Deleterious metabolic effects of high-carbohydrate, sucrose-containing diets in patients with non-insulin-dependent diabetes mellitus

The effects of variations in dietary carbohydrate and fat intake on various aspects of carbohydrate and lipid metabolism were studied in patients with non-insulin-dependent diabetes mellitus (NIDDM). Two test diets were utilized, and they were consumed in random order over two 15-day periods. One diet was low in fat and high in carbohydrate, and corresponded closely to recent recommendations made by the American Diabetes Association (ADA), containing (as percent of total calories) 20 percent protein, 20 percent fat, and 60 percent carbohydrate, with 10 percent of total calories as sucrose. The other diet contained 20 percent protein, 40 percent fat, and 40 percent carbohydrate, with sucrose accounting for 3 percent of total calories. Although plasma fasting glucose and insulin concentrations were similar with both diets, incremental glucose and insulin responses from 8 a.m. to 4 p.m. were higher (p less than 0.01), and mean (+/- SEM) 24-hour urine glucose excretion was significantly greater (55 +/- 16 versus 26 +/- 4 g/24 hours p less than 0.02) in response to the low-fat, high-carbohydrate diet. In addition, fasting and postprandial triglyceride levels were increased (p less than 0.001 and p less than 0.05, respectively) and high-density lipoprotein (HDL) cholesterol concentrations were reduced (p less than 0.02) when patients with NIDDM ate the low-fat, high-carbohydrate diet. Finally, since low-density lipoprotein (LDL) concentrations did not change with diet, the HDL/LDL cholesterol ratio fell in response to the low-fat, high-carbohydrate diet. These results document that low-fat, high-carbohydrate diets, containing moderate amounts of sucrose, similar in composition to the recommendations of the ADA, have deleterious metabolic effects when consumed by patients with NIDDM for 15 days. Until it can be shown that these untoward effects are evanescent, and that long-term ingestion of similar diets will result in beneficial metabolic changes, it seems prudent to avoid the use of low-fat, high-carbohydrate diets containing moderate amounts of sucrose in patients with NIDDM.     

The effects of high-carbohydrate and high-fat diets on the serum lipid and lipoprotein concentrations of endurance athletes

We examined the effects of high-carbohydrate and high-fat diets on the serum lipid levels of distance runners. For seven days before each study, subjects consumed a diet containing 15% protein, 32% fat, and 53% carbohydrate. During 14-day experimental periods, a control group (n = 10) continued the same diet while two other groups consumed 69% of their calories as either carbohydrate (n = 13) or fat (n = 14). High-density lipoprotein (HDL)-cholesterol decreased 9% during the high-carbohydrate diet because of a 26% fall in the HDL2 fraction (1.063 to 1.125 g/mL). These changes were not accompanied by changes in the levels of apolipoproteins (apo) A-I or A-II. Total and low-density lipoprotein (LDL)-cholesterol initially decreased but subsequently exceeded pre-diet values while triglyceride concentrations increased 30% to 50%. Postheparin lipoprotein lipase activity (LPLA) fell 20%. Despite these dietary effects, HDL and HDL2 cholesterol concentrations in the athletes remained above values typical of sedentary men. The high-fat diet produced different effects on the serum lipids and lipoprotein levels of the athletes. HDL levels changed little during the study although HDL-cholesterol and apo A-I on the last diet day were both slightly above initial values. The high-fat diet provided 111 g of saturated fat per day but had surprisingly little effect on total and LDL-cholesterol whereas serum triglycerides fell by 10% to 20%. Postheparin LPLA increased 30% with fat feeding and the changes in LPLA correlated with alterations in triglyceride levels (r = -0.53, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired HDL response to fat in men with coronary artery disease

