Role of weight loss and polyunsaturated fatty acids in improving metabolic fitness in moderately obese, moderately hypertensive subjects.

OBJECTIVE: While the exact regulatory interactions between blood pressure (BP) and obesity are not completely understood, weight loss provides an alternative to pharmacological treatment of hypertension. The intent of this repeated measures study of mild-moderate hypertensive, moderately obese subjects (34 females/18 males) was to determine if the reduction in BP following weight loss could be further affected by modifying the fatty acid (FA) composition of the hypocaloric diet. METHODS: BP, insulin sensitivity (Si), and lipid parameters were assessed before and after a 10-week calorie-restricted period. Subjects were randomized to one of three dietary groups differing in FA composition. Reduced body weight was maintained for a further 4 weeks and body composition assessment, BP and heart rate measurements were repeated. RESULTS: Weight loss (10%) in obese hypertensive subjects resulted in substantial improvements in BP, Si and lipid profile. There was no additional effect on the reduction in BP by the type of FA consumed in the diet. Following weight loss, there was a trend for omega-3 FAs to have a protective effect on fat-free mass loss (compared to omega-6 FA Group and saturated FA Group) and a trend to further enhance Si. There were significant improvements in circulating lipid profiles independent of the dietary FA intervention following the weight loss. The improvements in BP and body composition were maintained during the weight-loss maintenance period. The type of fat consumed had minor differential effects on some of the measured metabolic outcomes. CONCLUSION: These results provide strong support for modest weight loss as a treatment for hypertension.

Fat and carbohydrate overfeeding in humans: different effects on energy storage.

Both the amount and composition of food eaten influence body-weight regulation. The purpose of this study was to determine whether and by what mechanism excess dietary fat leads to greater fat accumulation than does excess dietary carbohydrate. We overfed isoenergetic amounts (50% above energy requirements) of fat and carbohydrate (for 14 d each) to nine lean and seven obese men. A whole-room calorimeter was used to measure energy expenditure and nutrient oxidation on days 0, 1, 7, and 14 of each overfeeding period. From energy and nutrient balances (intake-expenditure) we estimated the amount and composition of energy stored. Carbohydrate overfeeding produced progressive increases in carbohydrate oxidation and total energy expenditure resulting in 75-85% of excess energy being stored. Alternatively, fat overfeeding had minimal effects on fat oxidation and total energy expenditure, leading to storage of 90-95% of excess energy. Excess dietary fat leads to greater fat accumulation than does excess dietary carbohydrate, and the difference was greatest early in the overfeeding period.

Energy balance in endurance-trained female cyclists and untrained controls.

Reports of low energy intakes in trained female athletes imply they have an increased energetic efficiency. To address this question, we determined how energy balance was achieved in endurance-trained females cyclists and lean controls (n = 5 in each group). Daily energy expenditure was measured by using standardized physical activity protocols in a whole room calorimeter on two separate occasions: a cycling day and a noncycling day. Energy intake for weight maintenance was determined by a period of controlled feeding 5 days before and the day of each energy expenditure measurement. Energy balance was achieved in the cyclists on the cycling day while they consumed 2,900-3,000 kcal (their usual condition) and in controls on the noncycling day while they consumed 2,100-2,200 kcal (their usual condition). Total daily energy expenditure was not significantly different between the cyclists and controls on the noncycling day with both groups performing similar levels of activity. On the cycling day, daily energy expenditure was significantly greater in the cyclists vs. controls (P < 0.03) as a result of their greater amount of cycling activity. Components of daily energy expenditure, i.e., resting metabolic rate and thermic effect of food and activity (noncycling), were not significantly different between groups. Overall, we found no significant increase in the energetic efficiency of endurance-trained female cyclists compared with controls.

Obesity treatment: can diet composition play a role?

Diet composition can play a role in obesity treatment because it can influence energy intake and nutrient balance. The greatest potential effect of diet composition occurs not during weight reduction but during maintenance of a reduced body weight. During weight reduction, the extent of negative energy balance is the greatest determinant of the amount and rate of weight loss, and any effects of diet composition are likely to be very small. Conversely, during the maintenance period after weight reduction, maintenance energy requirements are reduced and the rate of fat oxidation may be low. Prevention of fat storage and regain of body weight can be achieved either by increasing fat oxidation (for example, by increasing exercise) or by reducing the fat content of the habitual diet. The treatment with the greatest chance for success combines a reduced-fat diet with aerobic exercise.

Comparison of dietary self-reports with energy expenditure measured using a whole-room indirect calorimeter.

In this study we used a whole-room indirect calorimeter to evaluate the accuracy of self-reported food intake. Daily measured energy expenditure was compared with 2 weeks of self-reported food intake. Additionally, oxidation of each macronutrient was compared with its self-reported intake to assess the accuracy of self-reported dietary composition. Participants (23 through 60 years old) were eight dietitians, eight subjects who were trained in keeping dietary records, and eight subjects who were not trained. Physical activity in the calorimeter was matched to usual daily physical activity. Overall, measured energy expenditure was approximately 200 kcal/day higher than reported metabolizable energy intake. However, this was the result primarily of a few subjects whose self-reported food intake was considerably below measured energy expenditure. Subjects who were trained in record keeping did not differ from untrained subjects. Dietitians had the lowest difference between intake and expenditure; none of them had the large discrepancies between intake and expenditure seen in the other groups. In all groups, there was a much greater discrepancy between self-reported intake and oxidation of each macronutrient than between self-reported total energy intake and expenditure.