Exercise isn’t very good way to lose weight, but it works like a charm in many other ways—including helping to keep you from gaining weight.

In his book Keep Sharp, Sanjay Gupta lauds exercise as the number one way to help keep your brain healthy. Leading into his discussion of exercise, he emphasizes the importance of prevention to avoid dementia in old age:

Prevention is the most powerful antidote to illness, and this is especially true of degenerative maladies like those in the brain and nervous system. Shockingly, half of adults don’t know the risk factors for dementia …

He points out that the roots of dementia in old age go way back in time:

Among people who are eighty-five years old, an age at which more than 30 percent have developed dementia, signs of brain decline began silently when they were between fifty-five and sixty-five years old. Similarly, the brain health of the 10 percent or so of people who are sixty-five years old and have developed dementia started to quietly degenerate when they were between thirty-five and forty-five years old.

Exercise isn’t the only thing that matters. He lays out some other risk factors for dementia as well:

Data from longitudinal observational studies accumulated over the past few decades have shown that aside from age, most other risk factors for brain disease can be controlled. That means you indeed have a powerful voice in controlling your risk for decline. As you might guess, some of the most influential and modifiable factors related to that decline are linked to lifestyle: physical inactivity, unhealthy diet, smoking, social isolation, poor sleep, lack of mentally stimulating activities, and misuse of alcohol. Half of Alzheimer’s cases in the United States alone could be caused or worsened by a combination of these bad habits. High blood pressure, obesity, diabetes, and high cholesterol, especially at midlife, substantially increase the chances of developing dementia later—sometimes decades down the road.

But in Sanjay’s view, exercise is the most important. He writes:

When people ask me what’s the single most important thing they can do to enhance their brain’s function and resiliency to disease, I answer with one word: exercise—as in move more and keep a regular physical fitness routine.

You can easily do the experiment for yourself to verify that exercise will make you feel more cheerful and clearer-headed. As Sanjay writes:

Go out for a fast-paced walk around the block, and when you return, note how you feel and how your mind is humming. My bet is you will have more mental energy even if the walk left you out of breath. And you will probably feel more optimistic and better able to tackle the challenges of the day.

Here is his claim about the many dimensions of well-being exercise can help with:

… exercise improves digestion, metabolism, body tone and strength, and bone density. Most of us think about it as a weight loss tool, which it is. But it’s much more than that. It can turn on your “smart genes,” support emotional stability, and stave off depression and dementia. When you choose the right exercise for you, it’s enjoyable and increases your self-worth and confidence. Don’t take this lightly because I really mean it: You can be smarter by some measures after one hour of exercise through the effects of movement on the brain.

Sanjay argues that because survival in the environment of evolutionary adaptation required a lot of physical activity, our bodies are designed on the assumption that we will get a lot of exercise:

Throughout most of human history, we’ve been physically active every day. We had to be in order to survive. Science has even proven that over millions of years, our genome evolved in a state of constant physical challenge—that is, it took a massive amount of physical effort to find food and water. Put another way, our genome expects and requires frequent movement. I often tell my students: “We humans were not designed to sit or lie down for twenty-three hours a day and then go to the gym for an hour. Science has revealed that we humans are designed to be pretty consistently active right down to our molecular core.”

Indeed, in the environment of evolutionary adaptation, survival required so much exercise that what opportunities there were to rest and thereby burn fewer calories were valuable. On that point, Sanjay quotes The Story of the Human Body, by Daniel Lieberman:

… Dr. Lieberman makes a strong case that our epidemic levels of chronic disease today are the result of a mismatch between our evolutionary roots and modern lifestyles: “We still don’t know how to counter once-adaptive primal instincts to eat donuts and take the elevator.” In a follow-up 2015 paper, Lieberman calls out the paradox: “Humans evolved to be adapted for regular, moderate amounts of endurance physical activity into late age,” but “humans also were selected to avoid unnecessary exertion.”

Here is Sanjay’s list of the benefits of exercise:

Benefits of Exercise

…

• Lowered risk of death from all causes

• Increased stamina, strength, flexibility, and energy

• Increased muscle tone and bone health

• Increased blood and lymph circulation and oxygen supply to cells and tissues

• More restful, sounder sleep

• Stress reduction Increased self-esteem and sense of well-being

• Release of endorphins, the brain chemicals that act as natural mood lifters and pain relievers

• Decreased blood sugar levels and risk for insulin resistance and diabetes

• Ideal weight distribution and maintenance

• Increased heart health, with lower risk for cardiovascular disease and high blood pressure

• Decreased inflammation and risk for age-related disease, from cancer to dementia

• Stronger immune system

Many of these benefits have good downstream effects as well. The effects Sanjay emphasizes—avoiding diabetes and the extremely common pre-diabetes (which goes by many names), reducing inflammation, stimulating growth factors that foster new neurons, improving the blood vessel network in the brain, reducing stress and anxiety, improving sleep and improving mood—help keep other bad things from happening.

The biggest benefits from exercise come from the first little bit. Equivalently, being a total couch potato is very, very bad compared to doing at least a little bit of exercise. So the most important thing is to get started on something. Don’t let the best be the enemy of the good. So try not to look at the next few lines until you are already doing something. Ideally however, you should do a moderately ambitious exercise program. Sanjay writes:

… you have to engage in regular physical exercise at least 150 minutes a week and incorporate interval and strength training into the mix. Interval training means you alternate between varying levels of speed, intensity, and effort. Think of it as surprising the body so you don’t fall into well-worn ruts that fail to challenge the body and lead to a plateau in your progress. Strength training refers to the use of weights or just your own body weight as resistance. This helps build muscle mass and tone and helps balance and coordination.

For annotated links to other posts on diet and health, see:

• Miles Kimball on Diet and Health: A Reader's Guide