Reducing saturated fat intake lowers LDL-C but increases Lp(a) levels in African Americans: the GET-READI feeding trial.

Reducing dietary saturated fatty acids (SFA) intake results in a clinically significant lowering of low-density lipoprotein cholesterol (LDL-C) across ethnicities. In contrast, dietary SFA's role in modulating emerging cardiovascular risk factors in different ethnicities remains poorly understood. Elevated levels of lipoprotein(a) [Lp(a)], an independent cardiovascular risk factor, disproportionally affect individuals of African descent. Here, we assessed the responses in Lp(a) levels to dietary SFA reduction in 166 African Americans enrolled in GET-READI (The Gene-Environment Trial on Response in African Americans to Dietary Intervention), a randomized controlled feeding trial. Participants were fed two diets in random order for 5 weeks each: 1) an average American diet (AAD) (37% total fat: 16% SFA), and 2) a diet similar to the Dietary Approaches to Stop Hypertension (DASH) diet (25% total fat: 6% SFA). The participants' mean age was 35 years, 70% were women, the mean BMI was 28 kg/m2, and the mean LDL-C was 116 mg/dl. Compared to the AAD diet, LDL-C was reduced by the DASH-type diet (mean change: -12 mg/dl) as were total cholesterol (-16 mg/dl), HDL-C (-5 mg/dl), apoA-1 (-9 mg/dl) and apoB-100 (-5 mg/dl) (all P < 0.0001). In contrast, Lp(a) levels increased following the DASH-type diet compared with AAD (median: 58 vs. 44 mg/dl, P < 0.0001). In conclusion, in a large cohort of African Americans, reductions in SFA intake significantly increased Lp(a) levels while reducing LDL-C. Future studies are warranted to elucidate the mechanism(s) underlying the SFA reduction-induced increase in Lp(a) levels and its role in cardiovascular risk across populations.

Reducing the glycemic index or carbohydrate content of mixed meals reduces postprandial glycemia and insulinemia over the entire day but does not affect satiety.

OBJECTIVE: We evaluated the effects of mixed meals differing in glycemic index (GI) and carbohydrate content on postprandial serum glucose and insulin response, hunger, and satiety over the course of a 12-h day. RESEARCH DESIGN AND METHODS: In this randomized crossover trial, 26 overweight or obese adults received four diets in random order (high GI, high carbohydrate [HGI-HC]; high GI, low carbohydrate [HGI-LC]; low GI, high carbohydrate [LGI-HC]; and low GI, low carbohydrate [LGI-LC]). All meals were prepared by a metabolic kitchen. Participants received breakfast, lunch, and dinner over the course of a 12-h day. Primary outcomes were postprandial serum glucose and insulin quantified as area under the curve. Hunger, fullness, and satiety were assessed by visual analog scale. RESULTS: The HGI-LC, LGI-HC, and LGI-LC diets significantly reduced glucose and insulin area under the curve compared with the HGI-HC diet (P < 0.001 for all comparisons). There were no significant differences in ratings of hunger, fullness, or satiety between the different dietary treatments. CONCLUSIONS: Reducing the GI or carbohydrate content of mixed meals reduces postprandial glycemia and insulinemia, and these changes can be sustained over the course of an entire day. However, there were no differences in subjective hunger and satiety ratings between the diets. These results demonstrate that maintaining a low GI or glycemic load diet is an effective method of controlling serum glucose and insulin levels.

Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial.

