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

Impact of body composition on very-low-density lipoprotein-triglycerides kinetics

Upper body obese (UBO) subjects have greater cardiovascular disease risk than lower body obese (LBO) or lean subjects. Obesity is also associated with hypertriglyceridemia that may involve greater production and impaired removal of very-low-density lipoprotein (VLDL)-triglycerides (TG). In these studies, we assessed the impact of body composition on basal VLDL-TG production, VLDL-TG oxidation, and VLDL-TG storage. VLDL-TG kinetics were assessed in 10 UBO, 10 LBO, and 10 lean women using a bolus injection of [1-(14)C]VLDL-TG. VLDL-TG oxidation was measured by (14)CO(2) production (hyamine trapping) and VLDL-TG adipose tissue storage by fat biopsies. Insulin sensititvity was assessed by the hyperinsulinemic-euglycemic clamp technique and body composition by dual X-ray absorptiometry in combination with computed tomography. Hepatic VLDL-TG production was significantly greater in UBO than in lean women [(mumol/min) UBO: 64.8 (SD 40.0) vs. LBO: 42.5 (SD 25.6) vs. lean: 31.8 (SD 13.3), P = 0.04], whereas VLDL-TG oxidation was similar in the three groups and averaged 20% of resting energy expenditure [(mumol/min) UBO: 38.3 (SD 26.5) vs. LBO: 23.5 (SD 13.5) vs. lean: 21.1 (SD 9.7), P = 0.09]. In UBO women, more VLDL-TG was deposited in upper body subcutaneous fat [VLDL-TG redeposition in abdominal adipose tissue (mumol/min): UBO: 5.0 (SD 2.9) vs. LBO: 4.0 (SD 3.2) vs. lean: 1.3 (SD 1.0), ANOVA P = 0.01]; in LBO women, more VLDL-TG was deposited in femoral fat [VLDL-TG redeposition in femoral adipose tissue (mumol/min): UBO: 5.1 (SD 3.1) vs. LBO: 5.8 (SD 4.3) vs. lean: 2.3 (SD 1.5), ANOVA P = 0.04]. Only a small proportion of VLDL-TG (8-16%) was partitioned into redeposition in either group. We found that elevated VLDL-TG production without concomitant increased clearance via oxidation and adipose tissue redeposition contributes to hypertriglyceridemia in UBO women.

[High-carbohydrate diets: effects on lipid metabolism, body adiposity and its association with physical activity and cardiovascular disease risk]

For many years the reduction in the dietary fat has been recommended to the population, in order to prevent cardiovascular diseases, obesity, type 2 diabetes mellitus, among other chronic diseases. The consequence has been the replacement of carbohydrates by fat, resulting in the adoption of high carbohydrate diets. However, it has been still discussed if very rich carbohydrate diets should be recommended to the general population. Researches point out controversies about the association between these dietary habits and harmful effects on health and metabolic aspects, such as raise in de novo lipogenesis and triglyceride concentration, reduction in HDL concentration and effects on adiposity. This review evaluates the effects of diet modification, particularly the high-carbohydrate diet, in cardiovascular risk factors such as dyslipidemia and obesity. It also reviews its interaction with physical activity since it is still unknown with which extension it can minimize possible harmful effects of high carbohydrate diets in the long term.

Reduced oxidation of dietary fat after a short term high-carbohydrate diet

BACKGROUND

Short-term high-carbohydrate (HC) diets induce metabolic alterations, including hypertriacylglycerolemia, in both the fasting and postprandial states. The underlying tissue-specific alterations in fatty acid metabolism are not well understood.

OBJECTIVE

We investigated alterations in exogenous and endogenous fatty acid metabolism by using stable isotope tracers to label meal triacylglycerol and plasma fatty acids.

DESIGN

Eight healthy subjects consumed isocaloric diets containing a high percentage of energy from carbohydrates or a higher percentage of energy from fat for 3 d in a randomized crossover dietary intervention study. A test meal containing [U-13C] palmitate was combined with intravenous infusion of [2H2] palmitate to label plasma fatty acids and VLDL triacylglycerol. Blood and breath samples were taken before the meal and for 6 h postprandially. Blood samples were drawn from the femoral artery and from veins draining subcutaneous adipose tissue and forearm muscle for monitoring of tissue-specific metabolic substrate partitioning.

RESULTS

Systemic triacylglycerol concentrations were increased in both fasting (P = 0.02) and postprandial (P = 0.02) periods, and a greater amount of infused labeled fatty acid appeared in VLDL triacylglycerol after the HC diet than after the higher-fat diet (P = 0.05). Significantly less 13CO2 was exhaled after the HC diet (P = 0.04) and significantly less production of 13CO2 was seen across forearm muscle (P = 0.04). Systemic 3-hydroxybutyrate was significantly lower, postprandially, after the HC diet (P = 0.02).

CONCLUSION

Metabolic alterations suggestive of repartitioning of fatty acids away from oxidation toward esterification in both liver and muscle occur in response to short-term adaptation to a HC diet.

Opposite lipemic response of Wistar rats and C57BL/6 mice to dietary glucose or fructose supplementation

The metabolic effects of carbohydrate supplementation in mice have not been extensively studied. In rats, glucose- and fructose-rich diets induce hypertriacylglycerolemia. In the present study, we compared the metabolic responses to two monosaccharide supplementations in two murine models. Adult male Wistar rats (N = 80) and C57BL/6 mice (N = 60), after 3 weeks on a standardized diet, were submitted to dietary supplementation by gavage with glucose (G) or fructose (F) solutions (500 g/L), 8 g/kg body weight for 21 days. Glycemia was significantly higher in rats after fructose treatment (F: 7.9 vs 9.3 mM) and in mice (G: 6.5 vs 10 and F: 6.6 vs 8.9 mM) after both carbohydrate treatments. Triacylglycerolemia increased significantly 1.5 times in rats after G or F supplementation. Total cholesterol did not change with G treatment in rats, but did decrease after F supplementation (1.5 vs 1.4 mM, P < 0.05). Both supplementations in rats induced insulin resistance, as suggested by the higher Homeostasis Model Assessment Index. In contrast, mice showed significant decreases in triacylglycerol (G: 1.8 vs 1.4 and F: 1.9 vs 1.4 mM, P < 0.01) and total cholesterol levels (G and F: 2.7 vs 2.5 mM, P < 0.05) after both monosaccharide supplementations. Wistar rats and C57BL/6 mice, although belonging to the same family (Muridae), presented opposite responses to glucose and fructose supplementation regarding serum triacylglycerol, free fatty acids, and insulin levels after monosaccharide treatment. Thus, while Wistar rats developed features of plurimetabolic syndrome, C57BL/6 mice presented changes in serum biochemical profile considered to be healthier for the cardiovascular system.

