Dietary oleic and palmitic acids modulate the ratio of triacylglycerols to cholesterol in postprandial triacylglycerol-rich lipoproteins in men and cell viability and cycling in human monocytes

The postprandial metabolism of dietary fats produces triacylglycerol (TG)-rich lipoproteins (TRL) that could interact with circulating cells. We investigated whether the ratios of oleic:palmitic acid and monounsaturated fatty acids (MUFA):SFA in the diet affect the ratio of TG:cholesterol (CHOL) in postprandial TRL of healthy men. The ability of postprandial TRL at 3 h (early postprandial period) and 5 h (late postprandial period) to affect cell viability and cycle in the THP-1 human monocytic cell line was also determined. In a randomized, crossover experiment, 14 healthy volunteers (Caucasian men) ate meals enriched (50 g/m(2) body surface area) in refined olive oil, high-palmitic sunflower oil, butter, and a mixture of vegetable and fish oils, which had ratios of oleic:palmitic acid (MUFA:SFA) of 6.83 (5.43), 2.36 (2.42), 0.82 (0.48), and 13.81 (7.08), respectively. The ratio of TG:CHOL in postprandial TRL was inversely correlated (r = -0.89 to -0.99) with the ratio of oleic:palmitic acid and with the MUFA:SFA ratio in the dietary fats (P < 0.05). Postprandial TRL at 3 h preferentially increased the proportion of necrotic cells, whereas postprandial TRL at 5 h increased the proportion of apoptotic cells (P < 0.05). Cell cycle analysis showed that postprandial TRL blocked the human monocytes in S-phase. Our findings suggest that the level of TG and CHOL into postprandial TRL is associated with the ratios of oleic:palmitic acid and MUFA:SFA in dietary fats, which determines the ability of postprandial TRL to induce cytotoxicity and disturb the cell cycle in THP-1 cells.     

Dietary protein effects on cholesterol and lipoprotein concentrations: a review.

Different dietary proteins exert different effects on plasma cholesterol concentrations. Animal studies have shown that animal proteins, most notably casein, increase plasma total cholesterol concentrations compared with vegetable proteins, such as soy. Soy protein has been shown to be hypocholesterolemic in rats, swine, primates, and rabbits. Epidemiologic studies have disclosed that vegetarians have lower mean plasma cholesterol concentrations than populations consuming diets of mixed proteins, but it is unclear whether this effect results specifically from the animal or vegetable nature of the protein. In human clinical experiments, substituting soy protein for mixed protein reduces plasma total cholesterol concentration in hypercholesterolemic subjects, but it causes only a small, nonsignificant change in persons with normal plasma cholesterol concentrations. The mechanism responsible for the effects of different proteins on plasma cholesterol concentrations has not been established. One hypothesis suggests that animal proteins, which have a greater content of phosphorylated amino acids than vegetable proteins, interfere with bile acid reabsorption. Another hypothesis suggests that the amino acid content of the protein affects cholesterol absorption, tissue storage, synthesis, and excretion. The dietary protein may also alter cholesterol metabolism by affecting plasma hormone concentrations, either postprandially or over weeks to months. Among the hormones thought to be affected by dietary protein source are insulin, glucagon, and thyroid hormones. Gastrointestinal hormones, such as gastrointestinal inhibitory polypeptide, may also be affected by dietary protein.     

Exchanging partially hydrogenated fat for palmitic acid in the diet increases LDL-cholesterol and endogenous cholesterol synthesis in normocholesterolemic women

Partial hydrogenation of oil results in fats containing unusual isomeric fatty acids characterized by cis and trans configurations. Hydrogenated fats containing trans fatty acids increase plasma total cholesterol (TC) and LDL-cholesterol while depressing HDL-cholesterol levels. Identifying the content of trans fatty acids by food labeling is overshadowed by a reluctance of health authorities to label saturates and trans fatty acids separately. Thus, it is pertinent to compare the effects of trans to saturated fatty acids using stable isotope methodology to establish if the mechanism of increase in TC and LDL-cholesterol is due to the increase in the rate of endogenous synthesis of cholesterol. Ten healthy normocholesterolemic female subjects consumed each of two diets containing approximately 30% of energy as fat for a fourweek period. One diet was high in palmitic acid (10.6% of energy) from palm olein and the other diet exchanged 5.6% of energy as partially hydrogenated fat for palmitic acid. This fat blend resulted in monounsaturated fatty acids decreasing by 4.9 % and polyunsaturated fats increasing by 2.7%. The hydrogenated fat diet treatment provided 3.1% of energy as elaidic acid. For each dietary treatment, the fractional synthesis rates for cholesterol were measured using deuterium-labeling procedures and blood samples were obtained for blood lipid and lipoprotein measurements. Subjects exhibited a higher total cholesterol and LDL-cholesterol level when consuming the diet containing trans fatty acids while also depressing the HDL-cholesterol level. Consuming the partially hydrogenated fat diet treatment increased the fractional synthesis rate of free cholesterol. Consumption of hydrogenated fats containing trans fatty acids in comparison to a mixtur e of palmitic and oleic acids increase plasma cholesterol levels apparently by increasing endogenous synthesis of cholesterol.     

