Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

Pauling was a brilliant chemist, but his advocacy of vitamin C was quackery.

Half the participants were given large doses of vitamins C and E; the other half received a placebo. Muscle biopsies taken before and after their exercise bouts showed that, as expected, physical activity induced plenty of oxidative stress, but those who took antioxidants incurred more oxidative damage because their bodies produced much lower levels of their own antioxidants.

The antioxidant pills apparently suppressed the body’s normal antistress response probably because oxidative damage from exercise itself is needed to trigger the body’s health-promoting antioxidative defense mechanisms. Along the same lines, it is possible that eating lots of carbohydrates during exercise diminishes the body’s anti-inflammatory response.

Although two of three Americans’ death certificates state they died of heart disease, cancer, or stroke, the deeper underlying causes of these illnesses were most likely smoking cigarettes, obesity, and physical inactivity.

As you can see, the healthy non-runners died at increasingly faster rates than the runners and by the study’s end were about three times more likely to pass away in a given year. In terms of cause of death, the non-runners were more than twice as likely to die of heart disease, about twice as likely to die of cancers, and more than three times as likely to die of neurological diseases. In addition, they were more than ten times as likely to die of infections like pneumonia. Just as important, the disability scores plotted on the bottom show that the non-runners lost functional capacity at double the rate of the runners. By the end of the study their disability scores were more than twice as high as the runners’, indicating that the runners’ bodies were approximately fifteen years younger by this measure. In sum, running caused a compression of morbidity, thus also extending lives.

Instead, physical activity triggers a suite of mechanisms that increase the chances of staying healthy with age by retarding senescence and preventing many chronic diseases that contribute over time to mortality.

Genetic variations influence plenty of chronic diseases such as coronary artery disease, heart arrhythmias, type 2 diabetes, inflammatory bowel disease, and Alzheimer’s.65 In these and other cases, genes help load the gun, but environment pulls the trigger.

Regardless of how people become obese, the harmful effects of obesity are not in question. Aside from overloading joints and interfering with breathing, excess fat cells overproduce hormones that alter metabolism, and when swollen, they become invaded by white blood cells that ignite chronic low-grade inflammation, damaging tissues throughout the body.

Big deposits of enlarged fat cells in and around organs (so-called visceral, abdominal, or organ fat) are especially hazardous because they react sensitively to hormones and connect more directly to the bloodstream.

Because too much sugar is toxic to many cells, excess sugar stimulates your pancreas to release the hormone insulin, whose basic function is to cause the body to store energy.

Type 2 diabetes arises when the effects of metabolic syndrome prevent insulin receptors on these cells from binding with insulin (a phenomenon termed resistance). A vicious cycle ensues.

Then, as blood sugar levels rise, the brain desperately commands the pancreas to produce yet more insulin, but with diminishing effect, causing blood sugar levels to stay dangerously high. Symptoms include frequent thirst and peeing, nausea, tingly skin, and swollen feet.

And most remarkably, exercise can reverse insulin resistance by restoring blocked insulin receptors and causing muscle cells to produce more of the transporter molecules that shuttle sugar out of the bloodstream.

Endurance athletes such as cross-country skiers had a stunning two-thirds lower risk of heart attacks than average Finns, while power athletes like weight lifters and wrestlers had one-third higher rates of heart attacks.48 Bottom line: weight training isn’t bad, but don’t skip the cardio.

When we demand more from our muscles, especially contractions involving resistance, we activate genes that increase the size of fibers as well as repair and maintain muscle cells.

Every once in a while, however, cells develop mutations that disrupt their function, and a tiny fraction of those mutations trigger cells to compete with each other. When such mutations occur, the cells become malignant. At this point, they divide uncontrollably, migrate throughout the body, and voraciously consume calories.

Further, the effects are impressive. An analysis of sixteen prospective studies including more than 160,000 individuals found that moderate levels of physical activity lowered the risk of Alzheimer’s by 45 percent.111 More physically intense activities may be associated with reduced risks for the disease.112 Physical activity also slows the rate of cognitive and physical deterioration in Alzheimer’s patients.113

Rodents that run on treadmills develop fewer plaques and tangles in their brains and have lower levels of inflammation associated with Alzheimer’s.119