Postprandial triglyceride response in men: role of overweight, abdominal fat and nutrition

OBJECTIVE

The study analyses i) the effect of overweight, waist circumference and dietary habits on postprandial (pp) triglyceride (TG) response and compares ii) pp TG response with fasting TG levels and iii) pp TG peak values with TG-AUC (area under curve) with respect to cardiometabolic risk assessment.

METHODS

In 100 men (44-68 years) body composition (air-displacement plethysmography), dietary habits, cardiometabolic risk and pp lipid metabolism (standardised lipid load) were assessed. A pp TG peak value of 260 mg/dl was used as a cut-off to classify TG normal- and high-responders.

RESULTS

pp TG response had positive associations with BMI (r = 0.24; p < 0.05), fat mass (r = 0.28; p < 0.01), waist circumference (r = 0.33; p < 0.01), systolic blood pressure (r = 0.21; p < 0.05), fasting (r = 0.29; p < 0.01) and pp glucose (r = 0.40; p < 0.001), fasting (r = 0.38; p < 0.001) and pp insulin levels (r = 0.46; p < 0.001), and inverse associations with HDL-C (r = -0.43; p < 0.001) and intake of dietary fibre (r = -0.31; p < 0.05). Fasting TG levels had a greater contribution to the variance in 12 of 14 cardiometabolic risk factors compared to pp TG response. TG-AUC was highly correlated to cardiometabolic risk.

CONCLUSION

Overweight, abdominal fat and a low intake of dietary fibre were determinants of increased pp TG response. Contrary to findings in younger normal-weight men, fasting TG levels had a stronger association with cardio metabolic risk compared to pp TG response. This might be explained by differences in fat mass.

Effects of advice on dietary intake and/or physical activity on body composition, blood lipids and insulin resistance following a low-fat, sucrose-containing, high-carbohydrate, energy-restricted diet

AIM

To determine the effect of dietary advice in conjunction with advice to increase physical activity on the body composition, blood lipid and insulin profiles in overweight women.

DESIGN

A 12-week randomized controlled intervention study. subjects were assigned to one of four groups: (1) no advice, (2) low-fat, high-carbohydrate (including sucrose) energy-reduced diet, (3) 60 min/day brisk walking, and (4) diet and activity advice as previous.

SUBJECTS

Sixty-nine overweight women (mean age 41 years).

MEASUREMENTS

Dietary compliance was assessed by 4-day diet diaries. Activity levels were assessed by Caltractrade mark accelerator monitors. Anthropometric changes were recorded at baseline, 6 and 12 weeks. Fasting blood samples measuring glucose, insulin, and blood lipids were recorded at baseline and 12 weeks.

RESULTS

Group 4 achieved greatest weight loss of 4.2 kg and greatest reduction in waist circumference of 6.5 cm. Groups 2 and 4 decreased the percentage energy from fat by 5.2%. Group 3 increased the percentage energy from fat by 4.0%. Group 4 significantly reduced total cholesterol by 0.45 mmol/l and low-density lipoprotein-cholesterol by 0.53 mmol/l.

CONCLUSION

A low-fat, high-carbohydrate, sucrose-containing diet combined with increased physical exercise resulted in greater health benefits than diet or physical activity advice alone.

A comparison of the influence of a high-fat diet enriched in monounsaturated fatty acids and conventional diet on weight loss and metabolic parameters in obese non-diabetic and Type 2 diabetic patients

AIMS

The aim of our study was to compare the influence of a hypocaloric, high-fat diet enriched with MUFA (M) and conventional diet (C) on weight loss and metabolic parameters in obese non-diabetic and obese Type 2 diabetic subjects over a 3-month period. It was our hypothesis that the enriched diet would be more effective in decreasing blood glucose and glycated haemoglobin (HbA(1c)) than the control diet.

METHODS

Twenty-seven Type 2 diabetic patients (54.5 +/- 3.5 years; DM), treated with diet or oral glucose-lowering agents, and 31 obese non-diabetic subjects (53.6 +/- 3.5 years; OB) were randomized to M or C. Individual calculations of energy requirements were based on the formula: [resting energy expenditure (REE) x 1.5] - 600 kcal. Subjects were assessed by a dietitian every 2 weeks and by a physician every month. Statistical analyses were carried out between the four groups--DM/M, DM/C, OB/M and OB/C--using pair Student's test and anova.

RESULTS

After 3 months, body weight, waist-hip ratio, total body fat, levels of C-peptide, triglycerides and homeostasis model assessment (HOMA) decreased in all four groups (P < 0.01). However, fasting blood glucose and HbA(1c) decreased (P < 0.01) and high-density lipoprotein cholesterol increased significantly only in the DM/M group (P < 0.05). In general, M was well tolerated.

CONCLUSIONS

Individualized M and C diets were successful in improving metabolic and anthropometric parameters in both the obese non-diabetic and the Type 2 diabetic subjects. Although the superiority of the higher fat diet did not reach statistical significance, the decline in blood glucose and HbA(1c) in the Type 2 diabetic group on M was encouraging.

