Teresa A. Sharp

Relation between calcium intake and fat oxidation in adult humans

OBJECTIVE: To determine if total calcium (Ca2+) intake and intake of Ca2+ from dairy sources are related to whole-body fat oxidation.DESIGN: Cross-sectional study.SUBJECTS: A total of 35 (21 m, 14 f) non-obese, healthy adults (mean±s.d., age: 31±6 y; weight: 71.2±12.3 kg; BMI: 23.7±2.9 kg m−2; body fat: 21.4±5.4%).MEASUREMENTS: Daily (24 h) energy expenditure (EE) and macronutrient oxidation using whole-room indirect calorimetry; habitual Ca2+ intake estimated from analysis of 4-day food records; acute Ca2+ intake estimated from measured food intake during a 24-h stay in a room calorimeter.RESULTS: Acute Ca2+ intake (mg· kcal−1) was positively correlated with fat oxidation over 24 h (r=0.38, P=0.03), during sleep (r=0.36, P=0.04), and during light physical activity (r=0.32, P=0.07). Acute Ca2+ intake was inversely correlated with 24-h respiratory quotient (RQ) (r=−0.36, P=0.04) and RQ during sleep (r=−0.31, P=0.07). After adjustment for fat mass, fat-free mass, energy balance, acute fat intake, and habitual fat intake, acute Ca2+ intake explained ∼10% of the variance in 24-h fat oxidation. Habitual Ca2+ intake was not significantly correlated to fat oxidation or RQ. Total Ca2+ intake and Ca2+ intake from dairy sources were similarly correlated with fat oxidation. In backwards stepwise models, total Ca2+ intake was a stronger predictor of 24 h fat oxidation than dairy Ca2+ intake.CONCLUSION: Higher acute Ca2+ intake is associated with higher rates of whole-body fat oxidation. These effects were apparent over 24 h, during sleep and, to a lesser extent, during light physical activity. Calcium intake from dairy sources was not a more important predictor of fat oxidation than total Ca2+ intake.

Thermogenesis in humans during overfeeding with medium-chain triglycerides

To test whether excess dietary energy as medium-chain triglycerides (MCT) affects thermogenesis differently from excess dietary energy as long chain triglycerides (LCT), ten male volunteers (ages 22 to 44) were overfed (150% of estimated energy requirement) liquid formula diets containing 40% of fat as either MCT or LCT. Each patient was studied for one week on each diet in a double-blind, crossover design. Resting metabolic rate (RMR) did not change during either week of overfeeding. The thermic response to food (TEF) was greater on day 1 following a meal (1,000 kcal) containing MCT than following an isocaloric meal containing LCT (8 +/- .8% v 5.8 +/- .8% of ingested energy; P less than .05). Moreover, the TEF observed after a 1,000 kcal meal containing MCT increased significantly to 12% (+/- 1.3%) overfeeding. The TEF of the 1,000 kcal meal containing LCT was unchanged by five days of LCT overfeeding (6.6 +/- 1.0% of ingested energy). Energy expenditure during a 20-hour continuous enteral infusion of the diet on day 7 was also significantly higher with the MCT diet than with the LCT diet (15.7 +/- 1.7% v 7.3 +/- .9% of ingested energy; P less than .05). Our results demonstrate that excess dietary energy as MCT stimulates thermogenesis to a greater degree than does excess energy as LCT. This increased energy expenditure, most likely due to lipogenesis in the liver, provides evidence that excess energy derived from MCT is stored with a lesser efficiency than is excess energy derived from dietary LCT.

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 distribution is altered in HIV‐infected men without clinical evidence of the HIV lipodystrophy syndrome

To determine if fat distribution is altered in HIV‐infected men without clinical evidence of lipodystrophy.

Effects of aerobic fitness on fat oxidation and body fatness.

OBJECTIVE This study investigated the contributions of physical fitness and body composition to 24-h fat oxidation in adults under sedentary conditions in a whole-room calorimeter. METHODS The following measurements were studied in 109 adults (49 male/45 female) at least 36 h after a bout of exercise: 1) aerobic fitness level assessed by VO2max, 2) body composition determined by underwater weighing, 3) resting metabolic rate (RMR) after an overnight fast, and 4) 24-h energy expenditure (EE) and substrate oxidation determined in a whole-room calorimeter. While in the calorimeter, subjects were provided with a diet (15% protein, 30% fat, and 55% carbohydrate) estimated to produce energy balance on a sedentary day and of similar nutritional composition to their daily dietary intake. RESULTS We found strong negative correlations between VO2max and % body fat in both male and female subjects, but no relationship between VO2max and 24-h EE under the sedentary conditions of this study. In male subjects, VO2max (mL O2 x kg(-1) fat-free mass x min(-1)) was negatively related to fat oxidation (r = -0.397, P < 0.005), and fat oxidation was more closely related to fat mass (r = 0.434, P < 0.0002) than to fat-free mass (r = 0.165, NS). In contrast, none of these relationships were significant in females. CONCLUSION The results show that in male subjects under sedentary conditions, 24-h fat oxidation is positively related to body fat mass and negatively related to VO2max (the marker used here for level of physical fitness). This supports our hypothesis that regularly active males maintain lower body fat stores as the low contribution to daily fat oxidation from a lower body fat mass is counterbalanced by the high contribution to fat oxidation from daily physical activity. The lack of a relationship between VO2max and 24-h EE under the sedentary conditions of this study suggests that the major effects of physical activity on total daily EE and fat oxidation may occur during and relatively quickly after an exercise bout. Further, these data also suggest that cessation of regular exercise will likely be associated with a high risk of positive fat balance and weight gain.

