Effect of physical activity on thiamine, riboflavin, and vitamin B-6 requirements.

Because exercise stresses metabolic pathways that depend on thiamine, riboflavin, and vitamin B-6, the requirements for these vitamins may be increased in athletes and active individuals. Theoretically, exercise could increase the need for these micronutrients in several ways: through decreased absorption of the nutrients; by increased turnover, metabolism, or loss of the nutrients; through biochemical adaptation as a result of training that increases nutrient needs; by an increase in mitochondrial enzymes that require the nutrients; or through an increased need for the nutrients for tissue maintenance and repair. Biochemical evidence of deficiencies in some of these vitamins in active individuals has been reported, but studies examining these issues are limited and equivocal. On the basis of metabolic studies, the riboflavin status of young and older women who exercise moderately (2.5-5 h/wk) appears to be poorer in periods of exercise, dieting, and dieting plus exercise than during control periods. Exercise also increases the loss of vitamin B-6 as 4-pyridoxic acid. These losses are small and concomitant decreases in blood vitamin B-6 measures have not been documented. There are no metabolic studies that have compared thiamine status in active and sedentary persons. Exercise appears to decrease nutrient status even further in active individuals with preexisting marginal vitamin intakes or marginal body stores. Thus, active individuals who restrict their energy intake or make poor dietary choices are at greatest risk for poor thiamine, riboflavin, and vitamin B-6 status.

Energy expenditure at rest and during exercise in nonobese female cyclical dieters and in nondieting control subjects.

The purpose of this research was to determine if resting energy expenditure (REE) and exercise energy expenditure (EEE) differed between nonobese female cyclical dieters (n = 11) and nondieting control subjects (n = 12). Dieters were defined as having intermittent periods of caloric restriction (less than or equal to 4184 kJ/d, or less than or equal to 1000 kcal/d) for greater than or equal to 7-10 d four times in the preceding year. Dieters were significantly (P less than 0.01) heavier (66 vs 57 kg) and fatter (26% vs 21% body fat) than controls subjects whereas fat-free tissue was similar in both groups. Dieters had significantly (P less than 0.003) lower relative REE than did control subjects (2.8 vs 3.1 mL O2.kg-1.min-1; 79 vs 92 kJ.kg body wt-1.d-1, or 19 vs 22 kcal.kg body wt-1.d-1) but absolute REE (kJ/d, or kcal/d) was similar. Regardless of the workload examined, relative EEE was significantly (P less than 0.009) lower in dieters than in control subjects whereas absolute EEEs were similar at each workload. Results indicate an increased efficiency of food utilization during exercise in dieters but no difference in absolute REE. In addition, repeated bouts of dieting may alter body composition.

Lower daily energy expenditure as measured by a respiratory chamber in subjects with spinal cord injury compared with control subjects.

BACKGROUND: This study was designed to determine the effect of chronic spinal cord injury on daily energy expenditure. OBJECTIVE: We hypothesized that both resting and total energy expenditure would be lower in spinal cord-injured (SCI) subjects than in control subjects because of lower sympathetic nervous system activity and reduced levels of physical activity in SCI subjects. DESIGN: Twenty-four-hour energy expenditure (24-h EE), resting metabolic rate (RMR), sleeping metabolic rate, spontaneous physical activity, the thermic effect of food (TEF), and 24-h respiratory quotient were measured by using a respiratory chamber in 10 male SCI subjects (injury ranged from level C6 to L3) and 59 age-matched, noninjured, male control subjects. RESULTS: The 24-h EE was lower in SCI than in control subjects (7824 +/- 305 compared with 9941 +/- 188 kJ, P < 0.01). After adjustment for fat-free mass, fat mass, and age, 24-h EE was still lower (-753 kJ/d, P < 0.01) in SCI than in control subjects. Spontaneous physical activity measured by a radar system was also significantly lower (4.6 +/- 0.6% compared with 6.5 +/- 0.3% of time, P < 0.01) in SCI than in control subjects. In absolute value (7347 +/- 268 compared with 9251 +/- 1326 kJ/d, P < 0.01) or after adjustment for fat-free mass, fat mass, and age (-678 kJ/d, P < 0.01), RMR was also lower in SCI than in control subjects. TEF was significantly lower in SCI than in control subjects (987 +/- 142 compared with 1544 +/- 213 kJ/d, representing 12.9% and 15.9% of total energy intake, respectively, P < 0.05). The sleeping metabolic rate and 24-h respiratory quotient did not differ significantly between groups. CONCLUSIONS: The 24-h EE was significantly lower in SCI than in control subjects. This difference can be explained by the lower levels of physical activity, and lower RMR and TEF values, in SCI subjects.