Metabolic interaction of dietary sugars and plasma lipids with a focus on mechanisms andde novolipogenesis

The elevation of blood lipid concentrations in response to the consumption of low-fat high-carbohydrate diets is known as carbohydrate-induced hypertriacylglycerolaemia (HPTG). An understanding of the mechanisms involved in the interaction between carbohydrates and plasma lipids may help determine whether carbohydrate-induced HPTG would increase cardiovascular risk. There is growing evidence to suggest that the sugar component of the diet may be largely responsible, rather than the total carbohydrate. In most studies designed to investigate the mechanisms of carbohydrate-induced HPTG, the amounts and types of sugars and starches used in the diets are not specified. Findings have been mixed and inconsistent. It is proposed that the elucidation of mechanisms from current studies could have been confounded by the different ways in which sugars are metabolized in the body. At present, there are few studies that have evaluated the independent effects of dietary sugars. Interest has been focused onde novolipogenesis (DNL), as it has recently been found to be positively correlated with increases in fasting TAG levels produced on high-carbohydrate diets, indicating that DNL may contribute to carbohydrate-induced HPTG. DNL has been found to be determined by starch:sugar in a high-carbohydrate diet and affected by different types of sugars. The presence of DNL in adipose tissue is supported by emerging gene-expression studies in human subjects. In the wake of rising intakes of sugars, further research is needed to investigate the mechanisms associated with different sugars, so that appropriate therapeutic strategies can be adopted.

Reproducibility of stable isotope-labeled tracer measures of VLDL-triglyceride and VLDL-apolipoprotein B-100 kinetics

To gain insight into the mechanisms regulating plasma lipid homeostasis, FFA, VLDL-triglyceride (TG), and VLDL-apolipoprotein B-100 (apoB-100) kinetics are commonly assessed using stable isotope-labeled tracer methods. The reproducibility of these measurements, which is critical for the experimental design, is unknown. Therefore, we investigated the repeatability of plasma FFA, VLDL-TG, and VLDL-apoB-100 kinetics in eight healthy men using stable isotope-labeled tracer techniques. There were no systematic differences in plasma FFA, VLDL-TG, and VLDL-apoB-100 concentrations and kinetics between the two studies. Intraindividual day-to-day variability for various outcome variables ranged from 15% to 25%, and almost all of this was of biological origin. The most robust outcome variables were FFA rate of appearance and hepatic VLDL-TG and VLDL-apoB-100 secretion rates; the least robust were VLDL-TG and VLDL-apoB-100 plasma clearance rates and mean residence times. Overall, physiologically meaningful differences in mean values (i.e., 25-30% in magnitude) can be obtained with a sample size of 6-10 subjects for paired studies and 12-20 subjects per group for cross-sectional studies, assuming a type I error rate of 0.05 and a type II error rate of 0.20 (i.e., 80% power). These findings will be useful for future studies investigating FFA, VLDL-TG, and VLDL-apoB-100 kinetics with the methods described.

No effect of menstrual cycle phase on basal very-low-density lipoprotein triglyceride and apolipoprotein B-100 kinetics

Dyslipidemia, manifested by increased plasma triglyceride (TG), increased total and LDL-cholesterol concentrations and decreased HDL-cholesterol concentration, is an important risk factor for cardiovascular disease. Premenopausal women have a less atherogenic plasma lipid profile and a lower risk of cardiovascular disease than men, but this female advantage disappears after menopause. This suggests that female sex steroids affect lipoprotein metabolism. The impact of variations in the availability of ovarian hormones during the menstrual cycle on lipoprotein metabolism is not known. We therefore investigated whether very-low-density lipoprotein (VLDL)-TG and VLDL-apolipoprotein B-100 (apoB-100) kinetics are different during the follicular (FP) and luteal phases (LP) of the menstrual cycle. We studied seven healthy, premenopausal women (age 27 +/- 2 yr, BMI 25 +/- 2 kg/m(2)) once during FP and once during LP. We measured VLDL-TG, VLDL-apoB-100, and plasma free fatty acid (FFA) kinetics by using stable isotope-labeled tracers, VLDL subclass profile by nuclear magnetic resonance spectroscopy, whole body fat oxidation by indirect calorimetry, and the plasma concentrations of lipoprotein lipase (LPL) and hepatic lipase (HL) by ELISA. VLDL-TG and VLDL-apoB-100 concentrations in plasma, VLDL-TG and VLDL-apoB-100 secretion rates and mean residence times, VLDL subclass distribution, FFA concentration and rate of appearance in plasma, whole body substrate oxidation, and LPL and HL concentrations in plasma were not different during the FP and the LP. We conclude that VLDL-TG and VLDL-apoB-100 metabolism is not affected by menstrual cycle phase.

Very low-carbohydrate versus isocaloric high-carbohydrate diet in dietary obese rats

OBJECTIVE

The effects of a very low-carbohydrate (VLC), high-fat (HF) dietary regimen on metabolic syndrome were compared with those of an isocaloric high-carbohydrate (HC), low-fat (LF) regimen in dietary obese rats.

RESEARCH METHODS AND PROCEDURES

Male Sprague-Dawley rats, made obese by 8 weeks ad libitum consumption of an HF diet, developed features of the metabolic syndrome vs. lean control (C) rats, including greater visceral, subcutaneous, and hepatic fat masses, elevated plasma cholesterol levels, impaired glucose tolerance, and fasting and post-load insulin resistance. Half of the obese rats (VLC) were then fed a popular VLC-HF diet (Weeks 9 and 10 at 5% and Weeks 11 to 14 at 15% carbohydrate), and one-half (HC) were pair-fed an HC-LF diet (Weeks 9 to 14 at 60% carbohydrate).

RESULTS

Energy intakes of pair-fed VLC and HC rats were less than C rats throughout Weeks 9 to 14. Compared with HC rats, VLC rats exhibited impaired insulin and glycemic responses to an intraperitoneal glucose load at Week 10 and lower plasma triacylglycerol levels but retarded loss of hepatic, retroperitoneal, and total body fat at Week 14. VLC, HC, and C rats no longer differed in body weight, plasma cholesterol, glucose tolerance, or fasting insulin resistance at Week 14. Progressive decreases in fasting insulin resistance in obese groups paralleled concomitant reductions in hepatic, retroperitoneal, and total body fat.

DISCUSSION

When energy intake was matched, the VLC-HF diet provided no advantage in weight loss or in improving those components of the metabolic syndrome induced by dietary obesity and may delay loss of hepatic and visceral fat as compared with an HC-LF diet.

