Energy stress during pregnancy and lactation: consequences for maternal nutrition in rural Bangladesh

OBJECTIVE: To assess the relationship of energy stress during pregnancy and lactation to maternal body stores in marginally nourished rural Bangladeshi women. SUBJECTS AND METHODS: Two-hundred and fifty-two women were followed from 5-7 months of pregnancy until 6 months postpartum. Energy intake was estimated during pregnancy and at 1, 3 and 6 month(s) postpartum using 24 h dietary recall. Body weight was measured on enrollment, another once or twice during pregnancy, and at 1, 3 and 6 month(s) postpartum. The weekly rates of pregnancy weight gain and postpartum weight changes were determined. Weight and length of the infants were measured at birth and at approximately 1, 3 and 6 month(s). RESULTS: Maternal energy intake at 5-7 months of gestation was 1464+/-416 kcal/day (mean+/-s.d.). Women gained a mean of 200 g/week or a total of 4 kg during the second half of pregnancy. An analysis of maternal weight showed no indication of accrual of fat stores during pregnancy. Dietary energy during lactation exceeded the intake during pregnancy by 248-354 kcal/day. Mothers lost an estimated average of 1 kg of weight during the first 6 months of lactation. The mean (+/-s.d.) birth weight was 2.55+/-0.38 kg, and the prevalence of low birth weight (<2500 g) was 48%. Infants exhibited some catch-up growth only during the first 3 months but overall growth during the first 6 months did not change from their relative status at birth when compared with NCHS reference. CONCLUSIONS: These rural Bangladeshi women failed to gain sufficient weight during the last half of pregnancy to maintain body weight during lactation when the energy demand is high. Poor growth of their primarily breastfed infants raises concern about the adequacy of lactation in this community.     

Energy cost of lactation, and energy balances of well-nourished Dutch lactating women: reappraisal of the extra energy requirements of lactation

At 9 wk postpartum the difference in energy intake of 40 lactating (2440 +/- 430 kcal/d) and 16 nonlactating women (1680 +/- 400 kcal/d) was 760 kcal/d but decreased to 550 kcal/d when adjusted for habitual intakes and body weight. Energy cost of lactation amounted to 650 kcal/d (breast-milk production, 745 +/- 130 g/d). When compared with nonlactating counterparts, the lactating women mainly achieved energy balance by eating more. Sixteen of the 40 lactating women were also studied at 56 wk. Their cost of lactation at 5-13 wk was 630 kcal/d (breast-milk production, 720 +/- 124 g/d); these women met their energy cost of lactation by eating more (415 kcal/d); by tissue mobilization (35 kcal/d), and by reducing energy expenditure (180 kcal/d). The present study helps in the understanding of how well-nourished women with an adequate lactational performance may cope in everyday life with the energy stress of lactation, and suggests that current recommendations of energy needs during lactation are too high.     

Energy intake, energy expenditure, and body composition of poor rural Philippine women throughout the first 6 mo of lactation.

Between 6 and 30 wk postpartum, body weight and body-fat mass of 40 healthy, rural, lactating Filipino women decreased by 1.5 (P < 0.05) and 0.7 kg (P < 0.05), respectively. Energy intake decreased slightly (NS) from 8.84 +/- 2.05 MJ/d (2113 +/- 489 kcal/d; mean +/- SD) at 6 wk to 8.67 +/- 2.37 MJ/d (2073 +/- 566 kcal/d) at 30 wk. Basal metabolic rate (BMR) remained unchanged throughout lactation, and physical-activity level increased significantly (P < 0.05) from 1.61 +/- 0.17 x BMR at 6 wk to 1.97 +/- 0.18 x BMR at 30 wk. Energy intakes at 6 and 30 wk of lactation were 1.02 and 0.77 MJ/d (244 and 185 kcal/d) higher (P < 0.05), respectively, than in early pregnancy. At ages 1-6 mo, mean weights and lengths of mainly breast-fed infants had Z scores between 0 and -1. By using the growth patterns of the breast-fed infants as proxy indicators for adequacy of lactational performance, this study suggests that present recommended energy intakes for lactation are too high for healthy Filipino women who show adequate lactational performance.     

