Low-carb diets lead to weight gain, diabetes

The fad of replacing carbs with more meat and fat has been found to do the opposite of what is claimed.

Low-carb diets – popular among celebrities for weight loss – actually promote weight gain and type 2 diabetes, a large, longitudinal study from Monash and RMIT has found.

The study, published in Diabetes and Metabolic Syndrome, used data from the Melbourne Collaborative Cohort Study, which recruited 41,513 people aged 40-69 between 1990 and 1994.

The team analysed the self-reported diets of over 39,000 participants and calculated a low-carbohydrate diet (LCD) score for percentage of energy from carbohydrate, fat, and protein – a higher LCD score reflected a lower carb intake.

Follow-up data collected 13-17 years later showed a clear association between LCD score and diabetes risk. People in the highest quintile had a 20% higher risk of developing type 2 diabetes than the lowest quintile.

The subjects on the lowest-carb diets were younger and more likely to be male, socioeconomically disadvantaged, former smokers, former drinkers and physically inactive than those on higher-carb diets. They had higher waist-hip ratio and BMI, and had lower intakes of fibre and higher intakes of saturated fat.

Adjusting for BMI and waist-to-hip ratio took away most of the association, meaning increased weight and adiposity explained most of the increased risk of diabetes. A mediation analysis confirmed that 76% of the extra risk came via increase in BMI.

Lead author Distinguished Professor Barbora de Courten, from RMIT and Monash, commented that while the effects of high-carbohydrate diets on weight and insulin resistance were well known, most previous research had looked at low-carb diets only in the context of managing diabetes, not as a risk factor for it.

“This study reveals that a low-carbohydrate diet intake might increase the long-term risk of type 2 diabetes through obesity, potentially through increased eating of fats and foods low in fibre,” she said.