How exercise helps prevent chronic disease
Lieberman concludes his book with a detailed section describing why regular moderate exercise is critical in preventing many common chronic diseases that we associate with aging. He points out that middle-aged and older hunter-gatherers never get to relax and retire. They remain active members of their tribe throughout their lives, participating in hunting and gathering food, doing tasks at camp, and helping with childcare.
In fact, many older tribe members are more active than their young adult children who are busy taking care of infants and toddlers. The average 65-year-old hunter-gatherer man has better aerobic capacity than the average 45-year-old American man.
One reason why exercise helps to prevent chronic disease is that exercise strengthens the immune system. This helps to prevent cancer as well as viral and bacterial infections. Research has clearly shown that moderate exercise, rather than no exercise or extreme exercise, is very effective at improving immunity.
Regular activity also helps to prevent chronic musculoskeletal conditions including osteoarthritis, osteoporosis, and sarcopenia. The more we use our muscles and bones, the stronger they stay throughout our lives, reducing the risk of osteoporosis and sarcopenia; as they say, use it or lose it.
And rates of osteoarthritis have risen dramatically since we’ve become more sedentary. Lieberman educates us that osteoarthritis is not caused by wear and tear as is commonly thought—it’s actually caused by inflammation that eats away at the cartilage in our joints. In many cases, this inflammation is caused by obesity and physical inactivity.
Exercise helps to prevent Alzheimer’s disease and other neurodegenerative diseases by stimulating the production of a protein called brain-derived neurotrophic factor (BDNF). BDNF was first produced by the brain to give mammals energy during physical activity. As we evolved, it also took on the role of being “Miracle-Gro” for the brain: encouraging the growth of new neurons, improving neuron function, preventing premature neuron death, and improving signal strength between neurons. Physical activity is the only way we can produce high levels of BDNF, so exercise is critical for preserving brain function as we age.
Regular exercise has proven to be as effective as pharmaceuticals and therapy for mental health conditions, which affect about one in five American adults. As I’ll describe in the next section, exercise increases levels of dopamine, serotonin, endorphins, and endocannabinoids, all of which make us feel happy and reduce our stress. Exercise stimulates the release of the neurotransmitters norepinephrine, glutamate, and GABA, which are often low in people who have depression and anxiety. Exercise also reduces levels of the stress hormone cortisol and improves sleep quality.
Cardiovascular disease, including high blood pressure and coronary artery disease, is clearly a mismatch disease. Researchers have found that hunter-gatherers in their 80s have the same low blood pressure as those in their 20s. Rates of hypertension and coronary artery disease only start to go up when populations become industrialized; that’s when levels of cholesterol and inflammation rise to unhealthy levels, leading to cardiovascular disease. Physical inactivity is a factor in this, as is obesity, poor diets, smoking, and stress.
While obesity is much more a result of diet than lack of exercise, physical inactivity does play a role. Experts agree that the overeating of high-calorie processed foods is the main factor in developing obesity. Thus, the most efficient way to lose weight is to eat only whole, unprocessed foods, and an appropriate amount of calories each day. If you use only exercise to lose weight, your results will be far more gradual. However, studies show that among people who have successfully lost weight, those who exercise regularly are much less likely to regain the weight.
Diet and exercise are both important in reversing metabolic syndrome (high blood sugar, high cholesterol, high blood pressure, and large waist circumference) and type 2 diabetes. These are two conditions which are clearly mismatch diseases, as they’re unheard of among hunter-gatherers and have only recently reached epidemic levels. Approximately 20% to 25% of the world’s adults have metabolic syndrome, and type 2 diabetes is now the fastest growing chronic disease in the world. Being overweight, eating a poor diet, and being sedentary are the main contributors. While drugs are often prescribed to manage these conditions, diet and exercise can reverse them permanently, and often quickly.
Lieberman notes that regular moderate cardiovascular workouts are the most effective type of exercise for prevention of most chronic diseases. An exception is metabolic syndrome and type 2 diabetes, which research show can benefit from a combination of cardio, high-intensity interval training, and strength training.