To drop 10 per cent of their body weight and keep it off for two years, obese and overweight women must exercise at least 55 minutes a day, five days a week, according to a new study.
Research published in the Archives of Internal Medicine this week said that in addition to limiting calories, overweight and obese women must exercise substantially more than was previously recommended.
"The less they exercised the less weight they lost and the less they kept off," said John Jakicic of the University of Pittsburgh, who led the study. "It seemed like this magic number of 275 [minutes a week]is what really made a difference."
Dr. Jakicic and his team spent two years studying 191 women between the ages of 21 and 45 with a body mass index of 27 to 40, which is above the threshold of healthy weight. Before taking part in the research, all of the women exercised less than 20 minutes a day, fewer than three days a week.
The women were prescribed diets of between 1,200 and 1,500 calories a day, and were divided into groups with different exercise goals.
While women in various groups lost weight, only those who exercised more than 55 minutes a day, five days a week, managed to keep the weight off two years later.
"We really wanted to delve into the issues around how much you might really need to do to keep this weight off long term," Dr. Jakicic said. "This study sheds some clear light on what those numbers need to be."
Before this study, health professionals often recommended that people exercise for a minimum of 30 minutes, five days a week. But that level is helpful only for those trying to maintain their health, Dr. Jakicic said, and is not effective for those who have managed to lose a large amount of weight and are trying to keep that weight off.
Obesity is a major issue in Canada, where 59 per cent of adults are overweight, including 23 per cent who are obese, according to Statistics Canada. Overweight is defined as having a BMI - an approximation of body fat based on height and weight - of more than 25, while a BMI of more than 30 indicates obesity.
But much of the focus on obesity has centred on issues of diet and ignored the impact of regular physical activity.
"There's been so much about the Atkins diet and the Zone diet and surgery," Dr. Jakicic said. "But even people who have the surgery gain weight again without a major lifestyle change."
Dr. Jakicic does not believe people should be discouraged by the exercise level required by his findings, even though working out 55 minutes a day, five days a week, may sound like too punishing a regimen.
Most of the women who were successful in the study were working mothers, he said, and got their exercise by walking. They were only required to reach a moderate level of intensity with their workouts, and few women put in serious hours at the gym.
"This shouldn't be discouraging. It can be done," he said. "They were able to find ways to make it work with their lifestyle."
Keeping up the intense workout schedule was sometimes difficult, Dr. Jakicic admitted, but because the women were focusing on both diet and exercise, they were able to make up for any momentary lapses of will.
"Not that over two years these women didn't flounder," he said. "But when they floundered with their diet, they were a little more diligent with their exercise."
The women exercised in periods that would previously have been designated as "sitting time," spent in front of a TV, a computer or a book.
"Most women say, 'I can't fit this into my lifestyle because it's going to negatively impact my family and children,' " he said. "When in fact what's negatively impacting the family is that they're not taking care of themselves."