CONTEXT: The role of diet composition in response to overeating and energy dissipation in humans is unclear. OBJECTIVE: To evaluate the effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition. DESIGN, SETTING, AND PARTICIPANTS: A single-blind, randomized controlled trial of 25 US healthy, weight-stable male and female volunteers, aged 18 to 35 years with a body mass index between 19 and 30. The first participant was admitted to the inpatient metabolic unit in June 2005 and the last in October 2007. INTERVENTION: After consuming a weight-stabilizing diet for 13 to 25 days, participants were randomized to diets containing 5% of energy from protein (low protein), 15% (normal protein), or 25% (high protein), which they were overfed during the last 8 weeks of their 10- to 12-week stay in the inpatient metabolic unit. Compared with energy intake during the weight stabilization period, the protein diets provided approximately 40% more energy intake, which corresponds to 954 kcal/d (95% CI, 884-1022 kcal/d). MAIN OUTCOME MEASURES: Body composition was measured by dual-energy x-ray absorptiometry biweekly, resting energy expenditure was measured weekly by ventilated hood, and total energy expenditure by doubly labeled water prior to the overeating and weight stabilization periods and at weeks 7 to 8. RESULTS: Overeating produced significantly less weight gain in the low protein diet group (3.16 kg; 95% CI, 1.88-4.44 kg) compared with the normal protein diet group (6.05 kg; 95% CI, 4.84-7.26 kg) or the high protein diet group (6.51 kg; 95% CI, 5.23-7.79 kg) (P = .002). Body fat increased similarly in all 3 protein diet groups and represented 50% to more than 90% of the excess stored calories. Resting energy expenditure, total energy expenditure, and body protein did not increase during overfeeding with the low protein diet. In contrast, resting energy expenditure (normal protein diet: 160 kcal/d [95% CI, 102-218 kcal/d]; high protein diet: 227 kcal/d [95% CI, 165-289 kcal/d]) and body protein (lean body mass) (normal protein diet: 2.87 kg [95% CI, 2.11-3.62 kg]; high protein diet: 3.18 kg [95% CI, 2.37-3.98 kg]) increased significantly with the normal and high protein diets. CONCLUSIONS: Among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00565149.

Dietary adherence to long-term controlled feeding in a calorie-restriction study in overweight men and women.

BACKGROUND: The success of clinical dietary interventions depends on the motivation and willingness of study participants to adhere to the prescribed or provided diet. The aim of this study was to assess participants' adherence to their provided diet over the 6-month duration of the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE). METHODS: Investigators assessed the dietary adherence of 46 men and women who completed the first phase of the CALERIE trial. Volunteers were randomized to 1 of 4 dietary intervention groups: control, calorie restriction, calorie restriction with exercise, and low-calorie diet. Participants were provided with foods during 2 weeks of baseline and during the first 12 weeks and the last 2 weeks of the intervention as outpatients, and they completed a daily self-report form to assess diet adherence. The data are expressed as mean ± standard deviation or standard error of the mean. Pearson's correlation coefficient was determined to examine the relationship between assigned energy levels and total energy intake. RESULTS: Deviations reported were for eating nonstudy foods as well as not eating study foods. There were few deviations, and when converted to mean calories per day these did not affect total energy (weeks -3 to 2 = 10.25 ± 4.82, weeks 1-4 = 9.93 ± 12.52, weeks 5-11 = 8.38 ± 7.42, weeks 22-23 = 0.53 ± 3.97 kcal/d). The associations between assigned energy level and actual intake were high for all groups (P = .001), weeks -3 to -2 (r = 0.999), weeks 1-4 (r = 0.998), weeks 5-11 (r = 0.999), and weeks 22-23 (r = 0.998). CONCLUSIONS: The data provide evidence that dietary adherence is good when all foods are provided and when participants are highly motivated.

Increased food intake and energy expenditure following administration of olanzapine to healthy men.