Plasma pyridoxal 5'-phosphate concentration and dietary vitamin B-6 intake in free-living, low-income elderly people.

Free-living, elderly persons (aged greater than or equal to 60 y, n = 198) were recruited to determine the effects of age, sex, health status, dietary vitamin B-6 intakes, and B-6 supplement use on plasma pyridoxal 5'-phosphate (PLP). Vitamin B-6 intakes were determined from 3-d diet records; supplementation was based on self-reported brand and frequency data. Fasting blood samples were analyzed for PLP. Subjects were primarily low-income Caucasians. There was no linear relationship between dietary vitamin B-6 intake, age, sex or health status, and PLP while accounting for supplemental vitamin B-6 use. PLP, however, was negatively correlated with age (p less than 0.001) in individuals with PLP values between 32 and 90 nmol/L. Vitamin B-6 status was low (PLP less than 32 nmol/L) in 32% of this elderly population (n = 198) and could be attributed to low dietary vitamin B-6 intakes and/or the presence of health problems reported to alter vitamin B-6 status. This research suggests that low vitamin B-6 status is prevalent in low-income, elderly persons, especially those with multiple health problems.

Predicted and measured resting metabolic rate of male and female endurance athletes.

OBJECTIVE: To measure the resting metabolic rate (RMR) of a group of endurance-trained male and female athletes and to compare it with values predicted using published equations. DESIGN: RMR was measured twice: 1 week apart for the men and approximately 1 month apart for the women. RMR was predicted using equations of Harris and Benedict, Owen et al, Mifflin et al, and Cunningham. SUBJECTS/SETTING: Subjects were 37 trained endurance athletes (24 men, 13 women) who had participated in studies previously completed in our laboratory. MAIN OUTCOME MEASURES: The primary outcome measure was the comparison of predicted RMR with measured RMR. An exploratory procedure for the determination of predictive variables in these athletes was also performed. STATISTICAL ANALYSES PERFORMED: The Root Mean Squared Prediction Error method was used to compare predicted RMR with measured RMR. The maximum R2 procedure method was used to determine the best possible combination of four variables that explained the largest amount of variance in RMR. RESULTS: The Cunningham equation was found to predict measured RMR most accurately (within 158 kcal/d for men and 103 kcal/d for women). Fat-free mass was the best predictor of RMR in men, whereas energy intake was the best predictor in women. APPLICATIONS/CONCLUSIONS: The Cunningham equation provides an accurate estimate of RMR when determining energy needs of highly active people. Equations specific to athletes need to be developed. Factors in addition to body weight, height, and age should be investigated as possible predictor variables in athletes.

Development and testing of a carbohydrate monitoring tool for athletes.

Improving carbohydrate intake in athletes will increase muscle glycogen storage. This in turn can improve exercise time and performance by delaying fatigue. However, planning and consuming a diet that contains 60% to 70% carbohydrate is difficult for most athletes. To develop a simple carbohydrate monitoring tool for athletes, we analyzed three sets of 3-day diet records from 17 male endurance runners over a 10-week competitive period and 9 female endurance runners over a 9-week training period. We then developed a simple carbohydrate monitoring tool. To validate the instrument, we compared each athlete's carbohydrate intake as estimated using the instrument with the athlete's actual carbohydrate intake from the 3-day diet records. Mean estimated percents of energy from carbohydrate using the carbohydrate monitoring tool were not significantly different from the actual mean carbohydrate intakes. Examination of individual diets showed that the estimated carbohydrate was always within 2% of the actual carbohydrate. Therefore, the instrument did a good job of estimating the percent of energy from carbohydrate in the diets of endurance runners. This instrument will provide a quick method by which the athlete can assess and improve carbohydrate intake on a daily basis without the use of daily diet records.

Nutritional status of female athletes with subclinical eating disorders.

