Antioxidant status of young children: response to an antioxidant supplement.

OBJECTIVE: To study oxidative stress indicators in healthy young children and their response to a commercially available fruit- and vegetable-based antioxidant supplement. DESIGN: Healthy children were randomly assigned to a placebo and a supplement (commercial antioxidant supplement produced from dried fruit and vegetable extracts and fortified with antioxidants, resembling a gummy-type candy). The placebo and the supplement were taken in 2 doses per day for 21 days. SUBJECTS: Participants were 39 children (26 boys and 13 girls) aged 5 to 10 years. Research was conducted at Primary Children's Medical Center and the University of Utah, Salt Lake City. MAIN OUTCOME MEASURES: Breath and urine samples were collected on days 1 and 21 and assayed for breath pentane and urine 8-hydroxydeoxyguanosine, malondialdehyde, nitrites, and 8-isoprostane as noninvasive indicators of oxidative stress. Urine oxygen radical absorbance capacity was measured at days 1 and 21 as an indirect indicator of the antioxidant capacity of the body. Three-day food records were collected at the beginning and end of the study to measure intake of dietary fruit; vegetable; and antioxidant vitamins A, C, and E. STATISTICAL ANALYSIS: Descriptive statistics, repeated measures analysis of variance, paired t tests, and Pearson r correlations. RESULTS: Markers of oxidative stress were not significantly different between the placebo and supplement groups at day 1 or day 21. The oxidative stress indicators of the healthy children in this study appear to be similar to those of healthy adults and were not changed by antioxidant supplementation. The diet record analyses indicated that mean fruit and vegetable intakes (2.75 servings/day) were similar to the national average intake for children in the United States. APPLICATIONS/CONCLUSIONS: This research presents original information on the subject of oxidative stress in healthy children. The results of this study may be useful as reference baseline markers to use in conjunction with clinical dietary evaluations and for future research with healthy children and with children in disease states who are subject to elevated levels of oxidative stress.

Work at high altitude and oxidative stress: antioxidant nutrients.

A significant portion of the world's geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS) and less frequently, high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The symptoms of AMS (headache, nausea, anorexia, fatigue, lassitude) occur in those who travel too high, too fast. Some investigators have linked the development of these symptoms with the condition of altered blood-brain barrier permeability, possibly related to hypoxia induced free radical formation. The burden of oxidative stress increases during the time spent at altitude and may even persist for some time upon return to sea level. The physiological and medical consequences of increased oxidative stress engendered by altitude is unclear; indeed, hypoxia is believed to be the trigger for the cascade of signaling events that ultimately leads to adaptation to altitude. These signaling events include the generation of reactive oxygen species (ROS) that may elicit important adaptive responses. If produced in excess, however, these ROS may contribute to impaired muscle function and reduced capillary perfusion at altitude or may even play a role in precipitating more serious neurological and pulmonary crisis. Oxidative stress can be observed at altitude without strenuous physical exertion; however, environmental factors other than hypoxia, such as exercise, UV light exposure and cold exposure, can also contribute to the burden. Providing antioxidant nutrients via the diet or supplements to the diet can reduce oxidative stress secondary to altitude exposure. In summary, the significant unanswered question concerning altitude exposure and antioxidant supplementation is when does oxidative stress become potentially damaging enough to merit antioxidant therapy and conversely, what degree of oxidative stress is necessary to foster the adaptive response of altitude exposure?

Oxidative stress in humans training in a cold, moderate altitude environment and their response to a phytochemical antioxidant supplement.

