The hyperlipemic effect of a low-fat, high-carbohydrate diet in diabetic subjects

Carbohydrate restriction for diabetes: rediscovering centuries-old wisdom

Carbohydrate restriction, used since the 1700s to prolong survival in people with diabetes, fell out of favor after the discovery of insulin. Despite costly pharmacological and technological developments in the last few decades, current therapies do not achieve optimal outcomes, and most people with diabetes remain at high risk for micro- and macrovascular complications. Recently, low-carbohydrate diets have regained popularity, with preliminary evidence of benefit for body weight, postprandial hyperglycemia, hyperinsulinemia, and other cardiometabolic risk factors in type 2 diabetes and, with more limited data, in type 1 diabetes. High-quality, long-term trials are needed to assess safety concerns and determine whether this old dietary approach might help people with diabetes attain clinical targets more effectively, and at a lower cost, than conventional treatment.

Lipoprotein and apolipoprotein abnormalities in familial combined hyperlipidemia: a 20-year prospective study

In order to characterize the lipoprotein abnormalities in familial combined hyperlipidemia (FCHL) and to describe factors associated with the stability of the FCHL phenotype during 20-year follow-up, 287 individuals from 48 families with FCHL originally identified in the early 1970s (baseline) were studied. Hyperlipidemia was defined as lipid-lowering medication use, or > or =age- and sex-specific 90th percentile for triglycerides or cholesterol. Triglyceride, cholesterol and medical history data were obtained at baseline and 20-year follow-up. Additional follow-up measures included HDL-C, LDL-C, LDL particle size, lipoprotein(a), apolipoprotein (apo) A-I, apoB, and apoE polymorphism. Longitudinally, two-thirds of relatives were consistently normolipidemic or hyperlipidemic, and one third were discordant for hyperlipidemic status at baseline and 20-year follow-up. Individuals with hyperlipidemia at baseline and/or follow-up had higher apoB levels than those with consistently normal lipids (P<0.05), whereas small LDL size was associated with concurrent hyperlipidemia. Among individuals who were normolipidemic at baseline, the following variables were independently associated with development of hyperlipidemia over 20 years: older age at baseline, male sex, greater increase in BMI during follow-up, and apoE alleles epsilon 2 or epsilon 4. In conclusion, apoB is associated with hyperlipidemia and apoE polymorphism is associated with later onset of hyperlipidemia in FCHL.

Dietary fiber prevents carbohydrate-induced hypertriglyceridemia

Plant foods rich in carbohydrate and dietary fiber have many health benefits. One concern often expressed about higher carbohydrate, lower fat diets is that they may increase fasting serum triglycerides. Recently the importance of hypertriglyceridemia as an independent risk factor for coronary heart disease has been reaffirmed. For 40 years, clinicians have noted "carbohydrate-induced hypertriglyceridemia" when persons were fed high-carbohydrate, low-fiber diets. The role of fiber in protecting from carbohydrate-induced hypertriglyceridemia has not been discussed by many reviewers. Systematic review of the literature documents that high fiber intakes clearly protect from carbohydrate-induced hypertriglyceridemia. These are reviewed. Thus, recent and earlier research indicates that use of a higher carbohydrate, higher fiber diet compared with a lower carbohydrate, higher fat diet is associated with a small reduction in fasting serum triglyceride values.

Cardiovascular disease mortality in familial forms of hypertriglyceridemia: A 20-year prospective study

BACKGROUND

Familial combined hyperlipidemia (FCHL) and familial hypertriglyceridemia (FHTG) are 2 of the most common familial forms of hyperlipidemia. There is a paucity of prospective data concerning the risk of cardiovascular disease (CVD) in such families. The purposes of this study were to estimate 20-year total and CVD mortality risk among relatives in these families and to evaluate plasma triglyceride as a predictor of death.

