Pamela D. Swan

Postprandial Thermogenesis Is Increased 100% on a High-Protein, Low-Fat Diet versus a High-Carbohydrate, Low-Fat Diet in Healthy, Young Women

Objective: The recent literature suggests that high-protein, low-fat diets promote a greater degree of weight loss compared to high-carbohydrate, low-fat diets, but the mechanism of this enhanced weight loss is unclear. This study compared the acute, energy-cost of meal-induced thermogenesis on a high-protein, low-fat diet versus a high-carbohydrate, low-fat diet. Methods: Ten healthy, normal weight, non-smoking female volunteers aged 19-22 years were recruited from a campus population. Using a randomized, cross-over design, subjects consumed the high-protein and the high-carbohydrate diets for one day each, and testing was separated by a 28- or 56-day interval. Control diets were consumed for two days prior to each test day. On test day, the resting energy expenditure, the non-protein respiratory quotient and body temperature were measured following a 10-hour fast and at 2.5-hour post breakfast, lunch and dinner. Fasting blood samples were collected test day and the next morning, and complete 24-hour urine samples were collected the day of testing. Results: Postprandial thermogenesis at 2.5 hours post-meal averaged about twofold higher on the high protein diet versus the high carbohydrate diet, and differences were significant after the breakfast and the dinner meals (p < 0.05). Body temperature was slightly higher on the high protein diet (p = 0.08 after the dinner meal). Changes in the respiratory quotient post-meals did not differ by diet, and there was no difference in 24-hour glomerular filtration rates by diet. Nitrogen balance was significantly greater on the high-protein diet compared to the high-carbohydrate diet (7.6 ± 0.9 and −0.4 ± 0.5 gN/day, p < 0.05), and at 24-hour post-intervention, fasting plasma urea nitrogen concentrations were raised on the high protein diet versus the high-carbohydrate diet (13.9 ± 0.9 and 11.2 ± 1.0 mg/dL respectively, p < 0.05). Conclusions: These data indicate an added energy-cost associated with high-protein, low-fat diets and may help explain the efficacy of such diets for weight loss.

Postexercise oxygen consumption and substrate use after resistance exercise in women

OBJECTIVE This study investigated the acute effects of 45 min of resistance exercise (RE) on excess postexercise oxygen consumption (EPOC) and substrate oxidation 120 min after exercise in moderately trained women. METHODS Ten RE trained women (age = 29 +/- 3 yr; ht = 168 +/- 8.3 cm; wt = 59 +/- 5.7 kg; VO2max = 38.3 +/- 4.7 mL.kg-1.min-1) underwent two trials: control sitting and RE. Subjects acted as their own controls in a random counterbalanced design. A 2-d nonexercise period was established between testing trials. Oxygen consumption (VO2) and respiratory exchange ratio (RER) were measured continuously by indirect calorimetry before, during, and after exercise and on a separate control day. RE consisted of 3 sets of 10 exercises at 10-repetition maximum with a 1-min rest period between each set. Fingertip samples of blood lactate concentration [BL] were collected immediately postexercise and every 30 min thereafter until [BL] returned to resting baseline values after exercise. RESULTS The overall 2-h EPOC was 6.2-L (RE = 33.4 +/- 5.1 L vs control = 27.2 +/- 0.3 L), corresponding to an 18.6% elevation over the control period. RER was significantly (P < 0.01) below the control RER from minute 30 to minute 120 postexercise (RE = 0.75 +/- 0.01 vs control = 0.85 +/- 0.01). During the last 30 min of recovery, VO2 and [BL] had returned to control/baseline values and fat oxidation was significantly (P < 0.0001) higher (29.2 vs 16.3 kcal) after RE compared with the control trial. CONCLUSION These data indicate that in young RE trained women, acute RE produces a modest increase in VO2 during a 2-h recovery period and an increase in fat oxidation.

Evaluation of air displacement for assessing body composition of collegiate wrestlers.

PURPOSE To evaluate the accuracy of air displacement plethysmography (ADP) by using the BOD POD in comparison with hydrostatic weighing (HW) in a collegiate wrestling population in hydrated and acutely dehydrated states. METHODS Body composition was determined by ADP, HW, and three-site skinfolds (SK) in 66 NCAA Division I collegiate wrestlers before and after acute dehydration (2.6% reduction in body mass). For all methods, body density (D(b)) was converted to percent body fat (%BF) by using the Brozek equation for Euro-Americans and the Schutte equation for African-Americans. RESULTS There were no significant differences between ADP and HW for D(b), %BF, and fat-free mass (FFM) in either the hydrated or dehydrated states. The standard errors of the estimate for %BF estimated from ADP with HW as the reference method were 2.12% (hydrated) and 2.16% (dehydrated); prediction errors were 2.35% (hydrated) and 2.49% (dehydrated). Bland-Altman plots of D(b) and %BF showed no systematic bias, and 64 out 66 subjects fell within the 95% limits of agreement (mean difference +/- 2 SD) for both variables. For SK, %BF was significantly higher than HW in both the hydrated and dehydrated state. All methods (ADP, HW, and SK) showed a significant decrease in FFM from the hydrated to the dehydrated state. CONCLUSIONS This study demonstrates that the BOD POD air displacement method provides similar estimates of D (b), %BF, and FFM when compared with HW in a heterogeneous collegiate wrestling population during hydrated and acutely dehydrated states. Pretest guidelines to ensure normal hydration status before body composition assessment using any method must be followed to minimize measurement error in %BF.

