Scientists at the National Cancer Institute, Harvard Medical School and other centers published a recent paper in JAMA Internal Medicine showing that exercise appears to substantially reduce the risk of developing 13 varieties of cancer. The benefits seem to hold true even if someone is overweight.
Researchers looked at 12 large studies involving 1.44 million men and women. They focused on specific information for each of those people about whether they exercised, how vigorously and how often. They also zeroed in on whether and when, after each study’s start, the participant was diagnosed with any type of cancer. People who reported exercising moderately, even if the time they spent exercising was slight, had significantly less risk of developing 13 different types of cancer than people who were sedentary.
The researchers found a reduced risk of breast, lung and colon cancers, findings that had been reported in earlier research. But they also found a lower risk of tumors in the liver, esophagus, kidney, stomach, uterus, blood, bone marrow, head and neck, rectum and bladder. When researchers compared the top 10 percent of exercisers—meaning those who spent the most time each week engaging in moderate or vigorous workouts—to the least active 10 percent, the exercisers were as much as 20 percent less likely to develop most of the cancers in the study.
On the other hand, they found an increased risk of two types of malignancies—melanoma and slow-growing prostate tumors—among people who exercised the most. Those findings are most likely explained by certain characteristics of active people, said Steven Moore, an investigator at the National Cancer Institute who led the study. “People who exercise generally go in for more checkups” than do sedentary people, he said, resulting in more screenings for conditions such as so-called indolent prostate cancers. (There was no discernible association, positive or negative, between exercise and aggressive prostate tumors.) “They also often exercise outside,” he continued, “and are more prone to sunburns” than people who rarely work out, potentially contributing to a greater risk for melanoma.
Encouragingly, the associations between exercise and reduced cancer risks held true even when the researchers factored in body mass. People who were overweight or obese but exercised had a much lower risk of developing most cancers than overweight people who did not move much.
The authors cautioned that this was an observational study, so it cannot directly prove that exercise reduces cancer risks, only that there is an association between more exercise and less disease. It also relied on participants’ memories of exercise, which can be unreliable. But even with those limitations, the findings sturdily suggest that exercise may help to reduce the risk of many types of cancer. Here in West Marin, we have walking and hiking trails, dirt roads, gyms in Stinson and Point Reyes, tennis courts, classes at community centers, and the ocean! Let’s keep moving.
Successful weight control
A recent article in the New York Times reported that people who succeeded in losing large amounts of weight—say, a decrease from 430 pounds to 190—were rarely able to stay at their new weights. Most of the dieters in the article had lost large amounts of weight rapidly as contestants in The Biggest Loser television program. When they began dieting they had normal metabolisms for their body size; after losing weight, their metabolisms slowed radically and their bodies were not burning enough calories to maintain their thinner sizes. As the years went by, their metabolisms did not recover, so they kept gaining back weight. It seemed that their bodies were working to pull the dieters back to their original weights. Investigators also found that the dieters had very low levels of leptin, a hormone made by fat cells that inhibits hunger. They were unable to detect satiety, or feeling full.
This is discouraging news to people who want to lose weight for health reasons, such as having diabetes or certain kinds of heart disease. Research about ways to improve this situation is ongoing.
Are there other models of weight loss that would be more effective in the long term? Let’s look at the National Weight Control Registry for ideas. This organization was started by researchers from Brown Medical School and the University of Colorado to examine people who have lost weight (at least 30 pounds) and kept it off for a year or more. People enroll voluntarily; 80 percent are women, and 20 percent are men. On average, weight loss has been 66 pounds, kept off for 5.5 years. Most people report maintaining a low-calorie, low-fat diet (25 percent fat) and doing high levels of physical activity. Seventy-eight percent eat breakfast daily, 75 percent weigh themselves at least once a week, 62 percent watch less than 10 hours of television per week and 90 percent exercise, on average, about one hour a day. Changing beverage consumption to low or no-calorie sweetened drinks is felt to be very important for weight loss and maintenance by the participants. People in the registry varied in the amount of exercise they did, and in their dietary plans. There was no one-size-fits-all formula being followed.
Dr. Barbara Rolls at Penn State University has written several popular books on making weight loss easier; her latest is “The Ultimate Volumetrics Diet.” She has looked at ways to change the amount of water in foods, thereby adding weight and volume but no calories. This is done by adding vegetables to each recipe, and making sure the food is tasty. The result, found in careful studies, is that people reduce their calorie intake by about 25 percent. In a trial of 700 people, she found that when people ate a diet that was less calorie-dense—meaning more vegetables were included—they were eating significantly more food (about a pound more food a day) but fewer calories and they were easily losing more weight. She has many good ideas, backed by research, that keep people healthy while losing weight slowly. Read this book if you are frustrated about your weight. Aim to lose weight slowly, so your metabolism can adjust more easily. And, whenever possible, keep moving!
Sadja Greenwood is a Bolinas resident and a retired physician. Read more of her work at sadjascolumns.blogspot.com.