OBJECTIVE: This study examined the effectiveness of an antioxidant mixture containing vitamin E, beta-carotene, ascorbic acid, selenium, alpha-lipoic acid, N-acetyl 1-cysteine, catechin, lutein, and lycopene to reduce oxidative stress in US Marines undergoing 24 days of cold-weather field training at a moderate altitude. METHODS: Forty physically active male volunteers (ages 18-40) were randomly assigned to a treatment (antioxidant) group (n = 21) or a control (placebo) group (n = 19). Breath pentane (BP), serum lipid hydroperoxides (LPO), urine malondialdehyde (MDA), urine 8-hydroxy deoxyguanosine (8-OHdG), ferric-reducing ability of plasma (FRAP), and serum and urine oxygen radical absorption capacity (ORAC) were measured as indicators of oxidative stress and antioxidant status. Urine was sampled at days 0, 12, and 24. Serum and breath were sampled on days 0 and 24. RESULTS: Both groups exhibited increased levels of oxidative stress after 24 days of field training, as indicated by an increased LPO, pentane, and 8-OHdG. There was no significant difference between the treatment and placebo groups at day 24; however, there was some indication that test subjects with initially low antioxidant capacity (ORAC) may have benefited from the antioxidant supplement. CONCLUSIONS: An increased level of oxidative stress was associated with high levels of physical exertion of training in a cold environment at moderate altitude. The antioxidant mixture tested did not attenuate the mean oxidative stress levels in the entire group of test subjects, but it may have reduced the oxidative stress of some individuals with low initial antioxidant status.

Antioxidant status and oxidative stress in elite alpine ski racers.

The goal of this study was to access antioxidant status and markers of oxidative damage in elite alpine ski racers during routine training. Subjects included 12 members of the U.S. Men's Alpine Ski Team attending a 10-day summer training camp. Blood draws were collected at rest and after exercise: (a) prior to training, (b) following 2 days of dry land training, and (c) after 4 days of on-snow skiing. Seven measures of antioxidant status were determined using colorimetric and HPLC methods (Trolox equivalent antioxidant capacity, uric oxidase, alpha-tocopherol, total glutathione, cytosolic glutathione peroxidase, and superoxide dismutase). Oxidative stress was assessed using 2 markers of lipid oxidation (malondialdehyde and lipid hydroperoxides) and 2 markers of protein oxidation (carbonylated total proteins and carbonylated hemoglobin). The results of this study suggest that antioxidant status of elite alpine skiers may decline over a period of intense training. However, elevations in markers of oxidative stress were not evident.

Endocrine markers of semistarvation in healthy lean men in a multistressor environment.

We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 achieved a minimum body fat, serum 3,5,3'-triiodothyronine (T(3)) was below normal (78 +/- 20 ng/dl), testosterone (T) approached castrate levels (4.5 +/- 3.9 nmol/l), insulin-like growth factor I (IGF-I) declined by one-half (75 +/- 25 microg/l), and cholesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T(3) and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T(3), T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T(3), and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.

Oxidative stress in humans during work at moderate altitude.

Increased oxidative stress has been associated with work at high altitude; however, it is not known whether oxidative stress is a significant problem at moderate altitudes. The oxidative stress indicators, breath pentane (BP), 8-hydroxydeoxyguanosine (8-OHdG), oxygen radical absorption capacity (ORAC), 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and lipid peroxides (LPO) were measured in breath, blood and urine samples of U.S. Marines engaged in moderate altitude ( approximately 3000 m) cold weather field training. The test subjects were divided into a placebo and four antioxidant supplement groups (n = 15/group) and received the following supplements for 28 d: 1) vitamin E, 440 alpha-tocopherol equivalents (alpha-TE); 2) vitamin A, 2000 retinol equivalents (RE) of beta-carotene; 3) vitamin C, 500 mg ascorbic acid; 4) a mixture of 440 alpha-TE, 2000 RE of beta-carotene, 500 mg ascorbic acid, 100 microg selenium and 30 mg zinc daily. Strenuous work ( approximately 23 MJ/d) in cold weather at moderate altitude was accompanied by increases in several indicators of oxidative stress that were not effectively controlled by conventional antioxidant supplements. The group receiving the antioxidant mixture exhibited lower BP (P < 0. 05) compared with those receiving single antioxidant supplements; however, not all markers of oxidative stress responded like BP. Because these markers did not respond in the same manner, it is important to include markers from more than one source to assess the effect of supplemental dietary antioxidants.

Effect of antioxidant supplementation on urine and blood markers of oxidative stress during extended moderate-altitude training.