A low HDL cholesterol is found frequently in subjects with premature coronary artery disease. We speculated that individuals with a normal total cholesterol and coronary artery disease have an impaired HDL response to dietary fat. Twenty-one men with recently diagnosed coronary artery disease and total plasma cholesterol of <6 mmol/l were matched by age, weight and cholesterol with 26 men with no personal or family history of coronary artery disease. They were placed sequentially on a 25% fat diet for 2 weeks, a high carbohydrate supplement which reduced fat to 16% of energy for 3 weeks and a high monounsaturated fat supplement which increased fat to 35% for a final 3-week period. Half of the subjects underwent an intravenous glucose tolerance test at the end of the intervention periods. The high fat supplement increased HDL cholesterol from 0.79 to 0.89 mmol/l in the men with coronary artery disease while HDL increased from 0.88 to 1.05 mmol/l in the control group (P<0.05 for group difference). Plasma triglyceride fell by 0.79 and 0.45 mmol/l in cases and controls respectively (P<0.05 for group difference). LDL cholesterol fell by 0.2 mmol/l in both groups. Men with coronary artery disease had an enhanced insulin response during the intravenous glucose tolerance test (P<0.03) particularly in the low fat phase. Thus men with premature coronary artery disease and a low HDL cholesterol appear to have an impaired elevation of HDL cholesterol in response to dietary fat, and insulin resistance may underlie this response.     

Urinary albumin excretion rate and 24-h ambulatory blood pressure in NIDDM with microalbuminuria: effects of a monounsaturated-enriched diet

Summary Previous studies have shown that unsaturated fat-enriched diets may have a beneficial effect on blood pressure in non-insulin-dependent diabetic (NIDDM) patients, whereas little is known about the effects on albuminuria. In a 3-week cross-over design we compared the effects of a currently recommended high-carbohydrate diet (50% carbohydrate, 30% fat [10% monounsaturated fat]) vs a diet rich in monounsaturated fat (30% carbohydrate, 50% fat [30% monounsaturated fat]) on urinary albumin excretion rate, 24-h ambulatory blood pressure and metabolic control in ten NIDDM patients with persistent microalbuminuria. The 24-h ambulatory blood pressure was similar before and after both the high-carbohydrate diet (mean±SD: 145/78±25/10 vs 143/79±19/10 mmHg (NS) and the monounsaturated fat diet: 140/78±16/8 vs 143/79±15/8 mmHg (NS). No changes were observed in day or night-time blood pressures. Urinary albumin excretion rate was unaffected after 3 weeks' treatment by the diets: from (geometric mean ×/÷ tolerance factor) 32.4×/÷2.1 to 36.0×/÷1.9 g/min (NS) vs from 34.2×/÷1.9 to 32.1×/÷2.1 g/min (NS). Fasting plasma glucose, serum fructosamine and HbA_1c as well as lipid and lipoprotein concentrations were stable during both diets. Compared to the high-carbohydrate diet a reduction in the LDL/HDL cholesterol ratio was observed during the monounsaturated fat diet (p<0.03). In conclusion, compared to a high-carbohydrate diet, 3 weeks' treatment with a monounsaturated fat diet did not affect the levels of 24-h ambulatory blood pressure or albuminuria in microalbuminuric NIDDM patients. Moreover, glycaemic control and lipoprotein levels were unchanged, although a potential beneficial effect on the LDL/HDL-cholesterol ratio was noted. Monounsaturated fat represents an alternative in the diets of NIDDM patients especially when caloric intake is not a concern.Abbreviations UAE Urinary albumin excretion rate - NIDDM non-insulin-dependent diabetes mellitus - MUFA monounsaturated fatty acids - PUFA polyunsaturated fatty acids - ANOVA analysis of variance - CHO carbohydrate - CI confidence interval     

