postprandial lipemia (PPL), particularly those related to triglyceride-rich lipoproteins, are considered an independent cardiovascular risk factor. As diet is known to be one of the main modulators of PPL, the aim of this review was to summarize and discuss current knowledge on the impact of diet and its components on PPL in humans; specifically, the impact of weight loss, different nutrients (quantity and quality of dietary fats, carbohydrates, and proteins), alcohol and other bioactive dietary components (i.e., polyphenols), as well as the effect of different dietary patterns. The possible mechanisms behind the metabolic effects of each dietary component were also discussed.

Effects of low-carbohydrate- compared with low-fat-diet interventions on metabolic control in people with type 2 diabetes: a systematic review including GRADE assessments

Background

It remains uncertain which diet is best for people with type 2 diabetes (T2D).

Objective

We compared the effects of dietary carbohydrate restriction with fat restriction on markers of metabolic syndrome and quality of life in people with T2D.

Design

This systematic review of randomized controlled trials (RCTs) and controlled clinical trials (CCTs) compares the effects of a low-carbohydrate [≤40% of energy (%)] diet with those of a low-fat (≤30%) diet over a period of ≥4 wk in patients with T2D. Two investigators independently selected studies, extracted data, and assessed risk of bias. The GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to assess the certainty of evidence. Pooled mean differences (MDs) and 95% CIs were calculated with the use of a random-effects model.

Results

Thirty-three RCTs and 3 CCTs (n = 2161) were included. Glycated hemoglobin declined more in people who consumed low-carbohydrate food than in those who consumed low-fat food in the short term (MD: -1.38%; 95% CI: -2.64%, -0.11%; very-low-certainty evidence). At 1 y, the MD was reduced to -0.36% (95% CI: -0.58%, -0.14%; low-certainty evidence); at 2 y, the difference had disappeared. There is low to high (majority moderate) certainty for small improvements of unclear clinical importance in plasma glucose, triglycerides, and HDL concentrations favoring low-carbohydrate food at half of the prespecified time points. There was little to no difference in LDL concentration or any of the secondary outcomes (body weight, waist circumference, blood pressure, quality of life) in response to either of the diets (very-low- to high-certainty evidence).

Conclusions

Currently available data provide low- to moderate-certainty evidence that dietary carbohydrate restriction to a maximum of 40% yields slightly better metabolic control of uncertain clinical importance than reduction in fat to a maximum of 30% in people with T2D. This systematic review is registered at http://www.crd.york.ac.uk/PROSPERO/display_record.php?ID=CRD42017052467 as CRD42017052467.

Does sucrose intake affect antropometric variables, glycemia, lipemia and C-reactive protein in subjects with type 1 diabetes?: a controlled-trial

BACKGROUND

It is unclear if the sugar intake may affect metabolic parameters in individuals with type 1 diabetes. Therefore, the purpose of this study was to evaluate the effects of sucrose intake in glycemic, lipemic, anthropometric variables, as well as in C-reactive protein (CRP) levels in these individuals.

METHODS

Thirty-three subjects with type 1 diabetes were evaluated at baseline and 3-months after intervention. Volunteers were randomized into groups: sucrose-free (diet without sucrose) or sucrose-added (foods containing sucrose in composition). Both groups received the same macronutrient composition and used the carbohydrate counting methods. All underwent an interview and anthropometric evaluation. Blood was drawn for glycated haemoglobin, glucose, total cholesterol, HDL, and CRP measurement, and the medical charts were reviewed in all cases.

RESULTS

At baseline, anthropometric, clinical and laboratory variables did not differ between groups, except for the triglycerides. Although at baseline triglycerides levels were higher in the sucrose-added group (p = 0.01), they did not differ between groups after the intervention (p = 0.92). After 3-months, CRP was higher in the sucrose-added than in the sucrose-free group (p = 0.04), but no further differences were found between the groups, including the insulin requirements, anthropometric variables, body composition, and glycemic control. Both groups showed sugars intake above the recommendations at baseline and after intervention.

CONCLUSIONS

Sucrose intake, along with a disciplined diet, did not affect insulin requirements, anthropometric variables, body composition, lipemic and glycemic control. However, although the sucrose intakes increase CRP levels, the amount of sugar in the diet was not associated with this inflammatory marker.