METHODS AND RESULTS

The study was based on lipid and medical history data from 101 families ascertained in 2 studies conducted in the early 1970s. Vital status and cause of death was determined during 1993 to 1997 for 685 family members, including first-degree relatives of the probands and spouse control subjects. Compared with spouse control subjects, 20-year CVD mortality risk was increased among siblings and offspring in FCHL (relative risk 1.7, P=0.02) after adjustment for baseline covariates. In FHTG families, the relative risk was also 1.7 but was not statistically significant (P=0.39). Baseline triglyceride was associated with increased CVD mortality risk independent of total cholesterol among relatives in FHTG families (relative risk 2.7, P=0.02) but not in FCHL families (relative risk 1.5, P=0.16) after adjustment for baseline covariates.

CONCLUSIONS

This prospective study establishes that relatives in FCHL families are at increased risk for CVD mortality and illustrates the need for effective prevention strategies in this group. Baseline triglyceride level predicted subsequent CVD mortality among relatives in FHTG families, adding to the growing evidence for the importance of hypertriglyceridemia as a risk factor for CVD.

Relationship of dietary fat to glucose metabolism

The relationship between dietary fat and glucose metabolism has been recognized for at least 60 years. In experimental animals, high fat diets result in impaired glucose tolerance. This impairment is associated with decreased basal and insulin-stimulated glucose metabolism. Impaired insulin binding and/or glucose transporters has been related to changes in the fatty acid composition of the membrane induced by dietary fat modification. In humans, high-fat diets, independent of fatty acid profile, have been reported to result in decreased insulin sensitivity. Saturated fat, relative to monounsaturated and polyunsaturated fat, appears to be more deleterious with respect to fat-induced insulin insensitivity. Some of the adverse effects induced by fat feeding can be ameliorated with omega-3 fatty acid. Epidemiological data in humans suggest that subjects with higher intakes of fat are more prone to develop disturbances in glucose metabolism, type 2 diabetes or impaired glucose tolerance, than subjects with lower intakes of fat. Inconsistencies in the data may be attributable to clustering of high intakes of dietary fat (especially animal fat) with obesity and inactivity. Metabolic studies suggest that higher-fat diets containing a higher proportion of unsaturated fat result in better measures of glucose metabolism than high-carbohydrate diet. Clearly, the area of dietary fat and glucose metabolism has yet to be fully elucidated.

Carbohydrate-induced hypertriacylglycerolemia: historical perspective and review of biological mechanisms

Current trends in health promotion emphasize the importance of reducing dietary fat intake. However, as dietary fat is reduced, the dietary carbohydrate content typically rises and the desired reduction in plasma cholesterol concentrations is frequently accompanied by an elevation of plasma triacylglycerol. We review the phenomenon of carbohydrate-induced hypertriacylglycerolemia, the health effects of which are among the most controversial and important issues in public health nutrition today. We first focus on how seminal observations made in the late 1950s and early 1960s became the basis for subsequent important research questions and areas of scientific study. The second focus of this paper is on the current knowledge of biological mechanisms that contribute to carbohydrate-induced hypertriacylglycerolemia. The clinical rationale behind mechanistic studies is this: if carbohydrate-induced hypertriacylglycerolemia shares a metabolic basis with endogenous hypertriacylglycerolemia (that observed in subjects consuming high-fat diets), then a similar atherogenic risk may be more likely than if the underlying metabolic mechanisms differ. The third focus of the paper is on both the positive metabolic changes that occur when high-carbohydrate diets are consumed and the potentially negative health effects of such diets. The review concludes with a summary of some important research questions that remain to be addressed. These issues include the level of dietary carbohydrate that induces carbohydrate-induced hypertriacylglycerolemia, whether the phenomenon is transient or can be avoided, whether de novo lipogenesis contributes to the phenomenon, and what magnitude of triacylglycerol elevation represents an increase in disease risk.

