Exchangeable magnesium pool masses reflect the magnesium status of rats

A sensitive and valid marker to assess magnesium (Mg) status in humans is not available. The kinetically determined exchangeable pool masses have been used for other minerals, such as zinc and selenium, as markers of whole-body mineral status. To evaluate the validity of this relationship for Mg, we measured the exchangeable pools of Mg in rats over a range of magnesium dietary intakes. Rats weighing approximately 170 g were fed a control diet (500 mg Mg/kg), a marginally Mg-deficient diet (200 mg/kg) or a severely Mg-deficient diet (60 mg Mg/kg) for 2 wk. Subsequently, rats were administered an intravenous injection of (25)Mg, and the plasma (25)Mg disappearance curve was followed for the next 7 d. The following two methods were employed to analyze the exchangeable pools of Mg: 1) formal compartmental modeling and 2) a simplified determination of the total mass of the rapidly exchangeable Mg pool (EMgP). The mass of the three exchangeable pools (two extracellular pools and one intracellular pool) determined by compartmental analysis decreased in proportion to dietary Mg intake. EMgP, the combined pools of Mg that exchange with the plasma Mg within 48 h, decreased significantly as dietary Mg was lowered. It was positively correlated with conventional markers of Mg status (total Mg in plasma, erythrocyte and tibia Mg levels). Compartmental analysis assesses Mg exchangeable pools more accurately, but determination of EMgP is simpler and faster. Our findings demonstrate that the exchangeable pools of Mg constitute a good marker of Mg status in rats.     

Exchangeable zinc pool masses and turnover are maintained in healthy men with low zinc intakes

Previous studies suggest that rapidly exchanging zinc pools (EZP), thought to supply the zinc required by tissues, are smaller and turn over more rapidly in individuals with lower zinc intakes. We studied the effects of low dietary zinc (4.6 mg/d) on EZP mass and turnover in seven healthy men confined during a 20-wk clinical study. Supplements of 9.1 mg zinc were given during the 5-wk baseline and repletion periods, and placebos were given during a 10-wk zinc-restriction period. Stable 70Zn tracers were administered intravenously at the end of baseline, 3 and 10 wk after the start of zinc restriction and at the end of repletion. Multiple plasma samples were collected over an 8-d period after tracer administration. 70Zn:66Zn ratios were measured using inductively coupled plasma mass spectrometry, and tracer-tracee data were analyzed by compartmental modeling. Activities of the zinc-dependent enzymes, alkaline phosphatase and 5'nucleotidase, were unchanged during the study. There were no significant changes in EZP masses or kinetic parameters. A three-compartment model indicated that the masses of plasma zinc and total EZP averaged 3.25 +/- 0.58 and 147.8 +/- 33.2 mg, respectively, at the four time points studied. Plasma zinc mass turned over at an average of 5.3 times per hour. There was an 11% reduction (P = 0.06) in plasma zinc flux 3 wk after the start of the low zinc diet period, but it returned to baseline values after 10 wk of zinc restriction. The results suggest that total EZP mass is maintained when dietary zinc is reduced to 4.6 mg/d over a 10-wk period.     

Utilization of magnesium during hypokinesia and magnesium supplementation in healthy subjects