One day of mixed meal overfeeding reduces hepatic insulin sensitivity and increases VLDL particle but not VLDL-triglyceride secretion in overweight and obese men

CONTEXT

The exact mechanisms responsible for increased plasma triglyceride (TG) concentration in obese people are unclear, and it is not known whether excess energy intake per se is involved in the pathophysiology of this abnormality.

OBJECTIVE

The purpose of our study was to examine how excess energy intake from a balanced diet for 1 day affects very-low-density lipoprotein (VLDL)-TG kinetics and its putative regulators hepatic insulin sensitivity and plasma free fatty acid availability.

SUBJECTS AND DESIGN

We used stable isotope-labeled tracer methods to evaluate glucose and lipid kinetics in 8 overweight and obese men (age, 38 ± 3 years; body mass index, 33.7 ± 1.7 kg/m(2); means ± SEM) on 2 occasions (randomized crossover design): once, the day after they consumed a balanced diet that provided an amount of energy that matched their energy expenditure, and another time, the day after they consumed a balanced diet that provided 30% excess calories. Eight healthy, lean men (34 ± 1 years; 22.5 ± 0.6 kg/m(2)) were studied under isocaloric conditions only to provide a reference for normal lipid kinetics.

RESULTS

VLDL-TG and VLDL-apolipoprotein B-100 (apoB-100) concentrations and secretion rates were significantly greater (P < .01) in overweight/obese compared with lean men. Hypercaloric, compared with isocaloric, feeding in overweight/obese men increased glucose rate of appearance in plasma (904 ± 21 vs 873 ± 26 μmol/min), the hepatic insulin resistance index (10.9 ± 2.2 vs 8.3 ± 1.8), and VLDL-apoB-100 concentration and secretion rate (1.91 ± 0.24 vs. 1.53 ± 0.13 nmol/min), whereas VLDL-apoB-100 plasma clearance rate, VLDL-TG secretion and plasma clearance rates, and free fatty acid rate of appearance in plasma were not affected by overfeeding.

CONCLUSION

One day of moderate overfeeding (30% excess energy intake) stimulates hepatic glucose and VLDL-apo B-100 secretion rates but has no effect on hepatic and adipose tissue fatty acid metabolism in overweight/obese men.

The tsim tsoum approaches for prevention of cardiovascular disease

The Tsim Tsoum Concept means that humans evolved on a diet in which nature recommends to ingest fatty acids in a balanced ratio (polyunsaturated(P) : saturated(S) =w-6 : w-3 = 1 : 1)as part of dietary lipid pattern where monounsaturated fatty acids(MUFA) is the major fatty acid(P : M : S = 1 : 6 : 1) in the background of other dietary factors; antioxidants, vitamins, minerals and fiber as well as physical activity and low mental stress. Several hundred years ago, our diet included natural foods; fruits, vegetables, green vegetables, seeds, eggs and honey. Fish, and wild meat were also available to pre-agricultural humans which shaped modern human genetic nutritional requirement. Cereal grains (refined), and vegetable oils that are rich in w-6 fatty acids are relatively recent addition to the human diet that represent dramatic departure from those foods to which we are adapted. Excess of linoleic acid, trans fatty acids (TFA), saturated and total fat as well as refined starches and sugar are proinflammatory. Low dietary MUFA and n-3 fatty acids and other long chain polyunsarurated fatty acids (LCPUFA) are important in the pathogenesis of metabolic syndrome. Increased sympathetic activity with greater secretion of neurotransmitters in conjunction of underlying long chain PUFA deficiency, and excess of proinflammatory nutrients, may damage the neurons via proinflammatory cytokines, in the ventromedial hypothalamus and insulin receptors in the brain.Since, 30–50% of the fatty acids in the brain are LCPUFA, especially omega-3 fatty acids, which are incorporated in the cell membrane phospholipids, it is possible that their supplementation may be protective.Blood lipid composition does reflect one's health status: (a) circulating serum lipoproteins and their ratio provide information on their atherogenicity to blood vessels and (b) circulating plasma fatty acids, such as w-6/w-3 fatty acid ratio, give indication on proinflammatory status of blood vessels, cardiomyocytes, liver cells and neurones; (a) and (b) are phenotype-related and depend on genetic, environmental and developmental factors. As such, they appear as universal markers for holistic health and these may be important in the pathogenesis of cardiovascular diseases and cancer, which is the main consideration of Tsim Tsoum concept.