Serum lipid effects of a high-monounsaturated fat diet based on macadamia nuts

BACKGROUND: Recent studies have identified potential beneficial effects of eating nuts, most of which have substantial amounts of monounsaturated fats. Macadamia nuts are 75% fat by weight, 80% of which is monounsaturated. OBJECTIVE: To examine variations in serum lipid levels in response to a high-monounsaturated fat diet based on macadamia nuts. METHODS: A randomized crossover trial of three 30-day diets was conducted in 30 volunteers aged 18 to 53 years from a free-living population. Each was fed a "typical American" diet high in saturated fat (37% energy from fat); an American Heart Association Step 1 diet (30% energy from fat); and a macadamia nut-based monounsaturated fat diet (37% energy from fat) in random order. Serum total cholesterol, high-density lipoprotein cholesterol, and triglyceride levels were measured. RESULTS: Mean total cholesterol level after the typical American diet was 5.20 mmol/L (201 mg/dL). After the Step 1 diet and the macadamia nut diet, total cholesterol level was 4.99 mmol/L (193 mg/dL) and 4.95 mmol/L (191 mg/dL), respectively. Low-density lipoprotein cholesterol level was 3.37 mmol/L (130 mg/dL) (typical diet), 3.21 mmol/L (124 mg/dL) (Step 1 diet), and 3.22 mmol/L (125 mg/dL) (macadamia nut diet). High-density lipoprotein cholesterol level was 1.43 mmol/L (55 mg/dL) (typical), 1.34 mmol/L (52 mg/dL) (Step 1), and 1.37 mmol/L (53 mg/dL) (macadamia nut). Lipid values after the Step 1 and macadamia nut diets were significantly different from those after the typical diet (P<.05). CONCLUSIONS: The macadamia nut-based diet high in monounsaturated fat and the moderately low-fat diet both had potentially beneficial effects on cholesterol and low-density lipoprotein cholesterol levels when compared with a typical American diet.     

Postprandial lipemia after short-term variation in dietary fat and carbohydrate

Replacement of dietary fat with carbohydrate may not reduce the overall risk of coronary heart disease (CHD), because this elevates plasma triacylglycerol (TAG) concentrations. The lipoproteinemic effects of a high-carbohydrate diet are likely to be more marked shortly after the initiation of such a diet than after longer periods of intervention during which adaptive processes may counteract the initial effects. Therefore, we studied the postprandial responses to a standard meal after 3-day dietary intervention periods. An additional objective was to establish a model for future study of the mechanisms involved. Nine normolipidemic men consumed the meal (1.2 g fat, 1.1 g carbohydrate, and 0.2 g protein per 1 kg body mass) after 3 days on a high-carbohydrate diet (68% +/- 3% energy from carbohydrate, mean +/- SD) and also after 3 days on an isoenergetic high-fat diet (66% +/- 5% energy). Venous blood samples were obtained from fasted subjects and for 6 hours after the meal. In the fasted state, TAG was higher after the high-carbohydrate diet (1.18 +/- 0.18 v0.62 +/- 0.09 mmol/L, mean +/- SEM, P = .02) and high-density lipoprotein (HDL) cholesterol was lower (1.01 +/- 0.08 v 1.10 +/- 0.09 mmol/L, P = .002). The area under the plasma TAG concentration versus time curve was 42% +/- 7% higher after the high-carbohydrate diet (P = .003). After the high-carbohydrate diet, the postprandial insulin response did not differ between trials, but glucose and 3-hydroxybutyrate responses were lower (P = .009 and P = .02, respectively) and the lactate response was higher (P = .001). Plasma nonesterified fatty acids (NEFAs) were lower after the high-carbohydrate diet in the fasted state and for 4 hours postprandially, but were higher thereafter (interaction of time x trial, P = .001). These results indicate that compared with a high-fat diet, the plasma TAG response to a standard high-fat meal is markedly higher after a few days on a high-carbohydrate diet, with major differences in the associated metabolic milieu. The magnitude of these changes and the rapidity with which they developed suggest that this model may be attractive for future studies of the underlying mechanisms.     

Characterization of high-density lipoprotein binding to guinea pig hepatic membranes: effects of dietary fat quality and cholesterol feeding

The effects of dietary fat quality and cholesterol intake on expression of guinea pig hepatic membrane high-density lipoprotein (HDL) binding sites were studied. Animals were fed semisynthetic diets containing 7.5% (wt/wt) of either corn oil (CO), olive oil (OL), or lard. The cholesterol diet was prepared by incorporating 0.25% recrystallized cholesterol into standard guinea pig chow. Plasma cholesterol levels of guinea pigs on the CO diet were significantly lower (P less than .02) than animals on the OL or lard diets. HDL cholesterol levels did not differ between the polyunsaturated, monounsaturated, and saturated dietary fat groups. Guinea pigs on the high cholesterol diet had increased total and HDL cholesterol levels compared with animals on the chow diet (P less than .01). Initial studies demonstrated that HDL binding to hepatic membranes was temperature-dependent. A threefold increase in binding was observed when assays were performed at 37 degrees C, as compared with 4 degrees C, for all membrane preparations. Dietary fat quality and dietary cholesterol intake significantly altered HDL binding to hepatic membranes with increased HDL binding to membranes of animals fed polyunsaturated fat and the high cholesterol diet. At 37 degrees C, HDL binding to hepatic membranes of CO-fed animals was 26% and 46% higher than for membranes of OL- and lard-fed guinea pigs, respectively. A high cholesterol intake increased HDL binding by 24% at both 4 degrees C and 37 degrees C. Scatchard analysis demonstrated that while membrane affinity for HDL (Kd) was not affected by diet, changes did occur in the total number of HDL binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effect of the Mediterranean diet on fasting concentrations of activated factor VII in healthy persons

