Inactive Americans are sevenfold more likely to gain over 10 kilograms during a 10-year period, compared with individuals who exercise regularly. Persons who rarely engage in physical activity are twice as likely to gain 5 kilograms in 5 years, compared with those who are often active. One investigation has shown that every 10 hours spent sitting is associated with a weight gain of .11 kg (about one-fourth of a pound).  Weight Loss Resaerch News

Clearly, exercise is important for controlling weight, but how much exercise is needed? A recent study carried out at the University of California at Berkeley with over 27,000 women indicates that the answer to this question may depend on a person's body composition. At Berkeley, noted epidemiologist Paul T. Williams explored the relationship between BMI and weekly walking distance. BMI, which is simply one's weight in kilograms divided by height in meters squared, is a decent indicator of fatness; as weight goes up, BMI also rises. Height is accounted for by the denominator (height squared) so that very tall persons are not penalized for their stature. If BMI is above 30, a person is said to be obese. BMIs of 25 to 29.99 are associated with the "overweight" condition, and a BMI below 25 is thought to represent "normal" body composition. Williams noted a threshold effect in his research. Weight Loss Research News

That is, beyond about 25 to 30 kilometers of weekly walking, there was little relationship between added amounts of weekly exercise and body composition in overweight and normal-weight women. For obese women, weekly walking volumes above 30 kilometers were linked with decreases in fatness, but the additional downturns in suet were not as great as those achieved when obese women increased their distance at lower levels of walking (between 0 and 30 km per week). In fact, Williams noticed that the link between walking volume and BMI was fairly tightly linked with a woman's BMI.

Specifically, for women in the 90th percentile for BMI (with BMI readings generally well above 30) there seemed to be a large reduction in BMI for each five kilometers of walking added to the weekly schedule. In contrast, for women at the 50th percentile of BMI (with readings between 25 and 29.99), there appeared to be a smaller downturn in BMI for each increment in walking distance. Finally, for women of normal body composition (the 10th percentile of BMI) there was little connection between weekly walking distance and BMI; on average, women who walked 60 kilometers per week were barely leaner than women who walked 20 weekly kilometers, for example.

Overall, increasing weekly walking distance from 10 kilometers to 11 kilometers was associated with a 15-fold greater decline in BMI for women in the 95th percentile of BMI, compared with women in the 5th percentile. The research suggests that increases in weekly walking volume can have a huge impact on BMI in obese women, and a more-moderate effect in overweight women.

What concerns do you have about maintaining your weight-loss program as the weather gets colder?