OBJECTIVE: To assess the energy and nutritional status of female athletes with subclinical eating disorders and compare them with that of control subjects and standard norms. DESIGN: Group classification (subclinical eating disorder or control) was based on responses to a health and diet history questionnaire, a battery of self-report eating disorder questionnaires, and an in-depth interview. Energy and nutrient intakes and energy expenditure were determined by means of 7-day weighed food records and 7-day activity logs. Micronutrient status was assessed for iron, zinc, magnesium, vitamin B-12, and folate. SUBJECTS: Twenty-four female athletes with subclinical eating disorders and 24 female control athletes. STATISTICAL ANALYSES: Descriptive statistics were used to analyze demographic data. One-way analysis of variance was used to determine group differences in energy and nutrient intakes, energy balance, and blood values. RESULTS: Groups were similar in age, height, weight, fat-free mass, and body mass index. Mean energy intake was lower in the group with subclinical eating disorders (1,989 kcal/day) than in the control group (2,300 kcal/day; P=.004), whereas mean energy expenditures were similar (2,405 and 2,293 kcal/day, respectively). The group with subclinical eating disorders had significantly (P<.05) lower mean protein and fat intakes compared with the control group; mean micronutrient intakes were not significantly different. Mean status measures for iron, zinc, magnesium, vitamin B-12, and folate were within the normal ranges for both groups and no differences were noted between the groups. A similar number of athletes within each group used vitamin/mineral supplements < or = 4 times per week. CONCLUSION: Although female athletes with subclinical eating disorders had dietary intakes of energy, protein, carbohydrate, and certain micronutrients that were below recommended levels, micronutrient status appeared relatively unaffected, probably due to their use of supplements.

Development and testing of a statistical and graphics-enhanced nutrient analysis program.

The authors have developed and tested a nutrient analysis program that will compute and present graphically summary statistics of population and population subgroup nutrient intakes. The program analyzes for 44 nutrients from 5,800 separate food items. Capabilities of the program include: storage of large numbers of diet records and evaluations of their nutrients; calculation of nutrient means and standard deviations; data sorting based on subject characteristics, such as age, sex, and supplement use; and generation of bar graphs and line plots for individual and/or group data. To test this computerized nutrient analysis program, two sets of 3-day diet records from 200 elderly individuals were analyzed. The program was then used to generate means, differences between means, and distribution frequencies of designated nutrients for various population subgroups (e.g., men greater than or equal to 65 years vs. men greater than or equal to 80 years) as well as comparisons with individual files (e.g., Mr. Smith vs. all men greater than or equal to 65 years). The statistical and graphics capabilities also function within the context of recipe analysis and menu planning, which enhances the application of this program in institutional and community nutrition settings.

Contribution of various food groups to dietary vitamin B-6 intake in free-living, low-income elderly persons.

Elderly persons are reported to have low dietary intakes of vitamin B-6. Knowing which foods are the primary contributors of dietary vitamin B-6 may be useful to health professionals working to improve the nutritional status of the elderly. Therefore, we examined the contribution of five food groups--flesh foods (including all meat/fish/poultry), grains/cereals, legumes/nuts, fruits/vegetables, and dairy products/eggs--to dietary vitamin B-6 intake in 198 free-living elderly persons aged 60 years or older. Subjects were primarily Caucasian, low-income non-smokers; their mean age was 72 years. Mean dietary vitamin B-6 intake, determined from 3-day diet records, was 1.6 +/- 0.6 mg/day. The fruit/vegetable group was the largest dietary contributor of vitamin B-6 (0.69 mg/day). Flesh foods and cereals/grains contributed equally to the vitamin B-6 intake (0.35 and 0.34 mg/day, respectively). The lowest contributors were dairy products/eggs and legumes/nuts. Approximately 96% of the vitamin B-6 intake could be accounted for by the five food groups. Twenty percent of the population (no. = 39) consumed less than 66% of the Recommended Dietary Allowance (RDA) for vitamin B-6; their vitamin B-6 intake from fruits/vegetables and grains/cereals was 0.36 and 0.10 mg/day, respectively. Individuals with vitamin B-6 intakes greater than or equal to 100% of the RDA (no. = 69) consumed greater amounts of fruits/vegetables (primarily bananas) and grains/cereals (primarily breakfast cereal) than did persons who consumed less than 66% of the RDA for vitamin B-6; their vitamin B-6 intake from fruits/vegetables and grains/cereals was 0.98 and 0.55 mg/day, respectively. In the elderly population studied, plant foods were the major dietary contributors of vitamin B-6.