Walnuts lower serum cholesterol in Japanese men and women

Recent studies have shown that incorporating moderate quantities of walnuts into the recommended cholesterol-lowering diet in the U.S. decreased serum concentrations of total cholesterol in normal American men. To explore whether walnut consumption would also prove effective as part of the Japanese diet, we studied the effects of walnut consumption on serum lipids and blood pressure in Japanese subjects. We randomly assigned 20 men and 20 women to two mixed natural diets, each to be consumed for 4 wk in a crossover design. Both diets conformed to the average Japanese diet (reference diet) and contained identical foods and macronutrients, except that 12.5% of the energy of the walnut diet was derived from walnuts (43-57 g/d) (offset by lesser amounts of fatty foods, meat and visible fat). Total cholesterol concentration was 0.16 mmol/L lower for men (P = 0.05) and 0.21 mmol/L lower for women (P<0.01) when they consumed the walnut diet than when they consumed the reference diet. The LDL cholesterol concentrations were 0.18 mmol/L lower for men (P = 0.13) and 0.22 mmol/L lower for women (P<0.01) when they consumed the walnut diet. The ratio of LDL cholesterol to HDL cholesterol and the apolipoprotein B concentration were also lowered by the walnut diet (P<0.05). Blood pressures did not differ between the walnut and reference diet periods. Incorporating moderate quantities of walnuts into the average Japanese diet while maintaining the intake of total dietary fat and energy decreases serum total cholesterol concentrations and favorably modifies the lipoprotein profile in Japanese, particularly in women.     

Effects of hazelnut-enriched diet on plasma cholesterol and lipoprotein profiles in hypercholesterolemic adult men

OBJECTIVE: Frequent consumption of nuts is associated with favorable plasma lipid profiles and reduced risk of coronary heart disease (CHD). This study was conducted to investigate the effects of hazelnut-enriched diet on plasma cholesterol and lipoprotein profiles in hypercholesterolemic adult men compared with baseline and control diet, and also to measure the anthropometric parameters, habitual physical activities, nutrient intake and endothelial function. SUBJECTS AND DESIGN: Fifteen hypercholesterolemic men aged 48+/-8 years were recruited voluntarily. A well-controlled, 2-period (P1 and P2) study design with a total of 8-week was implemented. In the P1, subjects consumed a control diet (low-fat, low-cholesterol and high-carbohydrate). During the P2, the control diet was supplemented with MUFA-rich hazelnut (40 g/day), which provided 11.6% of total energy content. Anthropometric parameters and habitual physical activities were recorded. Plasma total and HDL cholesterol, TAG, ApoA-1, Apo B, total homocysteine and glucose concentrations were measured. All parameters and measurements were obtained at baseline and end of each 4-week diet period. RESULTS: Body weights of subjects remained stable throughout the study. Compared with baseline, the hazelnut-enriched diet decreased (P<0.05) the concentrations of VLDL cholesterol, triacylglycerol, apolipoprotein B by 29.5, 31.8, and 9.2%, respectively, while increasing HDL cholesterol concentrations by 12.6%. Total/HDL cholesterol and LDL/HDL cholesterol ratios favorably decreased (P<0.05). Although insignificant there was a decreasing trend for the rest of parameters, particularly in total (5.2%) and LDL cholesterol (3.3%) in subjects consuming a hazelnut-enriched diet compared to that of the baseline. No changes were found in fasting levels of glucose, Apo A-1 and homocysteine between the control and hazelnut-enriched diets. CONCLUSIONS: This study demonstrated that a high-fat and high-MUFA-rich hazelnut diet was superior to a low-fat control diet because of favorable changes in plasma lipid profiles of hypercholesterolemic adult men and, thereby positively affecting the CHD risk profile. SPONSORSHIP: Funding provided by a grant from the Hazelnut Promotion Group, Giresun, Turkey.     

