Interactions among dietary fat, mineral status, and performance of endurance athletes: a case study.

In a pilot study, performance measures and mineral metabolism were assessed in 3 male endurance cyclists who consumed isoenergetic, isonitrogenous diets for 28-day periods in a randomized, crossover design in which dietary carbohydrate, polyunsaturated, or saturated fat contributed about 50% of daily energy intake. Peak aerobic capacity [62 ml/(kg á min)] was unaffected by diet. Endurance capacity at 70-75% peak aerobic capacity decreased with the polyunsaturated fat diet. Copper retention tended to be positive only with saturated fat. Less iron and zinc were retained (intake - losses), and fecal losses of these minerals increased with the polyunsaturated fat. Blood biochemical measures of trace element nutritional status were unaffected by diet, except serum ferritin, which tended to decrease during consumption of the polyunsaturated fat diet. These preliminary results suggest that diets high in polyunsaturated fat, particularly linoleic acid, impair absorption and utilization of iron and zinc, and possibly magnesium, and may reduce endurance performance.

Chromium supplementation and resistance training: effects on body composition, strength, and trace element status of men.

The effects of 8 wk of daily chromium supplementation (3.3-3.5 mumol as chromium chloride or chromium picolinate) or placebo (0.1 mumol Cr) and weight training were examined in 36 men in a double-blind design. Strength, mesomorphy, fat-free mass, and muscle mass increased with resistance training independently of chromium supplementation (P < 0.0001). Protein, magnesium, zinc, copper, and iron intakes equalled or exceeded the recommended dietary allowance (RDA) or estimated safe and adequate daily dietary intake (ESADDI) during training and did not change significantly from pretraining intakes (P > 0.05). Chromium supplementation increased the serum chromium concentration and urinary chromium excretion without a difference as a result of the chemical form of chromium (P < 0.05). Resistance training was associated with a significant decrease (P < 0.05) in serum ferritin, total-iron-binding capacity, transferrin saturation, the ratio of enzymatic to immunoreactive ceruloplasmin, and plasma copper, independently of chromium supplementation. However, transferrin saturation was decreased more with chromium picolinate supplementation (24%) than with chromium chloride or placebo (10-13%). Compared with pretraining values, urinary magnesium excretion increased (P < 0.05) and urinary zinc output tended to decrease during the first 4 wk of resistance training and then returned to baseline values for the final 4 wk, which suggests an adaptation in mineral excretion in response to weight training. These findings suggest that routine chromium supplementation has no beneficial effects on body- composition change or strength gain in men. Whether chromium supplementation of individuals with diminished chromium nutriture facilitates propitious changes in body structure and function remains to be determined.

Relationships among swimming performance, body composition and somatotype in competitive collegiate swimmers.

Relationships were determined between sprint swimming performance and estimates of body composition and somatotype components in competitive collegiate swimmers. Forty-three women and 31 men underwent anthropometric and hydrodensitometric measurements at the beginning of a competitive season. There were significant partial correlations (swim stroke was partialed out) between swimming performance (time in a competitive 100-yard swim of each swimmer's major competitive stroke) and height (-0.466, p < 0.01), the mesomorphic (0.404, p < 0.01) and ectomorphic (-0.398, p < 0.01) components of somatotype, percent body fat (0.351, p < 0.05), and fat-free weight (-0.332, p < 0.05) among the women, but no significant correlations among the men. Twenty-three of the women and 21 of the men were also measured and timed at the end of the competitive season. Again, there were significant (p < 0.01) partial correlations (season and stroke were partialed out) between swimming performance and height (-0.766), fat-free weight (-0.657), body weight (-0.437), and the ectomorphic (-0.441) and mesomorphic (0.392, p < 0.01) components of somatotype in women, but no significant correlations among the men. These findings indicate that measurements of body composition and somatotype may be predictors of swimming performance in women but not in men.

Effects of participation in a collegiate sport season on body composition.

