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Study shows higher protein diet can make regular exercise more effective in women trying to lose weight

It has long been established that weight-loss requires a combination of diet and exercise, but according to a visiting academic from the University of Illinois, any exercise plan will be much more effective when it’s coupled with a higher protein diet.

Professor Donald Layman, who has been invited to speak at the International Congress on Obesity this week by Meat & Livestock Australia, recently studied the weight-loss effects of four different types of diet and exercise plans in women wanting to lose weight. 

His study found that a higher protein diet boosted the weight-loss results in women exercising almost daily, and that the weight-loss these women experienced mostly came from body fat, not muscle mass.  Risk factors of heart disease also improved.

Published in the August 2005 issue of the Journal of Nutrition, the four month study followed two groups on a higher protein diet, and two groups on a diet based on the US food guide pyramid, which contains higher amounts of carbohydrates.  All groups consumed the same number of calories but the levels of exercise within the diet groups differed. 

One group from each diet ‘camp’ (control groups) were advised to walk five days a week.  Walking was voluntary and averaged less than 100 minutes a week.  The other two groups (exercise groups) walked for at least 30 minutes five times a week and did two 30 minute weightlifting sessions. They averaged more than 200 minutes of exercise a week.

“All groups lost weight but the greatest weight-loss results were seen in the two groups that consumed the higher protein diet,” says Professor Layman. 

“But when the higher protein diet was combined with a higher level of exercise, even greater weight-loss results were seen, and almost 100 percent of the weight loss was fat,” explained the researcher.

“There is an added, interactive effect when a higher protein diet is combined with exercise.  The two work together to correct body composition.  Dieters lose more weight, and they lose fat, not muscle.  Some people refer to this as the metabolic advantage of a higher protein diet.”

The higher carbohydrate, lower protein diet actually reduced the effectiveness of exercise, Layman said.  Between 25 to 30 percent of the weight lost on this diet was muscle.

Professor Layman thinks a little known essential amino acid in protein-rich foods like lean red meat called leucine is behind the benefit.  Leucine works in the body with insulin to maintain healthy muscles.

“Leucine, working together with insulin, helps stimulate protein synthesis in muscle.  The diet works because the extra protein reduces muscle loss while the low carbohydrate component gives you low insulin, allowing you to burn fat,” he said.

“We believe a high carbohydrate, low protein diet does not provide enough leucine to maintain healthy muscles.  A typical high carbohydrate diet might contain four or five grams of leucine, but to get the metabolic effects seen in this study, you need nine or ten grams,” he noted.

Foods that contain leucine include lean red meat such as beef and lamb, low fat dairy and eggs.

Dr Manny Noakes from the CSIRO, and one of the authors of the CSIRO Total Wellbeing Diet, says Professor Layman’s findings are exciting and an important addition to our knowledge on how higher protein diets for weight management work as part of an active lifestyle.

“We have known about the benefits of a nutritionally balanced higher protein diet for some time but this is one of the first studies to show that a higher protein diet can also make the benefits of exercise more effective,” explained Dr Noakes.

“The study has also made some important progress in broadening our understanding of what it is about a higher protein diet that influences weight-loss.  More than 60 percent of Australians are now overweight and obese which means they are more vulnerable to a range of chronic illnesses including heart disease, type 2 diabetes and metabolic syndrome.  When it comes to public health, the more we can learn about what works best when it comes to weight-loss, and the right kind of weight-loss, the better,” she added.

Dr Noakes explains that following a higher protein diet does not mean simply eating more protein-rich foods and completely eradicating all carbohydrates. 

 “For health and wellbeing you need to ensure you are getting plenty of micronutrients.  That means a healthy balanced diet including plenty of fresh fruit and vegetables, and a moderate amount of wholegrain carbohydrates, lean red meat, seafood and low fat dairy products ,” added Dr Noakes.

Professor Donald Layman is speaking at the “Role of higher protein, low fat diets on weight management” symposium as part of the International Congress on Obesity on Wednesday 6 September.  Dr Noakes is among the guest speakers.