process, such fierce activity generates a fair amount of toxic waste. In the case of food, this waste consists of a nasty pile of excess electrons shredded from the atoms in the glucose molecules. Left alone, these electrons slam into other molecules within the cell, transforming them into some of the most toxic substances known to humankind. They are called free radicals. If not quickly corralled, they will wreck havoc on the innards of a cell and, cumulatively, on the rest of the body. These electrons are fully capable, for example, of causing mutations in your DNA.
The reason you don’t die of electron overdose is that the atmosphere is full of breathable oxygen. The main function of oxygen is to act like an efficient electron-absorbing sponge. At the same time the blood is delivering glucose to your tissues, it is also carrying these oxygen sponges. Any excess electrons are absorbed by the oxygen and, after a bit of molecular alchemy, are transformed into equally hazardous—but now fully transportable—carbon dioxide. The blood is carried back to your lungs, where the carbon dioxide leaves the blood and you exhale it. So whether you are a competitive eater or a typical one, the oxygen-rich air you inhale keeps the food you eat from killing you. How important is oxygen? The three requirements for human life are food, drink, and fresh air. But their effects on survival have very different timelines. You can live for 30 days or so without food, and you can go for a week or so without drinking water. Your brain, however, is so active that it cannot go without oxygen for more than five minutes without risking serious and permanent damage. When the blood can’t deliver enough oxygen sponges, toxic electrons overaccumulate.
Getting energy into tissues and getting toxic electrons out are essentially matters of access. That’s why blood—acting as both waitstaff and hazmat team—has to be everywhere inside you. Any tissue without enough blood supply is going to starve to death, your brain included. More access to blood is better. And even in a healthy brain, the blood’s delivery system can be improved.
That’s where exercise comes in.
It reminds me of a seemingly mundane little insight that literally changed the history of the world. John Loudon McAdam, a Scottish engineer living in England in the early 1800s, noticed the difficulty people had trying to move goods and supplies over hole-filled, often muddy, frequently impassable dirt roads. He had the splendid idea of raising the level of the road using layers of rock and gravel. This immediately made the roads less muddy and more stable. As county after county adopted his process, now called macadamization, people instantly got more dependable access to one another’s goods and services. Offshoots from the main roads sprang up. Pretty soon entire countrysides had access to far-flung points using stable arteries of transportation. Trade grew. People got richer. By changing the way things moved, McAdam changed the way we lived.
What does this have to do with exercise? McAdam’s central notion wasn’t to improve goods and services, but to improve access to goods and services. You can do the same for your brain by increasing the roads in your body, namely your blood vessels, through exercise. Exercise does not provide the oxygen and the food. It provides your body greater access to the oxygen and the food.
How this works is easy to understand. When you exercise, you increase blood flow across the tissues of your body. Blood flow improves because exercise stimulates the blood vessels to create a powerful, flow-regulating molecule called nitric oxide. As the flow improves, the body makes new blood vessels, which penetrate deeper and deeper into the tissues of the body. This allows more access to the bloodstream’s goods and services, which include food distribution and waste disposal. The more you exercise, the more tissues you can feed and the more toxic waste you can remove. This happens all over the body. That’s why exercise improves the performance of most human functions. You stabilize existing transportation structures and add new ones, just like McAdam’s roads. All of a sudden, you are becoming healthier.
The same happens in the human brain. Imaging studies have shown that exercise increases blood volume in a region of the brain called the dentate gyrus. That’s a big deal. The dentate gyrus is a vital constituent of the hippocampus, a region deeply involved in memory formation. This blood-flow increase, likely the result of new capillaries, allows more brain cells greater access to the blood’s waitstaff and hazmat team.
Another brain-specific effect of exercise is becoming clear. Early studies indicate that exercise also aids in the development of healthy tissue by stimulating one of the brain’s most powerful growth factors, BDNF. That stands for brain-derived neurotrophic factor. “I call it Miracle-Gro, brain fertilizer,” says Harvard psychiatrist John Ratey. “It keeps [existing] neurons young and healthy, and makes them more ready to connect with one another. It also encourages neurogenesis—the creation of new cells.” The cells most sensitive to this are in the hippocampus, inside the very regions deeply involved in human cognition. Exercise increases the level of usable BDNF inside those cells. Most researchers believe this uptick also buffers against the negative molecular effects of stress, which in turn may improve memory formation. We’ll have more to say about this interaction in the Stress chapter.
Redefining normal
All of the evidence points in one direction: Physical activity is cognitive candy. Civilization, while giving us such seemingly forward advances as modern medicine and spatulas, also has had a nasty side effect. It gives us more opportunities to sit on our butts. Whether learning or working, we gradually quit exercising the way our ancestors did. Recall that our evolutionary ancestors were used to walking up to 12 miles per day. This means that our brains were supported for most of our evolutionary history by Olympic-caliber bodies. We were not sitting in a classroom for eight hours at a stretch. We were not sitting in a cubicle for eight hours at a stretch. If we sat around the Serengeti for eight hours—heck, for eight minutes—we were usually somebody’s lunch. We haven’t had millions of years to adapt to our sedentary lifestyle. That lifestyle has hurt both our physical and mental health. There is no question we are living in an epidemic of fatness, a point I will not belabor here. The benefits of exercise seem nearly endless because its impact is systemwide, affecting most physiological systems. Exercise makes your muscles and bones stronger, improving your strength and balance. It helps regulate your appetite, reduces your risk for more than a dozen types of cancer, improves the immune system, changes your blood lipid profile, and buffers against the toxic effects of stress (see the Stress chapter). By enriching your cardiovascular system, exercise decreases your risk for heart disease, stroke, and diabetes. When combined with the intellectual benefits exercise appears to offer, we have in our hands as close to a magic bullet for improving human health as exists in modern medicine. So I am convinced that integrating exercise into those eight hours at work or school will only make us normal.
All we have to do is move.
More ideas
I can think of a few simple ways to harness the effects of exercise in the practical worlds of education and business.
Recess twice a day
Because of the increased reliance on test scores for school survival, many districts across the nation are getting rid of physical education and recess. Given the powerful cognitive effects of physical activity, this makes no sense. Dr. Yancey described a real-world test: “They took time away from academic subjects for physical education … and found that, across the board, [adding exercise] did not hurt the kids’ performance on the academic tests. [When] trained teachers provided the physical education, the children actually did better on language, reading, and the basic battery of tests.”
Cutting off physical exercise—the very activity most likely to promote cognitive performance—to do better on a test score is like trying to gain weight by starving yourself. A smarter approach would be to insert more, not less, exercise into the daily curriculum. They might even
