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Calorie Restriction of Mice and Men

It turns out that mice and men are not that different after all, at least regarding the correspondence between Calorie Restriction (CR) and body weight. It has been known for a long time that mice or rats allowed to eat only 60% of the control animals, i.e. 40% CR, starting at weaning, grow to be adults which weigh only 50% of the control animals, but they live 30% longer. The longevity figures have been widely publicized, but the stunting effect of the low calorie diets has not received much attention. Masoro had some tables documenting the weights of his experimental rats [1], and Mattson [2] provided the following growth chart for mice:

In a recent blog entry about the Effect of Calorie Restriction on Body Size, I provided a graphic illustrating the silhouettes of humans corresponding to the various degrees of calorie restriction to which mice are subjected. Of course this was just speculation, or so I thought. However, after tabulating the Mifflin-St Jeor Energy Equations which are used to calculate Basal Metabolic Rate (BMR) for humans, I found that for proportionally shaped bodies with a Body Mass Index (BMI) of 22, the dependency of weight vs. CR for the humans was identical to the results for the mice. I had previously discussed this anecdotally in my Calorie Restriction page, but with some additional mathematical analysis, I found that the mouse equations could be derived from the human Mifflin-St Jeor equations.

I think that there is something intrinsic in the three-dimensional proportions of an organism. Our genes, or Mother Nature, try to balance the way in which our bodies grow based on the level of nutrients. A certain amount of muscle is required for every inch of bone growth, and during our growth, we are not overly lanky or overly squat. If you plant a maple seedling in a big field it will grow to be many feet high, whereas a similar seedling planted in a one-gallon flower pot will grow to be a miniature version of the big tree - a bonsai. And just like you cannot replant the big tree in the small pot, we cannot cut our calories to levels that cannot support our size.

The correspondence of the mice and human CR equations are discussed here:

Effect of Calorie Restriction on Body Weight

[1] E J Masoro, et al, "Action of food restriction in delaying the aging process", Proc Natl Acad Sci U S A., 1982 July; 79(13): 4239-4241.
[2] Mattson, et al. "Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake, Proc Natl Acad Sci USA, 2003 May 13; 100(10):6216-6220.

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