ObjectiveThe incompleteness of electrolyte utilization during hypokinesia and electrolyte supplementation is the defining factor of electrolyte metabolic changes, yet the effect of electrolyte supplementation and HK upon electrolyte utilization is poorly understood. To determine the influence of magnesium (Mg²⁺) supplementation and hypokinesia (diminished movement) on magnesium utilization, we investigated the use of Mg²⁺ supplementation to establish its effect upon muscle Mg²⁺ content and Mg2²⁺ losses.MethodsThis study was conducted in 40 physically healthy male volunteers during a pre-experimental period of 30 d and an experimental period of 364 d. Subjects were equally divided into four groups: unsupplemented control subjects (UCSs), unsupplemented experimental subjects (UESs), supplemented control subjects (SCSs), and supplemented experimental subjects (SESs). A daily supplementation of 3.0 mmol of magnesium-chloride per kilogram of body weight was given to subjects in the SCS and SES groups.ResultsMuscle Mg²⁺ content decreased (P < 0.05) and plasma Mg²⁺ concentration and Mg²⁺ loss in urine and feces increased (P < 0.05) in the SES and UES groups compared with their pre-experimental levels and values in their respective control groups (SCS and UCS). Muscle Mg²⁺ content decreased more (P < 0.05) and plasma Mg²⁺ concentration and Mg²⁺ loss in urine and feces increased more (P < 0.05) in the SES group than in the UES group.The muscle Mg²⁺ content and plasma Mg²⁺ level and Mg²⁺ losses did not change in the control groups.ConclusionDaily Mg²⁺ supplementation during prolonged hypokinesia decreases more muscle Mg²⁺ content and Mg²⁺-deficient muscle increases more Mg²⁺ loss in healthy subjects indicating lower Mg²⁺ utilization with than without Mg²⁺ supplementation.     

Long-term moderate zinc supplementation increases exchangeable zinc pool masses in late-middle-aged men: the Zenith Study

BACKGROUND: Zinc supplementation may be beneficial for health. Assessing exchangeable zinc pools may be a useful approach to evaluate zinc status. OBJECTIVE: We evaluated the effects of long-term supplementation with 2 moderate doses of zinc on the mass of exchangeable zinc pools. DESIGN: Three groups of healthy, late-middle-aged men (n = 16 per group) participated in a stable-isotope zinc kinetic study after 6 mo of daily supplementation with 0 (placebo), 15, or 30 mg Zn. At the end of the supplementation period, each subject received an intravenous injection of 0.89 mg (70)Zn, and the plasma zinc disappearance curve was monitored for the next 10 d. Two approaches were used to determine the characteristics of the exchangeable zinc pools: 1) formal 3-compartmental modeling and 2) a simplified determination of the total mass of the rapidly exchangeable zinc pool (EZP). RESULTS: In the placebo group, the exchangeable zinc pool masses for the 3 considered pools were as follows: 2.15, 12.7, and 100.5 mg Zn. The rapidly exchangeable zinc pool mass in the placebo group was 143 mg Zn. Zinc supplementation significantly increased the exchangeable zinc pool masses regardless of the approach used to determine these pools. In addition, these data confirm that exchangeable zinc pool masses correlate positively with total zinc intake and negatively with subject age and do not correlate with plasma zinc concentrations. CONCLUSION: Our data show that long-term supplementation with 2 moderate doses of zinc is an efficient way to increase exchangeable zinc pool masses in late-middle-aged men.     

Meal effect on magnesium bioavailability from mineral water in healthy women.

BACKGROUND: Magnesium intakes in many industrialized countries are below recommended daily allowances. Magnesium-rich mineral water may contribute to coverage of magnesium requirements by providing significant amounts of natural, energy-free, bioavailable magnesium. OBJECTIVE: The objectives were to determine magnesium bioavailability from magnesium-rich (110 mg/L) mineral water in healthy subjects when consumed alone and to evaluate the effect of simultaneous meal consumption. DESIGN: Magnesium bioavailability was measured in 10 healthy women with the use of a crossover design. Stable magnesium isotopes ((25)Mg and (26)Mg) were administered orally with mineral water, which was consumed with or without a meal. Apparent magnesium absorption was determined by fecal monitoring, and magnesium retention was determined from urinary excretion of magnesium isotopes. RESULTS: The mean (+/-SD) magnesium absorption from mineral water consumed alone was 45.7 +/- 4.6% (range: 40.2-55.5%) and was significantly greater (P = 0.0001) when it was consumed with a meal (52.3 +/- 3.9%; 46.2-60.2%), a relative difference of 14.4%. Magnesium retention also was significantly greater (P = 0.0004) when mineral water was consumed with a meal (41.5 +/- 4.2%; 35.2-50.6%) than when consumed alone (37.4 +/- 4.0%; 33.1-47.0%), a relative difference of 11.0%. CONCLUSIONS: In healthy young women, approximately 50% of the magnesium from magnesium-rich mineral water was absorbed when consumed alone. Magnesium bioavailability from mineral water is enhanced when the water is consumed with a meal, perhaps because of a slower gastrointestinal transit time, the presence of digestion products from the meal, or both. Regular consumption of magnesium-rich mineral water could make a valuable contribution to magnesium requirements.     