Fifty-three collegiate athletes (18 female and 35 male) were recruited from university varsity basketball, football, swim, and wrestling team rosters. Body composition was estimated before the beginning and before the end of sport seasons by using hydrodensitometry to determine the effect of participation in competitive sport seasons on the body composition of collegiate athletes. ANOVAs applied to the estimates of body composition indicated that the interaction of sport team by season was significant for body weight, F (5,47) = 3.2, p less than 0.05; fat weight, F (5,47) = 5.1, p less than 0.01; and fat-free weight, F (5,47) = 2.4, p less than 0.05. Only football players did not change in body composition. Wrestlers lost the greatest amount of body weight (3.4 kg). Female and male basketball players, female and male swimmers, and wrestlers lost significant amounts of body fat (2.6, 2.3, 1.8, 2.7, and 3.6 kg, respectively). Female and male basketball players and female and male swimmers gained significant amounts of fat-free weight (2.0, 1.6, 2.4, and 1.8 kg, respectively). It was concluded that participation in a collegiate sport season could affect changes in fat weight and fat-free weight components of body composition but that the nature of the changes are a function of the demands of the sport of participation.

The structural, functional, and nutritional adaptation of college basketball players over a season.

The purpose of this study was to determine the structural, functional and nutritional adaptation of college basketball players over a season. Structure was determined by somatotype and body composition, function was determined by peak work capacity and work efficiency, and nutrition was determined by plasma metals analysis. The tests were performed twice on each of the eight subjects, one preseason (PRS) and one postseason (PST). A small structural adaptation was indicated by a mean decrease (less than 1 kg) in fat free weight and an increase in ectomorphy (less than 0.03). Body weight and skinfolds did not change significantly. Functional adaptation was indicated by a one minute decrease in running time for the work capacity test (p less than 0.002), and an increase (p less than 0.02) in VO2 for the work efficiency test. Nutritional adaptation was indicated by a greater mobilization of plasma Zn after exercise during PST than PRS. Plasma Cu apparently was mobilized during exercise in PST but the change during the season (-10 to -6.6%) was not statistically significant because of the large interindividual variability in response. Structural and functional adaptation to basketball training over a collegiate season is small; however, the change in Zn mobility and the tendency for a concomitant change in Cu mobilization offers a unique finding to help explain the nutritional adaptation to training.

Body composition assessment of athletes using bioelectrical impedance measurements.

One hundred and four female and male athletes underwent determinations of hydrodensitometry (HD) and tetrapolar bioelectrical impedance (TBI) under uncontrolled (measurements made without regard to preceding exercise, level of hydration, or eating) and controlled conditions (measurements made two hours after consuming a light meal and no preceding exercise). Fat-free mass (FFM) was estimated from TBI measurements using a previously determined multiple regression equation. No difference (p greater than 0.05) was found in mean FFM values by method or experimental condition. In the uncontrolled state, fat mass and percent body fat (%BF) by impedance were lower (p less than 0.05) than that observed by HD or by TBI under controlled conditions. Linear regression analyses between FFM determined by HD and predicted by TBI under controlled and uncontrolled conditions yielded regression coefficients similar to the line of identify. The relationship between %BF by HD and calculated from impedance-predicted FFM and body mass under uncontrolled conditions was different (p less than 0.05) from the line of identify. In contrast, the regression of densitometric against impedance-predicted %BF under controlled conditions was similar to the line of identify with an error of 2.8%. These findings indicate the need for controlled measurement conditions to obtain valid body composition estimates using the TBI method in healthy people.

Physical training and copper, iron, and zinc status of swimmers.

The influence of physical training on copper, iron, and zinc nutriture was studied before and at the end of a competitive season in 16 female and 13 male swimmers and in 13 female and 15 nontraining control subjects. Mean daily energy, protein, and carbohydrate intakes increased (p less than 0.05) in the swimmers. Estimated copper, iron, and zinc intakes increased (p less than 0.05) in the male swimmers. Hematocrit and hemoglobin did not change but ferritin increased (p less than 0.05) in male swimmers. Plasma copper, iron and zinc were within the ranges of normal values and did not change. Erythrocyte superoxide dismutase (SOD) activity increased (p less than 0.01) after training. The findings indicate that copper, iron, and zinc nutriture is not adversely affected by physical training when dietary intakes are adequate, and that increases in red blood cell SOD activity without an increase in dietary copper are a functional adaptation of copper metabolism to aerobic training.

