Friday, September 26, 2008

Caloric Restriction is a NoGo for Humans

Differences between People and Animals on Caloric Restriction

Most people interested in health related issues have heard of caloric restriction, the only known laboratory method for extending life. In this study they recruited members of the CR Society who had been practicing caloric restriction for 7 or more years. The results are disappointing and back claims by other scientists that human beings may not benefit from caloric restriction. My personal view is that caloric restriction is too severe and cannot be applied in our busy and work oriented society. Additionally other studies have indicated that constant caloric restriction can cause the following problems

  • reduces immunity(some studies indicate it can lead to death of helper B cells, thereby restricting our adaptive immune capacity),
  • loss of fertility for both males and females,
  • cognitive issues, in fact a recent study claimed that chronic CR can actually cause brain damage.

In this study the researchers did find a way to alter the key physiological marker for the beneficial effects of CR: reducing IGF1 expression. IGF is Insulin Growth Factor. Under stimulation from human growth hormone, IGF is released by the liver and travels throughout the body. The researchers asked one set of the participants to lower their protein intake and within 3 weeks this caused a dramatic reduction in IGF levels. Again however I must stress: that reducing protein intake induced a favourable IGF response, one has to be consider that such a radical reduction in protein intake may have serious long term implications that easily outweigh the benefits of reduced IGF levels.

A point of clarification. Many people think that the more growth hormone the healthier they are. This is misleading and false. Reducing growth hormone levels in age is consistently associated with less pathology and a longer life.


Fontana L, Klein S, Holloszy JO. Long-term low-protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk. American Journal of Clinical Nutrition, vol. 84; pp. 1456-1462, Dec. 2006

Fontana et al. Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging Cell, 2008; 7 (5): 681 DOI:

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