Last week, researchers announced that they had completed the first study of the effects of a calorie-restriction diet on humans. Such diets, which drastically cut food intake, have been found to lead to longer life for simple organisms such as flatworms. However, the effects of the diets on people had not been studied.

In the new work, 48 volunteers cut back their food intake to as little as 890 calories a day, and maintained the diet for 6 months. "Our findings suggest that 2 biomarkers of longevity (fasting insulin level and body temperature) are decreased by prolonged calorie restriction in humans and support the theory that metabolic rate is reduced beyond the level expected from reduced metabolic body mass," the authors of the study wrote in the Journal of the American Medical Association. "Studies of longer duration are required to determine if calorie restriction attenuates the aging process in humans. "  This work was a pilot study, aimed at preparing for a larger and more thorough investigation. We'll talk about the diet and how it might affect the aging process.

Then, we'll turn our attention to the issue of mercury in fish. The US FDA and EPA have advised pregnant women, nursing mothers, women who may become pregnant, and nursing mothers not to eat fish that can contain high levels of mercury, such as shark, swordfish, king mackerel, and tilefish, and to limit consumption of many other fish due to potential mercury contamination. The agencies suggest limiting consumption of canned light tuna, for instance, to under 12 ounces a week. Reccomended consumption of albacore tuna, which can contain higher levels of mercury, is set at just 6 ounces a week.

Mercury is emitted into the air through various industrial processes, including burning coal. Bacterial and chemical reactions in the environment can convert mercury metal to methymercury, which can be absorbed by living things and which can bioaccumulate as it works its way through the food chain. Exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system.  On the other hand, fish and shellfish low in saturated fat, and contain omega-3 fatty acids. So what's a person to do -- and what can be done to clean up the mercury in the environment? Join Ira and guests in this hour for a look at the problem.

Call in with your questions and comments at 1-800-989-8255 (2-3 Eastern). Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests:

Eric Ravussin
Chief, Division of Health and Performance Enhancement
Professor and Douglas L. Gordon Chair in Diabetes and Metabolism
Pennington Biomedical Research Center
Baton Rouge, Louisiana

Michael Hawthorne
Environment Reporter
Chicago Tribune
Chicago, Illinois

Gary Myers, M.D.
Professor, Neurology and of Pediatrics
University of Rochester Medical Center
Rochester, New York

Books/Articles Discussed:
JAMA -- Abstract: Effect of 6-Month Calorie Restriction on Biomarkers of Longevity, Metabolic Adaptation, and Oxidative Stress in Overweight Individuals: A Randomized Controlled Trial, April 5, 2006, Heilbronn et al. 295 (13): 1539

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This segment produced by Karin Vergoth