INTRODUCTION AND OBJECTIVES: Many clinical and epidemiologic studies suggest that activated factor VII may be involved in the pathogenesis of coronary heart disease. Our objective was to determine the effect of a Mediterranean diet on plasma levels of activated factor VII in comparison to a low-fat diet and a diet rich in saturated fat. PATIENTS AND METHOD: The study population comprised 16 healthy normolipemic men who consumed 3 different diets in consecutive 28-day periods. The first diet was rich in saturated fat (38% calories as fat, 20% saturated fat), the second was a low-fat, high-carbohydrate diet (28% calories as fat, 10% saturated fat), and the third was enriched in monounsaturated fatty acids (38% calories as fat, 22% monounsaturated fat). At the end of each period, plasma concentrations of total cholesterol, HDL cholesterol, LDL cholesterol, total triglycerides, apolipoprotein A-I, apolipoprotein B, and glucose were measured. Activated factor VII was determined with a coagulation assay. RESULTS: The diet rich in saturated fat was associated with a significant increase in total cholesterol, LDL cholesterol, apolipoprotein AI, and apolipoprotein B in comparison to the other 2 diets. There were no significant differences between the carbohydrate-rich diet and the Mediterranean diet in any of the lipid parameters. The Mediterranean diet decreased plasma levels of factor VIIa in comparison to the diet rich in saturated fat (34.6+/-15.3 mU/mL vs 101.5+/-19.2 mU/mL; P<.05). CONCLUSIONS: In comparison to the diet rich in saturated fat or the high-carbohydrates diet, the Mediterranean diet decreased plasma concentrations of activated factor VII in healthy young men. This phenomenon may constitute another protective mechanism of the Mediterranean diet in reducing cardiovascular risk.     

Dietary fats, carbohydrates and vascular disease: Sri Lankan perspectives

The recent estimates for mortality from cardio and cerebrovascular diseases (CVD) for Sri Lanka--524 deaths per 100,000--is higher than that observed in many Western economies. However, neither an excessive total fat intake nor an increase in the more traditional plasma lipid markers, total and LDL cholesterol (LDL-c) levels may fully explain the increased vulnerability to CVD in this population. The average total fat intake of Sri Lankans is 25 percent of total energy (en%) and the reported total and LDL-c values are 4.9 and 2.5 mmol/l, respectively. With regard to the type of dietary fatty acids, the ratio of saturated/polyunsaturated fatty acids (PUFAs) in the average Sri Lankan diet is 9/1 as compared with the current recommended ratio of <1/1. In spite of an adequate total fat intake (25 en%), the relatively low intake of PUFAs in association with a high carbohydrate diet (65 en%), appear to be resulting in similar metabolic outcomes to those of very low fat diets (VLFD, < 15 en% from fat), as reflected by high triglycerides and low HDL levels. Metabolic abnormalities including elevated postprandial hyperlipidemia, more atherogenic lipoprotein particles, hyperglycemia with resultant hyperinsulinemia and increased oxidative stress are likely to be more relevant in such settings. The application of novel biomarkers for example, lipoprotein measurements in the postprandial state, LDL particle size, estimates of endothelial dysfunction, soluble markers of inflammation and coagulability status may provide further insight into cardiovascular disease states in populations where the dietary matrix represents high intakes of highly digestible carbohydrates and saturated fat.     

