12 Ways to avoid weight gain as you age

By Deborah Kotz, Globe Staff

Gaining weight through the decades -- we put on about a pound a year on average after age 20 -- seems impossible to avoid. Like slowly accumulating credit card debt, we’re never quite sure exactly how the pounds crept on.

Well, a study this week in the New England Journal of Medicine provides an accounting of sorts for more than 120,000 non-obese individuals who participated in the ongoing Nurses’ Health Study and the Health Professionals Follow-up Study from 1986 to 2006. The Harvard School of Public Health researchers identified a dozen individual things that contribute to weight gain or help keep the pounds off as you age.

“Weight gain often occurs gradually over decades making it difficult for most people to perceive the specific causes,” write the study researchers. “A habitual energy imbalance of about 50 to 100 kcal per day may be sufficient to cause the gradual weight gain seen in most persons. This means that unintended weight gain occurs easily but also that modest, sustained changes in lifestyle could mitigate or reverse such an energy imbalance.”

The study also looked at how lifestyle changes like quitting smoking or increasing the amount of sleep you get affects your body weight over time.

Here’s how much each contributes.

Potato chips. Increasing consumption of potato chips was the single biggest factor associated with weight gain through the years. For every extra daily serving that study participants ate, their weight increased by nearly 1.7 pounds over each four-year period in the study.

Other potato products. Everything from baked potatoes, to mashed potatoes, to French fries contributed to weight gain, an average of nearly 1.3 pounds over four years. But that extra daily serving of French fries was responsible for a 3.4 pound gain whereas mashed, baked, or boiled potatoes led to just an 0.5 gain for each added serving.

Sugary beverages. Sugar soda, energy drinks and other beverages containing sugar took third place on the weight gain list accounting for a one pound gain for every daily serving that was added through the years. Fruit juice and alcohol consumption also contributed to weight gain, but not as much. On the other hand, switching to calorie-free sodas led to a weight loss of about 1/2 a pound over the four years.

Red meat. Adding a daily serving of red meat contributed to weight gain of slightly less than a pound over a four year period. That includes, steak, burgers, deli meat and hot dogs. Reducing consumption led to less weight gain over time.

Refined grains and sweets. Each extra daily serving of white bread, pretzels, and other processed starches contributed slightly less than half a pound over four years. Same, too, for each extra sugary dessert.

Quitting smoking. Those who quit smoking within the previous four years had an average weight gain of five pounds -- not that this should be used as an excuse to keep smoking! Beyond that, however, former smokers who kept it up had just a small amount of subsequent weight gain, 0.14 pound per four years, that could be attributed to their old habit.

Sleep extremes. Getting fewer than six hours per night or more than eight hours led to slightly more weight gain over time compared to getting between six and eight hours per night.

TV watching. Every one hour a day that was added to TV time over the years contributed to a third of a pound gain over four years. But the researchers stress that TV viewing may also have indirect weight gain effects since it encourages snacking and may interfere with sleep and physical activity, both of which were measured separately.

Vegetables and fruits. Increasing consumption of produce resulted in less weight gain over time. Adding just one daily serving of vegetables and one daily serving of fruit prevented a ¾ pound gain over a four-year period. While it seems paradoxical that increasing portions would lead to less weight gain, the researchers pointed out that these foods probably substituted for higher calorie foods that were reduced in the diet.

Exercise. Interestingly, total amount of exercise wasn’t associated with weight changes over time, but changes in physical activity were. Those who started exercising more gained 1.76 fewer pounds over each four-year period compared to those who didn’t alter their activity habits.

Whole grains and nuts. Adding a daily serving of nuts reduced weight gain by about ½ pound over a four year period, while switching to whole-wheat products and brown rice also helped prevent weight gain, though by a smaller amount.

Yogurt. Consuming more of this food provided the biggest bang for the buck in terms of preventing weight gain. Every daily serving added was associated with a 0.82 pound prevention of weight gain.