Effects of Habitual Physical Activity on the Resting Metabolic Rates and Body Compositions of Women Aged 35 to 50 Years

OBJECTIVE To examine the effect habitual physical activity has on resting metabolic rate (RMR) and body composition (fat-free mass[FFM], fat mass, and percent body fat) in active compared to sedentary adult women. DESIGN RMR was measured (by indirect calorimetry) twice after a 12-hour fast at the same point of the menstrual cycle and 48 hours after exercise. FFM, fat mass and percent body fat were measured using whole body air displacement plethysmography. Energy intake and expenditure were determined using 7-day weighed-food records and activity logs. SUBJECTS Healthy, weight-stable premenopausal women aged 35 to 50 years classified as either active (approximately 9 hours per week of physical activity for 10 or more years) (n= 18) or sedentary (approximately 1 hour per week of physical activity) (n= 14). STATISTICAL ANALYSES Analysis of covariance was used to investigate differences in mean RMR (kcal/day) between the groups adjusted for FFM, and independent t tests were used to determine differences in demographic, energy expenditure, and diet variables. RESULTS Percent body fat and fat mass were lower (P<.0005) and RMR (adjusted for FFM) was significantly higher in the active women (P=.045) compared with sedentary controls. In the active and sedentary groups respectively, mean adjusted RMR was 1,510 kcal/day and 1,443 kcal/day, body fat was 18.9% and 28.8%, and fat mass was 11.1 kg and 18.8 kg. Groups were similar in body mass, FFM, body mass index, and age. Mean energy balance appeared to be more negative in the active group (P=.0059) due to significantly higher mean self-reported energy expenditures (P=.0001) and similar mean self-reported energy intakes (P=.52) compared with sedentary controls. These data indicate that active women who participate in habitual physical activity can maintain lower body fat and a higher RMR than sedentary controls with similar body mass, FFM, and body mass index. APPLICATIONS/CONCLUSIONS This research supports and emphasizes the benefits of habitual physical activity in maintaining RMR and lower body fat levels in middle-aged women.

Effects of intensity and volume on insulin sensitivity during acute bouts of resistance training.

Black, LE, Swan, PD, and Alvar, BA. Effects of intensity and volume on insulin sensitivity during acute bouts of resistance training. J Strength Cond Res 24(4): 1109-1116, 2010-This study evaluated the effects of various resistance exercise protocols on 24-hour postexercise insulin sensitivity. Seventeen participants with impaired fasting glucose (100-125 mg/dL) completed 4 separate bouts of resistance exercise under moderate intensity (65% 1 repetition maximum [1RM]) or high intensity (85% 1RM) conditions within the confines of single set and multiple set protocols. Intravenous fasting blood was taken at baseline and 24 hours postexercise for each exercise condition to measure fasting plasma glucose (G0) and fasting serum insulin (I0) to calculate insulin sensitivity (homeostasis model assessment-insulin resistance = (G0*I0)/405). A minimum of 3 days washout was given between each exercise protocol. A 4 x 2 factorial analysis of variance was performed to compare insulin sensitivity and fasting glucose within subjects and between treatments. All of the exercise protocols improved subsequent insulin sensitivity (p = 0.002) and G0 (p = 0.001). In comparison with single set, there was a significantly greater decrease in G0 (p = 0.021) 24 hours after multiple set bouts. High intensity showed significant decreases in insulin sensitivity as compared with moderate intensity protocols (p = 0.046). Effect size data suggest a dose response relationship between program variables of volume and intensity and 24-hour postexercise insulin sensitivity. High-intensity protocols resulted in greater effect sizes for insulin sensitivity (0.83 multiple set; 0.53 single set) as compared with moderate-intensity protocols. The high-intensity, multiple set bout yielded the greatest treatment effect in both fasting glucose (0.61) and insulin sensitivity (0.83). Overall, single set protocols were less effective than multiple set protocols in lowering fasting blood glucose. Findings suggest a dose-response relationship between volume and intensity on insulin sensitivity and fasting blood glucose. Results indicate that resistance exercise is an effective treatment for acutely enhancing insulin sensitivity and regulating blood glucose in individuals with impaired fasting glucose.

Body fat distribution and hemodynamic stress responses in premenopausal obese women: a preliminary study.