Brisk walking offsets the increase in postprandial TAG concentrations found when changing to a diet with increased carbohydrate

We tested the hypothesis that 30 min of brisk walking daily would offset the increase in plasma TAG concentrations associated with substituting dietary fat for carbohydrate. Fourteen subjects (six males) aged 57 (sd 5) years underwent three 4 d trials in a counterbalanced order: (i) 4 d on a typical UK diet (40 % energy from fat, 45 % carbohydrate and 15 % protein); (ii) 4 d on an isoenergetic diet but substituting fat for carbohydrate in line with the present recommendations (30 % fat, 55 % carbohydrate and 15 % protein); (iii) 4 d on the same recommended diet with 30 min of brisk walking each day. The food provided for the first 3 d of each trial was isoenergetic with each volunteer's previously determined daily energy intake. On day 4, the subjects consumed breakfast, lunch and an early evening meal, equivalent in total to 90 % of their daily energy intake. Blood samples were collected and substrate utilisation and energy expenditure were determined in the fasted state and for 9 h postprandially. Substrate utilisation differed significantly among trials (P = 0.003); RER was higher on the recommended diet trial than during either of the other two trials (P = 0.012 and 0.021 for the UK diet and recommended diet with walking, respectively). The rise in plasma TAG concentrations over the day was steeper on the recommended diet trial than on the other two trials (trial x time interaction, P = 0.040). The increase in postprandial TAG concentrations associated with substituting dietary fat for carbohydrate was offset by 30 min of brisk walking daily.

Hypolipidaemic activity of Helicteres isora L. bark extracts in streptozotocin induced diabetic rats

In this study, the hypolipidaemic effect of an aqueous extract of the bark of Helicteres isora was investigated in streptozotocin (STZ)-induced diabetic rats. Administration of the bark extract of Helicteres isora (100 and 200 mg/kgb.w.) for 21 days resulted in significant reduction in serum and tissue cholesterol, phospholipids, free fatty acids and triglycerides in STZ diabetic rats. In addition to that, significant (p<0.05) decrease in high-density lipoprotein (HDL) whereas significant increase (p<0.05) low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) were observed in STZ diabetic rats, which were normalized after 21 days of bark extract treatment. The bark extract at a dose of 200 mg/kgb.w. showed much significant hypolipidaemic effect than at the dose of 100 mg/kgb.w.

A low-protein diet exacerbates postprandial chylomicron concentration in moderately dyslipidaemic subjects in comparison to a lean red meat protein-enriched diet

OBJECTIVE

To investigate whether altering energy intake as red meat protein or carbohydrate modifies chylomicron homeostasis and postprandial lipaemia.

DESIGN

Randomized single-blind dietary intervention trial.

SETTING

School of Public Health, Division of Health Science, Curtin University, Perth, Western Australia.

SUBJECTS

A total of 20 moderately hypertriglyceridaemic but otherwise healthy subjects were recruited and completed the study.

INTERVENTION

Participants consumed an isocaloric weight maintenance diet low in protein (14, 53 and 30% of energy as protein, carbohydrate and fat, respectively) or high in protein (25, 35 and 30% energy as protein, carbohydrate and fat) for a period of 6 weeks. Fasting plasma lipids and postprandial lipoprotein studies (triglyceride and apolipoprotein B48) following an oral fat challenge were carried out at the start and conclusion of the dietary intervention period.

RESULTS

Consumption of the low- or high-protein diet had no significant effect on fasting plasma or postprandial lipaemia, the latter determined as the incremental area under the triglyceride curve following a fat challenge. However, subjects who consumed a low-protein diet for 6 weeks had a substantially exaggerated postprandial chylomicron response, indicated as the area under the apo B48 curve following a fat challenge. The change in postprandial chylomicron kinetics could not be explained by changes in insulin sensitivity, which appeared to be similar before and after intervention with either diet.

CONCLUSIONS

Daily moderate consumption of a lean red meat protein-enriched diet attenuates postprandial chylomicronaemia in response to ingestion of a fatty meal.