Body fat mass and basal metabolic rate in Dutch women before, during, and after pregnancy: a reappraisal of energy cost of pregnancy

Body weight, fat mass, and basal metabolic rate were measured longitudinally from early pregnancy until 2 mo postpartum in 57 healthy Dutch women; 23 of whom were also studied before pregnancy. Weight gain over pregnancy was 11.8 +/- 3.7 kg and weight gain from 12 wk gestation to delivery was 10.3 +/- 3.8 kg. Birth weights and placental weights were 3458 +/- 527 and 657 +/- 114 g, respectively. Gain in maternal fat stores over pregnancy was 2.0 +/- 2.6 kg and difference in fat mass from 12 wk gestation to 5 wk postpartum was 1.2 +/- 2.2 kg. The energy equivalent of the gain in fat stores, including costs of synthesizing, can be estimated as 22,000 kcal. The cumulative increment in basal metabolism over pregnancy was 34,350 +/- 30,000 kcal. When the energy equivalent of the gain in tissue other than fat stores is assumed to be approximately 11,750 kcal, total energy cost of pregnancy is at 68,100 +/- 38,560 kcal.     

Energy requirements during pregnancy based on total energy expenditure and energy deposition

BACKGROUND: Energy requirements during pregnancy remain controversial because of uncertainties regarding maternal fat deposition and reductions in physical activity. OBJECTIVE: This study was designed to estimate the energy requirements of healthy underweight, normal-weight, and overweight pregnant women and to explore energetic adaptations to pregnancy. DESIGN: The energy requirements of 63 women [17 with a low body mass index (BMI; in kg/m(2)), 34 with a normal BMI, and 12 with a high BMI] were estimated at 0, 9, 22, and 36 wk of pregnancy and at 27 wk postpartum. Basal metabolic rate (BMR) was measured by calorimetry, total energy expenditure (TEE) by doubly labeled water, and activity energy expenditure (AEE) as TEE - BMR. Energy deposition was calculated from changes in body protein and fat. Energy requirements equaled the sum of TEE and energy deposition. RESULTS: BMR increased gradually throughout pregnancy at a mean (+/-SD) rate of 10.7 +/- 5.4 kcal/gestational week, whereas TEE increased by 5.2 +/- 12.8 kcal/gestational week, which indicated a slight decrease in AEE. Energy costs of pregnancy depended on BMI group. Although total protein deposition did not differ significantly by BMI group (mean for the 3 groups: 611 g protein), FM deposition did (5.3, 4.6, and 8.4 kg FM in the low-, normal-, and high-BMI groups; P = 0.02). Thus, energy costs differed significantly by BMI group (P = 0.02). In the normal-BMI group, energy requirements increased negligibly in the first trimester, by 350 kcal/d in the second trimester, and by 500 kcal/d in the third trimester. CONCLUSION: Extra energy intake is required by healthy pregnant women to support adequate gestational weight gain and increases in BMR, which are not totally offset by reductions in AEE.     

Energy cost of physical activity throughout pregnancy and the first year postpartum in Dutch women with sedentary lifestyles

Basal metabolic rate (BMR), activity pattern, and energy costs of some daily activities were measured in 25 Dutch women throughout pregnancy and the first year postpartum. Physical activity index (PAI), which refers to daily energy expenditure expressed as a multiple of BMR, was calculated from activity-pattern data and activity costs. Mean PAIs (+/- SD) throughout pregnancy, during the first 6 mo postpartum, and at 1 y postpartum were 1.48 +/- 0.08, 1.49 +/- 0.07, and 1.53 +/- 0.10 X BMR, respectively. Because measured BMR at 1 y postpartum was 1440 +/- 168 kcal/d, costs for physical activity in pregnancy and the first 6 mo postpartum were, respectively, approximately 70 and approximately 50 kcal/d lower than at 1 y postpartum. For women with sedentary lifestyles the energy saved during pregnancy and lactation because of decreased physical activity and decreased costs of activities will be limited.     

