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Effect of Chromium Supplementation and Exercise on Body Composition, Resting Metabolic Rate and Selected Biochemical Parameters in Moderately Obese Women Following an Exercise Program

Department of Nutrition, University of Massachusetts, Amherst, Massachusetts (S.L.V., H.-W.H., K.L.)
Faculty of Medicine, School of Nutrition, University of Buenos Aires, Buenos Aires, Argentina (I.I.L.)

Address reprint requests to: Stella L. Volpe, Ph.D., R.D., Department of Nutrition, 210 Chenoweth Lab, 100 Holdsworth Way, University of Massachusetts, Amherst, MA 01003. E-mail: volpe{at}nutrition.umass.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Objective: To investigate the effect of chromium picolinate (CP) supplementation on body composition, resting metabolic rate (RMR), selected biochemical parameters and iron and zinc status in moderately obese women participating in a 12-week exercise program.

Methods: Forty-four women, 27 to 51 years of age, were randomly assigned to two groups based on their body mass index. Subjects received either 400 µg/day of chromium as a CP supplement or a placebo in double-blind fashion and participated in a supervised weight-training and walking program two days per week for 12 weeks. Body composition and RMR were measured at baseline, 6 and 12 weeks. Selected biochemical parameters and iron and zinc status were measured at baseline and 12 weeks.

Results: Body composition and RMR were not significantly changed by CP supplementation. No significant differences in fasting plasma glucose, serum insulin, plasma glucagon, serum C-peptide and serum lipid concentrations or in iron and zinc indices were found between the two groups over time. Serum total cholesterol concentration significantly decreased (p = 0.0016) over time for all subjects combined, probably as a result of the exercise training. Exercise training significantly reduced total iron binding capacity (TIBC) by 3% for all subjects combined (p = 0.0011).

Conclusions: Twelve weeks of 400 µg/day of chromium as a CP supplement did not significantly affect body composition, RMR, plasma glucose, serum insulin, plasma glucagon, serum C-peptide and serum lipid concentrations or iron and zinc indices in moderately obese women placed on an exercise program. The changes in serum total cholesterol levels and TIBC were a result of the exercise program.

Key words: chromium, body composition, glucose tolerance, iron, obese women, zinc

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Chromium, an essential trace element required for normal carbohydrate, protein and fat metabolism [1], may improve impaired glucose tolerance [2–4], decrease elevated blood lipid concentrations [5–7] and result in weight loss and improved body composition [8–11] in some individuals, but results have been equivocal. As the active component of chromodulin, chromium has been suggested to potentiate the action of insulin, possibly by increasing insulin binding, insulin binding receptor number, improving insulin internalization and increasing insulin sensitivity [12,13]. Signs and symptoms of chromium deficiency in mammals include glycosuria, neuropathy, encephalopathy, decreased insulin binding and receptor number and impaired immune response [14].

While much of the research on the role of nutritional chromium has focused on its effects on blood glucose and lipid concentrations, popular interest has centered on chromium as a means to increase muscle mass and reduce body fat in obese individuals. The suggested beneficial effect of chromium on body composition was based on the rationale that chromium potentiates the functions of insulin. Insulin functions in transporting glucose and amino acids into muscle cells, regulating protein metabolism and synthesis. Therefore, improvements in insulin utilization should theoretically lead to increased muscle mass and reduced body fat [15]. The link between these contradictory changes in body composition may be due to chromodulin’s ability to potentiate insulin’s effects on converting glucose to carbon dioxide or lipid [13,16]. However, the effects of chromium picolinate (CP) supplementation on lean body mass (LBM), percent body fat and body weight are equivocal. Evans [8] showed significantly increased LBM and decreased percent body fat in young males who supplemented with 200 µg of chromium/day as CP and participated in a resistance training program. However, skinfold thickness measurements, which have a high rate of error, were used to assess body composition. In contrast, Clancy et al. [17] did not observe any significant changes in body composition following supplementation with 200 µg of chromium/day as CP in football players on a weight training regimen. Under water weighing, considered the gold standard for body composition analysis, was used to assess LBM and percent body fat in their study. Several studies in untrained males also found no beneficial effects of CP supplementation on body composition [18,19].

