While effects of the two classes of proteins found in milk (i.e., soluble proteins, including whey, and casein) on muscle protein synthesis have been well investigated after a single bout of resistance exercise (RE), the combined effects of these two proteins on the muscle responses to resistance training (RT) have not yet been investigated. Therefore, the aim of this study was to examine the effects of protein supplementation varying by the ratio between milk soluble proteins (fast-digested protein) and casein (slow-digested protein) on the muscle to a 9-week RT program. In a double-blind protocol, 31 resistance-trained men, were assigned to 3 groups receiving a drink containing 20g of protein comprising either 100% of fast protein (FP(100), n = 10), 50% of fast and 50% of slow proteins (FP(50), n = 11) or 20% of fast protein and 80% of casein (FP(20), n = 10) at the end of training bouts. Body composition (DXA), and maximal strength in dynamic and isometric were analyzed before and after RT. Moreover, blood plasma aminoacidemia kinetic after RE was measured. The results showed a higher leucine bioavailability after ingestion of FP(100) and FP(50) drinks, when compared with FP(20) (p< .05). However, the RT-induced changes in lean body mass (p < .01), dynamic (p < .01), and isometric muscle strength (p < .05) increased similarly in all experimental groups. To conclude, compared with the FP(20) group, the higher rise in plasma amino acids following the ingestion of FP(100) and FP(50) did not lead to higher muscle long-term adaptations.
Marina Fabre, Christophe Hausswirth, Eve Tiollier, Odeline Molle, Julien Louis, Alexandre Durguerian, Nathalie Neveux and Xavier Bigard
Laurel Wentz, Pei-Yang Liu, Jasminka Z. Ilich and Emily M. Haymes
To compare female runners with and without a history of stress fractures to determine possible predictors of such fractures.
27 female runners (age 18–40 yr) who had had at least 1 stress fracture were matched to a control sample of 32 female runners without a history of stress fractures. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (iDXA). Subjects answered questionnaires on stress-fracture history, training, menstrual status, and diet.
No significant differences were found in menstrual characteristics, diet and dairy intake, or bone measurements. Weekly servings of milk during middle school significantly predicted BMD at the femur (p = .010), femoral neck (p = .002), Ward’s triangle (p = .014), and femoral shaft (p = .005). Number of menstrual cycles in the previous year predicted femoral-neck BMD (p = .004). Caffeine intake was negatively associated with BMD of the femur (p = .010), femoral neck (p = .003), trochanter (p = .038), and femoral shaft (p = .035). Weekly hours of training were negatively associated with total-body BMD (p = .021), total-body bone mineral content (p = .028), and lumbar-spine BMD (p = .011). Predictors for stress fractures included the number of years running, predominantly running on hard ground, irregular menstrual history, low total-body BMD, and low current dietary calcium intake when controlling for body-mass index (Nagelkerke R 2 = .364).
Servings of milk during middle-school years were positively correlated with hip BMD, although current calcium intake, low BMD, irregular menstrual history, hard training surface, and long history of training duration were the most important predictors of stress fractures.
Arnoud Carol, Renger F. Witkamp, Harry J. Wichers and Marco Mensink
The purpose of this study was to investigate the potential of bovine colostrum to attenuate postexercise decline in immune function. The authors evaluated the time course of a number of immune variables after short-term intense exercise in 9 male athletes after 10 d of supplementation with either colostrum or skim-milk powder. To increase the stress on the immune system subjects performed a glycogen-depletion trial the evening before the endurance trial (90 min at 50% Wmax). Blood samples were taken before the glycogen-depletion trial, before and after the endurance trial, and the next morning, ~22 hr after cessation of the exercise. Plasma cortisol levels increased over time, reaching the highest level directly after exercise, and were still elevated ~22 hr after exercise compared with baseline values (p < .001). Neutrophil cell count was increased after exercise and dropped below starting values 22 hr after exercise (time effect p < .001). Circulating immunoglobulins did not change over time. A significant time effect was seen for interleukin (IL)-6, IL-10, IL-1-receptor agonist, and C-reactive protein, with levels being higher directly after exercise (p < .05). Other cytokines (interferon-γ, IL-1a, IL-8, tumor necrosis factor-a) did not show a time effect. No differences were seen between colostrum and skim-milk powder in any of the investigated variables. Our results are consistent with the hypothesis that intense exercise affects several variables of the immune system. Colostrum did not alter any of the postexercise immune variables compared with skimmilk powder, suggesting no role for bovine colostrum supplementation in preventing postexercise immune suppression after short-term intense exercise.