Atypical antipsychotic medications like olanzapine (OLZ) induce weight gain and increase the risk of diabetes in patients with schizophrenia. The goal of this study was to assess potential mechanisms of OLZ-induced weight gain and accompanying metabolic effects. Healthy, lean, male volunteers received OLZ and placebo (PBO) in a randomized, double-blind, crossover study. In periods 1 and 2, subjects received OLZ (5 mg for 3 days then OLZ 10 mg for 12 days) or matching PBO separated by a minimum 12-day washout. Twenty-four hour food intake (FI), resting energy expenditure (REE), activity level, metabolic markers, and insulin sensitivity (IS) were assessed. In total, 30 subjects were enrolled and 21 completed both periods. Mean age and BMI were 27 years (range: 18-49 years) and 22.6 +/- 2.2 kg/m(2), respectively. Relative to PBO, OLZ resulted in a 2.62 vs. 0.08 kg increase in body weight (P < 0.001) and 18% (P = 0.052 or 345 kcal) increase in FI. Excluding one subject with nausea and dizziness on the day of OLZ FI measurement, the increase in FI was 547 kcal, (P < 0.05). OLZ increased REE relative to PBO (113 kcal/day, P = 0.003). Significant increases in triglycerides, plasminogen activator inhibitor-I (PAI-I), leptin, and tumor necrosis factor-alpha (TNF-alpha) were observed. No significant differences in activity level or IS were observed. This study provides evidence that OLZ pharmacology drives the early increase in weight through increased FI, without evidence of decreased energy expenditure (EE), activity level, or short-term perturbations in IS.

Dose effects of dietary phytosterols on cholesterol metabolism: a controlled feeding study.

BACKGROUND: Phytosterol supplementation of 2 g/d is recommended by the National Cholesterol Education Program to reduce LDL cholesterol. However, the effects of different intakes of phytosterol on cholesterol metabolism are uncertain. OBJECTIVE: We evaluated the effects of 3 phytosterol intakes on whole-body cholesterol metabolism. DESIGN: In this placebo-controlled, crossover feeding trial, 18 adults received a phytosterol-deficient diet (50 mg phytosterols/2000 kcal) plus beverages supplemented with 0, 400, or 2000 mg phytosterols/d for 4 wk each, in random order. All meals were prepared in a metabolic kitchen; breakfast and dinner on weekdays were eaten on site. Primary outcomes were fecal cholesterol excretion and intestinal cholesterol absorption measured with stable-isotope tracers and serum lipoprotein concentrations. RESULTS: Phytosterol intakes (diet plus supplements) averaged 59, 459, and 2059 mg/d during the 3 diet periods. Relative to the 59-mg diet, the 459- and 2059-mg phytosterol intakes significantly (P < 0.01) increased total fecal cholesterol excretion (36 +/- 6% and 74 +/- 10%, respectively) and biliary cholesterol excretion (38 +/- 7% and 77 +/- 12%, respectively) and reduced percentage intestinal cholesterol absorption (-10 +/- 1% and -25 +/- 3%, respectively). Serum LDL cholesterol declined significantly only with the highest phytosterol dose (-8.9 +/- 2.3%); a trend was observed with the 459-mg/d dose (-5.0 +/- 2.1%; P = 0.077). CONCLUSIONS: Dietary phytosterols in moderate and high doses favorably alter whole-body cholesterol metabolism in a dose-dependent manner. A moderate phytosterol intake (459 mg/d) can be obtained in a healthy diet without supplementation. This trial was registered at clinicaltrials.gov as NCT00860054.

Effects of dairy products on intracellular calcium and blood pressure in adults with essential hypertension.