Dose-response effects of fish-oil supplementation in healthy volunteers

We performed a randomized, controlled study on the dose-response effects of daily supplementation of 1.5, 3, and 6 g of the marine fatty acids eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) as their ethyl esters for 12 wk in 45 healthy normotriglyceridemic male volunteers. Significant dose-related increases of the n-3 fatty acids 20:5, 22:5, and 22:6 in plasma phospholipids (p less than 0.0001) were found, corresponding roughly to decreases of the n-6 fatty acids 18:2 and 20:4 (p less than 0.001). Serum triglycerides and HDL3-cholesterol concentrations showed a dose-dependent reduction (p less than 0.05) and HDL2 cholesterol increased (p less than 0.05). Results for 3 and 6 g n-3 fatty acids were similar. No dose-dependent effects were observed in the VLDL-, LDL-, and total HDL-cholesterol subfractions; blood pressure; bleeding time; erythrocyte deformability; or capacity of polymorphonuclear leukocytes to kill Staphylococcus aureus. This study indicates that 3 g n-3 ethyl ester fatty acids appears to be the appropriate supplementation dose in humans, at least regarding lipid-profile changes and the ability to incorporate such fatty acids in the plasma phospholipids.     

Betaine supplementation lowers plasma homocysteine in healthy men and women

Elevated levels of plasma total homocysteine are associated with a higher risk of cardiovascular disease. Betaine and 5-methyltetrahydrofolate can remethylate homocysteine into methionine via independent reactions. We determined the effect of daily betaine supplementation, compared with both folic acid and placebo, on plasma concentrations of total homocysteine after an overnight fast and after methionine loading in men and women with mildly elevated homocysteine. Groups of twelve subjects ingested 6 g betaine, 800 micro g folic acid with 6 g placebo or 6 g placebo each day for 6 wk. A methionine-loading test (i.e., ingestion of 100 mg L-methionine/kg body mass) was performed before and after 6 wk of supplementation. Fasting plasma homocysteine decreased by 1.8 micro mol/L (95% confidence interval [CI]: -3.6, 0.0, P < 0.05) in the betaine group and by 2.7 micro mol/L (95% CI: -4.5, -0.9, P < 0.05) in the folic acid group. These changes are relative to the change in the placebo group, in which fasting plasma homocysteine rose by 0.5 micro mol/L. Furthermore, betaine suppressed the total area under the plasma homocysteine-time curve after methionine loading by 221 micro mol. 24 h/L (95% CI: -425, -16, P < 0.05) compared with placebo, whereas folic acid had no effect. In conclusion, betaine appears to be highly effective in preventing a rise in plasma homocysteine concentration after methionine intake in subjects with mildly elevated homocysteine. It is not known whether this potential of betaine to "stabilize" circulating homocysteine concentrations lowers the risk of cardiovascular disease.     

Urinary calcium and magnesium excretion by women in response to short-term calcium supplementation

Two hundred sixteen women (34–69 years) participated in a clinical trial to study the short-term (14 days) effects of calcium supplementation (1000 mg extra calcium given as oyster shell calcium) on urinary calcium and magnesium excretion. Before supplementation the women consumed an average of 879 mg Ca/day in self-selected diets; during supplementation they consumed approximately 1915 mg Ca/day (diet and supplement). The women excreted significantly more calcium in the urine during the supplementation period than initially (114 vs. 149 mg Ca/day) but this increase accounted for only 3.4% of the supplemental calcium. Approximately 24% of the women did not respond to the calcium supplements; they excreted less or equal amounts of urinary calcium in response to calcium supplementation. Hypercalciuria (>250 mg Ca/day) was observed in 3% of the women prior to supplementation and 7% of the women during calcium supplementation. Calcium supplementation had no effect on urinary magnesium excretion.     