Hyperphagia modifies FA profiles of plasma phospholipids, plasma FFA, and adipose tissue TAG

Hyperphagia was achieved by continuous intracerebroventricular infusion of a melanocortin receptor antagonist (HS024; Neosystem, Strasbourg, France) in rats. The effects of hyperphagia on FA composition and concentration of plasma phospholipids (PL), plasma FFA, and adipose tissue TAG were studied in rats for 8 d [short-term hyperphagia (STH); n = 8], or 28 d [long-term hyperphagia (LTH); n = 9]. The control rats were treated with artificial cerebrospinal fluid for 8 d (n = 8) or 28 d (n = 10). The rats were fed the same regular diet. In STH rats the plasma PL and fasting plasma FFA contained higher concentrations of saturated FA (SFA) and monounsaturated FA (MUFA), and plasma FFA contained lower n-6 PUFA than in the control rats. In LTH rats the plasma PL contained higher concentrations of SFA, MUFA, and n-3 PUFA and higher proportions of 16:1n-7 and 18:1n-9 at the expense of 18:2n-6 than in the control rats. In LTH rats the abundant dietary intake of 18:2n-6 did not enrich 18:2n-6 of the plasma PL or adipose tissue TAG. In LTH rats the fasting plasma FFA contained more than twofold higher concentrations of SFA and MUFA, and higher proportions of 16:1n-7 and 18:1n-9 at the expense of 18:2n-6 than in the control rats. This animal obesity model shows that LTH affects the FA composition and concentration of plasma PL, plasma FFA, and adipose tissue TAG, a result consistent with changes associated with increased risk of various diseases in humans. These results also demonstrate that LTH alters the FA composition of plasma PL and adipose tissue TAG in a way that does not reflect the FA composition of dietary fat.

Exercise and postprandial lipid metabolism: an update on potential mechanisms and interactions with high-carbohydrate diets (review)

Endurance trained people exhibit low levels of postprandial lipemia. However, this favorable situation is rapidly reversed with de-training and it is likely that the triglyceride (TG) lowering effects of exercise are mainly the result of acute metabolic responses to recent exercise rather than long-term training adaptations. A large body of evidence suggests that postprandial lipemia can be attenuated following an individual exercise session, with the energy expended during exercise being an important determinant of the extent of TG lowering. Increased lipoprotein lipase-mediated TG clearance and reduced hepatic TG secretion are both likely to contribute to the exercise-induced TG reductions. These changes may occur in response to post-exercise substrate deficits in skeletal muscle and/or the liver. In addition, regular exercise can oppose the hypertriglyceridaemia sometimes seen with low-fat, high-carbohydrate diets. Levels of physical activity should therefore be taken into account when considering nutritional strategies for reducing the risk of cardiovascular disease.

Protective effect of dietary monounsaturated fat on arteriosclerosis: beyond cholesterol

The consumption of diets enriched in monounsaturated fat has been related to a lower rate of coronary heart disease. It is well known that this dietary model decreases LDL-cholesterol plasma levels when replacing a saturated fat enriched diet. For this reason, a high monounsaturated fat diet is now being advocated to prevent cardiovascular disease, especially in Mediterranean countries. However, some expert panels-the Joint Task Force of European and other Societies on Coronary Prevention and the International Task Force for Prevention of Coronary Heart Disease-recommend replacing dietary saturated fat by complex carbohydrates, limiting the intake of total fat to <30% of the energy and monounsaturated fat to no more than 10-15% of total calories, reaching a similar effect on LDL-cholesterol plasma levels to a high monounsaturated fat diet. The most appropriate nutritional model to prevent arteriosclerosis should be supported by research into other biological effects of both diets. Therefore, it is interesting to review the non-lipid effect of monounsaturated fat, starting with its influence on other cardiovascular risk factors, such as carbohydrate metabolism and blood pressure. Moreover, substantial evidence of the effect of dietary monounsaturated fat on a wide range of healthy benefits beyond cholesterol, which have been investigated in recent years, such as lipoprotein oxidation, coagulation, fibrinolysis and endothelium, will be discussed. Furthermore, many observational epidemiological studies suggest that a high intake of monounsaturated fat is associated with reduced coronary risk and this will be analyzed in accordance with the clinical evidence to discuss the best dietary model to prevent coronary artery disease.

Insulin stimulation of hepatic triacylglycerol secretion in the insulin-replete state: implications for the etiology of peripheral insulin resistance

Observations on humans, on rats in vivo, and on isolated perfused rat livers indicate that insulin stimulates hepatic very-low-density lipoprotein (VLDL)-TAG secretion when the liver is chronically exposed to the hormone. They suggest that frequent stimulation of insulin secretion throughout the diurnal cycle may result in a chronic stimulation of VLDL secretion and increased delivery of acyl moieties to the periphery, particularly to muscle, the most important site of insulin-sensitive glucose disposal. If acyl groups are provided in excess of the oxidative needs of the tissue, this may lead to induction of insulin resistance, irrespective of whether obesity is established concomitantly. Dietary factors that stimulate hepatic VLDL secretion may have the same effect and contribute to the induction of a vicious spiral leading to the development of the full-blown Metabolic Syndrome and its pathological consequences, including type-2 diabetes, stroke, and cardiovascular disease.