BACKGROUND: Consumption of dairy foods has been associated with lower blood pressure in certain populations. OBJECTIVE: This study examined the effects of dairy foods on blood pressure (BP) and intracellular calcium ((Ca)(i)) and the dependence of BP changes on changes in (Ca)(i). DESIGN: Twenty-three stage 1 hypertensive adults were fed the following 3 experimental diets (5 wk each) in a randomized cross-over design study; a dairy-rich, high fruits and vegetables diet (D-FandV; 30% fat, 7% saturated fat (SFA), 3.4 servings/d dairy), a high fruits and vegetables diet (FandV; 30% fat, 7% SFA, 0.4 servings/d dairy), and an average Western diet (control; 36% fat, 15% SFA, 0.4 servings/d dairy). Systolic (SBP) and diastolic (DBP) BP, calcium regulatory hormones, and erythrocyte (Ca)(i) were determined. RESULTS: SBP and DBP were significantly reduced by approximately 2 mm Hg following both D-F&V and F&V diets vs. the control (P < 0.05). The D-F&V diet significantly lowered 1,25-dihydroxyvitaminD compared with the F&V and control diets (P < 0.01). Serum calcium, parathyroid hormone, calcitonin, and renin activity were unchanged. The D-F&V diet lowered (Ca)(i) vs. the other two diets (P < 0.01), and this change correlated with the fall in DBP (r = 0.52, P < 0.05). Subjects who responded to the D-F&V diet by significantly reducing (Ca)(i) exhibited significantly greater net decreases in DBP on the D-F&V vs. the F&V (-2.8 +/- 1.0 mm Hg) and control diets (-5.4 +/-1.0 mm Hg; diet x group interaction, P < 0.02). CONCLUSION: Consumption of dairy foods beneficially affects (Ca)(i), resulting in improved BP in a subgroup defined by (Ca)(i) response.

Triiodothyronine increases calcium loss in a bed rest antigravity model for space flight.

Bed rest has been used as a model to simulate the effects of space flight on bone metabolism. Thyroid hormones accelerate bone metabolism. Thus, supraphysiologic doses of this hormone might be used as a model to accelerate bone metabolism during bed rest and potentially simulate space flight. The objective of the study was to quantitate the changes in bone turnover after low doses of triiodothyronine (T(3)) added to short-term bed rest. Nine men and 5 women were restricted to bed rest for 28 days with their heads positioned 6 degrees below their feet. Subjects were randomly assigned to receive either placebo or oral T(3) at doses of 50 to 75 microg/d in a single-blind fashion. Calcium balance was measured over 5-day periods; and T(3), thyroxine, thyroid-stimulating hormone, immunoreactive parathyroid hormone, osteocalcin, bone alkaline phosphatase, and urinary deoxypyridinoline were measured weekly. Triiodothyronine increased 2-fold in the men and 5-fold in the women during treatment, suppressing both thyroxine and thyroid-stimulating hormone. Calcium balance was negative by 300 to 400 mg/d in the T(3)-treated volunteers, primarily because of the increased fecal loss that was not present in the placebo group. Urinary deoxypyridinoline to creatinine ratio, a marker of bone resorption, increased 60% in the placebo group during bed rest, but more than doubled in the T(3)-treated subjects (P < .01), suggesting that bone resorption was enhanced by treatment with T(3). Changes in serum osteocalcin and bone-specific alkaline phosphatase, markers of bone formation, were similar in T(3)- and placebo-treated subjects. Triiodothyronine increases bone resorption and fecal calcium loss in subjects at bed rest.

Acceptability of sodium-reduced research diets, including the Dietary Approaches To Stop Hypertension diet, among adults with prehypertension and stage 1 hypertension.

OBJECTIVE: Examine the acceptability of sodium-reduced research diets. DESIGN: Randomized crossover trial of three sodium levels for 30 days each among participants randomly assigned to one of two dietary patterns. PARTICIPANTS/SETTING: Three hundred fifty-four adults with prehypertension or stage 1 hypertension who were participants in the Dietary Approaches to Stop Hypertension (DASH-Sodium) outpatient feeding trial. INTERVENTION: Participants received their assigned diet (control or DASH, rich in fruits, vegetables, and low-fat dairy products), each at three levels of sodium (higher, intermediate, and lower) corresponding to 3,500, 2,300, and 1,200 mg/day (150, 100, and 50 mmol/day) per 2,100 kcal. MAIN OUTCOME MEASURES: Nine-item questionnaire on liking and willingness to continue the assigned diet and its level of saltiness using a nine-point scale, ranging from one to nine. STATISTICAL ANALYSES PERFORMED: Generalized estimating equations to test participant ratings as a function of sodium level and diet while adjusting for site, feeding cohort, carryover effects, and ratings during run-in. RESULTS: Overall, participants rated the saltiness of the intermediate level sodium as most acceptable (DASH group: 5.5 for intermediate vs 4.5 and 4.4 for higher and lower sodium; control group: 5.7 for intermediate vs 4.9 and 4.7 for higher and lower sodium) and rated liking and willing to continue the DASH diet more than the control diet by about one point (ratings range from 5.6 to 6.6 for DASH diet and 5.2 to 6.1 for control diet). Small race differences were observed in sodium and diet acceptability. CONCLUSIONS: Both the intermediate and lower sodium levels of each diet are at least as acceptable as the higher sodium level in persons with or at risk for hypertension.