Blood pressure responses of white men with hypertension to two low-sodium metabolic diets with different levels of dietary calcium.

OBJECTIVE: To compare the blood pressure responses of men with hypertension consuming low-sodium (Na) metabolic diets differing in dietary calcium (Ca) for two 6-week periods. SUBJECTS: White men who had hypertension, were nonsmokers, and were sedentary. INTERVENTION: This study consisted of two separate 6-week metabolic feeding periods. In the first period, a high-Ca group (n = 6) was fed 1,400 mg Ca per day. In the second period, a low-Ca group (n = 5) was fed 400 mg Ca per day. Both groups were fed 1,500 mg Na per day. MAIN OUTCOME MEASURES: Blood pressure; urine and blood measured for electrolyte, calcitriol, renin, and parathyroid hormone (PTH) levels. To measure typical nutrient intakes, 3-day dietary records were collected before the beginning of each treatment period. STATISTICAL ANALYSES PERFORMED: Repeated-measures analysis of variance and split-plot analysis of variance were used to analyze, respectively, blood pressure responses and response variables over time. RESULTS: In both groups, serum Na level decreased (P < .05) over the 6-week period; urine Na decreased (P < .05) only in the low-Ca group. Serum PTH level decreased (P < .05) in the high-Ca group and increased (P < .05) in the low-Ca group; no change occurred in serum calcitriol level. Diastolic blood pressure decreased (8 mm Hg) in the low-Ca group (P < .05). The low-Ca group showed an 8% to 9% decrease in both systolic and diastolic blood pressure vs a 2% to 3% decrease in the high-Ca group. We also examined how the metabolic diet differed from subjects' typical diet. Results showed a positive correlation between the change in Na intake (usual to metabolic diet) and the change in systolic and diastolic blood pressure in both groups (P < .04). Results also showed a negative correlation between the change in the ratio of Na to Ca (usual to metabolic diet) and the change in diastolic blood pressure in the low-Ca group (P < .03). Directional change in blood pressure (either increase or decrease) could be predicted on the basis of how much the Na and Ca in the metabolic diet differed from subject's typical diet. APPLICATIONS: Results of this study suggest that in the dietary management of hypertension it may be more important to focus on specific changes in a person's diet (eg, decreasing Na intake by 1,000 mg/day and increasing Ca intake by 400 mg/day) rather than setting specific levels of Na and Ca to be consumed.

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.

Effect of carbohydrate and vitamin B6 on fuel substrates during exercise in women.

Pyridoxal 5'-phosphate is an essential co-factor for glycogen phosphorylase and certain enzymes in the alanine-glucose cycle. Glycogen phosphorylase is also proposed as a storage reservoir for vitamin B6. To examine the effect of vitamin B6 and carbohydrate on fuel substrates during exercise, 5 young/trained, 5 young/un-trained, and 5 post-menopausal/un-trained women were alternately fed four diets (varying carbohydrate and B6 level) over a 7-wk period. Subjects were exercised at the end of each dietary period at 80% VO2max for 20 min on a cycle ergometer. Blood was drawn pre-, post-, post-30, and post-60 min of exercise and analyzed for plasma pyridoxal 5'-phosphate, glucose, free fatty acid, and lactate. ANOVA showed no difference among groups or diets for lactate, although lactate was significantly different over time (P less than 0.0001) on all diets. ANOVA showed significant time x group x diet inter-actions for free fatty acid (P less than 0.05) and significant diet x time (P less than 0.04) and time x group (P less than 0.03) inter-actions for glucose. Supplementation and/or increased carbohydrate resulted in lower free fatty acid during exercise in all groups. ANOVA showed no difference in pyridoxal 5'-phosphate for groups with respect to diet or time, but did show a significant increase from pre- to post-exercise and a significant decrease from post- to post-60 min of exercise. These results indicate that a high-carbohydrate diet and/or supplemental vitamin B6 can alter plasma fuel substrates during exercise in women; however, the effect depends on age and level of training.

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.

Daily energy expenditure in male endurance athletes with differing energy intakes.