Metabolic and hemodynamic effects of magnesium supplementation in patients with essential hypertension

The effect of magnesium supplementation on blood pressure, erythrocyte cation metabolism, and serum lipids was evaluated in 13 patients with mild hypertension. After randomization and a 3-wk placebo run-in period, seven patients received 40 mmol Mg aspartate (20 mmol elemental Mg twice daily) and six received placebo for 3 mo. In comparison with placebo treatment, magnesium aspartate therapy had no effect on blood pressure, lipid concentrations, or erythrocyte cation metabolism. These results demonstrate that in magnesium-repleted hypertensive subjects, magnesium supplementation does not affect blood pressure or lipids probably because magnesium has no effect on cellular cation metabolism in magnesium-replete individuals.     

Effect of magnesium supplementation on strength training in humans.

This study investigated the effects of dietary magnesium (Mg) on strength development during a double-blind, 7-week strength training program in 26 untrained subjects (14 = control, C and 12 = Mg supplemented, M), 18-30 years old. Subjects' 3-day diet records were analyzed and Mg content was calculated. C received a placebo and M received a supplement (Mg oxide) to bring Mg intake, including diet, to 8 mg/kg body weight/day. Body composition was assessed with bioelectrical impedance. Pre and post quadriceps torque (T) measurements were made with an Orthotron at 120 deg/sec. Each subject performed three sets of 10 reps, leg press and leg extension, three times/week. Both groups gained strength, however, results indicated a significant (p less than 0.05) increase for the M group compared to the C group in absolute T, relative T adjusted for body weight (T/BWT), and relative T adjusted for lean body mass (T/LBM) when pre values were used as the covariate. M was consistently greater than C (T: 211 vs 174 Nm; T/BWT: 3.07 vs 2.58 Nm/kg; T/LBM: 3.84 vs 3.36 Nm/kg). Conclusion: Significant differences in T gains after strength training were demonstrated in M vs C. Mg's role may be at the ribosomal level in protein synthesis.     

Effect of magnesium supplementation on strength training in humans.

This study investigated the effects of dietary magnesium (Mg) on strength development during a double-blind, 7-week strength training program in 26 untrained subjects (14 = control, C and 12 = Mg supplemented, M), 18-30 years old. Subjects' 3-day diet records were analyzed and Mg content was calculated. C received a placebo and M received a supplement (Mg oxide) to bring Mg intake, including diet, to 8 mg/kg body weight/day. Body composition was assessed with bioelectrical impedance. Pre and post quadriceps torque (T) measurements were made with an Orthotron at 120 deg/sec. Each subject performed three sets of 10 reps, leg press and leg extension, three times/week. Both groups gained strength, however, results indicated a significant (p less than 0.05) increase for the M group compared to the C group in absolute T, relative T adjusted for body weight (T/BWT), and relative T adjusted for lean body mass (T/LBM) when pre values were used as the covariate. M was consistently greater than C (T: 211 vs 174 Nm; T/BWT: 3.07 vs 2.58 Nm/kg; T/LBM: 3.84 vs 3.36 Nm/kg). Conclusion: Significant differences in T gains after strength training were demonstrated in M vs C. Mg's role may be at the ribosomal level in protein synthesis.     

The effect of magnesium supplementation on biochemical markers of bone metabolism or blood pressure in healthy young adult females.

OBJECTIVES: To investigate the effects of increasing Mg intakes, above the usual dietary intake, on blood pressure and on biomarkers of bone metabolism in healthy young adult females. DESIGN: A double-blind, placebo-controlled, randomised crossover Mg intervention trial. SETTING: The study was conducted in the Department of Nutrition, University College, Cork, Ireland. SUBJECTS: Twenty-six healthy (normotensive) adult females aged 20-28 y were recruited from University College, Cork. INTERVENTION: Subjects were randomly assigned to their self-selected diets (approximately 11 mmol Mg/d) or their self-selected diet with a 10 mmol/d Mg supplement as Mg(OH)2 (approximately 22 mmol Mg/d) for 28 d followed by cross-over to the alternative diet for a further 28 d. During each dietary period urines (last 3 d) and blood (morning of 27 d) were collected and blood pressure was measured on the morning of 28 d. RESULTS: Increasing Mg intake from the usual level (11 mmol/d) to 22 mmol/d for 28d increased urinary excretion of Mg by 36% and erythrocyte Mg content by 5% but had no effect on serum Mg, Ca, PTH, osteocalcin or bone-specific alkaline phosphatase (biomarkers of bone formation), urinary pyridinium crosslinks of collagen (biomarkers of bone resorption), or on blood pressure. CONCLUSION: Increasing the mean Mg intake in healthy young adult females above the usual dietary intake, which is currently above the US EAR (estimated average requirement), but below the US RDA for Mg, does not affect blood pressure or the rate of bone turnover.     