OBJECTIVE: To investigate the increase in oxidative stress during work at moderate altitudes due to additional energy expenditure, tissue anoxia, and UV light exposure. METHODS: Thirty US Marine Corps volunteers were divided into placebo (P) and antioxidant supplement (S) groups and tested for markers of oxidative stress before (t0), at the midpoint of (t1), and after (t2) 14 days of winter training at a moderate altitude (approximately 2700 m). The antioxidant supplement consisted of a daily dose of 20,000 IU beta-carotene, 400 IU vitamin E, 500 mg vitamin C, 100 micrograms selenium, and 30 mg zinc. The following markers of oxidative stress were measured: urine thiobarbituric acid reactive substances (TBARSs), urine hydroxynonenal (HNE), urine 8-hydrodeoxyguanosine (8-OHdG), plasma total peroxyl radical trapping potential (TRAP), and plasma lipid hydroperoxides (LPOs). Urine was collected on a 24-hr basis at t0, t1, and t2; blood samples were collected at t0 and t2. RESULTS: P group LPOs increased 30% (p < 0.05) between t0 and t2, whereas S group LPOs did not increase. Both groups exhibited significant increases in urine TBARSs, HNE, and 8-OHdG by t2. Urine TBARSs, HNE, and 8-OHdG increased between t0 and t1 in both groups, with the greater increase in the S group. The conflicting results between the plasma and urine markers of oxidative stress may be due to a time-phase relationship. CONCLUSIONS: The results of this study suggest that work in a moderate-altitude cold-weather environment is accompanied by increased oxidative stress, despite relatively high intakes of dietary and supplemental antioxidants.

Effects of 30 days of undernutrition on reaction time, moods, and symptoms.

Few modern studies have addressed the effects of undernutrition on the behavior of healthy individuals. This study, conducted as part of a test of a nutritionally balanced but calorie-deficient experimental ratio, examined the effects of 30 days of undernutrition on healthy, physically active soldiers. Tests of reaction time and standardized questionnaires assessing mood and symptom parameters (known to be sensitive to nutritional and other factors) were administered prior to and following a 30-day field exercise. During the exercise, 17 soldiers consumed a calorie-deficient, lightweight ration (LW group, 1946 kcal/day) and 17 consumed a calorie-adequate control ration (FN group, 2782 kcal/day). Mean energy expenditure for both groups was 3200-3300 kcal/day. There were no differences between the two diet groups on any of the measures of reaction time, mood, or symptoms after 30 days of ration consumption. Additionally, there were no adverse changes in reaction time performance from pre- to post-testing. Adverse changes in moods and symptoms were seen in both groups at the conclusion of the test, possibly because of the rigors of living in the field for an extended period of time. This study demonstrates that, in healthy individuals, various aspects of mental performance, mood, and symptoms are not affected by up to 30 days of moderate undernutrition.

Dietary sodium and plasma volume levels with exercise.

Sodium is the major cation of the extracellular fluid and has a potent influence on fluid movement. Sodium has been likened to a sponge that draws fluids into the extracellular space, including the plasma volume, to equalize gradients in concentration. Conventional wisdom suggests limiting dietary intake of Na+ to decrease risk of hypertension. However, there are some extreme occupational or exercise-related conditions where sweat losses are great and Na+ losses may exceed normal dietary intake. This can occur acutely such as in an ultra-endurance event or chronically as in hard manual work in the hear. In such cases, additional Na+ in the form of a higher Na+ diet or adding Na+ to beverages used for fluid replacement may be warranted. A higher Na+ diet also appears to accelerate the cardiovascular and thermoregulatory adaptations that accompany heat acclimation or short term exercise training. Saline ingestion before exercise causes an expansion of plasma volume at rest and throughout the subsequent exercise bout. This expansion of plasma volume alters cardiovascular and thermoregulatory responses to exercise in ways that may lead to beneficial changes in endurance exercise performance. Plasma volume expansion also occurs with saline infusion during exercise, but exercise performance advantages have yet to be reported. The purpose of this article is to review the literature concerning dietary sodium and its influence on fluid balance, plasma volume and thermoregulation during exercise. It contains 2 major sections. First, we will discuss manipulations in daily Na+ intake initiated before or throughout an exercise regime. Second, we will examine studies where an acute Na+ load was administered immediately before or during an exercise trial. The dependent variables that we will discuss pertain to: (i) body water compartments, i.e. plasma volume; (ii) thermoregulatory variables, i.e. core temperature and sweat rate; (iii) cardiovascular variables, i.e. heart rate and stroke volume; and (iv) performance, i.e. time trial performance and time to exhaustion. Particular attention will be given to the route by which Na+ was administered, the environmental conditions, the level of acclimation of the participants and specifics relating to Na+ administration such as the osmolality of the Na(+)-containing beverage.