Resting metabolic rate and body composition of healthy Swedish women during pregnancy

Body weight, resting metabolic rate (RMR), total body potassium (TBK), and total body water were measured and total body fat (TBF) was calculated in a longitudinal study of 22 pregnant, healthy Swedish women. Measurements were made before pregnancy, at gestational weeks 16-18, 30, and 36, and 5-10 d and 6 mo postpartum. RMR increased more during pregnancy than previous estimates on well-nourished women showed and the increase was significantly correlated with the birth weight of the baby. TBK decreased during the first part of pregnancy; measurements at weeks 16-18 and 30 were significantly lower than the prepregnancy value and changes in TBK and RMR were significantly correlated. TBF gain during pregnancy was 5.8 +/- 4.0 kg and 60% was already gained by gestational weeks 16-18. Gain in fat was not correlated with birth weight.     

Lactation, weaning, and calcium supplementation: effects on body composition in postpartum women

BACKGROUND: Concern that long-term weight retention after pregnancy contributes to obesity underscores the need to identify factors that facilitate postpartum weight loss. Lactation is believed to facilitate postpartum weight loss and fat loss. Calcium intake also has been hypothesized to promote weight loss and fat loss. OBJECTIVE: We addressed the following questions: 1) whether lactation enhances loss of fat mass, and 2) whether loss of fat mass during lactation and after weaning is greater in women receiving calcium supplementation than in women receiving placebo. DESIGN: We used data from 87 lactating and 81 nonlactating women enrolled in a randomized, double-blind, calcium supplementation trial from 2 wk to 6 mo postpartum and data from 76 previously lactating and 82 nonlactating women enrolled in a parallel trial from 6 to 12 mo postpartum. Body fat and lean masses were measured by using dual-energy X-ray absorptiometry. RESULTS: Nonlactating women lost whole-body, arm, and leg fat at a faster rate than did lactating women between 2 wk and 6 mo postpartum (lactation group x time effect, P < or = 0.01). Fat mass of the trunk, arms, and legs decreased between 6 and 12 mo postpartum regardless of previous lactation status (time effect, P < or = 0.001). Calcium supplementation did not affect postpartum fat loss. CONCLUSIONS: Body-composition changes occur differently in nonlactating and lactating women during the first 6 mo postpartum and occur at some sites until 12 mo postpartum regardless of previous lactation status. Clinicians should use caution when advising lactating mothers about expected rates of postpartum fat loss. Calcium supplementation (1 g/d) does not promote postpartum weight loss or fat loss.     

Human milk intake and growth faltering of rural Mesoamerindian infants.

To determine whether growth faltering during early infancy was attributable to inadequate intake of human milk, the nutrient intakes and growth of 30 Otomi infants from Capulhuac, Mexico, were studied at 4 or 6 mo of age. Growth was monitored monthly from 1 through 6 mo of age. The 2H dose-to-the-mother method was used to measure human milk intake. Energy, protein, lactose, and fat concentrations in milk were analyzed by standard techniques. Mean (+/- SD) human milk intakes were 885 +/- 145 and 869 +/- 150 g/d at 4 and 6 mo, respectively. Protein and lactose concentrations in milk were normal but fat and consequently energy concentrations were abnormally low. Energy intakes averaged 81 +/- 14 kcal.kg-1.d-1 at 4 mo and 72 +/- 14 kcal.kg-1.d-1 at 6 mo. Growth faltering by 6 mo was evidenced by the significant decline in growth velocities and National Center for Health Statistics Z scores. Weight gain at 6 mo was 8.1 +/- 3.5 g/d and length gain was 1.0 +/- 0.34 cm/mo. Weight-for-age and length-for-age Z scores were -0.81 +/- 0.94 and -1.51 +/- 0.83, respectively. Growth velocities were not significantly correlated with nutrient intakes. Growth faltering among the Otomi infants despite energy intakes comparable to those of breast-fed infants in more protected environments may have resulted from an increase in the need for nutrients or from a growth-limiting nutrient, other than energy, in their diet.     

