Exercise alone is unlikely to help shift the pounds, say researchers.
Researchers at Bangor University in the United Kingdom found that women who engaged in exercise classes three times per week for 4 or 8 weeks — but who did not change their diets — failed to lose any weight.
Study co-author Dr. Hans-Peter Kubis, of the School of Sport, Health & Exercise Sciences at Bangor University, and colleagues recently reported their findings in the journal Applied Physiology, Nutrition, and Metabolism.
The study involved two experiments. For the first experiment, 34 women aged 18 to 32 years took part in a circuit exercise training session three times per week for a total of 4 weeks.
The second experiment included 36 women of the same age group, all of whom took part in the same training sessions, but for a total of 8 weeks.
At the beginning and end of each experiment, the weight, muscle, and fat mass of each woman were measured.
Blood samples were also taken from the participants, which allowed the team to measure levels of appetite hormones, including insulin, leptin, amylin, ghrelin, and peptide YY. Such hormones can influence feelings of hunger and food intake.
Appetite hormones may play a role
The aim of this study was to determine whether or not exercise alone would lead to weight loss in the women, but the subjects were not informed of this. Instead, they were told that the study would assess the effects of exercise on cognition and cardiorespiratory fitness. Dr. Kubis says that this was to avoid potential bias.
"When people take up exercise, they often restrict their diet — consciously or unconsciously — and this can mask the effects of the exercise," he explains.
At the end of the 4- and 8-week programs, the researchers found that none of the women had lost weight, regardless of whether they were lean, overweight, or obese prior to the intervention.
Lean women, however, did see an increase in muscle mass after the exercise training.
The researchers also found that women who were overweight or obese experienced changes to appetite hormones that were associated with increased hunger. The team says that this may partly explain why exercise alone may not lead to weight loss.
"Our body system is so well regulated, that it always finds a way to compensate for a loss in energy after exercise," says Dr. Kubis.
"Whether they are aware of it or not, someone undertaking more physical activity or exercise may experience increased appetite as a result, and this makes it difficult for people to achieve their goals."
Exercise isn't just about weight loss
The team stresses that they are not saying that exercise has no benefits — far from it. For weight loss, however, physical activity alone is unlikely to be enough.
"To be effective, exercise training for weight loss needs to be integrated into a lifestyle approach to weight loss, including exercise combined with diet."
Dr. Hans-Peter Kubis
That said, Dr. Kubis notes that when it comes to the benefits of exercise, weigh loss should not be the main focus.
"Knowing how much fat and muscle we have in our body is much more important than knowing how much we weigh," he says. "When we focus on weight alone, we miss the improvements achieved via exercise training."
"Seeing no change on [the] scales may be enough to make people give up on their exercise training, not realizing that they have actually improved their body by gaining muscle mass."
He adds that gyms and other exercise facilities should incorporate more equipment that focuses on improving body composition.