Fewer Americans 75 and older are obese compared to any other age group. But nearly 41 percent of adults 65-74 are considered obese, among the highest of any age group. The reason for lower obesity rates among older seniors is not because Americans suddenly decide to lose weight when they turn 75. It's because, on average, those who are severely overweight don't live as long.

What used to be known euphemistically as "middle-age spread" is spreading. The reasons are part evolutionary and part societal. "As you get older, your metabolism starts to slow down," says Eliza Kingsford, executive director of Wellspring Camps, an operator of six weight-loss and fitness campsites in the United States. "You couple that with poor eating habits you've had for years, and it's the perfect storm for weight gain."

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For many older adults, a lot of what they believe about good nutrition is wrong. Substituting a glass of juice for a sugary soft drink may sound like a healthy choice, but it often is more of the same. A 12-ounce serving of apple or orange juice has about the same amount of calories and sugar as a 12-ounce glass of Coke or Pepsi. And as far as your body is concerned, sugar is sugar. The solution? Eat the whole fruit, which has fiber and other important nutrients. "Once you take that away, a glass of orange juice is just sugar," Kingsford says.

Eating healthy needn't be costly. A home-cooked meal that begins with ingredients such as fresh chicken is almost always less expensive than buying a frozen entree that is often loaded with sugar and saturated fat. And it is far less expensive than eating out, where you lose control of what is in your food. And beware of those large restaurant servings that seem to have grown exponentially over the years. "You should probably halve the portions, especially if you're in your 50s or 60s," Kingsford says.

But many older adults don't have the time or don't feel motivated to cook. Kingsford says even if you cook just one or two days a week, make enough that you can use in several meals. For example, leftover grilled or baked chicken can be used in an array of healthy recipes throughout the week. "It's a good way to save a buck and also a good way to plan," she says.

The National Institutes of Health has healthy eating advice for older adults at nwsdy.li/eatingnih and nwsdy.li/eatingnia.