Total energy expenditure of healthy Swedish women during pregnancy and lactation.

Total energy expenditure (TEE) was estimated in healthy Swedish women by the doubly labeled water method in a longitudinal study during pregnancy and lactation. Measurements were made before pregnancy (A); in gestational weeks 16-18 (B), 30 (C), and 36 (D); as well as 2 (F) and 6 (G) mo after delivery. When the results were interpreted, earlier published data regarding resting metabolic rate (RMR), energy intake, and energy in breast milk were also considered. TEE (MJ/d) and TEE/RMR were 10.5 +/- 2.2 (mean +/- SD) and 1.87 +/- 0.42 (n = 28), 9.6 +/- 2.8 and 1.65 +/- 0.67 (n = 22), 12.5 +/- 3.4 and 1.82 +/- 0.45 (n = 22), 12.2 +/- 4.1 and 1.66 +/- 0.52 (n = 19), 10.6 +/- 2.0 and 1.82 +/- 0.41 (n = 23), and 10.8 +/- 2.7 and 1.79 +/- 0.42 (n = 23) at A, B, C, D, F, and G, respectively. The results indicated that physical activity tended to be decreased during early pregnancy. Taking changes in body energy stores into consideration, it was estimated that subjects recorded 86% and 77% of their energy intakes at A and F respectively.     

Weight loss in 108 obese women on a diet supplying 800 kcal/d for 21 d

A series of 108 obese women were studied for 21 d in a metabolic ward on a diet supplying 800 kcal/d (3.4 MJ/d), with 4.5 g protein nitrogen, 40% energy from fat, and 46% from carbohydrate. The average total weight loss was 5.0 kg. During the second and third week on the diet the rate of weight loss was 211 +/- 77 g/d (mean +/- SD) and individual values were well predicted by admission resting metabolic rate (RMR) (r = 0.66, p less than 0.0001). The calculated energy density of the weight lost in this phase was 7000 kcal/kg (29.3 MJ/kg). However, the weight loss in the first week had a labile component of 815 +/- 1202 g, which was not well predicted by RMR (r = 0.20, p less than 0.05). The effect of this labile component was to obscure the overall rate of weight loss so some of the patients did not show net weight loss until day 13 of the diet, although they were in negative energy balance.     

Lactation performance of rural Mesoamerindians.

Anthropometry, body composition and dietary intake of 30 lactating Otomi Indians of Capulhuac, Mexico, were studied to identify maternal factors which potentially limit lactation and thereby infant growth. Human milk production, milk composition, and maternal dietary intake, body weight, skinfold thicknesses, and body composition were measured at 4 and 6 months postpartum. The 2H2O dose-to-mother method was used to estimate milk production and maternal total body water (TBW). Fat-free mass (FFM) was calculated as TBW/0.73. Body fat was computed as body weight minus FFM. Human milk samples were analyzed for energy, nitrogen, lactose and fat using standard analytical methods. Maternal diet was assessed by three 24-h intake recalls. Mean (SD) milk production was 885 (146) and 869 (150) g/d at 4 and 6 months, respectively. Milk concentrations of protein nitrogen (1.23 (0.17) mg/g) and lactose (66.6 (2.8) mg/g) were comparable to, but the concentrations of fat (22.2 (6.7) mg/g) and energy (0.54 (0.06) kcal/g) were lower than, values observed in economically privileged populations. Maternal height, weight, and BMI were 1.47 (0.06) m, 50.3 (6.0) kg, and 23.4 (3.1) kg/m2, respectively. Maternal TBW, FFM and body fat were 55.8 (4.6)%, 76.4 (6.3)%, and 23.6 (6.4)%, expressed as a percentage of body weight, respectively. Maternal energy and protein intakes averaged 1708 (338) kcal/d and 40 (10) g/d, respectively. Milk production was negatively correlated with maternal body fat (P = 0.006). Energy and fat concentrations in the milk of the Otomi women were positively related to their weight (P = 0.002), BMI (P = 0.05), and body fat (P = 0.004). Energy concentrations in milk were not related to rates of milk production (r = 0.24; P = 0.23). Nor was milk production or composition significantly associated with maternal dietary intake. Lactation performance of these Otomi women correlated significantly with maternal body size and composition, but not current dietary intake.     

