The researchers say this effect may improve the success of obesity treatment, especially among people with high insulin secretion (insulin level 30 minutes after consuming a standard amount of glucose).
It is well known that energy expenditure declines with weight loss, as the body adapts by slowing metabolism and burning fewer calories, often resulting in weight regain. But little is known about how dietary composition influences this adaptive response over the long term.
One theory (known as the carbohydrate-insulin model) is that recent increases in the consumption of processed, high glycemic load foods trigger hormonal changes that increase hunger and make people more likely to gain weight.
To better understand the role of dietary composition on energy expenditure, researchers led by Cara Ebbeling and David Ludwig at Boston Children’s Hospital set out to compare the effects of diets varying in carbohydrate to fat ratio on energy expenditure over a 20-week period.
The trial involved 234 overweight adults aged 18 to 65 years with a body mass index (BMI) of 25 or higher who took part in an initial weight loss diet for about 10 weeks.
Of these, 164 achieved the target weight loss of around 10% of body weight and were then randomly assigned to follow either a high (60%), moderate (40%), or low (20%) carbohydrate diet for 20 weeks.
Each participant was provided with fully prepared meals with a similar protein and fat content. The researchers then tracked participants’ weight and measured energy expenditure to compare how the different groups burned calories at the same weight.
After adjusting for potentially influential factors, they found that over the 20 weeks, total energy expenditure was significantly greater in participants on the low carbohydrate diet compared with the high carbohydrate diet.
Participants on the low carbohydrate diet burned 209 to 278 kilocalories a day more than those on the high carbohydrate diet – or about 50 to 70 kilocalories a day increase for every 10% decrease in the contribution of carbohydrate to total energy intake.
In those with the highest insulin secretion at the start of the study, the difference in total energy expenditure between the low and high carbohydrate diets was even greater – up to 478 kilocalories a day, consistent with the carbohydrate-insulin model.
If this effect persisted “it would translate into an estimated 10 kg weight loss after three years, assuming no change in calorie intake,” write the authors.
Hormones involved in energy balance (ghrelin and leptin) changed in a potentially advantageous manner in participants assigned to the low carbohydrate diet compared with those assigned to the high carbohydrate diet.
The authors point to some study limitations and cannot rule out the possibility that some of the observed effects may be due to other unmeasured factors. Nevertheless, they say this large trial shows that dietary composition seems to affect energy expenditure independently of body weight.
“A low glycemic load, high fat diet might facilitate weight loss maintenance beyond the conventional focus on restricting energy intake and encouraging physical activity,” they conclude. And they call for additional research to explore these effects further and develop appropriate behavioral and environmental interventions for translation to public health.