Vol. 164 March 1, 2017 The Exercise Paradox

Hub thumbnail 2015

“You can’t outrun a bad diet”

It appears that an African native chasing a wounded giraffe through the bush and over the plains for 12 hours in order to get food for himself and his family burns the SAME NUMBER OF CALORIES per day as the modern couch potato. Researchers measuring the urine excretion of two radioactive isotopes of water ingested by the subjects (the “gold standard” of measuring energy expenditure) have confirmed this fact as postulated previously by several studies. These African hunter-gatherers burned about 2,600 calories a day, about the same as average adults in present day U.S. and Europe.

The researchers were looking to measure the size of the “energy shortfall” in Westerners to explain the global rise of obesity. They found none. In fact, another review of almost a hundred (98) world-wide studies of energy expenditure (calories burned per day) revealed that “the persons with all the modern conveniences have similar energy expenditures to those with more physically demanding lives in less developed countries.”  Therefore, “obesity is a disease of gluttony, not sloth.”

Physical activity does NOT cause weight loss, but exercise can help prevent weight gain.  A JAMA 2010 study of 34,000 middle-aged U.S. women showed that 60 minutes a day of moderate exercise (walking) prevented weight gain in those on a normal diet who had previously lost weight through dieting.

As someone who collected articles about  bad things happening to joggers to justify my ignoring Society’s “persistent call to go running”, this is music to my ears. The evidence that exercise, including just walking, is good for you is absolutely true and well accepted. It just doesn’t help you lose weight. Again, as someone who has made a resolution every January to lose weight by going to the gym only to peter out by the end of every March, this made me feel less inadequate, or at least less guilty.

Humans have a fixed rate of energy expenditure which is independent of their physical activity. A subsequent study of 300 people wearing Fit-bits showed that those doing moderate activity  (some exercise and always taking the stairs) burned only 200 more calories than couch potatoes. People doing intense physical activity did NOT burn more calories than the moderately active people. Again, the African bushman burns the SAME number of calories walking a mile as does the Westerner.

Studies of energy expenditure in zoo animals compared to animals in the wild reveal the same constancy. How can this be? No one really knows, but the authors speculate that since human energy expenditure is quite constant (and constrained), we modern adults who are not chasing wounded giraffes over the veld have evolved metabolic adaptations that spend our calories on supporting brain functions (the oxygen you take in with every fourth breath is needed just to feed your brain) , running our inflammatory processes (exercise may prevent inflammation by diverting energy from it), producing more and bigger babies, and living longer. But, I am not sure that I am any smarter than the African bushman who lives to 70 in his world, and many of them do.

Humans have learned to cook which increases the caloric value of many foods and makes them more efficiently digested.
We also have evolved to be fat. Our tendency to store fat is probably an adaptation for surviving lean times.
During lean times our survival is enhanced by us sharing what food there is.
Apes do not share.

“Exercise to stay healthy and vital;
focus on diet to look after your weight.”

References:
1. The Exercise Paradox, Herman Pontzer, Scientific American, Feb. 2017, 28-31

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