Hormonal responses to a fast-food meal compared with nutritionally comparable meals of different composition.

BACKGROUND: Fast food is consumed in large quantities each day. Whether there are differences in the acute metabolic response to these meals as compared to 'healthy' meals with similar composition is unknown. DESIGN: Three-way crossover. METHODS: Six overweight men were given a standard breakfast at 8:00 a.m. on each of 3 occasions, followed by 1 of 3 lunches at noon. The 3 lunches included: (1) a fast-food meal consisting of a burger, French fries and root beer sweetened with high fructose corn syrup; (2) an organic beef meal prepared with organic foods and a root beer containing sucrose, and (3) a turkey meal consisting of a turkey sandwich and granola made with organic foods and an organic orange juice. Glucose, insulin, free fatty acids, ghrelin, leptin, triglycerides, LDL-cholesterol and HDL-cholesterol were measured at 30-min intervals over 6 h. Salivary cortisol was measured after lunch. RESULTS: Total fat, protein and energy content were similar in the 3 meals, but the fatty acid content differed. The fast-food meal had more myristic (C14:0), palmitic (C16:0), stearic (C18:0) and trans fatty acids (C18:1) than the other 2 meals. The pattern of nutrient and hormonal response was similar for a given subject to each of the 3 meals. The only statistically significant acute difference observed was a decrease in the AUC of LDL cholesterol after the organic beef meal relative to that for the other two meals. Other metabolic responses were not different. CONCLUSION: LDL-cholesterol decreased more with the organic beef meal which had lesser amounts of saturated and trans fatty acids than in the fast-food beef meal.

Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial.

CONTEXT: Prolonged calorie restriction increases life span in rodents. Whether prolonged calorie restriction affects biomarkers of longevity or markers of oxidative stress, or reduces metabolic rate beyond that expected from reduced metabolic mass, has not been investigated in humans. OBJECTIVE: To examine the effects of 6 months of calorie restriction, with or without exercise, in overweight, nonobese (body mass index, 25 to <30) men and women. DESIGN, SETTING, AND PARTICIPANTS: Randomized controlled trial of healthy, sedentary men and women (N = 48) conducted between March 2002 and August 2004 at a research center in Baton Rouge, La. INTERVENTION: Participants were randomized to 1 of 4 groups for 6 months: control (weight maintenance diet); calorie restriction (25% calorie restriction of baseline energy requirements); calorie restriction with exercise (12.5% calorie restriction plus 12.5% increase in energy expenditure by structured exercise); very low-calorie diet (890 kcal/d until 15% weight reduction, followed by a weight maintenance diet). MAIN OUTCOME MEASURES: Body composition; dehydroepiandrosterone sulfate (DHEAS), glucose, and insulin levels; protein carbonyls; DNA damage; 24-hour energy expenditure; and core body temperature. RESULTS: Mean (SEM) weight change at 6 months in the 4 groups was as follows: controls, -1.0% (1.1%); calorie restriction, -10.4% (0.9%); calorie restriction with exercise, -10.0% (0.8%); and very low-calorie diet, -13.9% (0.7%). At 6 months, fasting insulin levels were significantly reduced from baseline in the intervention groups (all P<.01), whereas DHEAS and glucose levels were unchanged. Core body temperature was reduced in the calorie restriction and calorie restriction with exercise groups (both P<.05). After adjustment for changes in body composition, sedentary 24-hour energy expenditure was unchanged in controls, but decreased in the calorie restriction (-135 kcal/d [42 kcal/d]), calorie restriction with exercise (-117 kcal/d [52 kcal/d]), and very low-calorie diet (-125 kcal/d [35 kcal/d]) groups (all P<.008). These "metabolic adaptations" (~ 6% more than expected based on loss of metabolic mass) were statistically different from controls (P<.05). Protein carbonyl concentrations were not changed from baseline to month 6 in any group, whereas DNA damage was also reduced from baseline in all intervention groups (P <.005). CONCLUSIONS: Our findings suggest that 2 biomarkers of longevity (fasting insulin level and body temperature) are decreased by prolonged calorie restriction in humans and support the theory that metabolic rate is reduced beyond the level expected from reduced metabolic body mass. Studies of longer duration are required to determine if calorie restriction attenuates the aging process in humans. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00099151.