Effects of food restriction in military training on T-lymphocyte responses.

In a stress model which included food restriction, we examined the effects of physically rigorous military training and increased caloric intake on T-lymphocyte responses and lymphocyte subsets. T-lymphocyte proliferation and release of soluble receptor for interleukin-2 (slL-2R) in vitro were measured in two separate training classes of male U.S. Army ranger course (RC) trainees at the start and during the RC. Trainees in group 1 (n = 55) and 2(n = 50), respectively, had mean (+/- SD) energy intakes of 11.8 +/- 7.0 and 13.6 +/- 6.7 MJ/d, averaged total daily energy expenditures of 16.7 and 17.6 MJ/d, and experienced body weight losses of 15.]% and 12.6%. Both groups showed decreases T-lymphocyte responses in vitro: proliferation to phytohemagglutinin (PHA) and tetanus toxoid (TT), and released slL-2R to PHA. Group 2 with an intended 15% increase in energy during the RC over group 1 showed 22% and 26% less severe suppressions of T-lymphocyte proliferation and released slL-2R, respectively, in vitro. Group 2 also showed that short-term (9 days) removal of the food restriction stressor allowed for corrected body weight, total lymphocyte and T-lymphocyte subset counts but not suppressed T-lymphocyte responses in vitro. These results demonstrate that soldiers in physically rigorous military training are at risk of suppressed T-lymphocyte immunocompetence, and this is greater if they also experience inadequate energy intake.

Assessment of dietary intakes of cadets at the US Military Academy at West Point.

OBJECTIVE: A study was conducted at the US Military Academy, West Point, NY, to assess the nutritional adequacy of menus and dietary intakes of the cadets and to determine the effect of the optional weekday evening meal policy on nutrient intakes. METHODS: Dietary intakes were obtained over a 7-day period using a diary-interview technique. Volunteer cadets, 118 males and 86 females, recorded their own intakes and were interviewed by dietitians to verify food records. Cadets were categorized by gender and divided into three groups based on whether they consumed 0-1, 2-3, or 4-5 weekday evening meals in the Cadet Mess. RESULTS: Multivariate methods were used to assess compliance with Military Recommended Dietary Allowances (MRDA) and nutrient densities as well as the role of gender, number of weekday evening meals consumed in the West Point Cadet Mess, and the use of nutritional supplements during the study week. The number of weekday evening meals consumed in the Cadet Mess, was positively correlated with the nutrient intakes of the cadet groups. The female 0-1 group had the highest proportion of individuals with mean intakes providing < 70% MRDA for vitamin B6, folate, vitamin A, magnesium, or zinc. Snacks provided from 24% to 32% of the energy intakes of the female groups and were often substituted for meals, particularly by cadets who ate the fewest meals in the Cadet Mess. CONCLUSIONS: Diet counseling is recommended to help these cadets choose more nutritious meals and snacks. University and college students that choose not to purchase some of their meals from campus dining facilities could have similar dietary intake patterns and nutritional shortcomings.

Effects of reduced fat intake on serum lipids in healthy young men and women at the U.S. Military Academy.

To assess the benefits of Army nutrition initiatives reducing intakes of fat and cholesterol, the authors studied the dietary intakes of cadets at the U.S. Military Academy and compared these results and related nutritional indicators (body composition, serum lipid status) to data obtained one decade earlier. The regular Cadet Mess menu provided 16.6 MJ/day of energy with 34% derived from fat. Actual intakes, including supplements, averaged 14.9 +/- 2.9 and 9.7 +/- 2.1 MJ/day for 119 male and 86 female cadets, respectively. Most cadets derived < 35% of energy from dietary fat (11% from saturated fatty acids), representing a significant reduction since the previous study, in which nearly one-third of cadets received 40 to 45% of calories from fats; cholesterol intakes were markedly reduced. Serum cholesterol levels were approximately 7% lower, but were less affected than predicted by the reductions in fat and cholesterol intakes; serum low-density lipoprotein-cholesterol was also significantly reduced. Fasting serum insulin correlated with saturated fat intake in female cadets, indicating another health risk factor affected by intakes. The authors conclude that nutrition initiatives reducing energy derived from fats and total cholesterol intake have had a beneficial effect on the nutritional status of this fit young population.