Lipids and diabetes mellitus: a review of therapeutic options

Diabetes mellitus ia very common disease with a high cardiovascular morbidity and mortality. This articles reviews the types of lipid disorders that can accompany diabetes mellitus and the evidence that treatment of dyslipidaemia improves primary and secondary endpoints, i.e. lipid levels, cardiovascular events, and mortality. Specific lipid-lowering strategies are discussed, including diet and exercise, treatment of hyperglycaemia, and the use of lipid-lowering therapy such as statins, fibric acid derivatives, bile acid sequestrants, nicotinic acid and its derivatives, fish oil and hormone replacement therapy. An approach to the patient with diabetes mellitus and dyslipidaemia is provided.

Acute inhibition of glucose-6-phosphate translocator activity leads to increased de novo lipogenesis and development of hepatic steatosis without affecting VLDL production in rats

Glucose-6-phosphatase (G6Pase) is a key enzyme in hepatic glucose metabolism. Altered G6Pase activity in glycogen storage disease and diabetic states is associated with disturbances in lipid metabolism. We studied the effects of acute inhibition of G6Pase activity on hepatic lipid metabolism in nonanesthetized rats. Rats were infused with an inhibitor of the glucose-6-phosphate (G6P) translocator (S4048, 30 mg. kg(-1). h(-1)) for 8 h. Simultaneously, [1-(13)C]acetate was administered for determination of de novo lipogenesis and fractional cholesterol synthesis rates by mass isotopomer distribution analysis. In a separate group of rats, Triton WR 1339 was injected for determination of hepatic VLDL-triglyceride production. S4048 infusion significantly decreased plasma glucose (-11%) and insulin (-48%) levels and increased hepatic G6P (201%) and glycogen (182%) contents. Hepatic triglyceride contents increased from 5.8 +/- 1.4 micromol/g liver in controls to 20.6 +/- 5.5 micromol/g liver in S4048-treated animals. De novo lipogenesis was increased >10-fold in S4048-treated rats, without changes in cholesterol synthesis rates. Hepatic mRNA levels of acetyl-CoA carboxylase and fatty acid synthase were markedly induced. Plasma triglyceride levels increased fourfold, but no differences in plasma cholesterol levels were seen. Surprisingly, hepatic VLDL-triglyceride secretion was not increased in S4048-treated rats. These studies demonstrate that inhibition of the G6Pase system leads to acute stimulation of fat synthesis and development of hepatic steatosis, without affecting hepatic cholesterol synthesis and VLDL secretion. The results emphasize the strong interactions that exist between hepatic carbohydrate and fat metabolism.

Mechanism for the increase in plasma triacylglycerol concentrations after consumption of short-term, high-carbohydrate diets

BACKGROUND

High-carbohydrate (HC) diets are recommended for lowering the risk of coronary heart disease because they decrease plasma LDL-cholesterol concentrations. However, an unfavorable effect of HC diets is an increase in plasma triacylglycerol concentrations. The underlying mechanisms of this effect are still unclear.

OBJECTIVE

We examined the effect of diet composition on VLDL-triacylglycerol metabolism using in vivo isotopically labeled VLDL-triacylglycerol tracers.

DESIGN

Six healthy subjects were studied on 2 occasions: after 2 wk of an HC diet (75% carbohydrates, 10% fat, and 15% protein) and after 2 wk of an isoenergetic high-fat (HF) diet (30% carbohydrates, 55% fat, and 15% protein).

RESULTS

The plasma VLDL-triacylglycerol concentration was higher after the HC diet than after the HF diet (690 +/- 186 compared with 287 +/- 104 micromol/L; P < 0.05) because of higher rates of VLDL-triacylglycerol production (0.76 +/- 0.12 compared with 0.45 +/- 0.15 micromol x kg(-1) x min(-1); P < 0.05) rather than diminished VLDL-triacylglycerol clearance (1.5 +/- 0.5 compared with 1.7 +/- 0.5 mL x kg(-1) x min(-1) after the HC diet than after the HF diet, respectively). The increase in VLDL-triacylglycerol production was probably mediated by a decrease in hepatic fatty acid oxidation after the HC diet (0.13 +/- 0.02 compared with 0.69 +/- 0.24 micromol x kg(-1) x min(-1); P < 0.05), which presumably increased hepatic fatty acid availability for triacylglycerol synthesis.

