Fitness, training, and the growth hormone-->insulin-like growth factor I axis in prepubertal girls.

We recently demonstrated that a brief endurance type training program led to increases in thigh muscle mass and peak oxygen uptake (VO(2)) in prepubertal girls. In this study, we examined the effect of training on the GH-->insulin-like growth factor I (GH-->IGF-I) axis, a system known to be involved both in the process of growth and development and in the response to exercise. Healthy girls (mean age 9.17 +/- 0.10 yr old) volunteered for the study and were randomized to control (n = 20) and training groups (n = 19) for 5 weeks. Peak VO(2), thigh muscle volume, and blood samples [for IGF-I, IGF-binding proteins (IGFBP)-1 to -6, and GHBP] were measured. At baseline, IGF-I was significantly correlated with both peak VO(2) (r = 0.44, P < 0.02) and muscle volume (r = 0.58, P < 0.004). IGFBP-1 was negatively correlated with muscle volume (r = -0.71, P < 0.0001), as was IGFBP-2. IGFBP-4 and -5 were significantly correlated with muscle volume. We found a threshold value of body mass index percentile (by age) of about 71, above which systematic changes in GHBP, IGFBP-1, and peak VO(2) per kilogram were noted, suggesting decreases in the following: 1) GH function, 2) insulin sensitivity, and 3) fitness. Following the training intervention, IGF-I increased in control (19.4 +/- 9.6%, P < 0.05) but not trained subjects, and both IGFBP-3 and GHBP decreased in the training group (-4.2 +/- 3.1% and -9.9 +/- 3.8%, respectively, P < 0.05). Fitness in prepubertal girls is associated with an activated GH-->IGF-I axis, but, paradoxically, early in a training program, children first pass through what appears to be a neuroendocrine state more consistent with catabolism

Effect of exercise on cytokines and growth mediators in prepubertal children.

Many of the anabolic effects of exercise are mediated through insulin-like growth factor-I (IGF-I), but in adolescents, brief exercise training leads to reductions, rather than the expected increase, in circulating IGF-I. Certain cytokines--interleukin-(IL) 1beta (IL-1beta), IL-6 (IL-6), and tumor necrosis factor-alpha--are increased by exercise in adults and are known to inhibit IGF-I. To test the hypothesis that these cytokines might play a role in the adaptation to exercise, we measured the acute effects of exercise on selected cytokines and growth factors in 17 healthy 8- to 11-y-old children (4 females). Designed to mimic patterns and intensity of exercise found in the real lives of American children, the exercise protocol consisted of a 1.5-h soccer practice (of which about 40 min constituted of vigorous exercise). Pre- and postexercise urine and saliva samples were obtained in all subjects and both blood and urine in nine subjects. The exercise led to significant increases in circulating tumor necrosis factor-alpha (18 +/- 7%, p < 0.05) and IL-6 (125 +/- 35%, p < 0.01) as well as a significant increase in the antiinflammatory cytokine IL-1 receptor antagonist (33 +/- 10%, p < 0.01). Urine levels of IL-6 were also substantially increased by exercise (440 +/- 137%, p < 0.0001). Circulating levels of IGF-I were reduced to a small but significant degree (-6.4 +/- 3.2%, p < 0.05), although IGF-binding protein-1 (known to inhibit IGF-I) was substantially increased (156 +/- 40%, p < 0.001). Cytokines are systemically increased after relatively brief exercise in healthy children. This increase may alter critical anabolic agents such as IGF-I and its binding proteins

An isoenergetic very low carbohydrate diet improves serum HDL cholesterol and triacylglycerol concentrations, the total cholesterol to HDL cholesterol ratio and postprandial lipemic responses compared with a low fat diet in normal weight, normolipidemic women

Very low carbohydrate diets are popular, yet little is known about their effects on blood lipids and other cardiovascular disease risk factors. We reported previously that a very low carbohydrate diet favorably affected fasting and postprandial triacylglycerols, LDL subclasses and HDL cholesterol (HDL-C) in men but the effects in women are unclear. We compared the effects of a very low carbohydrate and a low fat diet on fasting lipids, postprandial lipemia and markers of inflammation in women. We conducted a balanced, randomized, two-period, crossover study in 10 healthy normolipidemic women who consumed both a low fat (<30% fat) and a very low carbohydrate (<10% carbohydrate) diet for 4 wk each. Two blood draws were performed on separate days at 0, 2 and 4 wk and an oral fat tolerance test was performed at baseline and after each diet period. Compared with the low fat diet, the very low carbohydrate diet increased (

