It's also no secret that the long-recommended advice to eat less and exercise more has done little to curb the inexorable rise in weight. No one likes to feel deprived or leave the table hungry, and the notion that one generally must eat less to control body weight really doesn't cut it for most people.
The new research, by five nutrition and public health experts at Harvard University, is by far the most detailed long-term analysis of the factors that influence weight gain, involving 120,877 men and women who were healthy and not obese at the start of the study. The study participants - nurses and doctors, in the Nurses' Health Study, Nurses' Health Study II and the Health Professionals Follow-up Study - were followed for 12 to 20 years.
The analysis, published in The New England Journal of Medicine, examined how an array of factors influenced weight gain or loss during each four-year period of the study. The average participant gained 3.35 pounds (1.5 kg) every four years, for a total weight gain of 16.8 pounds (7.6 kg) in 20 years.
"This study shows that conventional wisdom - to eat everything in moderation, eat fewer calories and avoid fatty foods - isn't the best approach," says lead author Dr Dariush Mozaffarian, a cardiologist at the Harvard School of Public Health. "What you eat makes quite a difference. Just counting calories won't matter much unless you look at the kinds of calories you're eating."
Good and bad foods
Also untrue is the food industry's claim that there's no such thing as a bad food. "There are good foods and bad foods, and the advice should be to eat the good foods more and the bad foods less," he said. "The notion that it's okay to eat everything in moderation is just an excuse to eat whatever you want."
Consistent with other findings, the study found that metabolism takes a hit from refined carbohydrates, such as white flour and polished rice. Refined grains slowed metabolism, which determines how many calories are used at rest, but stayed the same after consumption of whole grains.
Physical activity also had the expected benefits. Those who exercised less tended to gain weight, while those who increased their activity didn't. But the researchers found that the kinds of foods people ate had a larger effect than changes in activity.
Little things mean a lot
People don't become overweight overnight. Rather, the kilos creep up slowly, often unnoticed, until one day nothing in the closet fits the way it used to. Even more important than its effect on looks and wardrobe, this gradual weight gain harms health. Rising weight increases the risk in women of heart disease, diabetes, stroke and breast cancer, and the risk of heart disease, diabetes and colon cancer in men.
Based on real-life experience, the study shows conclusively how small changes in eating, exercise and other habits can result in large changes in body weight over the years.
The New York Times
Every bite you take...counts