Acute effects of monounsaturated fatty acids with and without omega-3 fatty acids on vascular reactivity in individuals with type 2 diabetes

AIMS/HYPOTHESIS

We examined the acute postprandial effects of meals containing unsaturated fatty acids on flow-mediated dilation (FMD) of the brachial artery and triacylglycerols in individuals with type 2 diabetes. We hypothesised that consumption of omega-3 fatty acids would enhance vascular function. Saturated fat reduces FMD for several hours, but there is inconsistent evidence about whether foods containing unsaturated fats impair FMD acutely. Little is known about the acute effects of omega-3 fatty acids on vascular reactivity.

METHODS

We measured FMD before and 4 h after 3 test meals (50 g fat, 2,615 kJ) in 18 healthy adults with type 2 diabetes. The monounsaturated fatty acids (MUFA) meal contained 50 g fat from high oleic safflower and canola oils. Two additional meals were prepared by replacing 7% to 8% of MUFA with docosahexaenoic acid and eicosapentaenoic acid from sardine oil or alpha-linolenic acid from canola oil.

RESULTS

In the sample as a whole, FMD was increased 17% at 4 h vs. the fasting baseline. After the MUFA meal, subjects with the largest increases in triacylglycerols had the largest FMD decreases. The opposite pattern was observed after meals containing docosahexaenoic acid and eicosapentaenoic acid or alpha-linolenic acid. In subjects with high fasting triacylglycerols, meals containing 3 to 5 g of omega-3 fatty acids increased FMD by 50% to 80% and MUFA alone had no significant effects on FMD.

CONCLUSIONS/INTERPRETATION

Endothelium-dependent vasodilation was not impaired 4 h after meals containing predominantly unsaturated fatty acids. The fatty acid composition of the meal and the metabolic status of the individual determine the vascular effects of a high-fat meal.

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

BACKGROUND

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Dietary compliance and cardiovascular risk reduction with a prepared meal plan compared with a self-selected diet

Noncompliance with therapeutic diets remains a major obstacle to achieving improvements in cardiovascular disease (CVD) morbidity and mortality. This study compared dietary compliance and CVD risk factor response to two dietary interventions designed to treat hypertension, dyslipidemia, and diabetes mellitus. In a multicenter trial, 560 adults were randomly assigned to either a self-selected, mixed-food plan (n = 277), or a nutrient-fortified prepared meal plan (n = 283); each was designed to provide 15-20% of energy from fat, 55-60% from carbohydrate, and 15-20% from protein. Nutrient intake was estimated from 3-d food records collected biweekly throughout the 10-wk intervention. Compliance was determined by evaluating the participants' ability to meet specific criteria for energy intake [+/-420 kJ (100 kcal) from the midpoint of the prescribed energy range], fat intake (< 20%, < 25%, or < 30% of energy from total fat), and the National Cholesterol Education Program/American Heart Association Step 1 and 2 diet recommendations. Compliance with energy, fat, and Step 1 and 2 criteria was better in participants who followed the prepared meal plan than in those who followed the self-selected diet (P < 0.0001). Compliant participants in both groups achieved greater reductions in body weight, systolic and diastolic blood pressure, and total and low-density-lipoprotein cholesterol than noncompliant participants (P < 0.05). In general, better endpoint responses were observed with lower fat intakes regardless of group assignment. The prepared meal plan is a simple and effective strategy for meeting the many nutrient recommendations for CVD risk reduction and improving dietary compliance and CVD endpoints.

Effects of dietary fat and fatty acids on coronary artery disease risk and total and lipoprotein cholesterol concentrations: epidemiologic studies

Because of their large sample sizes, epidemiologic studies can provide important data on the relation between diet, specifically dietary fat and fatty acids, and lipid and lipoprotein concentrations as well as the incidence of coronary artery disease. Although correlation coefficients vary widely (from 0.84 to 0.01) and are frequently low between dietary variables and coronary artery disease or lipids and lipoprotein fractions in the studies reviewed here, intakes of saturated fatty acids and dietary cholesterol are generally positively correlated with blood cholesterol in men and women. Associations between other fatty acids are less consistent and may be related to the considerable differences in these studies in dietary methodologies used, databases used for analyses, and homogeneity of intakes within populations. Relatively few data are available for women, cultural minorities within the United States, or young or elderly populations. However, the trends observed in the United States, ie, lower rates of coronary artery disease as well as lower reported intakes of both total and saturated fats, support the relations observed in the epidemiologic studies.

