The efficacy of insulin in stimulating whole-body glucose disposal (insulin sensitivity) was quantified using direct methodology in thirty lacto-ovo vegetarians and in thirty meat-eaters. All subjects were adult, lean (BMI <23 kg/m2), healthy and glucose tolerant. Lacto-ovo vegetarians were more insulin sensitive than meat-eaters, with a steady-state plasma glucose (mmol/l) of 4·1 (95 % CI 3·5, 5·0) v. 6·9 (95 % CI 5·2, 7·5; P=0·0028) respectively. In addition, lacto-ovo vegetarians had lower body Fe stores, as indicated by a serum ferritin concentration (μg/l) of 35 (95 % CI 21, 49) compared with 72 (95 % CI 45, 100) for meat-eaters (P=0·0012). To test whether or not Fe status might modulate insulin sensitivity, body Fe was lowered by phlebotomy in six male meat-eaters to levels similar to that seen in vegetarians, with a resultant approximately 40 % enhancement of insulin-mediated glucose disposal (P=0·0008). Our results demonstrate that lacto-ovo vegetarians are more insulin sensitive and have lower Fe stores than meat-eaters. In addition, it seems that reduced insulin sensitivity in meat-eaters is amenable to improvement by reducing body Fe. The latter finding is in agreement with results from animal studies where, no matter how induced, Fe depletion consistently enhanced glucose disposal.
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