With the increasing interest in chromium supplementation for improving glucose tolerance and body composition, the adverse affects of chromium supplementation in humans has been somewhat overlooked. It has been shown in vitro and in animal studies in vivo, that chromium and iron compete for the same binding site on transferrin [20,21]. Lukaski et al. [19] demonstrated that supplementation with 172 µg of chromium/day as CP and 182 µg of chromium/day as chromium chloride combined with a weight training program significantly reduced urinary iron excretion compared with a placebo in male subjects. Thus, chromium supplementation may result in reducing iron status, as the body tends to conserve iron by decreasing urinary iron loss [19]. In addition, because plasma zinc and iron compete for the same binding site, chromium could potentially impair zinc metabolism.

Therefore, the purpose of this study was to examine the effects of supplementation with 400 µg of chromium/day as chromium picolinate on body composition, resting metabolic rate (RMR), plasma glucose, serum insulin, serum C-peptide, plasma glucagon and serum lipid concentrations, iron indices and plasma zinc concentrations in sedentary, moderately obese women who participated in a 12-week exercise program. Plasma, red blood cell and urinary chromium concentrations were also assessed in order to monitor changes of chromium status after CP supplementation.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Subjects
Forty-four female subjects, with a body mass index (BMI) between 27 to 41, initially began the study. Subjects were between 27 to 51 years of age, pre-menopausal, sedentary, not taking any dietary supplements, not taking any vitamin or mineral supplements containing chromium (but could take supplements containing other vitamins and minerals), not on a weight-loss program, not taking any weight loss supplements, non-smoking and with no history of chronic diseases or recent acute illness. All subjects gave written and verbal informed consent, completed a medical history questionnaire and were required to obtain permission from their physician prior to participation. Subjects were asked not to alter their dietary habits during the course of the study, with the exception of taking the supplement or the placebo. Furthermore, subjects were asked to adhere to the supervised exercise program and not to perform any additional exercise. This study was first approved by the University of Massachusetts Human Subjects Committee.

Experimental Design
This was a double-blind, placebo-controlled study conducted for 12 weeks. Twelve weeks was chosen because other chromium supplementation studies, some with fewer subjects and lower chromium supplementation levels, were conducted for 12 weeks or less [8,9,15,19].

Forty-four free-living females were assigned, in a stratified randomized manner based on their BMI, to one of two groups: CP supplementation or placebo. The subjects received gel capsules containing either 400 µg of CP (400 µg of CP, with dicalcium phosphate as filler, and stearic acid as a lubricant) (Nutrition21, San Diego, CA) or identical looking placebo capsules (dicalcium phosphate as filler, stearic acid as a lubricant and natural pink colorant; no chromium was contained within the placebo capsules) (Nutrition21, San Diego, CA) at the beginning of the study. The chromium content of the capsules was analyzed by Nutrition21 (San Diego, CA) and contained 400 µg of chromium as chromium picolinate. Because subjects were obese, we chose to administer above the Dietary Reference Intakes (DRI) of 25 µg/day [22] and the former Estimated Safe and Daily Dietary Intake (ESADDI) of 50 to 200 µg/day [23] in order to assess if higher CP intakes would elicit significant body composition changes. The subjects were asked to take their capsules every morning during the entire 12-week study period. Capsule compliance was monitored by asking subjects how many capsules were left in their packet as well as assessment of plasma and red blood cell chromium concentrations and 24-hour urinary chromium analyses.

Measurements
Due to difficulty with scheduling subjects for data collection, all subjects were assessed for pre-test measurements within approximately two months prior to beginning the study. After stratified randomization, we staggered the subjects into groups to begin the supplementation and exercise regimen; therefore, when we assessed them at post-test, there was, on average, two weeks’ lag time from completion of the study and post-test assessment.

