12 January - 20 June 2016

Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance

A recent study, published in the British Medical Journal, and conducted by researchers from Boston Children’s Hospital amongst others, has explored the effects of a low carbohydrate diet on energy expenditure during weight loss maintenance following 10 weeks of steady weight loss.

It has long been known that as individuals lose weight, the body adapts by slowing the metabolism and so burns fewer calories. Energy expenditure thus declines, and this can often result in weight regain but there is little understanding on how composition of diet could alter this response. A recent theory, the carbohydrate-insulin model, suggests that consumption of high glycaemic load foods may lead to increased hunger and thus make individuals more likely to regain lost weight.

A recent study, published in the British Medical Journal, and conducted by researchers from Boston Children’s Hospital amongst others, has explored the effects of a low carbohydrate diet on energy expenditure during weight loss maintenance following 10 weeks of steady weight loss. They concluded that low carbohydrate diets lead to a linear increase in total energy expenditure, independently of body weight, which could ultimately lead to further weight loss, especially in individuals with high insulin secretion prior to initial weight loss.

Ebbeling et al. conducted a clinical trial consisting of two phases, involving 164 adults between the ages of 18 and 65 years classed as overweight with a BMI greater than 25 kg/m2. The trial was carried out over 30 weeks and assumed a light activity lifestyle. Participants were restricted to diets promoting 12% weight loss in the 10-week run-in phase. This was followed by a 20-week test-phase in which participants were randomly assigned a high (60%), moderate (40%), or low (20%) carbohydrate diet. Each diet had a fixed protein percentage of 20%, with the remaining percentage of the respective diets made up of fats. During the 10-week run-in phase, mean weight loss was 10.5% (± 1.7%) of initial body weight, corresponding to 9.6 kg (± 2.5 kg). This loss was maintained throughout the test phase for all participants to within 1 kg across all diet groups. Despite the consistent weight exhibited across all diet groups, the total energy expenditure for the low carbohydrate diet was found to be significantly greater than the moderate and high carbohydrate diets exhibiting a linear trend of +52 kcal/d for every -10% carbohydrates up to 209 kcal/d for the 20% group.

Ebbeling et al. state that the increased energy expenditure effect exhibited in individuals following the low carbohydrate diet could lead to approximately 10 kg weight loss over the course of 3 years for an average 30-year old male with a baseline weight of 100 kg. They also noted this effect was more distinctive in participants who exhibited high insulin secretion prior to the trial. The researchers also reported a decrease in energy intake during the maintenance period with the low carbohydrate group showing the greatest decrease compared to energy intake at the start of the trial.  This was observed along with a decline in the concentration of ghrelin, a hormone attributed to appetite stimulation and promotion of fat storage. The low carbohydrate group showed over double the decrease of those on the high carbohydrate diet. Additionally, Ebbeling et al.  note that, for the low carbohydrate group, concentrations of leptin, a hormone that signals body energy stores, “showed a lesser incline” and that this was “significantly lower in participants assigned to the low carbohydrate diet, suggesting improvement in leptin sensitivity”. They indicate that previous studies suggest that those “with the greatest declines in leptin levels after weight loss have the lowest risk for weight regain”

In conclusion, Ebbeling et al.  indicate that their results suggest that a low carbohydrate diet induces changes within the body to create an environment which increases total energy expenditure and decreases energy intake and fat-promoting hormones, post-weight loss, thus reducing the probability of weight regain. Ebbeling et al. hypothesised that over an extended period, a restrictive low carbohydrate diet may allow individuals to maintain their weight loss and potentially experience additional loss.  They indicate that further studies into managing weight loss through monitoring diet composition could potentially provide valuable insight into treating and preventing obesity.

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