Nutrient determinants of postprandial triglyceride response in a population-based sample of type II diabetic patients

BACKGROUND

Nutrient determinants of postprandial triglyceride (TG) are matter of debate, especially for type II diabetes.

OBJECTIVE

This study was performed to evaluate the impact of dietary habits on postprandial TG response in a population-based sample of type II diabetic patients.

DESIGN

One-hundred and forty type II diabetic patients (63 men/77 women, age 45-70 years) referring to the same health district, not on hypolipidemic drugs and without any other chronic disease, performed four TG profiles (at fasting, before, 2 and 3 h after lunch) with a specific device (Accutrend GCT, Roche Diagnostics Mannheim, Germany) validated previously. Dietary habits were recorded by a dietitian utilizing a previously validated semiquantitative questionnaire.

RESULTS

Triglyceride values (mmol/l, mean +/- s.d.) were 2.22 +/- 0.93 at fasting, decreased before lunch (2.03 +/- 0.81), reached peak values 3 h after lunch (2.73 +/- 1.11). Postprandial TG increments (3 h after lunch minus pre-lunch concentration) significantly correlated with the intake (g/day) of animal protein (r = 0.20, P < 0.02), total fat (r = 0.21, P < 0.01), animal fat (r = 0.19, P < 0.03) and vegetable fat (r = 0.19, P < 0.03), also after adjusting for fasting TG and high-density lipoprotein cholesterol levels. Expressing nutrient intake as percentage of total calorie intake, total and animal fat remained significantly and directly related to postprandial TG increment (r = 0.21, P < 0.01 for total fat; r = 0.19, P < 0.03 for animal fat) whereas the percentage of carbohydrates was inversely related (r = -0.23, P < 0.007).

CONCLUSIONS

Fat intake seems the major nutritional determinant of postprandial TG response in type II diabetic patients.

The atherogenic potential of dietary carbohydrate

OBJECTIVE

To investigate the role of dietary carbohydrate in atherogenesis.

METHOD

Search of the literature for relevant papers concerning the relationship of insulin/hyperinsulinemia and carbohydrate on the one hand, and the renin-angiotensin system, the sympathetic nervous system, growth factors, i.e. platelet-derived growth factor and insulin-like growth factor-I, C-reactive protein, and dyslipemia, on the other hand, factors well known to be involved in the atherogenic process, as well as for epidemiologic studies investigating the relationship between high-carbohydrate diets and the development of cardiovascular disease.

RESULTS

High-carbohydrate nutrition is shown to have the ability to induce vascular inflammation and plaque formation through an insulin-mediated activation of the RAS, growth factors, cytokines, the SNS, and C-reactive protein and to cause an atherogenic lipid profile in normal humans. Epidemiologic studies as well as studies in experimental animals corroborate an important role of dietary carbohydrate in atherogenesis.

CONCLUSION

High-carbohydrate diets, particularly in the form of high-glycemic index carbohydrate, have the ability to directly induce atherosclerosis. Based on anthropologic facts, the reason for these dietary-induced, insulin-mediated, atherogenic metabolic perturbations are suggested to be an insufficient adaptation to starch and sugars during human evolution. Restriction of insulinogenic food (starch and sugars) may help to prevent the development of atherosclerosis, one of the most common and costliest human diseases.

Effect of a low-carbohydrate, ketogenic diet program compared to a low-fat diet on fasting lipoprotein subclasses

BACKGROUND

Low-carbohydrate, ketogenic diets (LCKD) are effective for weight loss, but concerns remain regarding cardiovascular risk. The purpose of this study was to determine the effect of an LCKD program on serum lipoprotein subclasses.

METHODS

This was a randomized, two-arm clinical trial in an outpatient research clinic involving overweight, hyperlipidemic community volunteers motivated to lose weight. Subjects were randomized to either an LCKD (n = 59) and nutritional supplementation (including fish, borage and flaxseed oil), or a low-fat, reduced-calorie diet (LFD, n = 60). The main outcomes were fasting serum lipoprotein subclasses determined by nuclear magnetic resonance analysis.

RESULTS

The mean age of subjects was 44.9 years, the mean BMI was 34.4 kg/m(2), and 76% were women. Comparing baseline to 6 months, the LCKD group had significant changes in large VLDL (-78%), medium VLDL (-60%), small VLDL (-57%), LDL particle size (+2%), large LDL (+54%), medium LDL (-42%), small LDL (-78%), HDL particle size (+5%), large HDL (+21%), and LDL particle concentration (-11%). Compared with the LFD group, the LCKD group had greater reductions in medium VLDL (p = 0.01), small VLDL (p = 0.01) and medium LDL (p = 0.02), and greater increases in VLDL particle size (p = 0.01), large LDL (p = 0.004), and HDL particle size (p = 0.05).

CONCLUSIONS

The LCKD with nutritional supplementation led to beneficial changes in serum lipid subclasses during weight loss. While the LCKD did not lower total LDL cholesterol, it did result in a shift from small, dense LDL to large, buoyant LDL, which could lower cardiovascular disease risk.

Methodological approaches to the study of metabolism across individual tissues in man

PURPOSE OF REVIEW

This article is intended to briefly overview available methodological approaches for the study of regional metabolism in man in vivo, and to summarize recent advances in this field of research.

RECENT FINDINGS

Several methods have been developed and currently allow for the qualitative and quantitative assessment of energy interconversions and substrate fluxes across individual tissues of man, including the measurement of arteriovenous concentration differences, microdialysis, and nuclear magnetic resonance spectroscopy of carbon, hydrogen, and phosphorus isotopes. Each method alone has been used rather extensively to examine certain aspects of organ and tissue metabolism under a variety of experimental conditions, and has contributed novel information in this regard. The most exciting development appears to be the combined use of more than one investigational technique, across one or more tissues simultaneously. A handful of recent studies have employed complex experimental designs or hybrid methodologies, ultimately demonstrating the potential for a more detailed assessment of metabolism at the local level.

SUMMARY

Clearly, advances in the use, performance, and applications of available methods are expected to provide improved and more powerful tools for the metabolic investigation of organs and tissues in humans in vivo.