Environmental and physical stress and nutrient requirements.

When faced with hot, cold, or high-altitude environments, humans can either modify the microenvironment to fit human physiology, adapt their physiology to fit the environment, or use a combination of these two tactics. Metabolic adaptations to heat, cold, and high-altitude exposure may, in some instances, be accompanied by changes in nutrient requirements. Energy expenditure is increased in all three environments. B-vitamin cofactor requirements increase in proportion to energy expenditure (oxidation of fat and carbohydrate). Increased B-vitamin nutrient requirements are usually adequately met by an increased consumption of the diet to meet energy requirements. Other nutrients such as iron may be required in greater amounts to meet the altitude-induced hematopoietic response in females. Additional quantities of vitamins and minerals with antioxidant properties may be beneficial to reduce the increased oxidative stress associated with work in heat, cold, or high-altitude outdoor environments.

Lower limit of body fat in healthy active men.

We examined body composition changes in 55 normal young men during an 8-wk Army combat leadership training course involving strenuous exercise and low energy intake, with an estimated energy deficit of 5.0 +/- 2.0 MJ/day and a resultant 15.7 +/- 3.1% weight loss. Percent body fat (BF) measured by dual-energy X-ray absorptiometry (DEXA) averaged 14.3% (range 6-26%) and 5.8 +/- 1.8% (range 4-11%) at the beginning and end of the course, respectively. Men who achieved a minimum percent BF (4-6%) by 6 wk demonstrated only small additional total and subcutaneous fat losses in the final 2 wk and sacrificed increasingly larger proportions of fat-free mass. Percent BF estimated from skinfold thicknesses reflected relative changes in fat mass, although actual percent BF was overestimated. Instead of reaching a plateau after fat stores were substantially depleted, abdominal, hip, and thigh girths continued to decline with body weight loss. Final percent BF for the leanest men was similar to that observed after a 25% body weight reduction in the 1950 Minnesota study (5.2% by underwater weighting), and height-corrected final fat mass was the same (1.0 +/- 0.2 vs. 0.9 +/- 0.7 kg fat/m2), suggesting that these values represent a minimal body fat content in healthy men and that weight loss subsequent to achieving this level is contributed from the fat-free mass. Our results suggest that 4-6% BF or approximately 2.5 kg fat represents the lower limit for healthy men, as assessed by DEXA or by underwater weighing.

Doubly labeled water measurement of human energy expenditure during exercise at high altitude.

Estimates of total daily energy expenditure (TDEE) by the doubly labeled water (DLW, 2H(2)18O) and intake balance (I-B) methods were compared in six male soldiers studied over 6 days that included 5 days of strenuous winter exercise at 2,500- to 3,100-m elevation. Use of body energy stores [-9.54 +/- 1.54 (SD) MJ/day or -2,280 +/- 368 kcal/day] was estimated from changes in body weight, body density (hydrodensitometry), and total body water (H(2)18O dilution). The subjects wore computerized activity monitors and kept daily records of ration consumption (9.87 +/- 3.60 MJ/day or 2,359 +/- 860 kcal/day). Accuracy of individual DLW and I-B TDEE values was estimated from the correlations of TDEE with fat-free mass (FFM) or total weight (body wt + load). The DLW and I-B estimates of TDEE differed by -12.0 to 15.2% but provided comparable estimates of group mean TDEE (DLW = 19.07 +/- 2.37 MJ/day or 4,558 +/- 566 kcal/day; I-B = 19.41 +/- 3.72 MJ/day or 4,639 +/- 889 kcal/day; P > 0.05). The DLW TDEE was correlated with both FFM (r2 = 0.89, P < 0.01, power = 0.95) and total weight (r2 = 0.95, P < 0.01, power = 0.99), whereas I-B TDEE was correlated only with total weight (r2 = 0.75, P < 0.03, power = 0.81). Under adverse field conditions the DLW method provided individual TDEE estimates that were probably more accurate than those provided by the I-B method.

Cold-weather field feeding: an overview.