Lipoprotein response to a National Cholesterol Education Program step II diet with and without energy restriction

This study examined the efficacy of a National Cholesterol Education Program (NCEP) step II diet (25% fat with < 7% saturated fat [SFA]) with and without moderate energy restriction. We tested the hypothesis that moderate energy restriction would improve the lipid profile resulting from an isoweight NCEP step II diet. Twenty hypercholesterolemic subjets (10 men and 10 postmenopausal women) consumed the following three controlled diets, each of 4 weeks' duration, as outpatients: (1) high-fat, high-saturated-fat diet to establish baseline lipids and isoweight energy requirements, (2) NCEP step II diet at isoweight energy, and (3) NCEP step II diet with an energy level 15% less than isoweight. The NCEP step II diet at isoweight energy reduced total cholesterol (TC) by 4% (P = .015), high-density lipoprotein cholesterol (HDL-c) by 13% (P < .0001), and HDL2-c by 40% (P < .0001). The TC:HDL-c ratio increased from 4.9 to 5.5 (P < .0001) and was increased in 19 of 20 subjects. Apolipoprotein B (apo B)-containing lipoproteins changed reciprocally: low-density lipoprotein cholesterol (LDL-c) decreased 4% (P = .008) and very-low-density lipoprotein cholesterol (VLDL-c) increased 29% (P < .0001). Apo B levels did not change. Compared with the NCEP isoweight diet the NCEP hypocaloric diet significantly reduced VLDL-c (-9%, P = .014) and apo B (-5%, P = .015). There was an additional reduction in TC (-4%, P = .073) and LDL-c (-4%, P = .126) with no change in HDL-c (P = .807). These data indicate that a NCEP step II diet with energy restriction produces a more desirable lipoprotein response than a NCEP step II isoweight diet. Neither NCEP step II diet improved the TC:HDL-c ratio.

Comparison of a high-carbohydrate diet with a high-monounsaturated-fat diet in patients with non-insulin-dependent diabetes mellitus

We compared a high-carbohydrate diet with a high-fat diet (specifically, a diet high in monounsaturated fatty acids) for effects on glycemic control and plasma lipoproteins in 10 patients with non-insulin-dependent diabetes mellitus (NIDDM) receiving insulin therapy. The patients were randomly assigned to receive first one diet and then the other, each for 28 days, in a metabolic ward. In the high-carbohydrate diet, 25 percent of the energy was in the form of fat and 60 percent in the form of carbohydrates (47 percent of the total energy was in the form of complex carbohydrates); the high-monounsaturated-fat diet was 50 percent fat (33 percent of the total energy in the form of monounsaturated fatty acids) and 35 percent carbohydrates. The two diets had the same amounts of simple carbohydrates and fiber. As compared with the high-carbohydrate diet, the high-monounsaturated-fat diet resulted in lower mean plasma glucose levels and reduced insulin requirements, lower levels of plasma triglycerides and very-low-density lipoprotein cholesterol (lower by 25 and 35 percent, respectively; P less than 0.01), and higher levels of high-density lipoprotein (HDL) cholesterol (higher by 13 percent; P less than 0.005). Levels of total cholesterol and low-density lipoprotein (LDL) cholesterol did not differ significantly in patients on the two diets. These preliminary results suggest that partial replacement of complex carbohydrates with monounsaturated fatty acids in the diets of patients with NIDDM does not increase the level of LDL cholesterol and may improve glycemic control and the levels of plasma triglycerides and HDL cholesterol.

Effects of diets with high carbohydrate content on diabetic hyperlipidaemia and microalbuminuria