Body composition and hormonal responses to a carbohydrate-restricted diet

The few studies that have examined body composition after a carbohydrate-restricted diet have reported enhanced fat loss and preservation of lean body mass in obese individuals. The role of hormones in mediating this response is unclear. We examined the effects of a 6-week carbohydrate-restricted diet on total and regional body composition and the relationships with fasting hormone concentrations. Twelve healthy normal-weight men switched from their habitual diet (48% carbohydrate) to a carbohydrate-restricted diet (8% carbohydrate) for 6 weeks and 8 men served as controls, consuming their normal diet. Subjects were encouraged to consume adequate dietary energy to maintain body mass during the intervention. Total and regional body composition and fasting blood samples were assessed at weeks 0, 3, and 6 of the experimental period. Fat mass was significantly (

A ketogenic diet favorably affects serum biomarkers for cardiovascular disease in normal-weight men

Very low-carbohydrate (ketogenic) diets are popular yet little is known regarding the effects on serum biomarkers for cardiovascular disease (CVD). This study examined the effects of a 6-wk ketogenic diet on fasting and postprandial serum biomarkers in 20 normal-weight, normolipidemic men. Twelve men switched from their habitual diet (17% protein, 47% carbohydrate and 32% fat) to a ketogenic diet (30% protein, 8% carbohydrate and 61% fat) and eight control subjects consumed their habitual diet for 6 wk. Fasting blood lipids, insulin, LDL particle size, oxidized LDL and postprandial triacylglycerol (TAG) and insulin responses to a fat-rich meal were determined before and after treatment. There were significant decreases in fasting serum TAG (-33%), postprandial lipemia after a fat-rich meal (-29%), and fasting serum insulin concentrations (-34%) after men consumed the ketogenic diet. Fasting serum total and LDL cholesterol and oxidized LDL were unaffected and HDL cholesterol tended to increase with the ketogenic diet (+11.5%; P = 0.066). In subjects with a predominance of small LDL particles pattern B, there were significant increases in mean and peak LDL particle diameter and the percentage of LDL-1 after the ketogenic diet. There were no significant changes in blood lipids in the control group. To our knowledge this is the first study to document the effects of a ketogenic diet on fasting and postprandial CVD biomarkers independent of weight loss. The results suggest that a short-term ketogenic diet does not have a deleterious effect on CVD risk profile and may improve the lipid disorders characteristic of atherogenic dyslipidemia

Statistical analysis of fiber area in human skeletal muscle

Previous research has indicated that 50 fiber measurements per individual for type I and II fibers would be sufficient to characterize the fiber areas. This study replicated the work of McCall et al. (1998) using the three major fiber types (I, IIA, and IIB) and sampling larger populations of fibers. Random blocks of fibers were also examined to investigate how well they correlated with the overall mean average fiber area. Using random blocks of 50 fibers provided an accurate reflection of the type IIB fibers (r = 0.96-0.98) but not for the type I (r = 0.85-0.94) or IIA fibers (r = 0.80-0.91). Type I fibers were consistently reflected by a random block of 150 fibers (r = 0.95-0.98) while type IIA fibers required random blocks of 200 fibers (r = 0.94-0.98), which appeared to provide an accurate reflection of the cross-sectional area. These results indicate that for a needle biopsy different numbers of fibers are needed depending on the fiber type to accurately characterize the mean fiber population

Endurance capacity and high-intensity exercise performance responses to a high fat diet

The effects of adaptation to a high-fat diet on endurance performance are equivocal, and there is little data regarding the effects on high-intensity exercise performance. This study examined the effects of a high-fat/moderate protein diet on submaximal, maximal, and supramaximal performance. Twenty non-highly trained men were assigned to either a high-fat/moderate protein (HFMP; 61% fat diet) (n = 12) or a control (C; 25% fat) group (n = 8). A maximal oxygen consumption test, two 30-s Wingate anaerobic tests, and a 45-min timed ride were performed before and after 6 weeks of diet and training. Body mass decreased significantly (-2.2 kg; p < or = .05) in HFMP subjects. Maximal oxygen consumption significantly decreased in the HFMP group (3.5 +/- 0.14 to 3.27 +/- 0.09 L x min(-1)) but was unaffected when corrected for body mass. Perceived exertion was significantly higher during this test in the HFMP group. Main time effects indicated that peak and mean power decreased significantly during bout 1 of the Wingate sprints in the HFMP (-10 and -20%, respectively) group but not the C (-8 and -16%, respectively) group. Only peak power was lower during bout 1 in the HFMP group when corrected for body mass. Despite significantly reduced RER values in the HFMP group during the 45-min cycling bout, work output was significantly decreased (-18%). Adaptation to a 6-week HFMP diet in non-highly trained men resulted in increased fat oxidation during exercise and small decrements in peak power output and endurance performance. These deleterious effects on exercise performance may be accounted for in part by a reduction in body mass and/or increased ratings of perceived exertion