Longitudinal assessment of energy balance in well-nourished, pregnant women

BACKGROUND: Clinicians often recommend an additional energy intake of 1250 kJ/d to their pregnant patients. Previous studies have shown considerable variation in the metabolic response to pregnancy and thus in the additional energy required to support a pregnancy. OBJECTIVE: The purpose of this study was to assess how well-nourished women meet the energy demands of pregnancy and to identify factors that predict an individual's metabolic response. DESIGN: Resting metabolic rate (RMR), diet-induced thermogenesis (DIT), total energy expenditure (TEE), activity energy expenditure (AEE), energy intake (EI), and body fat mass (FM) were measured longitudinally in 10 women preconception; at 8-10, 24-26, and 34-36 wk of gestation; and 4-6 wk postpartum. RESULTS: Compared with preconception values, individual RMRs increased from 456 to 3389 kJ/d by late pregnancy. DIT varied from -266 to 110 kJ/meal, TEE from -105 to 3421 kJ/d, AEE from -2301 to 2929 kJ/d, EI from -259 to 2176 kJ/d, and FM from a 0.6-kg loss to a 10.6-kg gain. The only prepregnant factor that predicted FM gain was RMR (r = 0.65, P < 0.05). Women with the largest cumulative increase in RMR deposited the least FM (r = -0.64, P < 0.05). CONCLUSIONS: Well-nourished women use different strategies to meet the energy demands of pregnancy, including reductions in DIT or AEE, increases in EI, and deposition of less FM than anticipated. The combination of strategies used by individual women is not wholly predictable from prepregnant indexes. The use of a single recommendation for increased energy intake in all pregnant women is not justified.     

Chitosan supplementation and fecal fat excretion in men

OBJECTIVE: Few weight loss supplements are clinically tested for efficacy, yet their proliferation continues. Chitosan-based supplements are sold as fat trappers and fat magnets. They purportedly block fat absorption and cause weight loss without food restriction. We quantified the in vivo effect of a chitosan product on fat absorption. RESEARCH METHODS AND PROCEDURES: Participants (n = 15) consumed five meals per day for 12 days. Energy intake was not restricted. Participants consumed no supplements during a 4-day control period and two capsules five times per day (4.5 g chitosan/d), 30 minutes before each meal, during a 4-day supplement period. All feces were collected from days 2 to 12. Oral charcoal markers permitted division of the feces into two periods. The two fecal pools were analyzed for fat content. RESULTS: Participants were male, 26.3 +/- 5.9 years old, BMI of 25.6 +/- 2.3 kg/m(2). Subjects consumed 133 +/- 23 g of fat/d and 12.91 +/- 1.79 MJ/d (3084 +/- 427 kcal/d). Individual meals averaged 26.3 +/- 9.3 g of fat. With chitosan supplementation at 10 capsules/day, fecal fat excretion increased by 1.1 +/- 1.8 g/d (p = 0.02), from 6.1 +/- 1.2 to 7.2 +/- 1.8 g/d. DISCUSSION: The effect of chitosan on fat absorption is clinically negligible. Far from being a fat trapper, at 0.11 +/- 0.18 g of fat trapped per 0.45-g capsule or 1.1 g (9.9 kcal) fat trapped per day, this product would have no significant effect on energy balance. The fat trapping claims associated with chitosan are unsubstantiated.     

