142 TH E CH I NA STU DYAmericans and the least active Chinese, those who do office work. Fur-
thermore, studies done in IsraeF4 and the United Kingdom,ll neither of
which represent primarily agrarian cultures, also show that vegetarians
may consume the same or significantly more calories and still weigh
less.
What's the secret? One factor that I've mentioned previously is the
process of thermogenesis, which refers to our production of body heat
during metabolism. Vegetarians have been observed to have a slightly
higher rate of metabolism during rest,26 meaning they burn up slightly
more of their ingested calories as body heat rather than depositing them
as body fat. 27 A relatively small increase in metabolic rate translates to a
large number of calories burned over the course of twenty-four hours.
Most of the scientific basis for the importance of this phenomenon was
presented in chapter four.EXERCISE
The slimming effect of physical activity is obvious. Scientific evidence
concurs. A recent review of all the credible studies compared the rela-
tionship between body Weight and exercise^28 and showed that people
who were more physically active had less body weight. Another set of
studies showed that exercising on a regular basis helped to keep off
weight originally lost through exercise programs. No surprise here,
either. Starting and stopping an exercise program is not a good idea. It
is better to build it into your lifestyle so that you will become and con-
tinue to be more fit over all, not just burn off calories.
How much exercise is needed to keep the pounds off? A rough es-
timate derived from a good review^28 suggested that exercising a mere
fifteen to forty-five minutes per day, every day, will maintain a body
weight that is eleven to eighteen pounds lighter than it would otherwise
be. Interestingly, we should not forget our "spontaneous" physical activ-
ity, the kind that is associated with chores of daily life. This can account
for 100-800 calories per day (kcalJday)?9, 30 People who are regularly
"up and about" doing physical things are going to be well ahead of those
who get trapped in a sedentary lifestyle,
The advantages of combining diet and exercise to control body
weight were brought home to me by a very simple study involving our
experimental animals. Recall that our experimental animals were fed
diets containing either the traditional 20% casein (cow's milk protein)
or the much lower 5% casein. The rats consuming the 5% casein diets