Energy deficit without reducing dietary carbohydrate alters resting carbohydrate oxidation and fatty acid availability

Reduced carbohydrate (CHO) availability after exercise has a potent influence on the regulation of substrate metabolism, but little is known about the impact of fat availability and/or energy deficit on fuel metabolism when dietary CHO availability is not reduced. The purpose of this study was to determine the influence of a postexercise energy deficit, independent of CHO availability, on plasma substrate concentrations and substrate oxidation. Seven moderately trained men (peak oxygen uptake: 56 ± 2 ml·kg−1·min−1) performed exhaustive cycling exercise on two separate occasions. The two trials differed only by the meals ingested after exercise: 1) a high-fat diet designed to maintain energy balance or 2) a low-fat diet designed to elicit energy deficit. The CHO and protein contents of the diets were identical. The next morning, we measured plasma substrate and insulin concentrations and CHO oxidation, and we obtained muscle biopsies from the vastus lateralis for measurement of pyruvate dehydrogenase kinase (PDK)-2 and PDK-4 mRNA expression by using RT-PCR. Despite identical blood glucose (5.0 ± 0.1 and 4.9 ± 0.1 mM) and insulin (7.9 ± 1.1 and 8.4 ± 0.9 μU/ml) concentrations, plasma fatty acid and glycerol concentrations were elevated three- to fourfold during energy deficit compared with energy balance and CHO oxidation was 40% lower ( P < 0.01) the morning after energy deficit compared with energy balance (328 ± 69 and 565 ± 89 μmol/min). The lower CHO oxidation was accompanied by a 7.3 ± 2.5-fold increase in PDK-4 mRNA expression after energy deficit ( P < 0.05), whereas PDK-2 mRNA was similar between the trials. In conclusion, energy deficit increases fatty acid availability, increases PDK-4 mRNA expression, and suppresses CHO oxidation even when dietary CHO content is not reduced.

Metabolism of lipids in human white adipocyte

Adipose tissue is considered as the body's largest storage organ for energy in the form of triacylglycerols, which are mobilized through lipolysis process, to provide fuel to other organs and to deliver substrates to liver for gluconeogenesis (glycerol) and lipoprotein synthesis (free fatty acids). The release of glycerol and free fatty acids from human adipose tissue is mainly dependent on hormone-sensitive lipase which is intensively regulated by hormones and agents, such as insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). A special attention is paid to the recently discovered perilipins which could regulate the activity of the lipase hormono-sensible. Most of the plasma triacylglycerols are provided by dietary lipids, secreted from the intestine in the form of chylomicron or from the liver in the form of VLDL. Released into circulation as non-esterified fatty acids by lipoprotein lipase, those are taken up by adipose tissue via specific plasma fatty acid transporters (CD36, FATP, FABPpm) and used for triacylglycerol synthesis. A small part of triacylglycerols is synthesized into adipocytes from carbohydrates (lipogenesis) but its regulation is still debated in human. Physiological factors such as dieting/fasting regulate all these metabolic pathways, which are also modified in pathological conditions e.g. obesity.

Stable isotope tracer dilution for quantifying very low-density lipoprotein-triacylglycerol kinetics in man

BACKGROUND & AIM

A number of approaches have been employed in the past to measure very low-density lipoprotein (VLDL) triacylglycerol (TG) kinetics in humans in vivo, varying in the selection of tracer and mode of administration. All, however, make use of labeled TG precursors and more or less complicated mathematical models to derive the kinetic parameters of interest. The aim of the present study was to develop a conceptually straightforward method, based on the traditional tracer infusion technique, for quantifying VLDL-TG production rates in man using stable isotopes.

METHOD

Our approach involves ingestion of [U-13C3]glycerol to endogenously label the glycerol in VLDL-TG, plasmapheresis, isolation of the newly 13C-labeled VLDL from plasma, and administration within the next 2-3 days via a primed constant autologous reinfusion. This procedure produces enough tracer for a priming dose plus 2-3 h of infusion. In the physiological conditions examined (basal and hyperglycemic states, fat- and carbohydrate-rich diets), with almost 3-fold ranging VLDL-TG pool sizes, a steady state in plasma VLDL-TG glycerol tracer-to-tracee ratio was readily achieved within 2 h. Consequently, calculations are made according to the isotope dilution principle, thus avoiding assumptions implicit in more complicated models.

CONCLUSION

The stable isotope VLDL-TG tracer dilution method offers an alternative and reliable tool for the determination of endogenous VLDL-TG kinetics in man under a variety of metabolic states.

The associations between blood lipids and the Food Guide Pyramid: findings from the Third National Health and Nutrition Examination Survey

BACKGROUND

Dietary recommendations are based on nutrients, foods, and food groups, but the relationship between the Food Guide Pyramid (FGP) food groups and serum lipids has not been studied.

METHODS

NHANES III data were obtained for US adults who met the following criteria: aged 20-59 years, reliable participant, and typical 24-h recall. We examined whether serum lipids (serum total cholesterol (STC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triacylglycerol) were related to FGP food group intake (dairy, fruit, grain, meat, and vegetable).

RESULTS

A sample of 9111 participants qualified for this analysis. Fruit intakes were inversely related to STC, HDL-C, and LDL-C (P = 0.012, P = 0.001, and P = 0.014, respectively) and directly related to triacylglycerol levels (P = 0.003). Grain intake was inversely associated with both STC and HDL-C (P = 0.020 and P = 0.000). Dairy and meat intakes were directly related to LDL-C (P = 0.026 and P = 0.020).

CONCLUSIONS

Food groups are related to serum lipids. Universal definitions for food groups are needed in research and nutrition education. Studying the relationships between food groups and serum lipids is important for future dietary recommendations related to serum lipids.