Body Composition
Body composition was measured at pre-, mid- and post-test by hydrostatic weighing as described by McArdle et al. [24]. Prior to underwater weighing, vital capacity (VC) was measured using the metabolic cart (Cardio₂Max metabolic cart, Medical Graphics Corporation, St. Paul, MN). Residual lung volume (RLV) was then calculated from VC as RLV = 0.28*VC [25]. Body weight in air was measured before entering the water tank on a balance-beam scale accurate to ±0.5 kg while the subject was wearing a swim suit. Each subject performed the weighing procedure for at least ten trials. The three highest trials were averaged and used to compute body density, percent body fat, fat mass and LBM using Siri’s equation [26]: percent body fat = (4.95/density) - 4.5. Percent coefficient of variation (%CV) for hydrostatic weighing = 7.3% to 8.3%.

Circumferences (cm) of the waist and hips were measured three times consecutively at each site. A tape measure was firmly applied to all areas without compressing the skin. The average of each site was calculated. Measurements that were greater than 2 cm different were not used and a re-trial was performed; thus, there were always three measurements averaged per site.

Resting Metabolic Rate
RMR was measured at pre-, mid- and post-test. RMR was measured after a 12-hour fast while each subject was lying comfortably in a reclining chair in a room with comfortable temperature. Prior to assessing RMR, each subject rested approximately 10 to 15 minutes. RMR (kcal/day) was measured for 30 minutes using a dilution hood connected to a metabolic cart (Cardio₂Max metabolic cart, Medical Graphics Corporation, St. Paul, MN) (%CV = 10.8% to 12.2%).

Blood Collection and Analyses
A total of 50 mL of blood was drawn from each subject by a registered nurse at pre- and post-test: in the fasted state (30 mL), one hour post-meal consumption (10 mL) and two hours post-meal consumption (10 mL). Subjects were given a 300 kilocalorie (kcal) meal, high in sugar, provided by the researchers in order to assess the effects of a meal high in sugar on blood chromium, zinc, glucose, insulin, glucagon and C-peptide concentrations. The meal included juice (180 mL), fruit in heavy syrup (120 mL), toasted whole wheat bread (one slice) and grape jelly (15 g) (Table 1). Monovette (Sarstedt Inc., Princeton, NJ) mineral-free tubes were used for blood collection of plasma (lithium heparin) and serum. In addition, Monovette (Sarstedt Inc., Princeton, NJ) needles were used to draw the blood.

Blood Glucose, Insulin, Glucagon and C-Peptide Analyses.
Plasma glucose concentration (%CV = 1.0 to 1.5%) was measured by hexokinase phosphorylation (Hitachi 912, Japan) at University Health Services, University of Massachusetts, Amherst. Serum insulin (%CV = 3.0 to 4.5%), plasma glucagon (%CV = 3.2% to 6.5%) and serum C-peptide (%CV = 3.0% to 3.2%) concentrations were measured by radioimmunoassay (RIA) (Diagnostic Products, Corp., Los Angeles, CA). The radioactivity in each sample was determined using a gamma counter (Beckman gamma 4000 counting system, Beckman Instruments, Inc., Fullerton, CA). Serum C-peptide was measured for two reasons: it has a positive correlation with insulin concentrations, and it assesses pancreatic beta-cell secretory function [27].

Blood Lipid Analyses.
Serum total cholesterol (TC) (%CV = 1.2% to 1.7%), serum low density lipoprotein cholesterol (LDL-C) (%CV = 2.4% to 3.3%), serum high density lipoprotein cholesterol (HDL-C) (%CV = 2.2% to 3.7%), and serum triacylglycerol (TG) (%CV = 1.4% to 3.3%) concentrations were determined by enzymatic kits (Sigma Diagnostic Co., St. Louis, MO). A spectrophotometer (Beckman Instruments, Inc., Fullerton, CA) was used for analysis at 500 nanometers for TC, LDL-C and HDL-C and 540 nanometers for TG.