Metabolic effects of mental stress during over- and underfeeding in healthy women.

OBJECTIVE: To assess the short-term consequences of carbohydrate or fat overfeeding or of food restriction on the metabolic effects of mental stress in healthy lean women. RESEARCH METHODS AND PROCEDURES: The effects of a sympathetic activation elicited by mental stress were evaluated in a group of healthy women after standardized isocaloric feeding (ISO) or after a 3-day overfeeding with 40% excess calories as either carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). Oxygen consumption rate (VO(2)) was measured as an index of energy expenditure, and subcutaneous glycerol concentrations were monitored with microdialysis. The same measurements were performed in another group of healthy women after ISO and after a 3-day period of underfeeding with a protein sparing modified fast (UF). RESULTS: In all conditions, mental stress significantly increased heart rate, blood pressure, plasma norepinephrine and epinephrine concentrations, and VO(2), and produced a nonsignificant increase in subcutaneous glycerol concentrations. CHO OF and FAT OF did not alter the effects of mental stress on VO(2) and subcutaneous glycerol concentrations. In contrast, UF increased basal VO(2) but significantly reduced its stimulation by mental stress. UF also enhanced the increase in subcutaneous glycerol concentrations during mental stress. DISCUSSION: UF reduces the stimulation of energy expenditure and enhances lipolysis during sympathetic activation. These adaptations may be involved in mobilization of endogenous fat while limiting weight loss. In contrast, short-term overfeeding fails to alter the sympathetic control of energy expenditure and lipolysis.     

The association between magnesium intake and fasting insulin concentration in healthy middle-aged women

OBJECTIVE: We assessed the association between magnesium intake and fasting insulin levels in a large cohort of women. METHODS: Female nurses free of diabetes, cardiovascular diseases and cancer from the Nurses Health Study provided blood samples between 1989-1990. We selected a sub-sample of 219 women for this analysis. Magnesium intake was assessed by a food frequency questionnaire in 1990 and categorized into quartiles. Cross-sectional geometric means of fasting insulin concentrations by quartiles of magnesium intake were obtained with Generalized Linear Model and adjusted for several risk factors and lifestyle characteristics. RESULTS: After adjustment for age, body mass index (BMI), total energy, physical activity, hours per week spent sitting outside work, alcohol intake, smoking, and family history of diabetes, magnesium intake was inversely associated with fasting insulin concentration. The multivariate adjusted geometric mean for women in the lowest quartile of magnesium intake was 11.0 microU/mL and 9.3 microU/mL among those in the highest quartile of magnesium intake (p for trend = 0.04). The inverse association remained when we considered magnesium from only food sources. CONCLUSION: Higher magnesium intake is associated with lower fasting insulin concentrations among women without diabetes. Because lower fasting insulin concentrations generally reflect greater insulin sensitivity, these findings provide a mechanism through which higher dietary magnesium intake may reduce the risk of developing type 2 diabetes mellitus.     

