Concurrent physical activity increases fat oxidation during the shift to a high-fat diet

BACKGROUND

It takes several days to adapt to a high-fat diet. In an earlier study, we observed a large degree of interindividual variation in the capacity to adapt to a high-fat diet. We hypothesized that concurrent physical activity would accelerate fat oxidation during an isoenergetic high-fat diet.

OBJECTIVE

The objective of this study was to determine the effect of increased physical activity on the ability of young healthy men to increase fat oxidation during the shift to a high-fat diet.

DESIGN

Six young healthy men participated in a randomized, single-blind crossover study. The volunteers consumed a diet contributing 37% of energy as fat, 14% as protein, and 49% as carbohydrate for 4 d. Energy expenditure and macronutrient balance were then measured in a respiration chamber as the energy content of the isoenergetic diet was changed to 50% fat, 14% protein, and 36% carbohydrate. Treadmill walking, as the physical activity, was used to increase total daily energy expenditure to 1.8 times the resting metabolic rate during 1 of 2 stays in the metabolic chamber. Total daily energy expenditure was maintained at 1.4 times the resting metabolic rate for the other stay.

RESULTS

Energy balance was not significantly different between the 2 conditions. The 24-h respiratory quotient decreased more rapidly and to a greater extent under conditions of increased energy expenditure. Further, there was a decrease in the interindividual variability in the response of the respiratory quotient to a high-fat diet with increased energy expenditure (physical activity). Cumulative carbohydrate and protein balances were greater under conditions of increased physical activity. Conversely, cumulative fat balance was greater under sedentary conditions.

CONCLUSION

Concurrent physical activity increases fat oxidation during the shift to a high-fat diet.

Differential response to low-fat diet between low and normal HDL-cholesterol subjects

Heart attacks frequently occur in normolipidemic subjects with low concentration of high density lipoproteins (</=35 mg/dL). A low-fat diet is generally recommended to patients with coronary heart disease. A low-fat diet decreases both low density (LDL) and high density lipoproteins (HDL). We have shown that on an Average American Diet, subjects with different HDL-cholesterol (HDL-C) levels have different HDL subpopulation profiles. In low HDL-C subjects (</=35 mg/dL), the apoA-I-only subpopulation alpha(1) is significantly decreased compared to individuals with normal HDL-C levels (>35 mg/dL). We hypothesized that as subjects with low HDL-C already have low HDL concentrations, the major decrease of HDL-C will occur in subjects with normal HDL-C when a low-fat diet is consumed. Normolipidemic male subjects consumed three diets differing in total fat and saturated fat composition (AAD: 37%, Step-1: 28%, Step-2: 24% total fat) for 6 weeks in a three-period double-blind randomized crossover design. Plasma lipids and apolipoproteins were determined and changes in distribution of HDL subpopulations were evaluated. As a result of a low-fat diet, low HDL-C individuals slightly decreased their HDL-C, but substantially decreased their LDL-C resulting in a significant improvement in the LDL-C/HDL-C ratio. However, subjects with normal HDL-C levels decreased both their LDL-C and HDL-C resulting in an unchanged LDL-C/HDL-C ratio. We also observed significant differences in response to low-fat diets in HDL-C and alpha(1) concentrations between low and normal HDL-C subjects. In the normal HDL-C group, consumption of a low-fat diet also resulted in redistribution of apoA-I-containing HDL subpopulations, indicated by a decrease in the large apoA-I-only alpha(1) subpopulation. These data demonstrate that male subjects with low HDL-C respond to a low-fat diet differently than individuals with normal HDL-C.

Effects of microwave heat, packaging, and storage temperature on fatty acid and proximate compositions in rice bran

The effect of microwave heat, packaging methods, and storage temperatures on proximate and fatty acid compositions of rice bran during 16 weeks of storage was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and microwave heated for 3 min. Raw and microwave-heated brans were packed in zipper-top bags and/or vacuum-sealed bags and stored at 4-5 and/or 25 degrees C for 16 weeks. The moisture content decreased significantly from an initial 8.4 to 6.4% in microwave-heated samples regardless of packaging methods and storage temperatures. Protein, fat, linoleic, and linolenic contents did not change significantly in all raw and microwave-heated samples during 16 weeks of storage. The microwave-heated rice bran packed in zipper-top bags can be stored at 4-5 degrees C for up to 16 weeks without adverse effect on proximate and fatty acid composition quality under the conditions employed in this study.