Short-term effects of substituting protein for carbohydrate in the diets of moderately hypercholesterolemic human subjects

The short-term effects on plasma lipoprotein lipids of substituting meat and dairy protein for carbohydrate in the diets of 10 free-living moderately hypercholesterolemic human subjects (four men, six women) were studied under closely supervised dietary control during the consumption of constant, low intakes of fat and cholesterol and the maintenance of stable body weight as well as constant fiber consumption. Subjects were randomly allocated to either the high or low protein diets (mean, 23% v 11% of energy as protein, 24% as fat, and 53% v 65% as carbohydrate) and then switched to the other diet for another 4 to 5 weeks. Mean fasting plasma high-density lipoprotein cholesterol (HDL-C) was significantly higher by 12% +/- 4% (0.97 +/- 0.08 v 0.89 +/- 0.08 mmol/L, P less than .01), whereas mean total cholesterol (TC) was lower by 6.5% +/- 1.3% (5.7 +/- 0.3 v 6.1 +/- 0.3 mmol/L, P less than .001), mean low-density lipoprotein-cholesterol (LDL-C) lower by 6.4% +/- 2.0% (4.5 +/- 0.2 v 4.8 +/- 0.2 mmol/L, P less than .02), mean total triglycerides (TG) lower by 23% +/- 5% (1.7 +/- 0.1 v 2.4 +/- 0.3 mmol/L, P less than .02), and mean high versus low protein diet. Mean values for LDL-C were significantly lower during weeks 3 to 5 of the high protein diet than during either weeks 1 to 5 or weeks 1 to 2 of the high protein diet (4.3 +/- 0.3, 4.5 +/- 0.2, and 4.7 +/- 0.3 mmol/L, respectively, P less than .05) and 11% +/- 3% lower than on low protein diet, P less than .005. The ratio of plasma LDL-C to HDL-C was consistently lower by 17% +/- 3% during the high versus low protein diet (4.9 +/- 0.5 v 5.8 +/- 0.5, P less than .001). Lowering plasma TC and LDL-C and total TG and VLDL-TG and increasing HDL-C by chronic isocaloric substitution of dietary for carbohydrate may enhance the cardiovascular risk reduction obtained by restriction of dietary fat and cholesterol.     

Effects of a low-fat diet on plasma lipoprotein levels

Lowering the intake of fat to decrease serum cholesterol levels has unknown effects on the proportion of cholesterol in low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Twenty normolipidemic nonvegetarians were given dietary instruction and supervision in a low-fat, semivegetarian diet for three months. Mean consumption of total fat, saturated fat, and cholesterol decreased, whereas intake of carbohydrate increased significantly on a low-fat diet. Plasma LDL levels decreased by 18% and HDL levels by 7% from prestudy baseline levels. The LDL/HDL ratio declined by 11%. Plasma triglyceride levels and body weight were unchanged. In individual subjects, the decrements in consumption of saturated fat and the increments in ingestion of polyunsaturated fat were each significantly correlated with decreases in LDL. One year after the subjects had returned to a self-selected diet, levels of dietary saturated fat and cholesterol and the plasma LDL/HDL ratio remained significantly below prestudy levels. This study and others suggest that a low-fat, high-carbohydrate diet favorably affects the plasma LDL/HDL proportion by decreasing LDL on a percentage basis 2 1/2 to three times more than it decreases HDL.     