To examine the relationship between body fat distribution and hemodynamic stress responses, cardiovascular responses to a speech task and a forehead cold pressor task were evaluated with 24 premenopausal women classified a priori as either centrally or peripherally obese. Results showed that women with central adiposity exhibited greater stress-related increases in diastolic blood pressure and total peripheral resistance, whereas women with peripheral adiposity exhibited greater stress-related increases in cardiac output. Depression, self-consciousness, hostility, and mood scores did not explain significant variance in the stress response differences between regional adiposity groups. The findings suggest that central adiposity may increase the risk of cardiovascular disease in women at least in part by enhancing vascular responses to stress.

Association of negative and positive social ties with fibrinogen levels in young women.

The associations between positive and negative aspects of social relationships and fibrinogen, a risk factor for coronary heart disease (CHD), were examined in young, healthy women recruited from the community (n = 46) and from a college campus (n = 42). For community women, the perception that individuals in their social networks frequently undermined them was related to higher fibrinogen, independent of perceived frequency of support. For college women, fibrinogen was elevated among women with frequent undermining only when they also reported infrequent support. After controlling for other risk factors, the associations between social ties and fibrinogen remained significant in both samples. These results indicate that positive and negative social ties are associated with fibrinogen levels and suggest that social relationships may affect CHD risk in part through their influence on fibrinogen.

Comparison of anthropometry to dual energy X-ray absorptiometry: a new prediction equation for women.

Abstract The purpose of this study was to assess the accuracy of three recommended anthropometric equations for women and then develop an updated prediction equation using dual energy x-ray absorptiometry (DXA). The percentage of body fat (%BF) by anthropometry was significantly correlated (r = .896-.929; p < .01) with DXA, but each equation underestimated %BF (3.2-5.6 %BF; p < .01). The following DXA criterion (DC) equation was created: %BF = −6.40665 + 0.41946(S3SF) − 0.00126(S3SF)2 + 0.12515(hip) + 0.06473 (age); (S3SF = sum of triceps, suprailiac, thigh; hip = circumference in cm; age = years). The predicted residual sum of squares (PRESS) R 2 was high (0.86), and the PRESS standard error of estimate (SEE) was low (2.5 %BF) for our sample of 150 women. The DC equation was further crosschecked on a separate sample of women (n = 25) and again showed excellent agreement. The DC equation appears to be a more accurate estimation of %BF in women.

Energy expenditure estimates of the Caltrac accelerometer for running, race walking, and stepping

Objective To examine the accuracy of the Caltrac accelerometer for estimating energy expenditure (EE) during three exercise modes. Methods A subset of 31 women (mean (SEM) age 22.6 (5) years) was selected from a training study comparing various physiological parameters during race walking, running, and stepping. Subjects each performed mode specific graded exercise tests to peak V̇o2. Regression equations for V̇o2 v heart rate (HR) were generated from each individuals test data. EE (kcal and kJ) was estimated for each V̇o2 value based on the respiratory exchange ratio, and kcal v HR regression equations were generated to predict EE from each subjects HR data (EE-HR). HR in the field was monitored by telemetry, and two Caltrac monitors, one set for EE and one to give counts, were attached to a belt over opposite hips. Results EE-HR was not significantly different across exercise modes. Caltrac overestimated EE (P<0.01) in runners (14%) and walkers (19%) but underestimated EE in steppers by about 10% (P = 0.12). Conclusions The Caltrac is a reliable instrument but it did not accurately distinguish EE in running, race walking, or stepping in a group of young women.

Marginal vitamin C status is associated with reduced fat oxidation during submaximal exercise in young adults

BackgroundVitamin C is a cofactor in the biosynthesis of carnitine, a molecule required for the oxidation of fatty acids. A reduction in the ability to oxidize fat may contribute to the reported inverse relationship between vitamin C status and adiposity. To examine this possibility, we conducted a preliminary trial to evaluate the impact of vitamin C status on fat oxidation during submaximal exercise.MethodsFat energy expenditure was determined in individuals with marginal (n = 15) or adequate (n = 7) vitamin C status during a submaximal, 60-minute treadmill test. Subsequently, eight of the subjects with marginal vitamin C status completed an 8-week double-blind, placebo-controlled, depletion-repletion trial with submaximal exercise testing.ResultsIndividuals with marginal vitamin C status oxidized 25% less fat per kg body weight during the treadmill test as compared to individuals with adequate vitamin C status. Fat oxidation during exercise was inversely related to fatigue (r = -0.611, p = 0.009). Vitamin C repletion of vitamin C depleted subjects (500 mg vitamin C/d) raised fat energy expenditure during exercise 4-fold as compared to depleted control subjects (p = 0.011).ConclusionThese preliminary results show that low vitamin C status is associated with reduced fat oxidation during submaximal exercise. Low vitamin C status may partially explain the inverse relationship between vitamin C status and adiposity and why some individuals are unsuccessful in their weight loss attempts.