Blood Iron Analyses.
SmithKline Beecham Laboratory (Waltham, MA) analyzed the serum for the respective iron indices as follows: serum iron (%CV = 0.5% to 1.5%) and TIBC (%CV = 0.5% to 1.0%) were measured by spectrophotometry [28]; transferrin saturation (there is no %CV for transferrin saturation because it is a calculated value) was calculated from serum iron and TIBC [29]; serum ferritin (%CV = 6.7% to 7.0%) concentration was measured using RIA [30].

Blood Zinc Analysis.
Plasma zinc concentrations (%CV = 8.4% to 19.4%) were measured at fasting and one and two hours postprandially with an atomic absorption spectrophotometer (AAS) (Perkin Elmer 2380, Norwalk, CT). Plasma samples were diluted eightfold with 5% nitric acid. Zinc standards, prepared from zinc reference solution (Fisher Scientific, Pittsburgh, PA) in 5% nitric acid, were used as an internal control.

Blood Chromium Analysis.
Plasma chromium (%CV = 75% to 142%) and red blood cell (RBC) chromium (%CV = 159% to 256%) concentrations were measured at fasting and one and two hours postprandially with an AAS-Graphite Furnace (AAS-GF) (Perkin-Elmer 4100 ZL, Perkin-Elmer, Norwalk, CT). Note the exceptionally high %CV for both plasma and RBC chromium concentrations. This was a result of a combination of very low concentrations of chromium in plasma and RBC as well as a high degree of between-subject variation. Although the %CV’s were high, we observed increases in plasma chromium concentration in the CP group, as expected. The Perkin-Elmer 4100 ZL AAS was equipped with a longitudinal Zeeman background correction and a pyrolytically coated transversely heated graphite atomizer with an integrated L’vov platform. All measurements were conducted at 357.9 nm resonance line. Sample aliquots of 20 µL for plasma and RBC were delivered using the Perkin-Elmer AS-71 autosampler. Argon was used as the protective gas.

The needles (Sarstedt Inc., Princeton, NJ) used to draw blood were analyzed for chromium contamination by a Spectromass 2000 inductively coupled plasma-mass spectroscopy (ICP-MS) (Spectro Analytical Instruments, Fitchburg, MA). The needles analyzed were rinsed several times with saline to represent blood. Next, the saline solution was analyzed for chromium content and compared to blanks. The background equivalent concentration was analyzed to assess the lower limits of this approach.

Urine Collection and Analyses
At the end of each test day at pre-, mid- and post-test, acid-washed urine containers were distributed to the subjects for 24-hour urine collections. The 24-hour urine collections were weighed, aliquotted into acid-washed tubes and concentrated trace-element grade hydrochloric acid (Fisher Scientific, Pittsburgh, PA) was added to each sample to prevent leaching of minerals by the container. The sample tubes were then kept in a -80°C freezer until analyses. All samples were analyzed, in duplicate, for urinary iron (%CV = 80% to 184%) and urinary chromium (%CV = 49% to 66%) concentrations. Similar to blood chromium concentrations, both urinary iron and chromium concentrations had a high %CV. This again was a result of a combination of very low concentrations of urinary iron and chromium as well as a high degree of between-subject variation. Although the %CV’s were high, we observed increases in urinary chromium concentration in the CP group, as expected. Urinary sample analysis was similar to plasma and RBC analyses; however, sample aliquots of urine were delivered at 40 µL by the Perkin-Elmer AS-71 autosampler.

Urine samples were diluted 1:20 with distilled water prior to analysis. The chromium concentration was determined by AAS-GF (Perkin-Elmer 4100 ZL, Perkin-Elmer, Norwalk, CT). Twenty-four-hour urinary iron concentration was determined by AAS (Perkin-Elmer 703, Perkin-Elmer, Norwalk, CT) [31].

Dietary Intake
Nutrient intakes were assessed by three-day dietary records at pre-, mid- and post-test in order to monitor dietary patterns during the study. The dietary records included two weekdays and one weekend day. Subjects were instructed on how to report their dietary intakes properly and not alter their usual dietary habits for the duration of the study. The three-day dietary records were analyzed for total energy, carbohydrate, fat, protein, total dietary iron, absorbable iron, animal iron, zinc, calcium, vitamin C and dietary fiber using the University of Massachusetts Nutrient Data Bank (UMNDB). Dietary chromium intake was not analyzed by the UMNDB because of the lack of chromium reference data. However, estimation of dietary chromium was calculated on the basis of the estimated chromium concentration of the reported usual diet consumed in the United States, which is approximately 15 µg chromium/1000 kcal [32].