Hyperinsulinemic diseases of civilization: more than just Syndrome X

Compensatory hyperinsulinemia stemming from peripheral insulin resistance is a well-recognized metabolic disturbance that is at the root cause of diseases and maladies of Syndrome X (hypertension, type 2 diabetes, dyslipidemia, coronary artery disease, obesity, abnormal glucose tolerance). Abnormalities of fibrinolysis and hyperuricemia also appear to be members of the cluster of illnesses comprising Syndrome X. Insulin is a well-established growth-promoting hormone, and recent evidence indicates that hyperinsulinemia causes a shift in a number of endocrine pathways that may favor unregulated tissue growth leading to additional illnesses. Specifically, hyperinsulinemia elevates serum concentrations of free insulin-like growth factor-1 (IGF-1) and androgens, while simultaneously reducing insulin-like growth factor-binding protein 3 (IGFBP-3) and sex hormone-binding globulin (SHBG). Since IGFBP-3 is a ligand for the nuclear retinoid X receptor alpha, insulin-mediated reductions in IGFBP-3 may also influence transcription of anti-proliferative genes normally activated by the body's endogenous retinoids. These endocrine shifts alter cellular proliferation and growth in a variety of tissues, the clinical course of which may promote acne, early menarche, certain epithelial cell carcinomas, increased stature, myopia, cutaneous papillomas (skin tags), acanthosis nigricans, polycystic ovary syndrome (PCOS) and male vertex balding. Consequently, these illnesses and conditions may, in part, have hyperinsulinemia at their root cause and therefore should be classified among the diseases of Syndrome X.

Carbohydrate nutrition, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort

OBJECTIVE

The aim of this study was to examine the relation between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in the Framingham Offspring Cohort.

RESEARCH DESIGN AND METHODS

We examined cross-sectional associations between carbohydrate-related dietary factors, insulin resistance, and the prevalence of the metabolic syndrome in 2,834 subjects at the fifth examination (1991-1995) of the Framingham Offspring Study. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated using the following formula (fasting plasma insulin x plasma glucose)/22.5. The metabolic syndrome was defined using the National Cholesterol Education Program criteria.

RESULTS

After adjustment for potential confounding variables, intakes of total dietary fiber, cereal fiber, fruit fiber, and whole grains were inversely associated, whereas glycemic index and glycemic load were positively associated with HOMA-IR. The prevalence of the metabolic syndrome was significantly lower among those in the highest quintile of cereal fiber (odds ratio [OR] 0.62; 95% CI 0.45-0.86) and whole-grain (0.67; 0.48-0.91) intakes relative to those in the lowest quintile category after adjustment for confounding lifestyle and dietary factors. Conversely, the prevalence of the metabolic syndrome was significantly higher among individuals in the highest relative to the lowest quintile category of glycemic index (1.41; 1.04-1.91). Total carbohydrate, dietary fiber, fruit fiber, vegetable fiber, legume fiber, glycemic load, and refined grain intakes were not associated with prevalence of the metabolic syndrome.

CONCLUSIONS

Whole-grain intake, largely attributed to the cereal fiber, is inversely associated with HOMA-IR and a lower prevalence of the metabolic syndrome. Dietary glycemic index is positively associated with HOMA-IR and prevalence of the metabolic syndrome. Given that both a high cereal fiber content and lower glycemic index are attributes of whole-grain foods, recommendation to increase whole-grain intake may reduce the risk of developing the metabolic syndrome.

Effects of moderate-fat (from monounsaturated fat) and low-fat weight-loss diets on the serum lipid profile in overweight and obese men and women

BACKGROUND

Little evidence of the effects of moderate-fat (from monounsaturated fat) weight-loss diets on risk factors for cardiovascular disease exists because low-fat diets are typically recommended. Previous studies in weight-stable persons showed that a moderate-fat diet results in a more favorable lipid and lipoprotein profile (ie, lower serum triacylglycerol and higher HDL cholesterol) than does a low-fat diet.

OBJECTIVE

We evaluated the effects of energy-controlled, low-fat and moderate-fat diets on changes in lipids and lipoproteins during weight loss and subsequent weight maintenance.

DESIGN

We conducted a parallel-arm study design in overweight and obese [body mass index (in kg/m(2)): 29.8 +/- 2.4] healthy men and women (n = 53) assigned to consume a low-fat (18% of energy) or moderate-fat (33% of energy) diet for 6 wk to achieve weight loss, which was followed by 4 wk of weight maintenance. All foods were provided and body weight was monitored to ensure equal weight loss between groups.

RESULTS

The moderate-fat diet elicited favorable changes in the lipoprotein profile. Compared with baseline, HDL cholesterol was unchanged, whereas triacylglycerol and the ratios of total and non-HDL cholesterol to HDL cholesterol were lower at the end of the weight-maintenance period in the moderate-fat diet group. Despite similar weight loss, triacylglycerol rebounded, HDL cholesterol decreased, and the ratios of total and non-HDL cholesterol to HDL cholesterol did not change during the 10-wk interval in the low-fat diet group.

CONCLUSIONS

A moderate-fat weight-loss and weight-maintenance diet improves the cardiovascular disease risk profile on the basis of favorable changes in lipids and lipoproteins. There is merit in recommending a moderate-fat weight-loss diet.

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.

Comparison of the expression and activity of the lipogenic pathway in human and rat adipose tissue

Lipogenesis is considered less active in human than in rat adipose tissue. This could be explained by different nutritional conditions, namely high-carbohydrate (HCHO) diet in rats and high-fat (HF) diet in humans. Adipose tissue was sampled (postabsorptive state) in rats and humans receiving HCHO or HF diets, ad libitum fed humans, and obese subjects. We measured 1) mRNA concentrations of fatty acid synthase (FAS), acetyl-CoA carboxylase 1 (ACC1), sterol regulatory element binding protein 1c (SREBP-1c), and carbohydrate response element binding protein (ChREBP), 2) SREBP-1c protein, and 3) FAS activity. FAS, ACC1, ChREBP, and SREBP1-c mRNA concentrations were unaffected by diet in humans or in rats. FAS and ACC1 mRNA levels were lower in humans than in rats (P < 0.05). FAS activity was unaffected by diet and was lower in humans (P < 0.05). SREBP-1c mRNA concentrations were similar in rats and humans, but the precursor and mature forms of SREBP-1c protein were less abundant in humans (P < 0.05). ChREBP mRNA concentrations were lower in humans than in rats. In conclusion, the lipogenic capacity of adipose tissue is lower in humans than in rats. This is not related to differences in diet and is probably explained by lower abundance of SREBP-1c protein. A decreased expression of ChREBP could also play a role.