Prevention of oxidative rancidity in rice bran during storage

The effect of microwave heat on lipoxygenase (LOX) activity in rice bran under various storage conditions was examined. Raw rice bran from the long-grain variety Lemont was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran samples were packed in zipper-top bags or vacuum packs and stored at room temperature (25 degrees C) or in the refrigerator (4-5 degrees C) for 16 weeks. Samples were analyzed for LOX activity at 4-week intervals. LOX activity did not significantly change from its initial value at week 0 for zipper-top and vacuum-packed samples while stored at 4-5 degrees C for 12 weeks, but decreased at week 16. Vacuum packing did not show a significant impact on LOX activity during 16 weeks of storage. Microwave-heated samples stored in the refrigerator did not show significant change in LOX activity for up to 12 weeks but showed a significant (p < 0. 05) decrease at 16 weeks. Results showed that oxidative rancidity of rice bran could be prevented by microwave heating the samples, packing in zipper-top bags, and storing at 4-5 degrees C for up to 16 weeks.

Prevention of hydrolytic rancidity in rice bran during storage

The effect of microwave heating, packaging, and storage temperature on the production of free fatty acids (FFA) in rice bran was examined. Freshly milled raw rice bran was adjusted to 21% moisture content and heated in a microwave oven at 850 W for 3 min. Raw and microwave-heated rice bran were packed in zipper-top bags or vacuum-sealed bags and stored at 4-5 or 25 degrees C for 16 weeks. FFA content of bran was measured at 4-week intervals. Total FFA increased rapidly over the 16-week period from the initial value of 2.5% in raw bran stored at 25 degrees C to 54.9% in vacuum bags and 48.1% in zipper-top bags. However, total FFA of raw bran stored at 4-5 degrees C increased at a slower rate from an initial value of 2. 5 to 25.4% in vacuum bags and 19.5% in zipper-top bags. After 16 weeks of storage, total FFA of microwave-heated bran stored at 25 degrees C increased from 2.8 to 6.9 and 5.2%, respectively, for samples stored in vacuum bags and zipper-top bags. Total FFA of microwave-heated samples stored at 4-5 degrees C did not change significantly with storage time. Results showed that hydrolytic rancidity of rice bran can be prevented by microwave heating and that the recommended storage condition for microwaved rice bran is 4-5 degrees C in zipper-top bags.

Diet design for a multicenter controlled feeding trial: the DELTA program. Delta Research Group

OBJECTIVE

To describe the process and results of diet standardization, diet validation, and monitoring of diet composition, which were key components of protocol 1 of Dietary Effects on Lipoproteins and Thrombogenic Activity (DELTA-1), the initial protocol in a program of multicenter human feeding studies designed to evaluate the effects of amount and type of fat on lipoproteins and hemostasis parameters in various demographic groups.

DESIGN

DELTA-1 was based on a randomized, blinded, crossover experimental design. Three diets were fed for 8 weeks to 103 healthy men and women aged 22 to 67 years at 4 field centers. Diet A, an average American diet, was designed to provide 37% of energy from fat, 16% of energy from saturated fatty acids (SFAs); diet B (step 1 diet) was designed to provide 30% of energy from fat, 9% of energy from SFA; and diet C (low SFA diet) was designed to provide 26% of energy from fat, 5% of energy from SFA. Key features of diet standardization included central procurement of fat-containing foods, inclusion of standard ingredients, precision weighing of foods--especially sources of fat and cholesterol--and use of standardized written procedures.

SETTING

For menu validation, a set of 12 menus for each diet was prepared in duplicate and chemically assayed. For monitoring of diet composition during the study, an 8-day diet cycle (6 weekday and 2 weekend menus) was sampled by every field center twice during each of 3 feeding periods.

STATISTICAL ANALYSES

Means (+/- standard error) were calculated and compared with target nutrient specifications.

RESULTS

DELTA-1 was able to provide a standardized diet that met nutrient specifications across 4 field centers over 24 weeks of participant feeding spanning a total of 8 months.

APPLICATIONS

Prestudy chemical validation of menus and continuous sampling and assay of diets throughout the study are essential to standardize experimental diets and to ensure that nutrient target goals are met and maintained throughout a controlled multicenter feeding study.