Training Protocol
All subjects participated in a 12-week supervised moderately-intense exercise program at an exercise facility on the University of Massachusetts, Amherst campus. Subjects exercised two days per week, one hour per session. This frequency and duration were chosen to increase compliance and were sufficient to elicit a training response. Subjects performed 30 minutes of weightlifting and 30 minutes of moderately-intense walking. Prior to the program, the weightlifting workout was calculated from 60% of one-repetition maximum (1-RM). Subjects’ 1-RM was measured on each piece of weight-training equipment. Instruction on appropriate weight-training techniques was given; then, a warm-up of several repetitions at very low weights was performed by each subject. One-RM was recorded as the maximum amount of weight the subject could lift just once.

The weightlifting program consisted of two sets of 8 to 12 repetitions using the following isokinetic equipment: biceps curls, triceps press, chest press, latissimus dorsi pull down, leg curls, leg extension, calf raises, leg adduction and abduction. Training logs were reviewed weekly to increase the weight load, when necessary. Once subjects performed two sets of 12 repetitions, the weight load was increased by 10 pounds for each particular piece of equipment. Therefore, this was a progressive weight training program; exercise intensity was increased based on individual progress and represented a greater percentage of 1-RM than the initial 60%. Strength, which was recorded as 1-RM, was monitored at pre- and post-test for assessing the efficacy of the weight-training program.

Following the weight-training protocol, subjects performed a 30-minute walking regimen within their specified heart rate range ([220-age] x 60% to 80%); 60% to 80% represents a moderately intense aerobic exercise program [33]. Subjects were properly trained on how to take radial and carotid pulse for 10 seconds (then multiplied by six for the actual beat per minute). Pulse was recorded before walking, at ten-minute intervals while walking and five minutes post-walking.

Statistical Analyses
Data were analyzed with the Statistical Analysis Software (SAS version 6.12; SAS Institute, Inc, Cary, NC). A power estimation was calculated to determine sample size. A total of 40 subjects (20 per group) would have been required for 80% power. We initially had 44 subjects in this study and thus met the sample size necessary to detect statistical differences. A 2 x 3 factorial analysis of variance (ANOVA) for treatment (placebo and chromium supplementation) and time (pre-test, mid-test and post-test) with repeated measures over time was used to analyze body composition, RMR, urinary chromium, urinary iron, urinary creatinine and dietary data. A 2 x 2 factorial ANOVA for treatment (placebo and chromium supplementation) and time (pre-test and post-test) with repeated measures over time was used to analyze the serum and plasma biochemical data. Tukey’s post hoc test was performed when significant main effects or interactions occurred. The level of significance was set a priori at 0.05 for overall statistical analyses. Data are expressed as mean ± standard deviation (SD).

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Compliance
Thirty-seven of the initial 44 subjects (84%) completed this study. Sixteen subjects reported forgetting to take their capsules and 13 subjects missed exercise training; however, no subjects reported forgetting to take the capsules more than five days (average <3 days) during the study period. Furthermore, none of these subjects missed exercise training more than four times (average <3) during the entire study. Two subjects did have minor problems with their knees or ankles, so they were unable to perform all of the specified weight training exercises (e.g., leg extension and calf raises).

Anthropometric Parameters
Age, height, body weight and BMI of the chromium and placebo groups were not significantly different at baseline (Table 2).

View larger version (28K): [in this window] [in a new window]   Fig. 1. Resting metabolic rate (RMR) at pre-, mid- and post-test for the chromium and placebo groups. Values represent mean ± SD. Note: No significant differences within or between groups over time.