Effect of a high-protein, very-low-calorie diet on resting metabolism, thyroid hormones, and energy expenditure of obese middle-aged women

A 4-6 mo study was conducted to examine effects of a very-low-calorie, high-protein diet and realimentation on energy expenditure, resting metabolic rate (RMR), and serum thyroid hormones of obese women aged 30-54 yr. Fifteen healthy women, greater than or equal to 126% ideal body weight, were placed on the diet (420 kcal/day) and lost an average of 1.1 kg/wk until a predetermined goal weight was attained. RMR, triiodothyronine (T3), and reverse T3 decreased significantly (p less than 0.05). Thyroxine remained unchanged. Upon gradual realimentation onto solid foods, all metabolic parameters increased significantly within 5 wk toward pre-diet baseline values, but RMR (kcal/h) and T3 values remained significantly below pre-study values. Estimates of mean energy expenditure, utilizing a technique based on energy intake and body composition changes, averaged 1719 kcal/day during the diet period.     

Consumption of a dehydrated ration for 31 days at moderate altitudes: energy intakes and physical performance

Energy intake, body weight, maximal work capacity, and measures of muscle strength and endurance were obtained from eight men who consumed a high-carbohydrate (CHO) dehydrated ration during a 31-day period of high activity at moderate altitudes. Data were collected 2 months before exposure to moderate altitudes (PRE), multiple times during the month's expedition at moderate altitudes (ALT), and after return from the expedition (RET). Work capacity per kilogram of body weight increased significantly from the PRE phase to the ALT phase. Mean energy intake averaged 2,354 +/- 71, 3,430 +/- 79, and 3,384 +/- 117 kcal/day during PRE, ALT, and RET, respectively; mean CHO intake during ALT was 595 +/- 13 g/day. Mean weight loss and reduction in body fat were significant: 1.9 +/- 0.9 kg and 18.9 +/- 10.1%, respectively. Energy deficits calculated from changes in body weight and composition during ALT ranged from 473 to 963 kcal/day, whereas the energy deficit estimated from the Harris-Benedict equation was only 194 kcal/day. The rigorous physical activity and exposure to moderate altitudes necessitated a high energy intake, approximating 3,800 kcal/day. The results indicate that physical performance and nutritional status are maintained when a high-CHO diet, consisting primarily of commercially available dehydrated foods, is consumed over a 31-day period of rigorous activity. However, weight loss and gastrointestinal distress were noted. These events might be minimized when a dehydrated ration is consumed, if dietary fat is substituted for some of the CHO.     

Energy expenditure in underweight free-living adults: impact of energy supplementation as determined by doubly labeled water and indirect calorimetry

The effect of energy supplementation was evaluated in six underweight adults under free-living conditions. Customary energy intake (EI) over 4 wk and estimated body composition were defined. Then for 12 wk subjects were fed their customary EI under controlled conditions to assure stable energy reserve. Finally, intake was increased by a mean of 720 kcal/d for 8 wk adjusted to increase body fat from 9 to 18%. Body weight (means +/- SD) increased from 55.2 +/- 3.4 to 57.0 +/- 4.2 kg. Body fat gain was highly variable ranging from 0.6 to 3.8 kg. Energy expenditure (EE) by the factorial and doubly labeled water methods did not change. Fat storage accounted for 66% of the supplemental energy; 237 kcal/d remained unaccounted for. EE by the factorial method, which uses indirect calorimetry or isotopic measurements, were highly correlated (r = 0.8; p less than 0.01). Under the conditions of this study EI does not affect EE. The labeled water method permits the evaluation of energy expenditure in free-living conditions.     