Dietary protein effects on cholesterol and lipoprotein concentrations: a review

Different dietary proteins exert different effects on plasma cholesterol concentrations. Animal studies have shown that animal proteins, most notably casein, increase plasma total cholesterol concentrations compared with vegetable proteins, such as soy. Soy protein has been shown to be hypocholesterolemic in rats, swine, primates, and rabbits. Epidemiologic studies have disclosed that vegetarians have lower mean plasma cholesterol concentrations than populations consuming diets of mixed proteins, but it is unclear whether this effect results specifically from the animal or vegetable nature of the protein. In human clinical experiments, substituting soy protein for mixed protein reduces plasma total cholesterol concentration in hypercholesterolemic subjects, but it causes only a small, nonsignificant change in persons with normal plasma cholesterol concentrations. The mechanism responsible for the effects of different proteins on plasma cholesterol concentrations has not been established. One hypothesis suggests that animal proteins, which have a greater content of phosphorylated amino acids than vegetable proteins, interfere with bile acid reabsorption. Another hypothesis suggests that the amino acid content of the protein affects cholesterol absorption, tissue storage, synthesis, and excretion. The dietary protein may also alter cholesterol metabolism by affecting plasma hormone concentrations, either postprandially or over weeks to months. Among the hormones thought to be affected by dietary protein source are insulin, glucagon, and thyroid hormones. Gastrointestinal hormones, such as gastrointestinal inhibitory polypeptide, may also be affected by dietary protein.     

Dietary predictors of serum cholesterol in men: the Framingham cohort population.

This study examines the cross-sectional relationships between diet and serum cholesterol in a sample of 413 Framingham cohort males, ages 37-70. Regression analyses controlling for age, calories, and coronary heart disease risk factors showed that the direct predictors of serum cholesterol included: fat (g) (p less than 0.05), cholesterol (mg/1000 calories) (p less than 0.05), protein (g and calorie density) (p less than 0.05 and p less than 0.001, respectively), Metropolitan relative weight (p less than 0.05), and systolic blood pressure (p less than 0.001). Fat (calorie density) and cholesterol (mg) were marginally significant direct positive predictors (0.05 less than or equal to p less than or equal to 0.10). Inverse correlates of serum cholesterol were total carbohydrate (g and calorie density) and simple carbohydrate (calorie density) (p less than 0.001). A marginally inverse correlate of serum cholesterol was complex carbohydrate (calorie density) (0.05 less than or equal to p less than or equal to 0.10). These cross-sectional results show that dietary variables predict serum cholesterol levels in men independent of other coronary heart disease risk factors.     

Serum fatty acids,lipoprotein (a) and apolipoprotein profiles of middle-aged men and women in South Vietnam

In Vietnam, increasing fat consumption is a trend recognized recently in urban areas. To obtain a reasonable nutrition status and prevent cardiovascular disease (CVD), it is necessary to obtain information on habitual fat intake and biochemical parameters as risk factors for CVD in Vietnamese populations. Therefore, from the analysis of serum fatty acid composition, fat consumption patterns in Vietnamese populations in South Vietnam, with different incomes, are discussed in this study. In addition, some risk factors for premature CVD, serum lipoprotein (a) and apolipoprotein concentrations are also assessed in these Vietnamese populations. The study was carried out in men and women aged 40-59 in three different districts: urban (n = 100), suburban (n = 98) and rural (n = 98). The results of serum fatty acid composition analysis reflected differences in quality fat intake among the three populations. The urban population was estimated to consume more vegetable oil but less fish than their rural counterparts. Although serum lipoprotein (a) and apolipoprotein B levels were below the ranges associated with atherogenesis, ongoing attention to dietary fat intake for the prevention of CVD in Vietnamese populations is required.     

