Obesity results from energy imbalance: too many calories in, too few calories burned. A number of factors influence how many calories (or how much “energy”) people burn each day, among them, age, body size, and genes. But the most variable factor-and the most easily modified-is the amount of activity people get each day.
Keeping active can help people stay at a healthy weight or lose weight. It can also lower the risk of heart disease, diabetes, stroke, high blood pressure, osteoporosis, and certain cancers, as well as reduce stress and boost mood. Inactive (sedentary) lifestyles do just the opposite.
Despite all the health benefits of physical activity, people worldwide are doing less of it-at work, at home, and as they travel from place to place. Globally, about one in three people gets little, if any, physical activity. Physical activity levels are declining not only in wealthy countries, but also in low- and middle-income countries. And it’s clear that this decline in physical activity is a key contributor to the global obesity epidemic, and in turn, to rising rates of chronic disease everywhere.
The World Health Organization, the U.S. Dept. of Health and Human Services, and other authorities recommend that for good health, adults should get the equivalent of two and a half hours of moderate-to-vigorous physical activity each week. Children should get even more, at least one hour a day. There’s been some debate among researchers, however, about just how much activity people need each day to maintain a healthy weight or to help with weight loss, and the most recent studies suggest that a total of two and a half hours a week is simply not enough.
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