Lactation performance of exercising women

To determine whether vigorous exercise affects lactation performance, we compared well-nourished exercising (n = 8) and sedentary (n = 8) women whose infants were 9-24 wk old and exclusively breast-fed. Measurements included resting metabolic rate (RMR); maximum oxygen consumption (VO2max); plasma prolactin, cortisol, insulin, and T3; and body composition. Each subject completed a 3-d record of dietary intake, physical activity, and milk volume (by test weighing) and collected 24-h milk samples. Exercising women differed significantly from control subjects in VO2max (46.4 vs 30.3 mL.kg-1.min-1), percent body fat (21.7 vs 27.9%), total energy expenditure (3169 vs 2398 kcal/d), and energy intake (2739 vs 2051 kcal/d). There was no difference between the groups in plasma hormones or milk energy, lipid, protein, or lactose content. Exercising subjects tended to have higher milk volume (839 vs 776 g/d) and energy output in milk (538 vs 494 kcal/d). Thus, there was no apparent adverse effect of vigorous exercise on lactation performance.     

Conjugated linoleic acid supplementation alters the 6-mo change in fat oxidation during sleep

BACKGROUND: Conjugated linoleic acid (CLA) is a family of positional and geometric isomers with 2 conjugated double bonds formed from linoleic acid and linolenic acid. CLA has a wide range of biological effects, including body fat reduction. OBJECTIVE: The aim of our study was to determine CLA's effects on energy expenditure, macronutrient utilization, and dietary fat oxidation in overweight adults after 6 mo of supplementation. DESIGN: We recruited 23 subjects from our main CLA efficacy study who were receiving either 4 g/d of 78% active CLA isomers (3.2 g/d: 39.2% cis-9,trans-11 and 38.5% trans-10,cis-12) or 4 g/d of safflower oil. Energy expenditure and substrate utilization were measured before and after 6 mo of CLA supplementation by using whole-room indirect calorimetry. Dietary fat oxidation was measured by using stable isotope-labeled oleate and palmitate. RESULTS: Our substudy detected a difference in the change in fat utilization between the CLA (4 +/- 8 g) and placebo (-7 +/- 11 g) groups during sleep after 6 mo of supplementation. In addition, the percentage of energy from protein was reduced during sleep in the CLA group (CLA: -3.3 +/- 2.6%; placebo: 0.3 +/- 5.7%). We also detected a difference in the change in energy expenditure during sleep (CLA: 0 +/- 38 kcal; placebo: -43 +/- 90 kcal). We did not detect a change in labeled dietary fat oxidation after 6 mo of CLA supplementation given with a breakfast meal. CONCLUSION: Mixed isomer CLA supplementation, but not placebo, positively altered fat oxidation and energy expenditure during sleep.     

Body composition, nitrogen metabolism, and energy utilization with feeding of mildly restricted (4.2 MJ/d) and severely restricted (2.1 MJ/d) isonitrogenous diets.

To determine the effects on weight loss of feeding isonitrogenous diets in mildly restricted (4.2 MJ/d) and severely restricted (2.1 MJ/d) amounts, we measured body composition, weight loss-energy deficit ratio, and nitrogen metabolism in 14 obese women housed in a metabolic ward consuming hypoenergetic diets for 21 d. Subjects consumed either a 4.2-MJ/d diet (50 g protein, 175 g carbohydrate) or a 2.1-MJ/d diet (50 g protein, 75 g carbohydrate). Body composition and leucine oxidation and turnover were determined before and after weight loss. Energy deficit was calculated from resting metabolic rates. Subjects fed the 2.1-MJ/d diet showed a greater weight loss (6.1 +/- 0.5 vs 4.5 +/- 0.5 kg; mean +/- SE, P less than 0.05) and fat loss (3.9 +/- 0.3 vs 3.0 +/- 0.3 kg, P less than 0.05). Weight loss-energy deficit ratio was the same with both diets. Nitrogen balance and leucine oxidation and turnover were similar in both groups. We conclude that with feeding of isonitrogenous hypoenergetic diets, severe restriction of energy content (2.1 MJ/d, 75 g carbohydrate) will enhance weight and fat loss without increasing nitrogen loss compared with mild restriction of energy (4.2 MJ/d).