Everyone knows that eating a low-fat, low-kilojoule diet and getting regular exercise helps shed pounds, but a new study led by researchers at Fred Hutchinson Cancer Research Centre has found that when it comes to losing weight and body fat, diet and exercise are most effective when done together, compared to either strategy on its own.
The results of this randomised trial, led by Dr Anne McTiernan, director of the Prevention Centre and a member of the Hutchinson Centre's Public Health Sciences Division, were published in Obesity.
The majority of women in the study who both improved their diet and exercised regularly shed an average of nearly 11% of their starting weight, which exceeded the study's goal of a 10% or more reduction in body weight.
"We were surprised at how successful the women were," McTiernan said. "Even though this degree of weight loss may not bring an obese individual to normal weight, losing even this modest amount can bring health benefits such as a reduced risk of diabetes, heart disease and cancer."
The year-long intervention involved 439 overweight-to-obese, sedentary, postmenopausal Seattle-area women, ages 50 to 75, who were randomly assigned to one of four groups:
exercise only (goal: 45 minutes of moderate-to-vigorous aerobic exercise per day, five days a week, including three days at the Hutchison Centre's exercise facility);
diet only (goal: 5,040kJ to 8,400kJ a day, depending on starting weight, and fewer than 30% of daily kilojoules from fat);
exercise and diet (with the same goals as above); and
"Although numerous studies have examined the effect of lifestyle interventions on weight, few have focused on postmenopausal women, a group that experiences particularly high rates of overweight and obesity," McTiernan said.
At the end of the intervention, the researchers found that the women in the exercise-only group lost, on average, 2.4% of their starting weight (with a mean weight loss of 2kg) as compared to an average weight loss of 8.5% among women in the diet-only group (with a mean weight loss of 7kg).
The greatest weight loss was achieved by women who both changed their diet and exercised regularly. These women shed an average of 10.8% of their starting weight (with a mean weight loss of 9kg). Two-thirds of the women in this group achieved the study goal of losing at least 10% of their starting weight.
Body-mass index (height-to-weight ratio), waist circumference and percentage of body fat were also significantly reduced among the three intervention groups. The women who were assigned to the non-intervention control group, who did not change their diet or activity level, lost less than 500g on average – a statistically insignificant decrease.
"This study shows that you get the biggest bang for your buck by combining a healthy weight-loss diet – which in this case meant reducing calories by cutting fat intake and boosting the consumption of low-calorie foods – with regular, moderate-intensity aerobic exercise," McTiernan said.
"You don't need to be an athlete; walking, biking or gym cardio machines all work well. Start slowly and gradually increase to 45 minutes of activity a day, more if you are able."
Balance, strength and fitness
In addition to promoting weight loss and preventing weight gain over time, regular exercise helps with balance, strength and fitness. "This helps older people keep active overall, which has been shown to prolong a healthy life," McTiernan said.
The study also found that the women who lost the most weight and body fat kept a food journal, writing down everything they ate and drank, with the exception of water and no-kJ drinks. Other strategies associated with the most successful weight loss included preparing meals at home and eating out less often at restaurants.
"Doing your own cooking gives you the greatest control over calories," McTiernan said.
The combined diet-plus-exercise arm of the study followed the current nutrition and physical activity recommendations by the National Institutes of Health Obesity Education Initiative Expert Panel. "Our clinical trial supports these recommendations," McTiernan said.
Despite the overwhelming evidence for the benefits of lifestyle-induced weight loss, there are still major barriers to implementing these programmes, the authors wrote. To this end, McTiernan and colleagues are conducting ongoing follow up of these study participants to try to determine factors – both psychological and behavioural – that are associated with long-term weight-loss maintenance.
"Identifying factors that help women not only lose weight, but keep it off long term will help steer the development and implementation of obesity-treatment programs that have the greatest promise to impact public health," she said. - (EurekAlert!, April 2011)