Exercise is Medicine
In a review article titled “Hunter-gatherers as Models of Public Health”, Herman Pontzer and his colleagues refute a few of the more broadly accepted assumptions made popular by the Paleo diet and lifestyle movement that became popular in the early 2000’s. It is true that modern day hunter-gatherer and subsistence farmer societies are in much better health overall than Western populations regarding cardiovascular disease, high blood pressure, diabetes, and obesity. It is also true that the daily activity levels of these populations are much greater than those in Western cultures. Curiously, relative to lean body mass and age, the total energy expenditure of these individuals is not very different from Westerners with both active or sedentary lifestyles. This means that the average sedentary American and your average gym going American both burn about the same number of calories on average as your average hunter gatherer. (1)
That last bit may have perked your ears up a bit and quite honestly, it kind of blew my mind a bit as well. In another comprehensive review article on the energy expediture on primates, Pontzer demonstrated that this constrained total energy expediture is species specific with a definitive upper limit regardless of additional physical activity. Humans, as compared to other primates have a much higher total energy expenditure which means that unlike us, gorillas and chimpanzees are actually much better suited for laying on the couch for 8–10 hours a day and binging on the latest TV streaming series. Unfortunately for us, our higher total energy expenditure has little to do with our health. (2)
So does this mean we don’t have to exercise?
Absolutely not. Exercise is not for weight loss. It is a basic biological need.
Let me back that up a tad, exercise does help with weight loss to some degree, but its real benefits are so much more important. According to Pontzer in his Scientific American article, “Evolved to Exercise”, he states the following:
“ . . Exercising muscles release hundreds of signaling molecules into the body, and we are only beginning to learn the full extent of their physiological reach. Endurance exercise reduces chronic inflammation, a serious risk factor for cardiovascular disease. It lowers resting levels of the steroid hormones testosterone, estrogen and progesterone, which helps account for the reduced rate of reproductive cancers among adults who exercise regularly. Exercise may blunt the morning rise in cortisol, the stress hormone. It is known to reduce insulin insensitivity, the immediate mechanism behind type 2 diabetes, and helps to shuttle glucose into muscle glycogen stores instead of fat. Regular exercise improves the effectiveness of our immune system to stave off infection, especially as we age. Even light activity, such as standing instead of sitting, causes muscles to produce enzymes that help to clear fat from circulating blood ” (3)
Our bodies do increase daily energy expenditure (DEE) with exercise and the fitter you are, the higher your DEE is likely to be . . . to a point. We adapt to regular exercise in a couple of ways that reduce how much energy we expend. One is that our bodies get better at burning fat for fuel rather than sugar which makes us more fuel efficient. The other is that it has been shown repeatedly, and in multiple populations, that introducing a moderate to vigorous exercise routine to individuals often results in them being less active in other parts of their day. In other words, they rest more to make up for the energy they just expended. It has been shown in runners that energy expenditure increases to a certain point when they begin training but after several weeks, this plateaus and does not increase despite large increases in daily activity. (3,4,5)
At higher levels of activity, our bodies may begin to shunt calories during exercise away from temporarily non-essential functions. Beyond a certain point, however, no matter how many additional calories you add, how much sleep you get, or how well-trained you are, excess exercise will result in overtraining syndrome, a rather serious condition that results in chronic fatigue, depression, and damage to the nervous system and immune function. This is because that level of activity requires more calories than your body is willing to part with and as a result, begins to shut down. (6)
On the other end of the spectrum, how do we account for a relatively high DEE in obese, sedentary individuals? This one is a bit easier to answer and you can think of this as the antithesis of the overtrained elite athlete. In obese individuals, regular activities are much more physically taxing and so they are performed less often with more rest in between efforts. (4) And its not surprising, imagine how difficult it would be to do all of your daily activities with an extra hundred pounds strapped to your back. The upside to that is, barring any orthopedic issues, I can honestly say that most overweight or formerly overweight individuals I have trained are remarkably strong from carrying all that extra weight. Unfortunately, the bodies of obese individuals not only require more calories for basic movement, they also require a lot more physiological maintenance and repair than average individuals and this accounts for a large portion of the calories burned. Like the overtrained athlete, unfortunately, there is a limit on how energy can be spent on repair and maintenance and without the medicine of regular activity to normalize bodily functions, disease becomes prominent. This is another reason why it is important to ease into an exercise routine.
This upper limit on energy expenditure in humans regardless of activity level is important because less than half of the energy we expend is due to physical activity. The majority of the calories we burn are spent on our body’s basic operation and maintenance activities. The less healthy we are, the more maintenance we require. And so, instead of having energy to burn fighting off infections, climbing a tree, or playing basketball with friends, a lot of that energy is instead spent on things an otherwise healthy body doesn’t need. And in order to be optimally healthy, we have to move.
Moral of the story: You have to exercise, just not as much as you think you do. Weight loss is largely a function of diet, exercise can only account for so many calories burned.
There is a tremendous amount of information on this topic so check out my sources:
- Pontzer, Wood, and Raichlen, “Hunter-Gatherers as Models in Public Health.”
- Pontzer, “The Crown Joules: Energetics, Ecology, and Evolution in Humans and Other Primates.”
- Pontzer, “Evolved to Exercise”, Scientific American
- Melanson, “The Effect of Exercise on Non-Exercise Physical Activity and Sedentary Behavior in Adults.”
- Westerterp, “Control of Energy Expenditure in Humans.”
- Overtraining syndrome, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3435910/
And if you want to know more, here’s some recommended reading:
- O’Mara, Shane, In Praise of Walking
- Pontzer, “Economy and Endurance in Human Evolution.”
- Westerterp, “Physical Activity and Physical Activity Induced Energy Expenditure in Humans: Measurement, Determinants, and Effects.”
