If you read Everything Nutrition regularly, you will know that nutrients are not drugs. Unfortunately, many randomized clinical studies use a prescription drug approach. One of the pitfalls can be a failure in design (e.g., people studied are adequately nourished or healthy). Once healthy, it is difficult to measure “healthier.” This blog contributes to the proof of this principle.

Crandall and colleagues tested the hypothesis that resveratrol improves glucose metabolism and vascular function in older adults with impaired glucose tolerance. Ten subjects, average age of 72 years, with impaired glucose tolerance were enrolled into a 4-week trial with varying doses of resveratrol (1, 1.5, and 2 grams/day). Resveratrol supplementation significantly improved 3 hour postprandial glucose responses to a standardized meal, measured by area-under-the-curve (AUC). When adjusted for insulin sensitivity, Β-cell function improved. These large doses of resveratrol were well tolerated and no adverse events or changes in liver enzymes were found in this small number of individuals. In other words, Crandall and colleagues found a statistically significant resveratrol response on indicators of glucose metabolism in a small group of individuals with moderate glucose intolerance.

The Journal of Gerontology study corroborates the findings of Bhatt and colleagues who studied the effect of much smaller doses of resveratrol (250 mg/day) given for 3 weeks to individuals with type 2 diabetes. Resveratrol supplementation improved glycemic control, measured by HbA1C levels, in people with diabetes.

Not surprisingly however, nutritional supplementation does not necessarily improve metabolic function in healthy people with normal glucose tolerance. Really, how would one measure “better than normal” glucose tolerance?

The first sentence in the summary by Yoshino and colleagues should give some insight. It reads: “Resveratrol has been reported to improve metabolic function in metabolically abnormal rodents and humans.” Is it scientific optimism to study the effect of resveratrol supplementation in non-obese people with normal glucose tolerance? Another recent null study, one by of Poulsen and colleagues, underscores the same point. Poulsen and colleagues could not detect a resveratrol-related response on glucose metabolism in healthy obese individuals with normal glucose tolerance. Could the inconsistent findings be a function of the glucose tolerance of the participants studied rather than the metabolic impact of the test ingredient? It would seem to be a valid question.

Take-home message: Poor nutrient intakes can make people unhealthy. Nutrition interventions in healthy people are unlikely to make them super healthy.


Citations:

Crandall JP, Oram V, Trandafirescu G, Reid M, Kishore P, Hawkins M, Cohen HW, Barzilai N. Pilot study of resveratrol in older adults with impaired glucose tolerance. 2012 J Gerontol 67 (12) 1307-1312.

Yoshino J, Conte C, Fontana L, Mittendorfer B, Imai S, Schechtman KB, Gu C, Kunz I, Fanelli FR, Patterson BW, Klein S. Resveratrol supplementation does not improve metabolic function in nonobese women with normal glucose tolerance. 2012 Cell Metabolism 16(5):658-664.
Poulsen MM, Vestergaard PF, Clasen BF, Radko Y, Christensen LP, Stodkilde-Jorgensen H, Moller

N, Jessen N, Pedersen SB, Jorgensen JOL. High-dose resveratrol supplementation in obese men: An investigator-initiated, randomized, placebo-controlled clinical trial of substrate metabolism, insulin sensitivity, and body composition. 2012 Diabetes online Nov 28

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The ideas and opinions expressed in this article are those of the author and do not necessarily reflect views held by Nutraceuticals World.