CONCLUSIONS

The increase in fasting plasma triacylglycerol concentrations in response to short-term HC diets is due to accelerated VLDL-triacylglycerol secretion. Increased hepatic fatty acid availability, resulting from reduced hepatic fatty acid oxidation, is most likely responsible for the observed increase in VLDL-triacylglycerol secretion.

What is an optimal diet? Relationship of macronutrient intake to obesity, glucose tolerance, lipoprotein cholesterol levels and the metabolic syndrome in the Whitehall II study

OBJECTIVE

Saturated fats have adverse effects on health. To investigate which is more beneficial for energy replacement, we compare the effects of polyunsaturated fatty acid and carbohydrate intake on obesity and metabolic variables (fasting triglycerides, HDL-cholesterol, LDL-cholesterol and 2 h glucose). Further, because the optimum diet may differ according to glucose tolerance, we examine the same associations in glucose tolerant and intolerant groups. Finally, we test the effect of macronutrient intake on the presence or absence of the metabolic syndrome.

DESIGN

Cross-sectional analysis.

SUBJECTS

A total of 4497 men and 1865 women aged 39--62 in the Whitehall II study.

RESULTS

In men, higher intakes of both polyunsaturated fats and carbohydrates were linked to lower waist-hip ratio, triglycerides and LDL-cholesterol. Higher carbohydrate intake alone was linked to decreased body mass index (for 10 g higher carbohydrate intake, -0.12 kg/m(2), P<0.0001) and lower HDL-cholesterol (-0.01 mmol/l, P<0.01). In normoglycaemic men, higher carbohydrate intakes were associated with higher 2 h insulin and glucose levels (0.25 pmol/l, P<0.05 and 0.01 mmol/l, P=0.001, respectively). Dietary effects among women were similar, the exception being a positive association of polyunsaturated fat intake with body mass index and waist--hip ratio (0.47 kg/m(2), P<0.05 and 0.006, P<0.05, respectively). Dietary components, with the exceptions of cholesterol and protein in men, were unrelated to prevalence of the metabolic syndrome, and adjustment for differences in macronutrient intake did not account for the strong inverse association between socioeconomic position and the metabolic syndrome.

CONCLUSION

Our observational data provide evidence that both polyunsaturated fatty acids and carbohydrates offer small metabolic benefits with few adverse effects compared with saturated fats. International Journal of Obesity (2001) 25, 45-53

Diet and Syndrome X

Syndrome X is a cluster of abnormalities, associated with resistance to insulin-mediated glucose uptake, that increases risk of coronary heart disease. Increased carbohydrate intake (with reciprocal decreased fat intake) within the boundaries of menus that can be followed in the free-living state have not been shown to decrease insulin resistance directly, by enhancing insulin sensitivity, or indirectly, by producing and maintaining weight loss. Moreover, such diets accentuate the metabolic abnormalities that constitute Syndrome X. Substitution of monounsaturated fat, polyunsaturated fat, or both for saturated fat results in the same reduction in low-density lipoprotein-cholesterol concentration as seen in diets low in fat and high in carbohydrates but without any untoward effects on the various manifestations of Syndrome X. Consequently, substituting unsaturated fat for saturated fat, without increasing intake of dietary protein or carbohydrate, may be useful for patients with hypercholesterolemia, Syndrome X, or both.

Postprandial lipemia in young men and women of contrasting training status

This study compared the postprandial triacylglycerol (TAG) response to a high-fat meal in trained and untrained normolipidemic young adults after 2 days' abstinence from exercise. Fifty-three subjects (11 endurance-trained men, 9 endurance-trained women, 10 sprint/strength-trained men, 11 untrained men, 11 untrained women) consumed a meal (1.2 g fat, 1.1 g carbohydrate, 66 kJ per kg body mass) after a 12-h fast. Venous blood samples were obtained in the fasted state and at intervals until 6 h. Postprandial responses were the areas under the plasma or serum concentration-vs.-time curves. Neither fasting TAG concentrations nor the postprandial TAG response differed between trained and untrained subjects. The insulinemic response was 29% lower in endurance-trained men than in untrained men [mean difference -37.4 (95% confidence interval -62.9 to -22.9) microIU/ml x h, P = 0.01]. Responses of plasma glucose, serum insulin, and plasma nonesterified fatty acids were all lower for endurance-trained men than for untrained men. These findings suggest that, in young adults, no effect of training on postprandial lipemia can be detected after 60 h without exercise. The effect on postprandial insulinemia may persist for longer.