Sugars, hypertriglyceridemia, and cardiovascular disease

Short-term studies consistently show that raising the carbohydrate content of the diet increases serum triacylglycerol concentrations. As compared with starches, sugars (particularly sucrose and fructose) tend to increase serum triacylglycerol concentrations by approximately 60%. The magnitude of the effect depends on other aspects of the diet, including the total amount of carbohydrate and the types of fat, carbohydrate, and fiber, but definitive studies to describe the dose-response relations are not available. Longer-term studies show that some high-carbohydrate diets are not associated with increased fasting serum triacylgycerol concentrations. However, sedentary subjects with upper-body and visceral obesity who have the metabolic syndrome tend to be at higher risk for hypertriglyceridemia in response to high-sucrose and high-carbohydrate diets; moderate weight loss mitigates the effect. Hyperinsulinemia or insulin resistance may play a role in promoting higher rates of VLDL synthesis and hypertriglyceridemia in obesity, but the mechanisms remain unclear. The effect of fructose in promoting triacylglycerol synthesis is independent of insulinemia, however. In terms of the long-term effects of diets high in sugars on the risk of cardiovascular disease, available epidemiologic evidence indicates no association of sugars or total carbohydrate intake per se, but high dietary glycemic load is associated with higher serum triacylglycerol concentrations and greater risk of coronary heart disease in women. Studies are needed to delineate the independent effects of dietary sugars and glycemic load on serum triacylglycerol concentrations in lean and obese men and women and to determine whether the elevations in fasting and fed concentrations of serum triacylglycerol with high-carbohydrate and high-sugars diets are associated with increased risk of cardiovascular disease.

Effect of isoenergetic low- and high-carbohydrate diets on substrate kinetics and oxidation in healthy men

The effect of diet composition on post-absorptive (15 h fast) fatty acid and glucose metabolism was investigated in five healthy men after 2 weeks on a low-carbohydrate (Low-CHO) diet (30 % energy intake from carbohydrates, 55 % from fat, 15 % from protein) and after 2 weeks on a high-carbohydrate (High-CHO) diet (energy intake 75, 10 and 15 % from carbohydrates, fat and protein respectively). The diets were isoenergetic and comprised real foods. Stable-isotope tracer methodology and indirect calorimetry were employed to measure glucose and fatty acid kinetics and oxidation. The relative contribution of carbohydrate to the total energy expenditure was significantly higher after the High-CHO diet. After the High-CHO diet, total and plasma fatty oxidation (2.4 (SE 0.7) and 2.1 (SE 0.4) micromol/kg per min respectively) were significantly lower than after the Low-CHO diet (4.8 (SE 0.5) and 4.6 (SE 0.8) micromol/kg per min for total and plasma fatty oxidation respectively). The rate of appearance (Ra) of non-esterified fatty acids (NEFA) in plasma and the arterial NEFA concentration were both significantly lower following the High-CHO than the Low-CHO diet. However, even after the High-CHO diet, NEFA Ra was threefold higher than plasma fatty acid oxidation. Thus, the decrease in fatty acid oxidation after consumption of a high-carbohydrate diet for 2 weeks in healthy men is unlikely to result from decreased fatty acid delivery to the tissues. Glucose Ra and arterial plasma glucose concentration were similar after the two diets. After the High-CHO diet, arterial lactate concentration was higher and total carbohydrate oxidation rate well exceeded glucose Ra in plasma. Therefore, alterations in intracellular mechanisms may limit fatty acid oxidation after high-carbohydrate diets.

Carbohydrate intake and biomarkers of glycemic control among US adults: the third National Health and Nutrition Examination Survey (NHANES III)

BACKGROUND

Recommendations for preventing and treating type 2 diabetes include consuming carbohydrates, predominantly from whole grains, fruit, vegetables, and low-fat milk. However, the quantity and type of carbohydrates consumed may contribute to disorders of glycemic control.

OBJECTIVE

We evaluated the association between carbohydrate intakes and biomarkers of glycemic control in a nationally representative sample of healthy US adults who participated in a cross-sectional study, the third National Health and Nutrition Examination Survey.

DESIGN

The sample (5730 men and 6125 women aged > or = 20 y) was divided into quintiles of carbohydrate intake (as a percentage of energy). Carbohydrate intakes were examined in relation to glycated hemoglobin (Hb A(1c)), plasma glucose, serum C-peptide, and serum insulin concentrations by using logistic regression.

RESULTS

Carbohydrate intakes were not associated with Hb A(1c), plasma glucose, or serum insulin concentrations in men or women after adjustment for confounding variables. Carbohydrate intakes were inversely associated with serum C-peptide concentrations in men and women. Odds ratios for elevated serum C-peptide concentrations for increasing quintiles of carbohydrate intake were 1.00, 0.88, 0.57, 0.39, and 0.75 (P for trend = 0.016) in men, and 1.00, 0.69, 0.57, 0.36, and 0.41 (P for trend = 0.007) in women. When carbohydrate intakes were further adjusted for intakes of total and added sugar, the association of serum C-peptide with carbohydrate intakes was strengthened in men.

CONCLUSIONS

Carbohydrate intakes were not associated with Hb A(1c), plasma glucose, or serum insulin concentrations but were inversely associated with the risk of elevated serum C-peptide; this supports current recommendations regarding carbohydrate intake in healthy adults.

The effect of fiber-rich carbohydrates on features of Syndrome X

There has been much debate among nutritionists and scientists regarding the optimal dietary approach for the treatment of the Insulin Resistance Syndrome, also called Syndrome X. This condition, which may affect as many as 47 million individuals in the United States, significantly increases risk of coronary heart disease and stroke. Major health organizations have historically recommended high-carbohydrate, low-fat (HCLF) diets to reduce chronic disease risk. However, there is evidence that a high intake of carbohydrates may adversely affect one or more of the abnormalities associated with this syndrome. Studies in this area have often had limitations. For example, some studies showing adverse effects of an HCLF diet have not taken into account the dietary fiber content of the diet. This article describes abnormalities often associated with Syndrome X, reviews the beneficial effects of fiber-rich carbohydrates, discusses the effect of fiber-rich carbohydrates on features of this syndrome, and concludes with applications of these findings for those involved in treating individuals with features of this disorder. This review indicates that an HCLF dietary pattern such as that used in the DASH trial, with a level of dietary fiber consistent with the recommendations of the American Dietetic Association (eg, 20-35g/day), containing from 3 to 10 g soluble fiber/day, may be beneficial for treating those with Syndrome X.