Dietary omega-3 fatty acids prevent carbohydrate-induced hypertriglyceridemia

Dietary fish oils rich in omega-3 fatty acids are remarkably hypotriglyceridemic in both normal and hypertriglyceridemic subjects. This present study was designed to examine the hypothesis that dietary fish oils could prevent the usual sharp increase in plasma triglyceride and very low-density lipoprotein (VLDL) levels that occur physiologically after the induction by a high-carbohydrate diet. Seven healthy volunteers consumed three experimental liquid formula diets: the baseline diet (45% fat, 10% protein, 45% carbohydrate) and two high-carbohydrate diets (15% fat, 10% protein, 75% carbohydrate), one as a control diet and the other containing fish oil. The baseline and control dietary fats were a mixture of peanut oil and cocoa butter, whereas the fish oil diet contained high levels of omega-3 fatty acids. The plasma triglyceride levels rose from 105 mg/dL during baseline diet to 194 mg/dL during the high-CHO control diet (P less than 0.005). VLDL triglyceride levels increased from 69 to 156 mg/dL (P less than 0.005) and VLDL cholesterol from 18 to 34 mg/dL (P less than 0.005). When fish oil was substituted for the control fats, plasma triglyceride levels fell from 194 to 75 mg/dL (P less than 0.005), VLDL triglyceride and cholesterol levels were reduced from 156 to 34 mg/dL (P less than 0.005) and from 34 to 12 mg/dL (P less than 0.005), respectively. These effects were noted by two to three days after beginning the fish oil diet. Thus, dietary omega-3 fatty acids from fish oil rapidly and markedly reduced VLDL triglyceride levels even in the face of a high-carbohydrate diet.(ABSTRACT TRUNCATED AT 250 WORDS)     

A low-fat high-carbohydrate diet supplemented with long-chain n-3 PUFA reduces the risk of the metabolic syndrome

Objective

Dietary changes are major factor in determining cardiovascular risk. We assessed the effects of isoenergetic diets with different fat quantity and quality on the incidence and regression of the metabolic syndrome (MetS) from the LIPGENE project.

Methods and design

Clinical intervention study: the patients (n = 337) were randomly assigned to one of four diets for 12 weeks each: two high fat diets, one rich in saturated fat (HSFA) and the other rich in monounsaturated fat (HMUFA), and two low fat diets, one high in complex carbohydrates (LFHCC) supplemented with 1.24 g/day of long-chain n-3 polyunsaturated fatty acids (LFHCC n-3) and the other LFHCC diet with placebo (LFHCC). Measurements: the effects on MetS risk criteria were recorded before and after the intervention period.

Results

An enlarged waist circumference (≥88 cm for women and ≥102 cm for men) was present among 95% of the participants, 88% had elevated blood pressure (>130/85 mm Hg or antihypertensive drugs), 77% had elevated fasting plasma glucose (≥5.55 mmol/L), 51% were hypertriacylglycerolemic (≥1.7 mmol/L), and 72% had low HDL cholesterol (<1.0 mmol/L for men, and <1.3 mmol/L for women). The prevalence of enlarged waist circumference, hypertension and hypertriacylglycerolemia were reduced after the LFHCC n-3 diet (p < 0.05). Thus the prevalence of MetS fell by 20.5% after LFHCC n-3 diet compared with the HSFA (10.6%), HMUFA (12%) diet or LFHCC (10.4%) diets (p < 0.028).

Conclusions

The consumption of a low-fat high-carbohydrate supplemented with n-3 diet reduced the risk of MetS as compared with isoenergetic high-fat (HSFA and HMUFA) and LFHCC diets.     

Comparison of the effects on insulin sensitivity of high carbohydrate and high fat diets in normal subjects.

To examine whether achievable dietary changes influence insulin sensitivity, we performed euglycemic hyperinsulinemic glucose clamps in eight normal subjects who were prescribed high carbohydrate and high fat diets. The high carbohydrate diet was more than 50% (of energy intake) carbohydrate and less than 30% fat; the high fat diet was more than 45% fat (predominantly saturated) and less than 40% carbohydrate. The diets were consumed over consecutive 3-week periods in random sequence. The mean whole body glucose uptake during the glucose clamps was similar after the high carbohydrate (48.3 mumol/kg.min) and high fat diets (47.0 mumol/kg.min; P = 0.5; 95% confidence interval for the difference, -3.4 to 5.9 mumol/kg.min). Fasting blood glucose and serum insulin concentrations were also unchanged. In contrast, there were substantial effects on lipoprotein metabolism. During the high carbohydrate diet, fasting serum cholesterol decreased by 17% (P = 0.06), low density lipoprotein cholesterol decreased by 20% (P = 0.05), high density lipoprotein cholesterol decreased by 24% (P less than 0.005), and triglyceride increased by 33% (P = 0.06) compared with levels during the high fat diet. These results suggest that practically achievable high carbohydrate diets do not enhance insulin sensitivity in nondiabetic subjects and have net effects on lipoprotein metabolism that may be unfavorable.     