The 24-h energy expenditure (24-h EE), resting EE (REE), sleeping EE (SEE), and spontaneous physical activity (SPA) were compared between six male endurance athletes whose reported energy intake was low (LOW) and did not match that theoretically required for weight maintenance and four whose reported energy intake appeared adequate (ADQ) and matched their estimated EE. Groups did not differ in age, body weight, fat-free mass, and daily EE estimated from activity records. The LOW athletes reported an energy intake 6338 +/- 2164 kJ.d-1 less than estimated EE. The 24-h EE, REE, SEE, and SPA of the LOW athletes were significantly lower than the ADQ athletes (862, 523, 770 kJ.d-1, and 43 min.d-1, respectively). Using all subjects, there was a significant positive correlation between REE and free thyroxine (FT4) (r = 0.82) and SEE and FT4 (r = 0.66). Thus, part of the LOW athlete's ability to maintain body weight on a seemingly low energy intake appears due to a lower daily sedentary EE.

Differences in epinephrine and substrate responses between arm and leg exercise.

The purpose of this study was to determine epinephrine (EPI) and selected substrate responses during arm crank (AC) and leg cycle (LC) exercise at the same absolute and relative exercise intensity. Nine males performed 30 min AC and LC tests at 70% of ergometer-specific peak oxygen uptake (VO2), and a 30 min LC test eliciting a similar VO2 required during the AC test. Blood samples (30 ml) were collected via an indwelling arm catheter at rest, and at minutes 13 and 28 of exercise for determinations of plasma EPI, serum free fatty acid (FFA), serum glycerol (GLY), blood glucose (GLU), and blood lactate (LA) concentrations. At equivalent VO2, higher (P less than 0.05) EPI, LA, and respiratory exchange ratio (RER) responses were obtained during AC than LC exercise. However, these physiologic responses were similar during AC and LC exercise at the same relative intensity. No significant differences over time were observed for FFA, GLY, and GLU between AC and LC exercise at either the same absolute or relative intensity. The results support previous hypotheses that AC exercise is physiologically more stressful than LC exercise at the same VO2. The data further indicate that adrenomedullary activity (EPI response) and substrate utilization (LA and RER responses) are regulated by relative exercise intensity and not the exercising muscle mass.

Chronic dieting in active women: what are the health consequences?

Evidence suggests that there is ever increasing pressure on American women to be thin. This pressure drives women to want to be thinner than what might be realistically achieved or required for good health. Our goal as nutrition and health professionals is to help women achieve and maintain a healthy body weight throughout the life-cycle. This includes helping young females accept their body size and shape as well and placing more emphasis on health and fitness than on weight in this population. This process begins with the identification of what constitutes a healthy body weight for a particular individual based on genetic, physiological, social, and psychological factors. In addition, it should be a weight that can be realistically maintained while keeping risk factors for chronic disease low. Table 1 outlines some strategies for helping individuals to identify and maintain a healthy body weight.

Nutritional needs of the female athlete.

US women, including female athletes, are under ever increasing pressure to be thin ar thinner. this pressure to achieve and maintain a low body weight leads to potentially harmful patterns of long-term dieting or disordered eating, which can affect long-term health. Some of the health consequences of long-term energy restriction in female athletes may include poor energy and nutrient intakes, poor nutritional status, decreased RMR and total daily energy expenditure, increased psychological stress and risk for a clinical eating disorder, and increased risk for exercise-induced amenorrhea and osteoporosis. Female athletes participating in thin-build sports may be at risk for the disorders of the female athlete triad: disordered eating, amenorrhea, and osteoporosis. This triad of disorders can also produce severe health consequences that can influence present and future health. Strategies for helping active women get off the dieting "bandwagon" requires the identification of an appropriate and healthy body weight, good eating and exercise habits, and techniques for maintaining these habits throughout life.

Vitamin B6 and exercise.

This paper presents an overview of vitamin B6 and exercise, including the role that vitamin B6 plays in gluconeogenesis and glycogenolysis and changes in vitamin B6 metabolism during exercise. The dietary vitamin B6 intakes of athletes are also reviewed. Most studies report that male athletes have adequate dietary intakes of vitamin B6, whereas some females, especially those with low energy intakes, appear to have low vitamin B6 intakes. Few studies have assessed the vitamin B6 status of nonsupplementing athletes using the recommended status criteria. The role that vitamin B6 may play in attenuating the rise in plasma growth hormone observed during exercise is also reviewed. Finally, recommendations are given for further research in the area of vitamin B6 and exercise.