Comparison of metabolic responses and oxygen cost during maximal exercise using three treadmill protocols.

Sixteen healthy men aged 27.2 +/- 1.2 yr (mean +/- SEM) were tested to volitional exhaustion using the Balke, Bruce, and Ellestad treadmill protocols. Balke resulted in a greater (p less than 0.01) time to exhaustion and total work output, but a lower (p less than 0.05) peak oxygen consumption (ml.kg-1.min-1), and a lower (p less than 0.0001) cumulative net oxygen debt. Oxygen debt, expressed as a percent of total net oxygen cost, was smaller (p less than 0.001) on the Balke than the Bruce and Ellestad protocols (9.9 +/- 0.5, 18.7 +/- 0.6, and 19.3 +/- 0.6%, respectively). The rate of increase in oxygen consumption (p less than 0.0001) and blood lactate concentration (p less than 0.05) were lower on the Balke than on the Bruce and Ellestead protocols. Therefore, the observed differences in oxygen debt and lactate concentrations probably reflect differences in the rate of energy requirement, aerobic and anaerobic metabolism and physiological stress associated with each protocol.

Maintenance of aerobic capacity and body composition of volunteers residing on a metabolic research unit.

To achieve steady-state energy equilibrium, a program of physiological assessment and aerobic exercise prescription was developed and evaluated in healthy men participating in 3 month (n = 21) and 6 month (n = 12) nutritional studies. Using reliable maximal exercise tests, exercise was prescribed at an intensity to elicit 50% peak oxygen uptake, 15 minutes/day on 3 nonconsecutive days/week. Under controlled controlled conditions of energy intake and exercise prescription, body weight (+/- 2%), body composition, and peak oxygen uptake (+/- less than 5%) were maintained for periods up to 6 months. This approach may be useful in regulating energy expenditure in volunteers participating in controlled metabolic studies for prolonged periods of time.

Relationship between body composition and the components of somatotype.

In a sample of 422 adults (200 females and 222 males) aged 18-73 years, the relationship was determined between somatotype estimated by the Health-Carter (Am. J. Phys. Anthropol. 27:57-74, 1967) method and body composition variables determined by using hydrodensitometry (HD) and Bioelectrical Impedance Analysis (BIA). The anthropometric (ANC) dimensions used to estimate somatotype were positively correlated with the endomorphic and mesmorphic components and negatively correlated with the ectomorphic component. For the BIA measurements, resistance (R) was negatively correlated with the mesomorphic component; and reactance (XC) was negatively correlated with the endomorphic component; both measurements were positively correlated with the ectomorphic component. The HD-negative correlations were observed between mass in water and the endomorphic and mesomorphic components, and positive correlations were observed with the ectomorphic component. Body volume and surface area were positively correlated with the endomorphic and mesomorphic components and negatively correlated with the ectomorphic component. Percent fat and fat weight were related to each of the three components of somatotype for males and females. Fat-free weight for males was also related to the mesomorphic and the ectomorphic components.

Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements.

Mathematical equations using tetrapolar bioelectrical resistive (R) and reactive (Xc) impedance measures were developed and crossvalidated to predict total body water (TBW) and corrected bromide space (CBS) in two independent samples (n = 110). Height2 per low R was the best predictor of TBW (R = 0.96) and CBS (R = 0.92). When the influence of TBW was removed from CBS and dependent variables, height2 per low Xc was the best predictor (R = 0.50) of CBS. Double crossvalidation of each sample showed that observed and predicted TBW (R = 0.978 and 9.986) and CBS (0.937 and 0.907) were significantly related (p less than 0.001), and there was no difference (p greater than 0.05) between the values. The lines representing the relationships between observed and predicted values had regression coefficients not different than the line of identity. Data from both samples were combined to give a representative multiple regression equation to predict TBW and CBS. This study establishes the validity of the tetrapolar bioelectrical impedance method to assess body fluid volumes in humans.