Pre- and post-test plasma chromium and RBC chromium concentrations are shown in Table 8. After 12 weeks of CP supplementation and exercise training, fasting plasma chromium concentration in the chromium group significantly increased ten-fold compared with pre-test values. At post-test, plasma chromium concentrations in the chromium group in the fasted state and two hours after a high carbohydrate meal were significantly higher than in the placebo group. However, plasma chromium concentration did not change in response to a high carbohydrate meal within either group at pre- or post-test. The RBC chromium concentration in the fasted state and one and two hours after a high carbohydrate meal were not significantly different within and between groups over time.

Daily urinary chromium concentrations at pre-, mid- and post-test for both groups are presented in Fig. 2. Urinary chromium concentrations were significantly elevated at mid-test (p < 0.05) in the chromium group and returned to near baseline at post-test. In addition, mid-test urinary chromium concentration in the chromium group was significantly higher than in the placebo group (p < 0.05).

View larger version (17K): [in this window] [in a new window]   Fig. 2. Urinary chromium levels at pre-, mid- and post-test for the chromium and placebo groups. Values expressed as Mean ± SD. *Significantly different from pre-test (p < 0.05). a,bValues in the same time-point with different letters are significantly different from one another (p < 0.05). Note: Average reported pre-supplementation range = 0.2 to 0.8 ppb (from [4] and [45]). Average reported post-supplementation range = 0.8 to 1.5 ppb (from [4]).

Because there is insufficient information on chromium in the database, a crude estimation of dietary chromium intake was calculated by multiplying the energy intakes at each time point by 15 µg chromium/1000 kcal on the basis of the estimated chromium concentration of the usual diet consumed in the United States [32]. The estimated dietary chromium intakes in the chromium and placebo groups ranged from 21 to 43 µg/day and 23 to 44 µg/day, respectively.

Strength Gains
The average of 1-RM values at pre- and post-test are presented in Table 10. There were no significant differences between groups; however, when all subjects were combined, there were significant increases in all strength measurements from pre- to post-test (p < 0.05) as a result of the weight training regimen. This demonstrates that the exercise program was effective.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

Body Composition
Although subjects in the chromium picolinate supplemented group experienced a greater loss in percent body fat than the placebo group, it was not statistically significant. However, when subjects were combined into one group, differences in percent body fat, LBM and fat mass were significantly different from pre-test values (p < 0.05), which were a result of the exercise program and not the CP supplementation. This observation is consistent with others [17–19,34]. Trent and Thieding-Cancel [34] reported no beneficial effects of supplementation with 400 µg/day of chromium as CP combined with aerobic exercise training on body composition in obese Navy personnel. A number of researchers [17–19,34] do not support chromium supplementation to positively alter body composition. Although several studies have demonstrated positive body composition alterations due to chromium supplementation [8,9], their study designs have been criticized.

Body Weight
In our study, body weight did not significantly change in response to either chromium supplementation or exercise training. Other researchers have attempted to investigate the effects of chromium supplementation on weight loss [10,11]. Grant et al. [11] reported that 400 µg/day of chromium picolinate without exercise training was contraindicated for weight loss in young, obese women because it caused significant weight gain in these subjects. However, supplementation of 400 µg/day of chromium nicotinate combined with exercise training resulted in more beneficial effects than exercise alone in weight loss and insulin response to an oral glucose load [11].

Resting Metabolic Rate
There were no significant differences in RMR between the chromium and placebo groups in our study; however, there was a trend for RMR to increase over time in both groups combined. Because the subjects were previously sedentary, 12 weeks of exercise may have resulted in an increase in RMR. Perhaps 12 weeks of intervention was not long enough to elicit a significant increase in RMR. In a study by Kaats et al. [10], 30 obese subjects given a combination of chromium picolinate, L-carnitine, ascorbic acid, pyridoxine, niacin, potassium, magnesium and L-lysine had an average increase in RMR of 21%. Chromium picolinate may have contributed to the increase in RMR; however, the results were confounded by the other nutrients provided. We did not demonstrate an effect of chromium picolinate supplementation on RMR.