Globin digest: no evidence for a weight loss mechanism.

This study was designed to document the mechanism through which globin digest, a dietary herbal supplement, might cause weight loss by exploring possible fat malabsorption, calorie malabsorption, energy expenditure, and fat oxidation. Six healthy subjects were placed on an outpatient diet for 14 days and given a meal containing 40.9 g of fat on days 5 and 11, and stools were collected for 72 hours after each meal for analysis of fecal fat content. Four grams of globin digest was given with one meal and placebo with the other. In another separate study, six subjects were placed on a 100-g fat, weight-maintaining diet for 14 days. All food was prepared by the Pennington Center (Baton Rouge, LA) metabolic kitchen. Globin digest (2 g) or placebo was given with each of three meals per day, and stool was collected for calorie determinations during the last 72 hours of each week. Subjects received globin digest during one of the 2 weeks and placebo during the other. Resting metabolic rate and respiratory quotient were measured on the last day of each 1-week period. There was no increase in 72-hour fecal fat or fecal calories by bomb calorimetry during either of the studies. There was no difference in the respiratory quotient. Globin digest did result in an increase in resting metabolic rate. However, this increase was not statistically significant. Globin digest, if effective, does not cause weight loss or fat loss through fat malabsorption or a relative increase in fat oxidation. Future studies are needed to document the efficacy of globin digest for weight loss in humans before further mechanistic investigation is attempted.

Individual variability in cardiovascular disease risk factor responses to low-fat and low-saturated-fat diets in men: body mass index, adiposity, and insulin resistance predict changes in LDL cholesterol.

BACKGROUND: Although reductions in total and saturated fat consumption are recommended to reduce the risk of cardiovascular disease, individual variability in plasma lipid responses exists. OBJECTIVE: Our aim was to determine the effect of adiposity and insulin resistance on the lipoprotein response to diets lower in total and saturated fat than the average American diet (AAD). DESIGN: A randomized, double-blind, 3-period crossover controlled feeding design was used to examine the effects on plasma lipids of 3 diets that differed in total fat: the AAD [designed to contain 38% fat and 14% saturated fatty acids (SFAs)], the Step I diet (30% fat with 9% SFAs), and the Step II diet (25% fat with 6% SFAs). The diets were fed for 6 wk each to 86 free-living, healthy men aged 22-64 y at levels designed to maintain weight. RESULTS: Compared with the AAD, the Step I and Step II diets lowered LDL cholesterol by 6.8% and 11.7%, lowered HDL cholesterol by 7.5% and 11.2%, and raised triacylglycerols by 14.3% and 16.2%, respectively. The Step II diet response showed significant positive correlations between changes in both LDL cholesterol and the ratio of total to HDL cholesterol and baseline percentage body fat, body mass index, and insulin. These associations were largely due to smaller reductions in LDL cholesterol with increasing percentage body fat, body mass index, or insulin concentrations. Subdivision of the study population showed that the participants in the upper one-half of fasting insulin concentrations averaged only 57% of the reduction in LDL cholesterol with the Step II diet of the participants in the lower half. CONCLUSION: Persons who are insulin resistant respond less favorably to Step II diets than do those who are insulin sensitive.