Extremely cold environments are a challenge to military field feeding operations due to freezing and inadequate intakes of rations and water. The U.S. Army Research Institute of Environmental Medicine conducted a series of three cold-weather field feeding studies to test, modify, and contribute data for the development of Cold-Weather Feeding Doctrine. Conclusions from these studies show that command emphasis is essential for ration and water storage and distribution to prevent freezing, and adequate ration and water consumption to prevent weight loss and dehydration. Since any ration mix can be configured to meet cold-weather feeding requirements, the decision of which ration to use should be based on logistical support and constraints, mission requirements, and water availability.

Maintenance of iron status in healthy men during an extended period of stress and physical activity.

Body weight loss and iron status of 55 male soldiers were measured during 62 d of intense physical activity and sustained stress and sleep deprivation. Body weight declined from (mean +/- SD) 75.9 +/- 9.0 to 63.8 +/- 6.7 kg (P < 0.05). Serum iron fell from 13.7 +/- 5.6 to 8.3 +/- 3.6 mumol/L by 14 d (P < 0.05), but returned to baseline values by 8 wk. Total iron-binding capacity declined from 53.4 +/- 6.8 at baseline to 47.5 +/- 6.3 mumol/L at 8 wk (P < 0.05). During the study, hematocrit, serum hemoglobin, and erythrocyte count did not change, whereas ferritin increased from 116 +/- 84 to 202 +/- 106 micrograms/L (P > 0.05). Adequate dietary iron, initiation of training with adequate body iron stores, and physical activity not in excess of pretraining workloads contributed to the maintenance of iron status during prolonged physical activity and stress. Our results suggest that some acute phase-like disturbances in iron metabolism may be a normal component of adaptation to stress and physical activity in healthy men.

Nutrition issues of military women.

Nutritional data were collected from 147 female soldiers in four surveys (two field and two dining hall studies) conducted by the US Army Research Institute of Environmental Medicine and Letterman Army Institute of Research. The 49 female soldiers observed in the field studies had suboptimal mean energy (1751 kcal), protein (52.3 g), calcium (620 mg), and iron (11.8 mg) intakes. In addition, 54 female soldiers in the dining hall studies also had lower than desirable mean iron (16.2 mg) intakes. These data suggest that nutritional problems encountered by military women are similar to those faced by their civilian counterparts, based on NHANES II and CSFII reports. Although the impact of sporadic low nutrient intakes during short 10-14-day field training exercises may be of little consequence, this may be significant when inadequate intakes occur routinely or for extended periods during military conflicts. Viable solutions to the nutritional problems of military women could include ration supplementation and nutrition education.

Cold weather field evaluation of the 18-Man Arctic Tray Pack Ration Module, the meal, ready-to-eat, and the Long Life Ration Packet.

The Army Field Feeding System was evaluated for its ability to provide adequate nutrition and hydration during a 10-day cold weather field exercise. Soldiers consumed the 18-Man Arctic Tray Pack Ratio Module with either a wet-pack (Meal, Ready-to-Eat) or a dehydrated (Long Life Ration Packet) individual ration. Both feeding regimens were acceptable, meeting protein and micronutrients requirements. However, the soldiers consumed only 70% of their energy requirement, thus losing an average of 0.9% of body weight. This weight loss, although not excessive, underscores the importance of maintaining an adequate food intake during extended cold weather military field operations.

Responses to moderate and low sodium diets during exercise-heat acclimation.

This investigation examined whether low sodium (Na+) (LNA; 68 mEq Na+.d-1) or moderate Na+ (MNA; 137 mEq Na+.d-1) intake allowed humans to maintain health, exercise, and physiologic function during 10 days of prolonged exercise-heat acclimation (HA). Seventeen volunteers, ages 19 to 21, consumed either LNA (n = 8) or MNA (n = 9) during HA (41 degrees C, 21% RH; treadmill walking for 30 min.h-1, 8 h.d-1 at 5.6 km.h-1, 5% grade), which resulted in significantly reduced heart rate, rectal temperature, and urine Na+ for both groups. There were few between-diet differences in any variables measured. Mean plasma volume in LNA expanded significantly less than in MNA by Days 11 and 15, but reached the MNA level on Day 17 (+12.3 vs. +12.4%). The absence of heat illness, the presence of normal physiologic responses, and the total distance walked indicated successful and similar HA with both levels of dietary Na+.