Reducing saturated fat intake is associated with increased levels of LDL receptors on mononuclear cells in healthy men and women

Studies with animal models suggest that saturated fatty acids raise low density lipoprotein (LDL)-cholesterol levels by reducing LDL receptor-mediated clearance. To examine this directly in humans, we studied the effects of lowering dietary saturated fat on LDL-receptor abundance in peripheral mononuclear cells which reflects hepatic LDL-receptor status. Healthy males and females (n = 25) participating in the DELTA (Dietary Effects on Lipoproteins and Thrombogenic Activity) Study consumed three experimental diets in a randomized cross-over design. Diets provided 34% fat, 15% saturated fatty acids (Average American Diet); 29% fat, 9% saturated fatty acids (Step-One Diet); and 25% fat, 6% saturated fatty acids (Low SAT Diet). Peripheral mononuclear cells were isolated from blood samples collected after 6 and 8 wk. An ELISA was used to quantify LDL-receptor protein in total cell membranes. LDL-receptor abundance increased by 10.5% after the Low SAT Diet (P < 0.05). This was associated with an 11.8% decrease in serum LDL-cholesterol (P < 0.05). A linear inverse relationship was observed between the percentage change in LDL-cholesterol and the percentage change in LDL-receptor abundance (r = -0.59; P < 0.01). In addition, LDL-receptor abundance also was correlated inversely (P < 0.001) with serum levels of LDL-cholesterol (r = -0.747) and apoB (r = -0.593). In summary, reducing dietary saturated fat is associated with an increase in LDL-receptor abundance of magnitude similar to the decrease in serum LDL-cholesterol. Thus, an important mechanism by which reductions in dietary saturated fatty acids decrease LDL-cholesterol in humans is through an increase in LDL-receptor number.

Dietary linoleic acid increases and palmitic acid decreases hepatic LDL receptor protein and mRNA abundance in young pigs

The present study was conducted to determine the effects of dietary fatty acids on hepatic LDL receptor (LDLr) protein abundance and mRNA levels. Sixty pigs were randomized into 10 groups and fed corn-soybean meal diets containing three cholesterol levels (0.25%, 0.5%, and 1.0%, w/w) with no added fat, or fats rich (30% of calories) in palmitic acid or linoleic acid. A control group was fed the base diet with no added fat. After 30 days, plasma LDL-cholesterol (LDL-C) levels increased as the dietary cholesterol increased (P < 0.05); however, there was no significant effect of either fatty acid. Dietary fatty acids, however, had distinctly different effects on hepatic LDLr protein (analyzed by ELISA) and mRNA (analyzed by Northern blot) abundance. When pigs consumed diets containing 0.25% cholesterol, linoleic acid increased hepatic LDLr protein 40% whereas palmitic acid reduced it 40% (P < 0.05). These changes in LDLr protein abundance were accompanied by parallel changes in hepatic LDLr mRNA; linoleic acid increased LDLr mRNA 2-fold (P < 0.01), whereas palmitic acid decreased it 60% (P < 0.01). The differential effects of fatty acids on LDLr expression were only observed at 0.25% cholesterol, suggesting that higher intakes of cholesterol have a dominant and repressive effect on regulation of LDLr expression. Cholesterol intake increased hepatic total cholesterol levels (P < 0.01) while dietary fatty acids had no effect on hepatic sterols. In summary, our results indicate that dietary linoleic acid and palmitic acid have markedly different effects on hepatic LDLr protein abundance that are mediated by differential effects on LDLr mRNA and protein levels. Further studies are needed to fully elucidate the molecular mechanisms by which fatty acids regulate LDLr mRNA and protein levels.

Chocolate feeding studies: a novel approach for evaluating the plasma lipid effects of stearic acid

Milk chocolate does not adversely affect plasma lipids and lipoproteins despite its relatively high content of saturated fatty acids (SFAs). Evidence from well-controlled feeding studies indicates that this unique response is due to the high proportion of stearic acid in milk chocolate. In experimental diets containing very high amounts (eg, 280 g/d, or 10 oz/d) and more typical amounts (46.2 g, or 1.65 oz) of milk chocolate, plasma total- and low-density-lipoprotein-cholesterol concentrations are not elevated. Furthermore, isoenergetic substitution of one milk chocolate bar per day for a high-carbohydrate snack in a National Cholesterol Education Program/American Heart Association Step 1 Diet does not adversely affect the cholesterol-lowering response. These findings indicate that stearic acid is not hypercholesterolemic as are the other long-chain SFAs. Thus, as illustrated by the different results generated from the predictive equations that group all long-chain SFAs vs those that consider stearic acid separately, grouping stearic acid with other SFAs appears to misrepresent the actual blood cholesterol response.