James R. Rowe, Kyle D. Biggerstaff, Vic Ben-Ezra, David L. Nichols and Nancy DiMarco
This study examined the effect of prior exercise on postprandial lipemia (PPL) concentration following a mixed meal (MM) made with either glucose or fructose. Sedentary women completed four trials in random order: 1) Rest-Fructose: RF, 2) Rest-Glucose: RG, 3) Exercise-Fructose: EF, 4) Exercise-Glucose: EG. Exercise expended 500 kcal while walking at 70%VO2max. Rest was 60 min of sitting. The morning after each trial, a fasting (12 hr) blood sample was collected followed by consumption of the MM. The MM was blended with whole milk and ice cream plus a glucose or fructose powder. Glucose and fructose powder accounted for 30% of the total kcal within the MM. Blood was collected periodically for 6 hr post-MM and analyzed for PPL. Magnitude of PPL over the 6 hr postmeal was quantified using the triglyceride incremental area under the curve (TG AUCI). Significant differences (p < .05) between trials were determined using repeated-measures ANOVA and Bonferroni post hoc test. There was no significant difference in the TG AUCI between the four trials (p > .05). A significant trial by time interaction for TG concentration was reported (p < .05). Despite lack of change in the AUCI with prior exercise, the lower TG concentration at multiple time points in the EG trial does indicate that prior exercise has some desirable effect on PPL. This study suggests that replacing fructose with glucose sugars and incorporating exercise may minimize PPL following a mixed meal but exercise will need to elicit greater energy expenditure.
Paula J. Ziegler, Judith A. Nelson, Chloe Tay, Barbara Bruemmer and Adam Drewnowski
Dietary energy density (kcal/g) is defined as available dietary energy per unit weight or volume of food. The consumption of energy-dense foods has been associated with increased obesity risk and with excessive weight gain. The objectives of this study were to compare how dietary energy density, calculated using three different methods relates to food choices and nutrient composition of the diets of elite figure skaters. Participants were 159 elite figure skaters attending training camps. Mean age was 18.4 y for boys (n = 79) and 15.9 y for girls (n = 80). Heights and weights were measured to calculate body-mass indices (BMI). Dietary intakes were based on 3-d food records analyzed using the Nutritionist IV program. Mean energy intakes were 2326 kcal/d for boys and 1545 kcal/d for girls. Dietary energy density, based on foods and caloric beverages only, was 1.0 kcal/g. Dietary ED was positively associated with percent energy from fat and negatively with percent energy from sugar. The main sources of dietary energy in this group were baked goods, cereals, regular soda, low-fat milk, fruit juices, bagels and pizza. Percent energy from fast foods was associated with higher dietary energy density, whereas percent energy from dairy products, soft drinks, vegetables, and fruit was associated with lower dietary energy density. These results are consistent with past observations; higher energy density diets were higher in fat. In contrast, there was a negative relationship between sugar content and energy density of the diet.
Wendy M. Sandoval and Vivian H. Heyward
This paper describes the changes in the food selection patterns of male (n=7) and female (n=12) bodybuilders as they prepared for competition. Noncompetition dietary data were obtained 6 to 17 weeks (M = 12.5 wks) prior to competition using a 3-day food record. Precompetition food intake was recorded for the 3 days preceding competition. Foods were classified using the Exchange System and three additional categories which included desserts, alcoholic beverages, and other beverages. The noncompetition diets of the bodybuilders contained servings from each exchange, with the largest number of selections coming from the meat and bread/starch exchanges. Choices from the milk and meat exchanges were almost exclusively low-fat or lean. Primarily complex carbohydrates and high-fiber foods were selected from the bread/starch exchange. The number of different food items reported over 3 days and the total number of food items were greater in the noncompetition diet than in the precompetition diet. Also, variety among food groups and within some of the exchange groups was less in the precompetition diet. Although there was not much variety in the precompetition diets of the bodybuilders, the average nutrient density of their diets exceeded the Index of Nutritional Quality for all nutrients except calcium and zinc.
Hazzaa M. Al-Hazzaa, Mohammad A. Alahmadi, Hana I. Al-Sobayel, Nada A. Abahussain, Dina M. Qahwaji and Abdulrahman O. Musaiger
Few studies have reported comprehensive and valid physical activity (PA) data for Saudi youth. Therefore, the purpose of this study was to examine patterns and determinants of PA among Saudi adolescents.
A cross-sectional study was conducted in Saudi secondary schools (15–19 years) during 2009/2010 and used multistage stratified cluster sample (N = 2866, 51.7% females). Weight, height, sedentary behaviors, PA, and dietary habits were assessed.
Roughly 44% of males and 20% of females were active (≥ 1 hour/day). Males in public schools were more active than in private schools, whereas the opposite was true for females. Females exercise mostly at home, whereas males exercise at public places. The majority of females exercise alone or with relatives, whereas males largely exercise with friends. Males were active for health and recreation whereas females were active for weight loss and recreation. Lack of time was the primary reason for inactivity in both sexes. The predictors of total PA time were gender, intakes of fruit, milk, energy drinks and vegetables and waist/height ratio (R 2 = 0.145).