Comparison of the acute response to meals enriched with cis- or trans-fatty acids on glucose and lipids in overweight individuals with differing FABP2 genotypes.

Trans-fatty acids have been implicated as a risk factor for cardiovascular disease and diabetes. In addition, a polymorphism at codon 54 (Ala54Thr) in the fatty acid-binding protein 2 (FABP2) gene has been suggested to modify an interaction between dietary fat and insulin sensitivity. We examined the postprandial metabolic profiles after meals enriched with C18:1trans- relative to a similar meal with C18:1cis-fatty acid in individuals who were either FABP2 Ala54 homozygotes or Thr54 carriers. Moderately overweight men and women ate 2 breakfast test meals, separated by 1 week, each providing 40% of their daily energy requirement and containing 50% of energy as fat. In one meal, 10% of energy was from C18:1trans, and in the other meal, the C18:1trans was replaced with C18:1cis. Metabolic parameters were assessed during an 8-hour period. Insulin and C-peptide levels increased more after the C18:1trans meal, and this was associated with a greater fall in free fatty acids. Postprandial glucose levels and oxidation of fatty acids and carbohydrate were not different between the 2 test meals. The Thr54 allele for FABP2 increased the rise in postprandial glucose but not triacylglycerols. Fractional triacylglycerol synthetic rates were higher after consumption of the C18:1trans meal relative to the C18:1cis meal only in Thr54 carriers. These data show that a single meal enriched with C18:1trans-fatty acids can significantly increase insulin resistance, and that in the presence of the FABP2 Thr54 allele, may contribute to increased partitioning of glucose to triacylglycerols and insulin resistance.

Dietary adherence in well-controlled feeding studies.

In well-controlled feeding studies, participants are expected to adhere to a strict diet by consuming only and all foods provided by the research kitchen. They may find adherence more of a challenge with certain study design features. To assess this we mailed a post-study anonymous questionnaire to participants who had completed one of eight controlled feeding studies at the Pennington Biomedical Research Center, Baton Rouge, LA. Of the 154 respondents, more than 90% always or usually adhered to the diet. Of those who did not adhere, many deviated fewer than four times. Eating all of the foods provided was a greater challenge than refraining from eating foods not allowed. Diet assignment, the allowance of alcohol, and a self-selected Saturday meal affected adherence. The results of this research may be useful in designing controlled feeding studies. Our data indicate that diet adherence is good, and because deviations are few, they are unlikely to jeopardize study results.

Daily intake of multivitamins during long-term intake of olestra in men prevents declines in serum vitamins A and E but not carotenoids.

The objective of this study was to determine whether vitamin supplementation during long-term (36 wk) ingestion of olestra supplemented with vitamin E could prevent decreases in vitamin E, vitamin A, and carotenoids. This was a 36-wk study of 37 healthy males randomly assigned to consume a control diet composed of 33% energy from fat, a similar diet in which one third of the energy from fat had been replaced with olestra, or a fat-reduced (25% of energy from fat) diet. Subjects also ingested a daily multivitamin (Centrum). Serum concentrations of alpha-tocopherol, retinol, beta-carotene, lycopene, and lutein + zeaxanthin were analyzed by HPLC. Subjects eating the olestra-containing diet had substantial decreases in serum beta-carotene, lycopene, and lutein + zeaxanthin, which occurred by 12 wk; these changes were found despite correcting for serum total cholesterol or BMI. Serum beta-carotene and lycopene concentrations were below the lower limit of the reference range (<0.186 and <0.298 mumol/L, respectively) at one or more time points. The slight decline in serum alpha-tocopherol concentration, significant at 24 wk, was caused by the decline in serum cholesterol. Retinol concentrations decreased with time in all 3 groups, but were not affected by olestra. We conclude that supplementation with a multivitamin containing vitamins A and E was adequate to prevent olestra-induced decrease in serum alpha-tocopherol and retinol. Olestra-induced decreases in serum beta-carotene, lycopene, and lutein + zeaxanthin were not prevented by the vitamin supplement used in this study.

