Food craziness, part 3: of tiny mice and men

(a digression before I get back to exercise)

Have you noticed that large breeds of dogs don't live as long as smaller breeds? There seems to be some connection between growth and longevity. A lab strain of mice was developed that lacked one gene involved in growth, Insulin-like Growth Factor 1 (IGF-1); it is a dwarf strain that unexpectedly lives 40% longer than average. This one gene may be very important for longevity, but the exact reason why is not entirely clear. [The obvious experiment of testing methionine restriction or caloric restriction on IGF-1 deficient mice has not been done.] There are humans who also lack this gene, called Laron dwarfs; the largest population of them are in Venezuela, coincidentally near the Vilcabamba valley which has been renowned for long-lived residents. Laron dwarfs appear to never get cancer or diabetes. They do not, however, have unusually long lifespans, due it seems to poverty, alcoholism and obesity.

In part 2, I mentioned methionine restriction diets and here I'm bringing up growth factors - two very odd subjects - and the two may be related. Insulin and IGF-1 are similar in structure, have similar cell receptors and have overlapping effects. Insulin causes sugars (and to a lesser extent) amino acids to enter muscle cells and IGF-1 appears to cause amino acids (and to a much lesser extent, sugars) to enter muscle cells, effects necessary for growth of muscle cells. Experimentally, low levels of methionine appear to cause low levels of IGF-1, which should mimic the health benefits of increased longevity through decreases in cancer and diabetes. As Laron dwarfs show, it is not sufficient however to ensure longevity; other diet changes and exercise are also necessary.

The very illnesses to which Laron dwarves seem to succumb appear to be prevented and even reversed by very low fat diets. The first major proponent of a diet both low in protein and fat was Nathan Pritikin, who ironically died at 70 after commiting suicide because of side-effects from hairy cell leukemia chemotherapy. His diet of 80% carbs, 10% protein and 10% fat was found to be too difficult (too tasteless) for most people to follow. Dean Ornish has since shown that heart disease can be reversed with this diet, while the most recent books from Pritikin's health center now advocate a much higher protein diet. The China Study suggests that it is not fat intake that correlates to heart disease, but intake of fat from animal sources only; clinical evidence for this is sketchy.

There is one group with a diet averaging 12% protein and 13% fat and which gets plenty of exercise that still does not have extended healthy lives, the Raramuri (commonly called the Tarahumara) of Mexico. There are stories that they used to live longer, but times have changed (one specifically says "since they started planting soybeans"). Reports from the 1960s suggest the elderly ate a diet similar to the elderly found in "Blue Zones." A study of the diet of their famous distance runners showed that they ate an average of 2818 calories per day (at an average height of 5'6" and weight of 135 pounds), consisting primarily of corn, beans, squash and squash seeds, citrus, tomatoes and other vegetables (not named in that source) and that they had adequate daily intakes of all vitamins and minerals (though only 800 mg of calcium and the 1 microgram of B-12 seems impossible given no animal products commonly eaten).

The Tarahumara diet appears to be very low in methionine (maize is uncommonly low among grains), but the quantity of food eaten to get all the other nutrients causes the total methionine level to exceed that threshold for lowered IGF-1. If the calories are decreased to 2000 or fewer, their diet becomes very similar to what I gave in part 2 as a low-methionine diet.

A low calorie, low protein, low fat, near-vegan diet might make sense if one is elderly, but it makes no sense if one is growing and active. There may be a way to mimic and extend the diet effects of methionine restriction with exercise. That will be the focus of the last part of this series.