Stanford Medicine Newsletter Updates For the Local Community


A weighty problem

How inactivity is making us obese


Popular thinking holds that the nation's obesity epidemic, which accounts for roughly 20 percent of health-care spending in the United States, is the result of greater consumption of calories.

But a recent study by Uri Ladabaum, MD, a Stanford professor of gastroenterology, and his team points out the contribution of physical inactivity to the obesity epidemic. Between 1988 and 2010, the percentage of women reporting no physical activity skyrocketed from 19 percent to 52 percent, the researchers found. And the percentage of inactive men jumped from 11 percent to 43 percent over the same period.

Surprisingly, the number of calories consumed did not increase during that time period, the team wrote in the study, published in August in The American Journal of Medicine. The solution isn't quite as simple as telling patients to exercise, Ladabaum said. 

Were the study results a surprise?

We were aware of the published trends in obesity and the fact that not all studies reached the same conclusions regarding caloric intake and physical activity in the United States. But we were surprised at the dramatic changes in self-reported leisure-time physical inactivity in the data we analyzed—and the contrast with the relatively stable self-reported caloric intake over the last two decades. We were also struck by the particularly worrisome trends in obesity in younger women.

What is driving this surge in inactivity?

This is a complex question that we did not address in this study. First, it is important to note that survey methods changed over time—participants answered slightly different questions in the early, middle and later years in the database. But assuming that our results reflect what has been happening in the general population, one can speculate that contributing factors might include longer work hours, competing demands at home, long commutes and more time driving in general, and time spent in the "electronic or virtual world" instead of the physical world.

Why is exercise so fundamental to maintaining a healthy body weight?

The simple answer is that weight reflects energy balance: calories in and calories out. In this simplified view, calories ingested that are not expended are stored, and we gain weight. The more complex reality is that there are multiple mechanisms with feedback loops and interactions that regulate appetite and a person's individual "weight set point." Individuals differ in the amount of energy they expend as a part of daily life, including the fact that some can sit completely still through a two-hour movie while others tap their feet and fidget. Exercise is one part of the energy expenditure side of the equation, but it's one that we can control. In addition, exercise can also modulate appetite. 


Does this mean that what we eat isn't as important to health as other factors, such as exercise?

Absolutely not. It is absolutely clear that both caloric intake and physical activity matter a lot.
Exactly how much of the obesity problem in the population can be attributed to the calories in versus calories out sides of the equation is difficult to tease out. We may never know, and I would argue that it may not really matter. We know enough about the importance of both factors to make recommendations that support a sensible diet and regular physical activity.
Furthermore, the importance of both diet and exercise go far beyond their impact on weight. A healthy diet decreases the risk of many diseases, including cardiovascular disease and cancer. The same goes for exercise. It has many benefits beyond its contribution to weight management, including improved fitness, overall health and well-being.

How much exercise is enough? Is it possible to exercise too much?

I don't think there is an absolute answer to this. The federal Centers for Disease Control and Prevention have guidelines on their website, with recommendations that vary by age. For instance, for adults aged 18 to 64, the CDC recommends 2½ hours of moderate-intensity aerobic activity (like brisk walking) or one hour and 15 minutes of vigorous-intensity aerobic activity (like jogging or running) every week, and muscle-strengthening activities at least twice a week.

There is a very broad range in what people are actually doing. Some people, including those in their 70s or 80s, are extremely active — running long distances or doing other sustained vigorous physical activities many times a week. Clearly, you can't say this is "too much" when these people are fit and healthy.

I think there is a problem when "over-exercise" is part of a body-image problem or an eating disorder, but that is as much a mental-health issue as a physical fitness question. Also, one needs to be aware of the long-term mechanical consequences of certain types of exercise — but this relates to personal decisions about what activities we enjoy doing.

What do you recommend to your patients who are inactive?

Start slowly — walk 10 to 15 minutes several times a week. Then, as tolerated, try to build up to the types of recommendations like the CDC's. Depending on a person's physical limitations, the type of activity may need to be adjusted.

What type of exercise do you do?

I play soccer. I do strengthening exercises several times a week. I take walks. I sometimes swim or bike with our kids on weekends. I try to make physical activity a part of daily life — taking the stairs, walking, not sitting still, and so on. These ways of moving during a typical day must also be emphasized — it's not only about going to the gym. 

As health-care providers, we sometimes do a bad job of caring for our own health. We need to do that for ourselves and for our families, and maybe even for our patients. Our messages are probably more believable if we do what we are asking our patients to do.

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