Rice bran oil, not fiber, lowers cholesterol in humans.

BACKGROUND: The cholesterol-lowering abilities of rice bran's fiber and oil apart from its fatty acid composition remain unclear. OBJECTIVE: The objective of the study was to assess the effects of defatted rice bran and rice bran oil in an average American diet on blood lipids in moderately hypercholesterolemic persons. DESIGN: Study 1 used a parallel-arm design. Twenty-six healthy volunteers consumed a diet with 13-22 g dietary fiber/d for 3 wk, and then 13 of the volunteers were switched to a diet with defatted rice bran to double the fiber intake for 5 wk. Study 2 was a randomized, crossover, 10-wk feeding study performed in 14 volunteers who consumed a diet with rice bran oil (1/3 of the total dietary fat) substituted for an oil blend that had a fatty acid composition similar to that of the rice bran oil. Serum lipids and factor VII were measured in both studies. RESULTS: Defatted rice bran did not lower lipid concentrations. In study 2, total cholesterol was significantly lower with consumption of the diet containing rice bran oil than with consumption of the control diet. Moreover, with consumption of the rice bran oil diet, LDL cholesterol decreased by 7% (P < 0.0004), whereas HDL cholesterol was unchanged. CONCLUSIONS: Rice bran oil, not fiber, lowers cholesterol in healthy, moderately hypercholesterolemic adults. There were no substantial differences in the fatty acid composition of the diets; therefore, the reduction of cholesterol was due to other components present in the rice bran oil, such as unsaponifiable compounds.

Estimated phytochemical content of the dietary approaches to stop hypertension (DASH) diet is higher than in the Control Study Diet.

The Dietary Approaches to Stop Hypertension (DASH) diet substantially lowers blood pressure and reduces blood lipid levels. The DASH diet menus were designed to reach beneficial levels of fiber, potassium, magnesium, and calcium, and therefore contain more fruits, vegetables, and whole grains relative to the control menus, and consequently more phytochemicals. Using the US Department of Agriculture food composition databases, the polyphenol, carotenoid, and phytosterol contents of the diets used in the DASH study were estimated. When compared with the control diet, the DASH diet is higher in flavonols, flavanones, flavan-3-ols, beta-carotene, beta-cryptoxanthin, lycopene, lutein+zeaxanthin, and phytosterols. Flavone levels are similar, whereas isoflavones are present in a small amount in the DASH diet. The roles of these compounds in disease risk reduction are becoming recognized. It therefore is possible that the health benefits of the DASH diet are partially attributable to the phytochemicals and might extend beyond cardiovascular disease risk reduction.

Dietary quality assurance processes of the DASH-Sodium controlled diet study.

A thorough quality assurance (QA) program upholds the integrity of nutrition research studies by yielding reliable data and results. Continually evaluating the implementation of a procedure against a goal and making adjustments when needed enhance the quality of a study's conduct and outcomes. Controlled diet studies require QA processes at various steps beginning with the screening of study participants, through diet preparation and delivery to data collection. Staff training and observations with monitoring activities, are important so tasks are completed according to protocol. When several clinical sites participate as partners in a controlled diet study, uniform procedures must be followed and a formal standardized QA program will assist. The Dietary Approaches to Stop Hypertension (DASH)-Sodium study employed such a program, described in this article, that included training staff, observing procedures, monitoring data for completeness and accuracy, evaluating processes, giving feedback, and documenting that tasks were done according to protocol. Furthermore, QA processes were used in the areas of participant screening, orientation, diet adherence, food procurement and preparation, and exit interviews. Other researchers may implement similar activities to ensure quality in their nutrition research programs.