Cochrane review of low-carb diets

Executive summary

* A 456 page Cochrane review has been published. It examined low-carbohydrate diets vs balanced-carbohydrate diets for reducing weight and cardiovascular risk. This note focuses on the weight comparisons.

* As with most studies that claim to review low-carbohydrate diets, this didn't study low-carbohydrate diets. The accepted definition of very low-carb diets was used – intake of below 50g carb/day or below 10% of energy intake. However, the study definition of low-carb was below 45% of total energy and that would be considered moderate carb-intake by low-carb definitions (Noakes & Windt).

* The researchers reviewed people with and without type 2 diabetes separately and they reviewed weight loss in studies lasting between 3 and 12 months and those lasting longer than 12 months.

* The main finding was that there was “little to no difference" in change in body weight (barely a kilogram difference) between their defined low-carb diets and balanced-carb diets. This was correct. However:

- Examination of the key analyses found that they all favoured low-carb diets – even using the researchers’ definition of these.

- Low-carb diets fared almost 3kg better than balanced-carb diets when both diets had no restrictions in energy intake. This confirmed that when people eat freely, low-carb diets perform even better.

- Very low-carb diets achieved over 2kg greater weight loss than balanced-carb diets. This confirmed that when genuinely low-carb diets are studied, the results are better than when low to moderate carb diets are studied.

* Some of the researchers have previous history on finding against low-carb diets. The main finding didn’t present the whole picture.