Effects of Maintained Weight Loss on Sleep Dynamics and Neck Morphology in Severely Obese Adults

The goals of the study were to determine if moderate weight loss in severely obese adults resulted in (i) reduction in apnea/hypopnea index (AHI), (ii) improved pharyngeal patency, (iii) reduced total body oxygen consumption (VO2) and carbon dioxide production (VCO2) during sleep, and (iv) improved sleep quality. The main outcome was the change in AHI from before to after weight loss. Fourteen severely obese (BMI > 40 kg/m2) patients (3 males, 11 females) completed a highly controlled weight reduction program which included 3 months of weight loss and 3 months of weight maintenance. At baseline and postweight loss, patients underwent pulmonary function testing, polysomnography, and magnetic resonance imaging (MRI) to assess neck morphology. Weight decreased from 134 ±6.6 kg to 118 ± 6.1 kg (mean ± s.e.m.; F = 113.763, P < 0.0001). There was a significant reduction in the AHI between baseline and postweight loss (subject, F = 11.11, P = 0.007). Moreover, patients with worse sleep‐disordered breathing (SDB) at baseline had the greatest improvements in AHI (group, F = 9.00, P = 0.005). Reductions in VO2 (285 ± 12 to 234 ±16 ml/min; F = 24.85, P < 0.0001) and VCO2 (231 ± 9 to 186 ± 12 ml/min; F = 27.74, P < 0.0001) were also observed, and pulmonary function testing showed improvements in spirometry parameters. Sleep studies revealed improved minimum oxygen saturation (minSaO2) (83.4 ± 61.9% to 89.1 ± 1.2%; F = 7.59, P = 0.016), and mean SaO2 (90.4 ± 1.1% to 93.8 ± 1.0%; F = 6.89, P = 0.022), and a significant increase in the number of arousals (8.1 ± 1.4 at baseline, to 17.1 ± 3.0 after weight loss; F = 18.13, P = 0.001). In severely obese patients, even moderate weight loss (∼10%) boasts substantial benefit in terms of the severity of SDB and sleep dynamics.

Twenty-Four-Hour Metabolic Responses to Resistance Exercise in Women

Seven nonobese adult females (40 ± 8 years) were studied in a room calorimeter on a day that resistance exercise (REX) was performed (4 sets of 10 exercises) and on a nonexercise control day (CON). Twenty-four-hour energy expenditure (EE) on the REX day (mean ± SD, 2,328 ± 327 kcal·d-1) was greater than CON (2,001 ± 369 kcal·d-1, p < 0.001). The net increase in EE during and immediately after (30 minutes) exercise represented 76 ± 12% of the total increase in 24-hour EE. Twenty four–hour RQ on the REX day (0.86 ± 0.06) did not differ from CON (0.87 ± 0.02). Twenty four–hour carbohydrate oxidation was elevated on the REX day, but 24-hour fat and protein oxidation were not different. Thus, in women, the increase in EE due to resistance exercise is largely seen during and immediately after the exercise. The increased energy demand is met by increased carbohydrate oxidation, with no increase in 24-hour fat oxidation.

Effect of Acclimation on Resting Energy Expenditure Measurements

BACKGROUND Development of an acclimation protocol for use when measuring resting energy expenditure (REE) would simplify and standardize data collection. The purpose of this study was to determine if our 2 metabolic carts could be used interchangeably and to determine if excluding the first 3 or 5 minutes of data collected as an acclimation period would significantly improve the coefficients of variation (CVs) for oxygen consumed (VO(2)) and carbon dioxide produced (VCO(2)) when performing REE assessments with our metabolic cart systems. METHODS Thirteen healthy, nonsmoking adults ranging in age from 32 to 45 years, with activity levels ranging from sedentary to highly active, participated. Indirect calorimetry was performed twice in the morning after 30 minutes of supine resting. Subjects had fasted for 12 hours, and did not exercise within the last 24 hours. The system order for testing was randomized for the first measurement. When the first measurement was completed, subjects were crossed over for measurement using a second metabolic cart. RESULTS The CVs for VO(2) and VCO(2) were significantly lower when excluding the first 3 (VO(2), p = .0005), (VCO(2), p = .0024) or 5 minutes (VO(2), p = .0001, VCO(2), p = .0021) of data compared with no exclusions. No significant differences in CVs between the 3- and 5-minute exclusions were found for VO(2) (p = .3224) or VCO(2) (p = .2255). CONCLUSIONS Clearly, our machines cannot be used interchangeably within a study. An acclimation period improves CVs of VO(2) and VCO(2.) The similarities in CVs led us to adopt a 3-minute acclimation period for measuring REE.