Correlates of serum high-density lipoprotein cholesterol: a community-based study of middle-aged and older men and women in Japan

The authors examined the relationships of high-density lipoprotein (HDL) cholesterol with sex, age, body composition, and lifestyle related factor including dietary patterns, alcohol consumption, smoking, and physical activity in a community-based sample from Mie prefecture, Japan. The study population comprised of 463 men (65.7+/-8.6 years) and 845 women (61.9+/-10.1 years) who participated in an annual healthy examination and a lifestyle related survey in 2001. Using factor analysis based on data from the lifestyle-related questionnaires, three dietary patterns were identified: prudent, Western, and high-salt dietary patterns. Univariate and multivariate analyses indicated that important predictors of higher HDL cholesterol levels were being female and a higher frequency of alcohol consumption. Less strongly related were age and a prudent dietary pattern. Smoking and body mass index (BMI) were strongly negatively related to HDL cholesterol levels. We suggested that efforts to reduce coronary heart disease risks focus on weight control and good daily lifestyles in middle-aged and older Japanese population.     

Dietary alpha-linolenic acid is as effective as oleic acid and linoleic acid in lowering blood cholesterol in normolipidemic men.

The effect of dietary oleic acid (OA), linoleic acid (LA), and linolenic acid (LNA) on plasma lipid metabolism was studied in eight normolipidemic men. A mixed-fat diet composed of conventional foods was fed during 6-d pre- and post-experimental periods. The same basic diet but with 75% of the fat (26% of total energy) provided by sunflower and olive; canola; soybean; and sunflower, olive, and flax oils was fed during four 18-d experimental periods. Mean plasma total cholesterol (-18%), low-density-lipoprotein-cholesterol, (-22%) and very-low-density-lipoprotein-cholesterol (-41%) concentrations were significantly (P less than 0.004) lower after the experimental diets than after the mixed-fat diet. Mean serum apolipoprotein B (-19%) and apolipoprotein A-I (-9%) concentrations were also significantly (P less than 0.0007) lower after the experimental diets. The experimental diets were equally effective in lowering total and lipoprotein cholesterol and apolipoprotein concentrations in plasma, indicating that dietary OA, LA, and LNA were equally hypocholesterolemic.     

Dietary cholesterol, fatty acids, and the risk of lung cancer among men.

The relation between dietary cholesterol and fatty acids and the incidence of lung cancer was studied among 4,538 Finnish men aged 20-69 years and initially free of cancer. During 20 years of follow-up, 117 lung cancer cases were diagnosed. Cholesterol intake was not associated with lung cancer risk, the age-, smoking-, and energy-adjusted relative risk between the lowest and highest tertiles being 1.0 [95% confidence interval (CI) = 0.6-1.9]. The intake of saturated fatty acids was nonsignificantly related with lung cancer incidence, the relative risk for the lowest compared with the highest tertile being 1.6 (CI = 0.8-3.2). The association was stronger among smokers than among nonsmokers, the relative risks being 2.1 (CI = 1.0-4.3) and 1.3 (CI = 0.4-4.1), respectively. The relative risk among smokers, however, decreased to 1.5 after adjustment for the amount they smoked. In the total cohort, there was a significantly elevated risk of lung cancer among men with a high intake of butter, one of the main sources of saturated fatty acids, the relative risk being 1.9 (CI = 1.1-3.2). The present data do not confirm previous results suggesting that dietary cholesterol predicts the occurrence of lung cancer among men. The association between intake of saturated fatty acids and lung cancer observed in the present study may be partly due to heavy smoking among high consumers of saturated fat.     

Coffee consumption is correlated with serum cholesterol in middle-aged Finnish men and women.

The association between coffee consumption and serum cholesterol was studied in a cross-sectional epidemiological study in Finland where the annual per capita consumption of coffee (13.0 kg) is the highest in the world. Coffee consumption was assessed by a questionnaire in a representative population sample of 4744 men and 4495 women aged 25 to 64 years. Serum total cholesterol and HDL-cholesterol concentrations were determined in fresh sera by the enzymatic method. Data on a large number of potential confounding variables were also collected. In the age group 25 to 44 years, the level of serum total cholesterol increased linearly with increasing coffee consumption in both sexes, but in people aged 45 to 64 the peak level of serum cholesterol was found in those who consumed 4 to 6 cups of coffee per day. In the analysis of covariance controlling for age, body mass index, intake of fat, sugar, and alcohol, smoking, physical activity, and fasting time, the mean level of serum cholesterol of men was lower (p less than 0.001) in those who drank no coffee (5.9 mmol/l) than in those who drank 1 to 3 cups (6.1 mmol/l) or 4 or more cups (6.2 mmol/l) per day. In women, the corresponding mean serum cholesterol values were 5.8 mmol/l, 6.1 mmol/l, and 6.1 mmol/l (p less than 0.05). Serum HDL-cholesterol levels did not vary significantly with coffee consumption. There was a slight inverse association between tea drinking and serum total cholesterol in men (p less than 0.05) but not in women. Although our results suggest a positive association, the impact of coffee drinking on serum cholesterol seems to be minimal. The results also indicate that the possible mechanisms do not include caffeine.     