Treatment of hypertriglyceridemia by two diets rich either in unsaturated fatty acids or in carbohydrates: effects on lipoprotein subclasses, lipolytic enzymes, lipid transfer proteins, insulin and leptin

BACKGROUND

There is lack of agreement on which dietary regimen is most suitable for treatment of hypertriglyceridemia, especially if high triglyceride concentrations are not due to obesity or alcohol abuse. We compared the effects on blood lipids of a diet high in total and unsaturated fat with a low-fat diet in patients with triglyceride concentrations of > 2.3 mmol/l.

METHODS

Nineteen non-obese male outpatients with triglycerides ranging from 2.30 to 9.94 mmol/l received two consecutive diets for 3 weeks each: first a modified high-fat diet (39% total fat, 8% SFA, 15% monounsaturated fatty acids, 1.6% marine n-3 polyunsaturated fatty acids), and then a low-fat diet (total fat 28%, carbohydrates 54%).

RESULTS

The high-fat diet significantly decreased triglycerides (-63%), total cholesterol (-22%), VLDL cholesterol (-54%), LDL cholesterol ( 16%), total apoC-III (-27%), apoC-III in apoB containing lipoproteins (apoC-III LpB; -31%) and in HDL (apoC-III nonLpB; -29%), apoE in serum (-33%) and apoB-containing lipoproteins (nonHDL-E; -42%), LpA-I (-16%), insulin (-36%), and leptin (-26%) and significantly increased the means of HDL cholesterol (+8%), LDL size (+6%), lipoprotein lipase (LPL, +11%), hepatic lipase (+13%), and lecithin: cholesterol acyltransferase (LCAT, +2%). The subsequent low-fat diet increased triglycerides (+63%), VLDL cholesterol (+19%), apoC-III (+23%), apoC-III LpB (+44%) apoC-III nonLpB (+17%), apoE (+29%) and nonHDL-E (+43%), and decreased HDL cholesterol (-12%), LPL (-3%), and LCAT (-3%). Changes in triglycerides correlated with changes in LPL activity and insulin levels.

CONCLUSIONS

In hypertriglyceridemic patients, a modified diet rich in mono- and n-3 polyunsaturated fatty acids is more effective than a carbohydrate-rich low-fat diet in correcting the atherogenic lipoprotein phenotype.

Weight loss is correlated with an improved lipoprotein profile in obese postmenopausal women

BACKGROUND

Changes in plasma lipid and lipoprotein distributions that occur after menopause increase the risk of cardiovascular disease in women, especially in those who are overweight.

OBJECTIVE

The purpose of this study was to evaluate the impact of a nine-month weight reduction program on plasma lipids, dietary intake and abdominal fat obesity.

DESIGN

A partial crossover design was used to study a weight loss treatment consisting of Phentermine hydrochloride (Fastin, SmithKline Beecham Pharmaceuticals, Philadelphia, PA) therapy plus a low energy diet (5040 kJ/d). Forty-seven obese, postmenopausal Caucasian women (BMI of 30-38 kg/m2) were randomized into two groups, both of which received drug and diet treatment over six months. However, Group I started the intervention program three months later than Group II. Plasma total, HDL and LDL cholesterol and triacylglycerol were measured, body composition was assessed by anthropometry and dual energy x-ray absorptiometry, and food frequency records were collected at four timepoints.

RESULTS

Over nine months, women in Group II reduced body weight (14.4%), lowered plasma concentrations of LDL cholesterol (14% to 26%) and triacylglycerol (15%) and raised plasma HDL cholesterol concentration (15%). These plasma lipid changes decreased the total cholesterol/HDL cholesterol ratio from 4.3 to 3.2. All subjects decreased abdominal fat measurements and energy and cholesterol intakes, as well as percentage of energy derived from total and saturated fat during the study. Most subjects also increased dietary fiber consumption.

CONCLUSION

Both weight loss and diet modifications are associated with an improved plasma lipid profile in obese postmenopausal women.