Glucose Tolerance
Several studies have shown that some subjects with hypoglycemia, hyperglycemia and non-insulin-dependent diabetes mellitus (NIDDM) may respond to supplemental chromium [2–5,35]. However, individuals with normal glucose tolerance, adequate dietary chromium and good chromium status do not respond to supplemental chromium [4,35–37]. Anderson et al. [4] showed that glucose tolerance and circulating insulin and glucagon concentrations of subjects with marginally elevated blood glucose concentrations and consuming low-chromium-controlled diets were improved after they were supplemented with 200 µg/day of chromium as chromium chloride for five weeks. However, the control group with normal glucose concentration did not show any signs of chromium deficiency after the low-chromium diets and no changes after supplementation. The results presented in our study agree with these aforementioned investigations and are not surprising, because none of the moderately obese women in our study had ever been diagnosed with impaired glucose tolerance.

Serum Lipid Concentrations
We reported no significant differences in serum lipid levels as a result of the chromium picolinate supplementation. The decrease of TC concentration for all subjects may have been a result of the 12-week exercise program. Although an increase in serum HDL-C concentration would be expected as a result of the exercise training, it decreased; perhaps this was because body weight did not significantly decrease. Also, a 12-week exercise period is typically not long enough to elicit an increase in HDL-C levels. The lack of an effect of chromium supplementation on serum lipid concentrations has been shown in previous studies [2]. However, others have shown positive effects of chromium supplementation with respect to serum lipid concentrations [5–7]. The varying results of chromium’s impact on blood lipid concentrations may relate to the basal level of the serum lipid concentrations and subjects’ initial chromium status as well as glucose metabolism. In addition, the exercise regimen may have played a significant role on the beneficial changes in several experiments, including our study.

Iron Status
Although trivalent chromium has been determined as a potential inhibitor of iron metabolism, competing with iron by binding to transferrin (siderophilin) in rats and in vitro [20,21,38], the mechanism has not been determined in humans in vivo. In our study, iron indices were not affected by CP supplementation. Furthermore, dietary iron intakes were not significantly different between groups over time. Lukaski et al. [19] observed a weak tendency (p = 0.17) for transferrin saturation to decrease more in their CP supplemented group than in groups supplemented with chromium chloride or placebo. Furthermore, they reported a significantly lower urinary iron concentration in both chromium supplemented groups compared to the placebo group. TIBC was significantly decreased by 3% with exercise training in our study; this is in contrast to Lukaski et al. [19], who reported a 9% increase in TIBC, and similar to that reported by Campbell et al. [39], who found that hematological and iron indices were not affected by chromium supplementation in male subjects, 56 to 69 years of age, who consumed either 17.8 µmol/day of chromium picolinate or a placebo and participated in a high-intensity resistive training program for 12 weeks. Thus, depending on the dose and duration of chromium supplementation, iron metabolism may be adversely affected as a result of the body’s maintaining a normal iron status by preventing urinary iron loss [19].

It is possible that the mechanical stress on red blood cells and increased rate of intravascular hemolysis induced by the activation of large muscle mass by strength training alone may lead to an increased iron requirement [40]. The decrement in serum ferritin concentration in our study was not as significant as the finding of others [40]. The difference may have been due to different training programs and gender differences.

Zinc Status
Our findings on zinc status are consistent with Lukaski et al. [19]. We found no significant differences between groups over time. The significant variations we found between the fasted state and the post-prandial states in both groups are similar to those reported by Lowe et al. [41], who found a 13% and 18% decline in plasma zinc concentration following two different types of meals. The post-prandial decline in plasma zinc levels could be due to zinc uptake by the pancreas to facilitate the synthesis of digestive enzymes and by the liver where it is required for phosphorylation reactions [41].

Blood Chromium
Twelve weeks of CP supplementation had a significant effect on plasma chromium concentration, with an approximately tenfold increase in fasting levels in the chromium group. Our findings were similar to a three-month chromium chloride supplementation study (200 µg/day) that resulted in an approximately threefold increase in serum chromium concentration [37]. Nonetheless, the change in serum chromium concentration following chromium supplementation is suggested to be a reflection of higher chromium intake, but not a meaningful indicator of tissue chromium concentrations [14].

