LOS ANGELES -- Blame the potato chip. It's the biggest demon behind that pound-a-year weight creep that plagues many of us, a major diet study found. Bigger than soda, candy and ice cream.
And the reason is partly that old advertising cliche: You can't eat just one.
"People generally don't take one or two chips. They have a whole bag," said obesity expert Dr. F. Xavier Pi-Sunyer of the St. Luke's-Roosevelt Hospital Center in New York.
What we eat and how much of it has far more impact than exercise and most other habits do on long-term weight gain, according to the study by Harvard University scientists. It's the most comprehensive look yet at the effect of individual foods and lifestyle choices like sleep time and quitting smoking. The results are in today's New England Journal of Medicine.
Two-thirds of U.S. adults are overweight or obese. Childhood obesity has tripled in the past three decades. Pounds often are packed on gradually over decades, and many people struggle to limit weight gain without realizing what's causing it.
The new study finds choice of food is key. The message: Eat more fruits, vegetables, whole grains and nuts. Cut back on potatoes, red meat, sweets and soda.
"Diet and exercise are important for preventing weight gain," said one study leader, Dr. Frank Hu, "but diet clearly plays a bigger role."
The study found that each daily serving of potato chips containing 1 ounce (about 15 chips and 160 calories) led to a 1.69-pound uptick over four years. French fries were worse for the waist than boiled, baked or mashed potatoes. That's because a serving of large fries contains between 500 to 600 calories, compared with a serving of a large baked potato at 280 calories.