Padmavathi et al. (1) examined the effects of two diets, AIN-93G and AIN-93G with the chromium (Cr) removed from the mineral mixture normally added to the diet. The authors considered the diet lacking the added Cr to be “restrictive” in terms of this element. The normal diet contained 1.56 mg Cr/kg diet, while the diet lacking the added Cr contained 0.51 mg Cr/kg diet. We believe that the “restrictive” diet is not restrictive and that the results of the study need to be reinterpreted in this light.

Given that a 100-g rat consumes about 15 g of food a day, a diet containing 0.51 mg Cr/kg would provide 77 μg/kg body mass/day. The adequate intake for a human as recommended by the National Research Council (2) is 30 μg Cr/day. Given that the average body mass of a human is generally assumed to be ∼65 kg, a human requires ∼0.5 μg Cr/kg body mass/day. Thus, the “restrictive” contained 102 more Cr than is probably essential for the rats. While one can argue whether scaling by body mass is the most appropriate method (compared with metabolic rate, body surface area, etc.), use of a different scaling method would only lead to small changes in the results compared with the greater than two order of magnitude difference. Observations of effects from dietary Cr deficiency in otherwise healthy rats have been reported by Striffler et al. (3,4) using a diet that contained 33 μg Cr/kg food; however, even in this case, whether the diet is actually Cr deficient has been questioned as additional dietary stresses were also invoked (including high-sugar or high-fat content and altered mineral content) (5). Thus, the diet lacking the added Cr used by Padmavathi et al. should not be considered deficient or restrictive. The study by Padmavathi et al. should be considered as a supplemental Cr study with the different effects between the two diets attributed to the supplemental Cr in the “control” diet.

No potential conflicts of interest relevant to this article were reported.

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