The China Study - T. Colin Campbell and Thomas M. Campbell

Q&A: Protein Effect in Experimental Rat Studies

COULD THE DIETARY PROTEIN EFFECT
BE DUE TO OTHER NUTRIENTS IN THE RAT DIET?
Decreasing dietary protein from 20% to 5% means finding something to replace the missing 15%. We used a carbohydrate to replace the casein because it had the same energy content. As dietary protein decreased, a 1:1 mixture of starch and glucose increased by the same amount. The extra starch and glucose in the low-protein diets could not have been responsible for the lower development of foci because these car- bohydrates, when tested alone, actually increase foci development.! If anything, a little extra carbohydrate in the low-protein diet would only increase cancer incidence and offset the low-protein effect. This makes prevention of cancer by low-protein diets even more impressive.
MIGHT THE PROTEIN EFFECT BE DUE TO THE RATS ON A LOW-PROTEIN DIET EATING LESS FOOD (I.E., LESS CALORIES)?
Many studies done in the 1930s, 1940s and 1950s2 had shown that decreasing total food intake, or total calories, decreased tumor devel- opment. A review of our many experiments, however, showed that animals fed the low-protein diets did not consume less calories but, on
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average, actually consumed more calories. ,4 Again, this only reinforced the tumor-promoting effect observed for casein.
WHAT WAS THE OVERALL HEALTH OF THE RATS ON A LOW-PROTEIN DIET?
Many researchers have long assumed that animals fed diets this low in protein would not be healthy. However, the low-protein animals were healthier by every indication. They lived longer, were more physically active, were slimmer and had healthy hair coats at 100 weeks while the high-protein counterpart rats were all dead. Also, animals consuming less dietary casein not only ate more calories, but they also burned off more calories. Low-protein animals consumed more oxygen, which is required for the burning of these calories, and had higher levels of a spe- cial tissue called brown adipose tissue,5,6 which is especially effective in burning off calories. This occurs through a process of "thermogenesis," i.e., the expenditure of calories as body heat. This phenomenon had
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already been demonstrated many years before. - Low-protein diets en-
hance the burning off of calories, thus leaving less calories for body weight gain and perhaps also less for tumor growth as well.
WAS PHYSICAL ACTIVITY RELATED TO THE CONSUMPTION OF THE LOW-PROTEIN DIET?
To measure the physical activity of each group of rats, we compared how much they voluntarily operated an exercise wheel attached to their cages. A monitor recorded the number of times the animals turned the exercise wheel. The low-casein animals12 exercised about twice as much, when measured over a two-week period! This observation seems to be very similar to how one feels after eating a high-protein meal: slug- gish and sleepy. I have heard that a side effect of the protein-drenched Atkins Diet is fatigue. Have you ever noticed this feeling in yourself after a high-protein meal?