The effects of conjugated linoleic acid supplementation on immune function in healthy volunteers

OBJECTIVE: To assess the effects of dietary supplementation using two isomeric blends of conjugated linoleic acid (CLA) on immune function in healthy human volunteers. DESIGN: Double-blind, randomised, placebo-controlled intervention trial. SUBJECTS AND INTERVENTION: A total of 55 healthy volunteers (n=20 males, n=35 females) were randomised into one of three study groups who received 3 g/day of a fatty acid blend containing a 50:50 cis-9, trans-11: trans-10, cis-12 CLA isomer blend (2 g CLA), and 80:20 cis-9, trans-11: trans-10, cis-12 (80:20) CLA isomer blend (1.76 g CLA) or linoleic acid (control, 2 g linoleic acid) for 8 weeks. RESULTS: Supplementation with the 80:20 CLA isomer blend significantly (P< or =0.05) enhanced PHA-induced lymphocyte proliferation. CLA decreased basal interleukin (IL)-2 secretion (P< or =0.01) and increased PHA-induced IL-2 and tumor necrosis factor alpha (TNF(alpha)) production (P< or =0.01). However, these effects were not solely attributable to CLA as similar results were observed with linoleic acid. CLA supplementation had no significant effect on peripheral blood mononuclear cells IL-4 production, or on serum-soluble intercellular adhesion molecule-1 (sICAM-1) or plasma prostaglandin E2 (PGE2) or leukotreine B4 (LTB4) concentrations. CONCLUSIONS: This study shows that CLA supplementation had a minimal effect on the markers of human immune function. Furthermore, supplementation with CLA had no immunological benefit compared with linoleic acid.     

Exchangeable zinc pool size at birth is smaller in small-for-gestational-age than in appropriate-for-gestational-age preterm infants

BACKGROUND: Small-for-gestational-age (SGA) infants are susceptible to postnatal zinc deficiency, but whether this susceptibility is due to intrauterine factors or to high postnatal growth requirements is unknown. OBJECTIVE: We hypothesized that the size of the exchangeable zinc pool (EZP), which reflects metabolically available zinc, would be smaller in SGA than in appropriate-for-gestational-age (AGA) infants born prematurely. DESIGN: Intravenous 70Zn (45 microg/kg) was administered to 10 SGA infants (8 boys) with a mean (+/-SD) gestational age of 33.3 +/- 1.8 wk and to 11 AGA infants (8 boys) with a mean (+/-SD) gestational age of 32.4 +/- 1.2 wk within 24 h of birth. The EZP was determined from isotope enrichment in spot urine collections on days 3-7. RESULTS: The mean birth weight of the SGA infants was 1.30 +/- 0.2 kg and of the AGA infants was 1.84 +/- 0.3 kg (P = 0.0001). The EZP size was significantly smaller in the SGA than in the AGA infants on an absolute basis (13.3 +/- 2.8 and 25.2 +/- 8.1 mg; P = 0.0002) and relative to body weight (10.3 +/- 2.5 and 13.9 +/- 4.5 mg/kg; P = 0.02). The difference remained significant after adjustment for gestational age and birth weight. CONCLUSION: These data provide evidence for differential zinc status at birth between SGA and AGA infants born prematurely at similar stages of gestation and offer at least a partial explanation for the reported benefits of postnatal zinc supplementation.     

Effect of supplementation with fortified olive oil on biochemical markers of bone turnover in healthy women

Osteocalcin (OC) is a bone Gla protein synthesized by osteoblasts which have a high affinity for calcium. To adequately carboxylate OC to form carboxylated OC (cOC), the osteoblasts require sufficient vitamin K. If vitamin K is deficient, under-carboxylated OC (ucOC) is produced. The ratio between ucOC and cOC (UCR) as well as the levels of circulating ucOC are used as indicators of the vitamin K status of bone. The aim of the present study was to compare the vitamin K status of bone by measuring the plasma levels of ucOC and UCR in healthy adult women before and after 3 weeks of oral supplementation with 20 ml/day Petrini Plus extra virgin olive oil. Petrini Plus is an organic olive oil enriched with vitamins D₃, K₁ and B₆. Enrolled in the study were 15 healthy female volunteers (aged 25–40 years). Plasma levels of ucOC and cOC were measured by ELISA. ucOC was found to be reduced and UCR was reduced by 44% after Petrini Plus olive oil supplementation. Petrini Plus extra virgin olive oil might therefore be useful for bone protection as it was able to counteract bone loss in healthy volunteers.     

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.