There are no acceptable indicators to assess chromium status because chromium concentrations in biological tissues and fluids do not reflect metabolically active chromium pools in the body [14]. In addition, there are limited reports of actual chromium concentrations in serum/plasma, whole blood, erythrocytes and urine due to methodological difficulties [29]. The best method to diagnose marginal chromium deficiency is based on an improvement in glucose tolerance after chromium supplementation [29]. As there were no changes in glucose concentration in the fasted state, and one and two hours after a high carbohydrate meal from pre- to post-test, we can assume these female subjects not only had normal glucose tolerance, but normal chromium status as well. We found no changes in serum chromium concentration 90 minutes after a glucose load compared to the fasted state in either the placebo or chromium supplementated periods. These findings are consistent with Anderson et al. [37].

RBC chromium was unchanged due to chromium picolinate supplementation; however, we expected it to parallel the plasma chromium level changes. As there are no published data about the changes of RBC chromium concentration after chromium supplementation, we are unable to compare our results to others. We had hoped that RBC chromium would be a better indicator than plasma chromium as an indicator of chromium supplementation, but this was not the case.

Urinary Chromium
Urinary chromium excretion decreased at post-test after a transient increase in urinary chromium excretion at mid-test in the chromium group. These changes were significant, while in the placebo group there was only a trend. The increase in chromium excretion was consistent with previous studies [17,42]. Although urinary chromium excretion is considered an indicator of excessive dietary intake [29], exercise has been suggested to induce urinary chromium excretion. Rubin et al. [42] demonstrated that both acute and 16 weeks of chronic resistive exercise training increased urinary chromium excretion in ten men. However, Anderson et al. [43] reported that trained subjects had significantly lower basal urinary chromium concentrations compared with untrained sedentary control subjects. The decline in urinary chromium excretion may be an adaptive mechanism caused by strenuous exercise [43]. People who engage in strenuous exercise tend to conserve more chromium, possibly through increased tissue storage and decreased urinary loss. Therefore, further study is required to investigate the long-term effects of resistive training and aerobic exercise on urinary chromium loss.

Dietary Intake
Dietary intake was not a confounding factor in this study, because the dietary intakes were similar in both groups according to their three-day dietary records. Compared with the DRI for chromium of 25 µg/day [22], our subjects consumed from 21 to 44 µg of chromium/day and, thus, were within or above the recommended intakes.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Twelve weeks of supplementation with 400 µg/day of chromium as chromium picolinate did not significantly impact body composition, RMR, plasma glucose, serum insulin, plasma glucagon, serum C-peptide and serum lipid concentrations or iron and zinc indices in moderately obese women placed on an exercise program. The changes in serum total cholesterol and TIBC were a result of the exercise program.

	ACKNOWLEDGMENTS

 
The authors would like to thank Nutrition21 (San Diego, CA) for funding this project. This research is based upon work partially supported by the Cooperative State Research Extension, Education Service, U.S. Department of Agriculture Experiment Station, under Project No. MAS00757 Manuscript No. 3280.

The authors would also like to acknowledge all of the individuals who assisted with this project: Kattia Corrales, Elizabeth Della Ratta, Heather Fantini, Kathy Fitzsimmons, Bethany Howe, Timothy McMillen, Anthony Ramy, Penny Harris, James Stevens, Emily Turner, Dr. Ramon Barnes, Dr. Priscilla Clarkson, Dr. Rajesh Gupta, Dr. Trina Hosmer, Dr. Janet King, Bruce Krasin, Mary Jane Laus, Dr. Joaquim Nóbrega, Dr. Frank Rife and University of Massachusetts Health Services (especially Kevin Rhines). Finally, the authors would like to thank all the dedicated subjects who participated in this study.

	FOOTNOTES

 
Supported by Nutrition21, San Diego, CA and USDA Hatch Project #MAS00757.

Received October 19, 2000. Accepted May 18, 2001.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 

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