Dietary restriction of saturated fat and cholesterol decreases HDL ApoA-I secretion

We examined the mechanisms responsible for the decrease in HDL cholesterol (HDL-C) levels after the consumption of a diet low in total fat, saturated fat, and cholesterol. Twenty-one subjects with a mean age of 58+/-12 years were placed on a baseline isocaloric diet (15% protein, 49% carbohydrate, 36% fat, and 150 mg/1000 kcals of cholesterol) and then switched to an NCEP Step 2 diet (15% protein, 60% carbohydrate, 25% fat, and 45 mg/1000 kcals of cholesterol). After 6 or 24 weeks on each diet, subjects received a 15-hour primed-constant infusion of [5,5,5-2H3]-L-leucine. HDL apoA-I and apoA-II tracer curves were determined by gas chromatography-mass spectrometry and fitted to a monoexponential equation. Compared with the baseline diet, consumption of the Step 2 diet lowered HDL-C mean levels by 15% (1.03+/-0.23 to 0.88+/-0.16 mmol/L, P<0.001), apoA-I by 12% (1.25+/-0.15 to 1.10+/-0.13 g/L, P<0. 001) and the TC/HDL-C ratio by 5% (0.145+/-0.04 to 0.137+/-0.03). No significant changes were observed in apoA-II levels and HDL particle size with diet. HDL apoA-I fractional catabolic rate did not change (0.219+/-0.052 to 0.220+/-0.043 pools/day, P=0.91) but HDL apoA-I secretion rate decreased by 8% (12.26+/-3.07 to 10.84+/-2.11 mg. kg-1. day-1, P=0.03) during consumption of the Step 2 diet. There was no effect of diet on apoA-II fractional catabolic rate or secretion rate. Our results indicate that the decrease in HDL-C and apoA-I levels during the isocaloric consumption of a Step 2 diet paralleled the reductions in apoA-I secretion rate.     

Isocaloric substitution of plant sterol-enriched fat spread for carbohydrate-rich foods in a low-fat, fibre-rich diet decreases plasma low-density lipoprotein cholesterol and increases high-density lipoprotein concentrations

BACKGROUND AND AIM: The aim of the study was to determine the effects on plasma cholesterol of replacing a plant sterol-enriched fat spread with carbohydrate-rich foods relative to a diet high in saturated fat. METHODS AND RESULTS: Twenty-nine men and women, from the general community, with mean age (SD) 48 (14)y, body mass index 29.0 (6.2)kg/m(2), and plasma total cholesterol concentration 6.48 (0.97)mmol/L completed the randomised, crossover dietary intervention. There were three diets: New Zealand diet (NZ diet) high in total (34%kJ) and saturated (15%kJ) fat, a cholesterol-lowering fibre-rich diet reduced in total (30%kJ) and saturated fat (8%kJ) but including a plant sterol spread (PS diet), and the same cholesterol-lowering diet with the plant sterol spread isocalorically replaced with carbohydrate (CHO diet); total fat, 26%kJ; saturated fat 7%kJ. All foods were provided and each diet was followed for four weeks. Mean (SD) plasma low-density lipoprotein cholesterol concentration declined from 4.68 (0.91)mmol/L on the high saturated fat diet to 4.12 (0.83)mmol/L (P<0.001) on the carbohydrate diet and 3.76 (0.84)mmol/L (P<0.001) on the plant sterol diet. The 20% decrease on the plant sterol diet was significantly greater (P<0.001) than the 12% decrease on the carbohydrate diet. Relative to the NZ diet, mean (95% CI) plasma high-density lipoprotein cholesterol concentration changed by -0.11 (-0.16, -0.06)mmol/L on the CHO diet but was not different at the end of the PS diet, -0.03 (-0.09, 0.02). CONCLUSION: Including a plant sterol-enriched fat spread in a cholesterol-lowering diet produces a more favourable plasma lipid profile than the same diet made lower in total and saturated fat by replacing the spread with carbohydrate-rich foods.     