Comparative lipid and lipoprotein responses to solid-food diets and defined liquid-formula diets

BACKGROUND

Liquid-formula diets (LFDs) are useful in metabolic studies of the cholesterolemic effects of dietary lipids because they can be formulated with accuracy, facilitating precise delivery of fatty acids of interest. However, because of differences in composition and nutrient delivery between LFDs and solid-food diets (SFDs), there is a need to determine differences in their effects.

OBJECTIVE

Our objective was to compare lipid and lipoprotein responses to changes in total fat, saturated fatty acids (SFAs), and cholesterol in subjects consuming an SFD or LFD.

DESIGN

Twenty-one healthy subjects consumed controlled diets representative of an average American diet [AAD; 37% of energy from fat (15% from SFAs), and <50 mg cholesterol/MJ] or a National Cholesterol Education Program (NCEP) Step II diet [26% fat (5% from SFAs) and <25 mg cholesterol/MJ]. Other nutrients were similar between diets. Diets were consumed for 23 d in a randomized, crossover design.

RESULTS

For the AAD and NCEP Step II diet, there were no significant differences in lipids and apolipoproteins when the LFD or SFD versions were consumed. In contrast, consumption of the SFD was associated with significantly lower total cholesterol and triacylglycerols than was consumption of the corresponding AAD or Step II LFD (P < 0.05). Subjective ratings of satiety, hunger, and quality of life between diet forms did not differ significantly.

CONCLUSIONS

Both LFDs and SFDs yield quantitatively similar cholesterolemic responses to changes in dietary fat, SFAs, and cholesterol. LFDs may offer advantages because they provide easily administered, complete, balanced nutrition without affecting satiety.

Sweetener augmentation of serum triacylglycerol during a fat challenge test in humans

OBJECTIVE

High concentrations of fructose enhance postprandial lipemia following lipid loading whereas glucose exerts a negative or minimal effect. This study evaluated the effect of lower sweetener concentrations and the contribution of their sweetness level and palatability.

METHODS

At each of four test sessions, twelve male and ten female healthy adults ingested one of four milkshakes containing 108 g dairy cream alone or supplemented with 30 g fructose, 17.5 g glucose or 1 g aspartame. Blood samples were collected at baseline, two, four, six and eight hours after ingestion. Sensory discrimination tests were conducted after the last two sessions.

RESULTS

Fructose and glucose led to 37% (p = 0.03) and 59% (p = 0.08) rises in triacylglycerol area under the curve (TG AUC) when compared to the plain milkshake, respectively. Although the sweetened shakes were equisweet and were more palatable than the plain shake, the TG rise after the aspartame milkshake did not differ from the plain milkshake.

CONCLUSIONS

These data indicate that low levels of glucose and fructose consumed with lipid enhance postprandial lipemia. Sweetness and palatability did not account for the effect.

Dietary carbohydrates and triacylglycerol metabolism

There is a growing body of scientific evidence which demonstrates that plasma triacylglycerol (TAG) concentration, especially in the postprandial state, is an important risk factor in relation to the development of CHD. Postprandial hypertriacylglycerolaemia is associated with a number of adverse metabolic risk factors, including the preponderance of small dense LDL, low HDL-cholesterol concentrations and elevated factor VII activity. Traditionally, a low-fat high-carbohydrate diet was used to prevent CHD because it effectively reduces plasma cholesterol concentrations, but this dietary regimen increases plasma TAG concentrations and reduces HDL-cholesterol concentrations. There is substantial epidemiological evidence which demonstrates that high plasma TAG and low plasma HDL concentrations are associated with an increased risk of CHD. Thus, there is reason for concern that the adverse effects of low-fat high-carbohydrate diets on TAG and HDL may counteract or negate the beneficial effect of reducing LDL-cholesterol concentrations. Although there have been no prospective studies to investigate whether reduced fat intake has an adverse effect on CHD, there is strong epidemiological evidence that reducing total fat intake is not protective against CHD. On the other hand, high-fat diets predispose to obesity, and central obesity adversely affects TAG metabolism. There is substantial evidence that in free-living situations low-fat high-carbohydrate diets lead to weight loss, which in turn will correct insulin resistance and plasma TAG metabolism. Clearly there is a need for prospective studies to resolve the issue as to whether low-fat high-carbohydrate diets play an adverse or beneficial role in relation to the development of CHD.