Validation of tetrapolar bioelectrical impedance method to assess human body composition.

This study was conducted to validate the relationship between bioelectrical conductance (ht2/R) and densitometrically determined fat-free mass, and to compare the prediction errors of body fatness derived from the tetrapolar impedance method and skinfold thicknesses, relative to hydrodensitometry. One-hundred and fourteen male and female subjects, aged 18-50 yr, with a wide range of fat-free mass (34-96 kg) and percent body fat (4-41%), participated. For males, densitometrically determined fat-free mass was correlated highly (r = 0.979), with fat-free mass predicted from tetrapolar conductance measures using an equation developed for males in a previous study. For females, the correlation between measured fat-free mass and values predicted from the combined (previous and present male data) equation for men also was strong (r = 0.954). The regression coefficients in the male and female regression equations were not significantly different. Relative to hydrodensitometry, the impedance method had a lower predictive error or standard error of the estimates of estimating body fatness than did a standard anthropometric technique (2.7 vs. 3.9%). Therefore this study establishes the validity and reliability of the tetrapolar impedance method for use in assessment of body composition in healthy humans.

Assessment of fat-free mass using bioelectrical impedance measurements of the human body.

A method which involves the measurement of bioelectrical resistive impedance (R) for the estimation of human body composition is described. This method is based upon the principle that the electrical conductivity of the fat-free tissue mass (FFM) is far greater than that of fat. Determinations of R were made in 37 healthy men aged 28.8 +/- 7.1 yr (mean +/- SD) using an electrical impedance plethysmograph with a four electrode arrangement that introduces a painless signal (800 microA at 50 kHz) into the body. FFM was assessed by hydrodensitometry and ranged from 44.6-98.1 kg. Total body water (TBW) determined by D2O dilution and total body potassium (TBK) from whole body counting were 50.6 +/- 10.3 L and 167.5 +/- 38.1 g, respectively. Test-retest correlation coefficient was 0.99 for a single R measurement and the reliability coefficient for a single R measurement over 5 days was 0.99. Linear relationships were found between R values and FFM (r = -0.86), TBW (r = -0.86), and TBK (r = -0.79). Significant (p less than 0.01) increases in the correlation coefficients were observed when the predictor Ht2/R was regressed against FFM (r = 0.98), TBW (r = 0.95), AND TBK (r = 0.96). These data indicate that the bioelectrical impedance technique is a reliable and valid approach for the estimation of human body composition. This method is safe, noninvasive, provides rapid measurements, requires little operator skill and subject cooperation, and is portable. Further validation of this method is recommended in subjects with abnormal body composition.

Changes in plasma zinc content after exercise in men fed a low-zinc diet.

For 30 days five healthy men aged 23-57 yr consumed a diet adequate in zinc (8.6 mg/day); they ate a low-zinc diet (3.6 mg/day) for the next 120 days and then received a zinc-supplemented (33.6 mg/day) diet for 30 days. Copper intake was constant at 1.8 mg/day. Aerobic capacity was determined periodically during each diet period. Relative zinc balance (% of control) declined during depletion (r = -0.28, P less than 0.009). Pre- and postexercise zinc concentrations decreased when dietary zinc was restricted (r = -0.61, P less than 0.0001 and r = -0.78, P less than 0.0001) and increased with supplementation (r = 0.61, P less than 0.008 and r = 0.76, P less than 0.0003, respectively). Both plasma zinc and hematocrit increased (P less than 0.01) after maximal exercise. To minimize the effect of hemoconcentration during exercise, the van Beaumont quotient (J. Appl. Physiol. 34: 102-106, 1973) was calculated using pre- and postexercise hematocrit and plasma zinc. The initial quotient of 1.8 +/- 1.8% (mean +/- SE) declined (P less than 0.05) to -7.4 +/- 2.3% during depletion. With zinc repletion, the quotient increased to 6.9 +/- 3.6%, which was greater (P less than 0.05) than the quotient in depletion but similar to the initial quotient. The quotient was a strong predictor (r = 0.71, P less than 0.0005) of the change in relative zinc balance during zinc depletion. In contrast, no changes were found in plasma copper content. These data suggest that zinc mobilization from tissues is impaired during zinc depletion, and they validate the use of the van Beaumont quotient as an index of change in body zinc stores.