Effects of cholesterol and fat modification of self-selected diets on serum lipids and their specific fatty acids in normocholesterolemic and hypercholesterolemic humans

A 6-month crossover diet plan was employed to study the effects on human serum lipids of adding margarine or butter to otherwise self-selected diets that included two eggs daily. Two groups of subjects were studied: 51 free-living normocholesterolemic and 20 hypercholesterolemic (greater than 240 mg dl). Four-day diet records in each interval showed that subjects ate about 16% of total dietary fat as either butter or margarine. Blood samples taken every 6 weeks showed variable mean serum total cholesterol (SCHOL), high-density-lipoprotein cholesterol (HDL-C), and serum triglycerides (STG). The normocholesterolemic subjects who ate butter first had by 24 weeks mean SCHOL values equal to their entry values; those who ate margarine first had increased SCHOL values throughout the study. By the end of the study, the hypercholesterolemic subjects showed either no change or a slight decrease in both SCHOL and HDL-C values. Specific fatty acids were distributed differently in the serum fractions of triacylglycerol (TGFA), cholesteryl esters (CEFA), and phospholipids (PLFA). These distributions remained constant in both normocholesterolemic and hypercholesterolemic subjects regardless of the type and amount of fat consumed.     

Dietary fish protein modulates high density lipoprotein cholesterol and lipoprotein lipase activity in rabbits.

To explore the pathways by which fish protein feeding influences HDL metabolism, postheparin plasma lipoprotein lipase and hepatic triglyceride lipase activities were measured in rabbits fed fish protein or soybean protein combined with corn oil or coconut oil in a 2 x 2 factorial arrangement. In addition to greater serum total and LDL-cholesterol concentrations, the elevated HDL cholesterol concentration caused by feeding fish protein, compared with soybean protein, was accompanied by lower VLDL triglycerides and parallel higher lipoprotein lipase activity in fish protein-fed rabbits. These results suggest an enhanced assembly of circulating HDL through promoted lipoprotein lipase activity in rabbits fed fish protein. Moreover, dietary proteins and lipids interacted with one another to alter HDL triglycerides and liver cholesterol concentrations. Diet-induced changes in lipoprotein lipase activity were, however, not related to insulinemia, which was unaltered by purified diet feeding. The present results suggest that fish protein may affect HDL metabolism through the modulation of lipoprotein lipase activity in rabbits.     

Dietary fatty acids were not independently associated with lipoprotein subclasses in elderly women

Dietary fatty acids are known to affect serum lipoproteins; however, little is known about the associations between consumption of dietary fatty acids and lipoprotein subclasses. In this study, we hypothesized that there is an association between dietary fatty acids and lipoprotein subclasses and investigated the cross-sectional association of dietary fat intake with subclasses of lipoproteins in elderly women. Altogether, 547 women (aged ≥65 years) who were part of OSTPRE cohort participated. Dietary intake was assessed by 3-day food records, lifestyle, and health information obtained through self-administrated questionnaires, and lipoprotein subclasses were determined by nuclear magnetic resonance spectroscopy. To analyze the associations between fatty acids and lipoprotein subclasses, we used Pearson and Spearman correlation coefficients and the analysis of covariance (ANCOVA) test with, adjustment for physical activity, body mass index, age, smoking status, and intake of lipid-lowering drugs. There were significant correlations between saturated fatty acids (SFA; % of energy) and concentrations of large, medium, and small low-density lipoproteins (LDL); total cholesterol in large, medium, and small LDL; and phospholipids in large, medium, and small LDL, after correction for multiple testing. After adjustment for covariates, the higher intake of SFA was associated with smaller size of LDL particles (P = .04, ANCOVA) and lower amount of triglycerides in small very low-density lipoproteins (P = .046, ANCOVA). However, these associations did not remain significant after correction for multiple testing. In conclusion, high intake of SFA may be associated with the size of LDL particles, but the results do not support significant, independent associations between dietary fatty acids and lipoprotein subclasses.