Recent dietary recommendations for patients with diabetes mellitus have focussed on the liberalisation of carbohydrate intake to at least 50% of total calories. However, there are reports that this diet may cause adverse metabolic effects as a result of high intake of carbohydrate. Whether this high-carbohydrate diet will exacerbate hypertriglyceridaemia, which increases the risk of atherosclerosis, and diabetic microalbuminuria, which predisposes to progressive renal failure, is unknown. The dietary intake of 28 patients with insulin-dependent diabetes mellitus was assessed by diet histories with both questionnaire surveys and 3-day recall methods. The dietary contents of different constituents were graded according to the type and amount of food typically eaten, and the frequency of their consumption in the past 6 months. Twelve patients were found to have a high dietary intake of carbohydrate and this was confirmed by detailed assessment of food intake records over a 3-day period. The carbohydrate intake of these 12 patients amounted to at least 55% of total calories. Total calorie intake, body weight, mean blood pressure, glycaemic control, and glomerular filtration rate were similar between the 12 patients with high intake of carbohydrate and the other 16 patients with low intake. Urinary protein and albumin appearance as measured by dye binding and immunoassay, fasting cholesterol, triglyceride and high-density lipoprotein cholesterol were also comparable between the two groups. This study provides evidence that a high-carbohydrate diet in the treatment of diabetes mellitus is not associated with significant alterations in the amount of microalbuminuria or in hypertriglyceridaemia.

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.

Long-term effects of guar gum on blood lipids

While guar gum has been shown to lower total cholesterol and low density lipoprotein cholesterol (LDL-C) in diabetic patients over the short-term, the long-term effects are less well studied and may be unpredictable. Granola bars with and without 6.6 g guar gum were developed and fed to 16 adult volunteers with Type II diabetes mellitus who had been randomized in a double-blind fashion into guar and placebo groups of equal size. Four to six bars were consumed daily with an ad lib diet over a 6-month period. Total cholesterol, total high density lipoprotein cholesterol (HDL-C), subfractions HDL2-C and HDL3-C, LDL-C, and beta-apoprotein were measured at 0 and 6 months. Although LDL-C was lower and triglycerides higher at 6 months than at baseline, these changes were of equal magnitude and direction in both guar and placebo groups. Using each subject as his own control, only the change in triglycerides was statistically significant (P less than 0.025). When male subjects alone were analyzed, the guar group showed a statistically significant decrease in LDL, while the placebo group did not. Other lipid parameters were not significantly changed during the study, despite a positive effect on carbohydrate metabolism from the guar bars. The data suggest either that the hypolipemic effects of guar gum in patients with Type II diabetes mellitus are not sustained for 6 months, or the effects occur only in men.

The effects of a high-carbohydrate low-fat cholesterol-restricted diet on plasma lipid, lipoprotein, and apoprotein concentrations in insulin-dependent (type I) diabetes mellitus

Six women with well-defined insulin-dependent diabetes mellitus (IDDM) were studied for 4 weeks during a control diet containing 45% of the calories as carbohydrate, 40% fat (P/S ratio 0.14), 15% protein, and 580 mg of cholesterol, and for 6 weeks during a high-carbohydrate low-fat cholesterol-restricted diet with 65% carbohydrate, 20% fat (P/S ratio 1.40), 15% protein, and 62 mg cholesterol. All subjects completed both dietary periods in a crossover experimental design. Individual menus were subject-selected from a calculated exchange list containing conventional food items consistent with current American dietary patterns. The diets were well-tolerated by all subjects. Total plasma cholesterol decreased from 201 to 156 mg/100 mL (P less than 0.05) during the cholesterol-restricted diet, while total plasma triglyceride (TG) increased from 96 to 115 mg/100 mL (P less than 0.01). During this same period, very low-density lipoprotein cholesterol (VLDL-C) and VLDL-TG increased from 17 to 21 mg/100 mL (P less than 0.05) and from 59 to 76 mg/100 mL (P less than 0.001), respectively, while low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) decreased from 126 to 90 mg/100 mL (P less than 0.05) and from 50 to 39 mg/100 mL (P less than 0.05), respectively. LDL-C/HDL-C and total-C/HDL-C ratios were lower but not significantly different, and LDL-TG and HDL-TG were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed clearance of chylomicron remnants following vitamin-A-containing oral fat loads in broad-beta disease (type III hyperlipoproteinemia)

