Chromium is known to be an essential mineral in humans that is required for correct insulin function. Chromium lowers blood glucose levels because it is an essential component of the insulin receptor. Chromium forms a complex in cells that binds to the insulin receptor to facilitate the uptake of blood glucose. Following this process, chromium dissociates from the receptor and is excreted in the urine. If the chromium is not replaced in the diet, insulin sensitivity decreases which can result in weight gain as more glucose is shunted to storage in adipose tissue. Under certain circumstances, increases in the intake of chromium are recommended. For example, high carbohydrate diets are able to cause significant chromium losses because of the increase in insulin to receptor binding. In addition, exercise has been shown to increase the excretion of chromium perhaps due to improved glucose and insulin metabolism.
Researchers1 have attempted to estimate the chromium losses caused by resistance training in healthy male subjects. Ten previously sedentary men between the ages of 53 and 63 undertook 16 weeks of whole body resistance training. Subjects also consumed an American Heart Association phase I diet that consisted of 30% fat, 55% carbohydrate and 15% protein. The subjects also had their body composition monitored using hydrostatic weighing. Chromium excretion was measured using radiolabelled 53Cr as CrCl2 in water. Subjects received 300 µg chromium either before an exercise session or during a period of no exercise, and urinary chromium was measured for 72 hours. The dosing of chromium in this manner was repeated twice at different durations into the 16 week study. The subjects diets were also analysed for their chromium content using gas chromatography and mass spectrometry.
The subjects gained 40% and 41% in upper and lower body strength, respectively. In addition, lean mass increased and body fat decreased significantly. Analysis of food sample showed that the chromium content was 30 µg/d, which is just below the recommended level for this age group in the United States (35 µg/d). Urinary chromium losses were increased by a single bout of resistance exercise from 0.65% to 0.94% and after 16 weeks of resistance training from 0.25% to 0.34%. These results support previous findings that large amounts of people do not attain the recommended intakes of chromium from their diet, even those that follow diets that have been developed by health care professionals. Although the excretion of chromium increased following exercise, this loss was mainly from the radiolabelled chromium ingested, which suggests that exercise chromium losses are replenished with increased intestinal absorption, and tissue chromium is not greatly affected.
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