The evidence continues to weigh in: for health and longevity, it pays to be thin - considerably thinner than current guidelines for middle-aged Americans recommend.
A major new study suggests that even a moderate gain, of 22 pounds or more above a person’s weight at age 18, incurs a greater risk of earlier death.
Though the risks of being seriously overweight are well known, there is still medical controversy as to whether moderate weight gain poses a risk to health.
The new study, conducted among more than 115,000 women nurses who were followed for 16 years, sought to clarify the question by excluding people who were lean because of smoking or pre-existing diseases.
An earlier study of the same group of women, reported in February, concluded that moderate weight gain of even 11 to 18 pounds in adult life, resulted in a higher risk of heart disease specifically.
The new analysis, published in today’s New England Journal of Medicine, has found that a surprising one-third of cancer deaths as well as more than half of cardiovascular deaths were due to excess weight, according to the study’s director, Dr. JoAnn E. Manson.
Excess weight was linked to deaths from cancers of the colon, breast and endometrium, said Dr. Manson, an endocrinologist at Brigham and Women’s Hospital and Harvard Medical School in Boston. She suggested that bile acids formed from fats in the diet and estrogens produced in body fat raise the risk of developing these cancers.
The study is of particularly wide relevance because a third of adult Americans are overweight - defined as 20 percent or more above desirable levels - and the national girth is still growing: over the past 15 years the mean body weight of American adults has increased by 7.9 pounds.
The new study confirms the risks of being seriously overweight. Over all, in this group of women, who were healthy and 30 to 55 years old when the study began in 1976, obesity - defined as being 30 percent or more above desirable weight - accounted for more than half the 4,726 deaths that occurred during the study period, Manson said in an interview.
Women who were obese were four times as likely to die of heart disease and twice as likely to die of cancer as were women whose weights were below average for their age.
Among women who had never smoked, even those who were slightly or moderately overweight had death rates higher than did the leanest women, who weighed at least 15 percent less than the average American woman of the same height.
For example, for women 5 feet 5 inches tall (the average American woman), weighing from 120 to 149 pounds increased the risk of early death by 20 percent above that for women weighing less than 120 pounds. At a weight of 161 to 175 pounds, the risk rose by 60 percent and for women weighing more than 176 pounds, the risk more than doubled.
For all women categorized as obese, the chances of an early death were doubled, a statistic that is expected to get worse as the women age and heart disease overtakes cancer as their leading cause of death.
Although women and men often show minor differences in health characteristics, other studies suggest that the new findings in nurses probably apply to men as well.
In projecting her results to the U.S. population as a whole, Manson estimated that “about 300,000 deaths a year are attributable to overweight, second only to cigarette smoking, which causes 400,000 deaths a year.” She added that if current trends continue, “it won’t be long before obesity surpasses cigarette smoking as a cause of death in this country.”
A second study published in today’s New England Journal of Medicine, and conducted among 6,500 Japanese-American men, found no harm in losing weight or in a repeated cycle of weight loss and gain, again if the men were initially healthy and had never smoked.
But as with the study in women, this one showed that to ward off an early death, it is best to start lean and maintain a stable weight throughout adulthood. The analysis, directed by Dr. Carlos Iribarren, an epidemiologist at the University of Minnesota School of Public Health, was conducted among participants in the ongoing Honolulu Heart Study.
Dr. Tim Byers, professor of preventive medicine at the University of Colorado School of Medicine in Denver, said in an interview that the two studies “show once again that being overweight shortens your life.”
Furthermore, he said, “they dispel the myth that being too thin is also harmful.” This notion, which formed the basis for current weight guidelines suggesting it is healthiest to weigh more in middle age than in early adulthood, was based on “flawed data,” he and other experts maintain.