Chylomicron "remnants" are formed by the selective removal of triglyceride catalyzed by lipoprotein lipase. To investigate a possible defect in the clearance of these remnants in the pathophysiology of broad-beta disease (type III hyperlipoproteinemia), subjects with this disorder and comparison subjects with endogenous hypertriglyceridemia (and type IV lipoprotein patterns) ingested an oral fat load (corn oil: cocoa butter, 1:1, 50 g/sq M) containing retinyl ester, 100 mg, with or without 15 muCi 15-(14) C-retinol (43.7 mCi/mg). The content of triglyceride and vitamin A was sequentially determined in chylomicrons (Sf more than 400) and very low density lipoproteins (VLDS, Sf20-400) over the ensuing 24-72 hr. Vitamin A was chosen as a marker for exogenous sterol assimilation since, like cholesterol, it is absorbed in the small intestine and cosecreted in esterified form with triglyceride in the chylomicron core; however, unlike cholesterol, once having been removed by the liver, it cannot be recycled inot VLDL, but subsequently circulates only as a complex with the high density retinol binding protein. Thus measurements of the vitamin A/triglyceride ratio in Sf greater than 20 lipoproteins reflected the relative efficiency of vitamin A versus triglyceride removal within these lipoproteins. These studies confirmed the intital concentration of exogenous vitamin A in chylomicrons but invariably disclosed an increasing proportion of the remaining Sf greater than 20 vitamin A in VLDL 24 hr after its ingestion. The vitamin A/triglyceride ratio also invariably increased between 6 and 24 hr in the Sf20-30 subfraction, reflecting the formation of vitamin A-rich "remnants" as intermediate species in the catabolism of chylomicrons and VLDL. Among those with mild to moderate endogenous hypertriglyceridemia the Sf greater than 400 vitamin A/triglyceride ratio declined between 6 and 24 hr, reflecting the efficient passage of the vitamin A through this fraction and/or continued secretion of Sf greater than 400 particles rich in triglyceride. Among those with severe endogenous hypertriglyceridemia, both the peak and decline in the Sf greater than 400 vitamin A/triglyceride ratio were delayed. However, among those with broad-beta disease, an increasing vitamin A/triglyceride ratio between 6 and 24 hr was frequent within all VLDL subfractions and invariable among lipoproteins of Sf greater than 400 regardless of the degree of antecedent hypertriglyceridemia. Although additional experiments disclosed a similar delay in both vitamin A and triglyceride assimilation when basal triglyceride levels were high in these subjects, marked reduction of triglyceride levels did not correct the rise in the Sf greater than 400 vitamin A/triglyceride ratio between 6 and 24 hr. Experiments employing preparative electrophoresis confirmed the identity of VLDL containing a high vitamin A/triglyceride ratio with the beta-VLDL which accumulate in broad-beta disease...

Evidence for diabetes mellitus and genetic forms of hypertriglyceridemia as independent entities

Among 91 index cases whose diagnosis of a genetic type of hypertriglyceridemia was based on family studies, 27% had diabetes. To determine whether the familial forms of hypertriglyceridemia and genetic diabetes mellitus are inherited together or independently, the adult first degree relatives of these propositi were investigated for the presence of diabetes. Frequency of diabetes in first degree relatives of the 25 diabetic patients with a familial form of hypertriglyceridemia was identical whether such relatives were hyperlipidemic or not (13% versus 14.7%). The frequency of diabetes in both the hyperlipidemic and normolipidemic relatives of the 66 nondiabetic hypertriglyceridemic index cases also was not significantly different from each other (6.2% versus 4.0%). These results indicate that while diabetes is frequently associated with hypertriglyceridemia, genetic hypertriglyceridemia, per se, does not carry an increased risk of diabetes. Following treatment of diabetes, elevated triglyceride levels in index cases with both familial hypertriglyceridemia and untreated diabetes returned to lower but still elevated levels resembling those of affected (hypertriglyceridemic) relatives. Thus, the interaction of untreated diabetes and a familial form of hypertriglyceridemia determines the level of plasma triglyceride in a patient with both disorders.