Effects of a milk chocolate bar per day substituted for a high-carbohydrate snack in young men on an NCEP/AHA Step 1 Diet

This study compares the plasma cholesterol response with the isoenergetic substitution of a milk chocolate bar (46 g) given daily for a high-carbohydrate snack in healthy young men on a Step 1 Diet. Normocholesterolemic men (n = 42) were fed a Step 1 Diet for 21 d (run-in diet) followed by a 27-d experimental period during which they consumed the same diet plus either a milk chocolate bar or a high-carbohydrate snack; after this they consumed the run-in diet for 21 d followed by the other snack for 27 d. When subjects consumed a milk chocolate bar instead of the high-carbohydrate snack, high-density-lipoprotein (HDL) cholesterol was 0.08 +/- 0.03 mmol/L higher (P < 0.01) and plasma triglycerides were 0.06 +/- 0.03 mmol/L lower (P < 0.05). Substitution of a milk chocolate bar for a high-carbohydrate snack did not adversely affect the low-density-lipoprotein-(LDL) cholesterol response to a Step 1 Diet despite an increase in total fat and saturated fatty acid content of the diet. This response may be due to stearic acid.

Comparison of the effects of diets rich in stearic acid versus myristic acid and lauric acid on platelet fatty acids and excretion of thromboxane A2 and PGI2 metabolites in healthy young men

The present study compared the effects of diets rich in stearic acid (C18:0) versus one high in lauric and myristic acid (C12:0, C14:0) on platelet phospholipid fatty acid levels and concentrations of urinary thromboxane B2 (TXB2) and 6-keto-PGF1 alpha, which are stable metabolites of thromboxane A2 (TXA2) and PGI2 and indicators of cardiovascular hemostasis. A diet high in dairy butter (B) was the source of C12:0 and C14:0; C18:0 was provided by diets high in cocoa butter (CB), milk chocolate (CHOC) or CB+B in a 4:1 ratio (MIX). A randomized, crossover double-blind experimental design was used. Experimental subjects (n = 15) consumed each diet for 26 days, with a 1-month washout period between each experimental period. Urine and blood were collected from each subject at the beginning and end of each dietary period. Urinary TXB2 and 6-keto-PGF1 alpha were analyzed by radioimmunoassay (RIA). There were no effects of diet on the 24-hour excretion of either metabolite or on the ratio of 6-keto-PGF1 alpha/TXB2, even though there were significant changes in the eicosanoid precursor, arachidonic acid (C20:4n-6), in platelet phospholipids. C20:4n-6 levels increased (44.8% +/- 1.0% to 47.1% +/- 1.3%; P < .05) in the phosphatidylethanolamine phospholipid subclass in subjects on the B diet and decreased in the phosphatidylcholine subclass on the CB diet (16.5% +/- 1.0% to 14.2% +/- 1.1%; P < .05) compared with baseline values.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of fatty acid saturation on plasma lipids, lipoproteins, and apolipoproteins: I. Effects of whole food diets high in cocoa butter, olive oil, soybean oil, dairy butter, and milk chocolate on the plasma lipids of young men

The present studies were conducted to evaluate the cholesterolemic effects of whole-food diets high in stearic acid. In study no. 1, normocholesterolemic young men were fed diets high in stearic acid provided by cocoa butter (CB); oleic acid provided by olive oil (OO); linoleic acid provided by soybean oil (SO); and myristic acid (and lauric acid) provided by dairy butter (B). In study no. 2, different subjects with similar baseline characteristics were fed diets high in stearic acid provided by milk chocolate (C), CB, CB+B (4:1, MIX), and myristic (and lauric) acid provided by B. Both studies used a randomized, crossover, double-blind experimental design, and experimental subjects (n = 18 for study no. 1 and n = 15 for study no. 2) in each study consumed every diet for 26 days with a 1-month wash-out period between each experimental period. The diets provided 37% of calories from fat, of which 81% was provided by the test fat. Ten ounces (280 g) C was provided daily by the C diet. In study no. 1, the B diet was hypercholesterolemic, whereas the SO diet was hypocholesterolemic, compared with the other diets. The OO and SO diets were hypocholesterolemic compared with the CB diet. Low-density lipoprotein (LDL) cholesterol levels, in general, paralleled the changes in plasma total cholesterol levels. SO significantly decreased apolipoprotein (apo) B levels compared with the other diets. Plasma very-low density lipoprotein (VLDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and apo A-I levels were unaffected by the experimental diets.(ABSTRACT TRUNCATED AT 250 WORDS)