Normolipidemic subjects with low HDL cholesterol levels have altered HDL subpopulations

Epidemiological studies have established that plasma concentration of HDL is inversely correlated with the risk of coronary heart disease, even in the absence of increased LDL cholesterol levels. We postulate that specific HDL subpopulations may be responsible for antiatherogenic properties of HDL. HDL subpopulations were quantitated by two-dimensional gel electrophoresis in 79 normolipidemic healthy male subjects. To eliminate the influence of diet, volunteers consumed an average American diet for 6 weeks. After the diet period, subjects were stratified according to their HDL cholesterol (HDL-C) levels to low HDL-C < 0.91 mmol/L (< 35 mg/dL), medium > 0.91 < 1.30 mmol/L (> 35 < 50 mg/dL), and high > or = 1.30 mmol/L (> or = 50 mg/dL) groups. Plasma triglycerides and insulin levels were in the normal range, but subjects with low HDL-C levels had higher concentrations of plasma triglycerides and insulin than subjects with medium or high HDL-C concentrations. The absolute concentration (mg/dL) of apoA-I in the largest alpha-migrating HDL subpopulation (alpha 1) was (P < .01) lower in the low HDL-C subjects compared with the medium and high HDL-C groups. The relative concentration (percent distribution) of apoA-I was decreased (P < .01) in alpha 1 and increased (P < .01) in alpha 3 subpopulations. A positive correlation between HDL-C and alpha 1 (P < .001) and a negative correlation between HDL-C and alpha 3 were observed. The inverse correlation of apoA-I distribution (relative concentration) between alpha 1 and alpha 3 suggests an interconversion of alpha 1 and alpha 3 subpopulations, possibly by cholesteryl ester transfer protein. Pre-beta subpopulations showed an inverse trend with HDL-C, while the pre-alpha subpopulation behaved similarly to the alpha-migrating subpopulation. Colocalization of apoA-I and apoA-II particles in the different HDL subpopulations demonstrated that alpha 1, pre-beta 1, and pre-beta 2 subpopulations are apoA-I-only particles rather than apoA-I:A-II particles.

A paradigm of experimentally induced mild hyperthyroidism: effects on nitrogen balance, body composition, and energy expenditure in healthy young men

Although T3 exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short term. The present study examined the effects of more than 2 months (63 days) of low dose T3 treatment on nitrogen balance, body composition, 24-h energy expenditure (EE), and protein turnover in seven healthy men studied at an in-patient metabolic unit. Subjects were also randomly assigned to either high or low fat diets to determine the effects of diet composition. T3 treatment produced significant losses in both lean mass (1.5 +/- 0.3 kg) and fat mass (2.7 +/- 0.4 kg) by 6 weeks, with similar reductions in both at 9 weeks. The high fat diet somewhat attenuated the loss of body fat. Nitrogen balance was significantly negative for the first 3 weeks of T3 treatment, but tended to return to baseline thereafter. There were no significant effects of treatment on protein turnover at 9 weeks, although there was a slight increase in leucine oxidation (P = 0.07). Despite the apparent adaptation in nitrogen balance, total 24-h EE and sleeping EE were significantly increased at 9 weeks. We conclude that although healthy men are able to adapt to mild hyperthyroidism in terms of nitrogen balance, they exhibit significant and persistent changes in fat and fat-free mass as well as energy balance.

The thermogenic effect of a carbohydrate feeding during exposure to 8, 12 and 27 degrees C

The increased metabolic heat production in humans exposed to cold stress results from an increased oxidation of both carbohydrate and fat to provide energy to sustain temperature homeostasis. Research suggests that dietary manipulations may enhance metabolic heat production, thereby delaying hypothermia. Therefore, the present investigation examined the thermogenic effect of a sequential timed feeding regime of either a carbohydrate (CHO) or a placebo beverage (PL) before and again midway through 120 min of exposure to 8, 12 and 27 degrees C in well-nourished men. The following were examined: tissue insulation (I), rectal temperature (Tre), mean skin temperature (Tsk), metabolism (M), time-weighted heat production and respiratory exchange ratio (R). Tre, delta Tre, Tsk, M, delta M, I and time-weighted heat production revealed no significant differences between treatment (PL vs CHO) at any temperature (8, 12 and 27 degrees C). However, Tre decreased (P < 0.05) as time increased at 8, 12 and 27 degrees C while M increased (P < 0.05) and I decreased (P < 0.05) at 8 and 12 degrees C. At 8 and 27 degrees C, R differed (P < 0.05) between the PL and CHO treatments. In addition, at 8 and 12 degrees C, R increased (P < 0.05) across time reflecting the feeding. From these data it appears that while substrate utilization differed between dietary treatment (8 and 27 degrees C) and across time, this feeding regime did not differentially affect M, Tre, Tsk and I during 120 min of exposure to 8, 12 and 27 degrees C.