The APOB -516C/T polymorphism has no effect on lipid and apolipoprotein response following changes in dietary fat intake in a healthy population

Our goal was to determine whether the presence of the −516C/T polymorphism in the APOB gene promoter modifies the lipid response to changes in the amount and quality of dietary fat. We studied 97 young healthy volunteers (70 males and 27 females), 62 homozygotes for the −516C allele (C/C) (47 males and 15 females), 34 heterozygotes for the −516T allele (C/T) (22 males and 12 females) and one male homozygote for the −516T allele (T/T). Subjects consumed three different diets in successive 4-week dietary periods. During the first 28 days, all subjects consumed a saturated fatty acid (SFA)-rich diet (38% fat and 20% SFA). Then, using a randomized crossover design, subjects were assigned a carbohydrate (CHO)-rich diet (30% fat and 55% carbohydrate) or a monounsaturated fatty acid (MUFA)-rich diet (38% fat and 22% MUFA). At the end of each dietary period, plasma concentrations of triacylglycerols and of total, LDL, and HDL cholesterol were measured. No differences in plasma lipid and apolipoprotein response were found after changes in dietary fat intake in relation to the −516C/T polymorphism in our study population. In conclusion, our data suggest that the APOB −516C/T polymorphism has no effect on the lipid profile after changes in dietary fat intake in a healthy population.     

Effects of soy protein and casein in low cholesterol diets on plasma lipoproteins in normolipidemic subjects

Dietary plant proteins may lower plasma cholesterol and LDL concentrations in hypercholesterolemic patients when substituted for animal proteins, particularly in diets with low cholesterol and saturated fat content. Plant protein diets appear, however, to be without effect on plasma lipoprotein levels in normal subjects. In the present study, we have examined whether the origin of the dietary protein, i.e. plant (soy) or animal (casein), affects the plasma lipoproteins in normolipidemic subjects when these proteins are presented as components of diets low in cholesterol and saturated fat. The study followed a crossover design. Five men and 5 women consumed liquid formula diets containing 20% of calories as casein or soy protein, 28% as fat (mainly monounsaturated), and 52% as carbohydrate; the intake of cholesterol was less than 100 mg per day. The two dietary periods, each of 1 month duration, were separated by an interim period of 1 month on self-chosen food. Following an initial 30% reduction of cholesterol and LDL plasma levels on both diets, the concentrations of each of the major lipoprotein classes (VLDL, IDL, LDL, HDL2 and HDL3) were similar during the two experimental dietary periods. Body weights were essentially constant. Dietary soy protein and casein could not be distinguished in their effects on the plasma concentrations and chemical composition of the major lipoprotein classes in normolipidemic subjects.     

A low-carbohydrate/high-fat diet improves glucoregulation in type 2 diabetes mellitus by reducing postabsorptive glycogenolysis

The aim of this study was to examine the mechanisms by which dietary carbohydrate and fat modulate fasting glycemia. We compared the effects of an eucaloric high-carbohydrate (89% carbohydrate) and high-fat (89% fat) diet on fasting glucose metabolism and insulin sensitivity in seven obese patients with type 2 diabetes using stable isotopes and euglycemic hyperinsulinemic clamps. At basal insulin levels glucose concentrations were 148 +/- 11 and 123 +/- 11 mg/dl (8.2 +/- 0.6 and 6.8 +/- 0.6 mmol/liter) on the high-carbohydrate and high-fat diet, respectively (P < 0.001), with insulin concentrations of 12 +/- 2 and 10 +/- 1 microIU/ml (82 +/- 11 and 66 +/- 10 pmol/liter) (P = 0.08). Glucose production was higher on the high-carbohydrate diet (1.88 +/- 0.06 vs. 1.55 +/- 0.05 mg/kg.min (10.44 +/- 0.33 vs. 8.61 +/- 0.28 micromol/kg.min) (P < 0.001) because of higher glycogenolysis. Gluconeogenic rates were not different between the diets. During the use of hyperinsulinemic euglycemic clamps, insulin-mediated suppression of glucose production and stimulation of glucose disposal were not different between the diets. Free fatty concentrations were suppressed by 89 and 62% (P < 0.0001) on the high-carbohydrate and high-fat diet, respectively. We conclude that short-term variations in dietary carbohydrate to fat ratios affect basal glucose metabolism in people with type 2 diabetes merely through modulation of the rate of glycogenolysis, without affecting insulin sensitivity of glucose metabolism.