Influence of type and amount of dietary lipid on plasma lipid concentrations in endurance athletes.

Changes in plasma total cholesterol, triglyceride, and lipoprotein concentrations were assessed in three male endurance cyclists who consumed isoenergetic diets for 28-day periods in which carbohydrate, polyunsaturated fat, or saturated fat contributed about 50% of the daily energy intake. Dietary cholesterol was similar among the diets. Maximal aerobic capacity was maintained at 62 ml O2/(kg X min). Body weights were held within 3% of admission levels. The polyunsaturated fat diet significantly (p less than 0.05) reduced mean fasting plasma total cholesterol in comparison to the saturated fat and carbohydrate diets (160 versus 254 and 243 mg/dl, respectively). Similarly, the polyunsaturated fat diet depressed (p less than 0.05) mean plasma triglycerides relative to the saturated fat and carbohydrate diets (37 versus 62 and 79 mg/dl, respectively). No significant dietary effects were seen on high-density lipoprotein cholesterol. The observed changes in plasma total cholesterol were not significantly different than the values predicted by the Keys' equation, delta CHL = 1.35(2 delta S-delta P) + 1.5 delta Z. We conclude that under controlled conditions in which physical activity is constant l) dietary lipid differences influence fasting serum lipid and lipoprotein concentrations among men with high energy expenditures, and 2) the Keys' equation gives useful predictions of changes in plasma total cholesterol among vigorous men consuming different types and amounts of dietary lipid.

Potential errors in body composition as estimated by whole body scintillation counting.

Vigorous exercise has been reported to increase the apparent potassium content of athletes measured by whole body gamma ray scintillation counting of 40K. The possibility that this phenomenon is an artifact was evaluated in three cyclists and one nonathlete after exercise on the road (cyclists) or in a room with a source of radon and radon progeny (nonathlete). The apparent 40K content of the thighs of the athletes and whole body of the nonathlete increased after exercise. Counts were also increased in both windows detecting 214Bi, a progeny of radon. 40K and 214Bi counts were highly correlated (r = 0.87, p less than 0.001). The apparent increase in 40K was accounted for by an increase in counts associated with the 1.764 MeV gamma ray emissions from 214Bi. Thus a failure to correct for radon progeny would cause a significant error in the estimate of lean body mass by 40K counting.

Maximal oxygen consumption as related to magnesium, copper, and zinc nutriture.

Forty-four healthy male university athletes and 20 untrained men underwent maximal treadmill exercise testing to determine the relationship between maximal oxygen consumption and various measurements of elemental nutriture. Hb and mean plasma and erythrocyte concentrations of magnesium, copper, and zinc were within established norms for both groups after a 12-h fast. Mean plasma copper concentration was significantly (p less than 0.01) higher in the athletes (90 +/- 14.3 versus 81 +/- 8.0 micrograms/dl). Average maximal oxygen consumption also was significantly (p less than 0.001) higher in the athletes [4.5 +/- 0.5 versus 3.3 +/- 0.6 L/min and 55.5 +/- 7.1 versus 47.0 +/- 6.0 ml/(kg x min)]. Plasma magnesium was significantly correlated (r = 0.46; p less than 0.002) with maximal oxygen consumption, ml/(kg x min), among the athletes. This relationship persisted when the effect of Hb concentration was removed by covariance analysis (p less than 0.005). Only a weak association (r = -0.32; p = 0.17) was found between oxygen consumption and plasma magnesium in the untrained men. We hypothesize that ionic magnesium may facilitate oxygen delivery to working muscle tissue in trained subjects.