Effects of a hypocaloric, low-carbohydrate diet on weight loss, blood lipids, blood pressure, glucose tolerance, and body composition in free-living overweight women

The purpose of the current study was to examine the effects of a very low-carbohydrate diet on weight loss and biochemical parameters in overweight women. Twenty women completed an 8-week trial that reduced their daily carbohydrate intake from 232 to 71 g (p < 0.05) and reduced energy by 2,644 kJ/day (8,384 to 5,740 kJ, p < 0.001). The average weight loss was 5.0 kg (p < 0.0001), with a net decrease in body mass index of 1.82 kg/m2, a loss of 3.4% body fat (4 kg, p < 0.0001), and a loss of 1.0 kg lean mass (p < 0.05). There were no significant changes in fasting blood glucose, fasting serum insulin, oral glucose tolerance, free or total insulin-like growth factor-1, or total IGFBP-3. Systolicblood pressure decreased by an average of 9.0 mmHg (1 mmHg = 133.322 Pa) (p < 0.01) and diastolic blood pressure decreased by 7 mmHg (p < 0.05). Total cholesterol decreased 1.2 mM (p < 0.001), all of which was accounted for by a decrease in low-density lipoprotein cholesterol (p < 0.001) with no change in high-density lipoprotein cholesterol (baseline, 1.17 mM; week 8, 1.22 mM). Total triacylglycerol decreased 0.6 mM (p < 0.01), and the ratio of triacylglycerol/HDL also significantly decreased (baseline, 1.40; week 8, 0.87; p < 0.001). Serum beta-hydroxybutyrate concentrations rose significantly by week 2 and declined thereafter but remained significantly higher than baseline values for the duration of the intervention. Therefore, carbohydrate restriction to 70 g or less with concomitant energy restriction, without changes in protein or fat consumption, promotes weight loss, and improvements in body composition, blood pressure, and blood lipids without compromising glucose tolerance in moderately overweight women.

Changes in fat synthesis influenced by dietary macronutrient content

DE NOVO: lipogenesis is the biological process by which C2 precursors of acetyl-CoA are synthesized into fatty acids. In human subjects consuming diets higher in fat (> 30 % energy), lipogenesis is down regulated and extremely low; typically < 10 % of the fatty acids secreted by the liver. This percentage will increase when dietary fat is reduced and replaced by carbohydrate, although the extent of carbohydrate-induced lipogenesis is dependent on the type of carbohydrate (monosaccharide v. polysaccharide) and the form in which the carbohydrate is fed (liquid meals, solid less-processed food). Clearly, massive overconsumption of carbohydrate can also increase lipogenesis. A second related phenomenon that occurs when dietary fat is reduced is hypertriacylglycerolaemia. This rise in blood triacylglycerol concentration could be due to increased de novo lipogenesis or to reduced clearance of lipid from the blood. The present paper will review the metabolic mechanisms leading to the elevations in blood triacylglycerol concentration that occur with dietary fat reduction. Studies considered will be those investigating fatty acid synthesis in subjects chronically fed low-fat high-carbohydrate diets and studies in which data were obtained in both the fasted and fed states. Also summarized will be data from subjects who had consumed diets of different carbohydrate types, as well as the most recent data from postprandial studies investigating factors that affect the magnitude of the rise in blood lipids following a meal. Given the changing availability of carbohydrate in the food supply, it will be important to understand how the balance of fat and carbohydrate in the diet influences lipogenesis, and the relative contribution of the process of de novo lipogenesis to the escalating incidence of obesity observed around the world.

Carbohydrate-induced hypertriglyceridemia: modifying factors and implications for cardiovascular risk

High-carbohydrate/low-fat, isocaloric diets have repeatedly been shown to increase plasma triglyceride concentrations. The present review addresses recent developments relevant to several important unresolved issues. These include the type of dietary carbohydrate that is most likely to induce hypertriglyceridemia, predictors of individual susceptibility, modifiable physiologic factors that may mitigate the plasma triglyceride response, underlying metabolic mechanisms that are responsible for increased plasma triglycerides, and implications of altered serum lipid profiles for atherogenic risk. Although some progress has been made in this field, the central public health issue - the net effect on cardiovascular risk - remains unresolved.

Exercise prevents the accumulation of triglyceride-rich lipoproteins and their remnants seen when changing to a high-carbohydrate diet

We tested the hypothesis that daily aerobic exercise opposes the fasting hypertriglyceridemia and exaggerated postprandial lipemia observed after substituting dietary fat with carbohydrate. Eight healthy postmenopausal women aged 51 to 66 years consumed the same high-fat mixed meal on 3 occasions: (1) after 3 days on a low-carbohydrate diet (35%, 50%, and 15% energy from carbohydrate, fat, and protein, respectively); (2) after 3 days on an isoenergetic high-carbohydrate diet (corresponding values 70%, 15%, and 15%); and (3) after 3 days on the same high-carbohydrate diet with 60 minutes of brisk walking daily. Plasma triglycerides were higher after the high-carbohydrate diet than after the low-carbohydrate diet: fasting, 1.58+/-0.19 versus 0.96+/-0.12 mmol/L, respectively; 6-hour postprandial area under concentration versus time curve, 13.74+/-1.57 versus 10.12+/-1.15 (mmol/L)xhour, respectively (both P<0.01). In the fasted and postprandial states, concentrations of apolipoproteins B-48 and B-100 in the triglyceride-rich lipoprotein fraction were significantly higher after the high-carbohydrate diet, as was the concentration of remnant-like lipoprotein particle cholesterol (a measure of lipoprotein remnants). These carbohydrate-induced increases in the number of circulating triglyceride-rich particles and their remnants were abolished when subjects had exercised daily during the high-carbohydrate diet.