The high inactivity levels, especially among females, are of great concern. Promotion of active living among youth should be a national public health priority.
Lori W. Turner and Martha A. Bass
Female athletes often engage in harmful dietary and weight control practices that can impair bone health and hinder performance. To promote related positive health behavior practices, nutrition educators may be more effective if they understand the osteoporosis knowledge, attitudes, and behaviors among female athletes. A questionnaire including items related to osteoporosis and dietary calcium knowledge, attitudes, and behavioral practices was administered to 114 female collegiate athletes (19.6 ± 1.4 years). Self-reported intakes of dairy product consumption were also obtained; subjects were asked how many times per week they drank milk and ate cheese, yogurt, and ice cream. The mean score for osteoporosis knowledge was 7.1 ± 1.9 (out of 10 items). The mean score for favorable responses to attitude items was 2.1 ± 0.8 (out of 3 items). Correct responses to dietary calcium knowledge items were 2.2 ± 0.7 (out of 3 items). On average, subjects consumed 2.4 ± 1.6 servings of dairy products per day; 31% of subjects consumed the recommended 3 or more servings per day. Osteoporosis knowledge, osteoporosis attitudes, and dietary calcium knowledge were not correlated (p > .05) with dairy product intake. Because of the importance of achieving a high peak bone mass to prevent osteoporosis, our data suggest that further research is needed regarding other factors that might influence dairy product intake among female athletes.
Tricia Nemoseck and Mark Kern
Although physical activity is known to improve bone mineralization, it is unclear whether this occurs through altered absorption and/or excretion. The purpose of this study was to investigate the effects of a high-impact and resistance-training exercise program versus a period of restricted physical activity on urinary calcium excretion. Ten healthy, moderately active men (27.0 ± 5.8 yr) participated in a 3-wk randomized crossover study. Participants were assigned to complete either a period of daily participation in exercise including high-impact and resistance-training activities (EX) or a period of restriction in physical activity (NE) for 7 consecutive days. After a 1-wk washout period, participants completed the opposite trial. During both phases, participants consumed four 8-oz servings of low-fat (1%) milk daily and avoided other dietary and supplemental sources of calcium. Urine was collected throughout the final 72 hr of each study phase. Urinary calcium and sodium excretions were 14.7% ± 17.1% and 15.8% ± 9.9% lower (p < .05), respectively, during the EX phase than the NE phase. These results occurred despite participants consuming more (p < .05) sodium during the EX phase than the NE phase. These results suggest that healthy, moderately active men excrete significantly less urinary calcium concurrent with lower sodium excretion during a week of performing high-impact and resistancetraining exercises versus a week of restricted physical activity. The reduction in urinary loss of calcium might be at least partially responsible for improved bone mineralization that has been observed during periods of greater physical activity.
Whitney R.D. Duff, Philip D. Chilibeck, Julianne J. Rooke, Mojtaba Kaviani, Joel R. Krentz and Deborah M. Haines
Bovine colostrum is the first milk secreted by cows after parturition and has high levels of protein, immunoglobulins, and various growth factors. We determined the effects of 8 weeks of bovine colostrum supplementation versus whey protein during resistance training in older adults. Males (N = 15, 59.1 ± 5.4 y) and females (N = 25, 59.0 ± 6.7 y) randomly received (double-blind) 60g/d of colostrum or whey protein complex (containing 38g protein) while participating in a resistance training program (12 exercises, 3 sets of 8–12 reps, 3 days/week). Strength (bench press and leg press 1-RM), body composition (by dual energy x-ray absorptiometry), muscle thickness of the biceps and quadriceps (by ultrasound), cognitive function (by questionnaire), plasma insulin-like growth factor-1 (IGF-1) and C-reactive protein (CRP, as a marker of inflammation), and urinary N-telopeptides (Ntx, a marker of bone resorption) were determined before and after the intervention. Participants on colostrum increased leg press strength (24 ± 29 kg; p < .01) to a greater extent than participants on whey protein (8 ± 16 kg) and had a greater reduction in Ntx compared with participants on whey protein (–15 ± 40% vs. 10 ± 42%; p < .05). Bench press strength, muscle thickness, lean tissue mass, bone mineral content, and cognitive scores increased over time (p < .05) with no difference between groups. There were no changes in IGF-1 or CRP. Colostrum supplementation during resistance training was beneficial for increasing leg press strength and reducing bone resorption in older adults. Both colostrum and whey protein groups improved upper body strength, muscle thickness, lean tissue mass, and cognitive function.