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Low carbohydrate diets are widely promoted for weight loss and associated health benefits, including for diabetes management and cardiovascular health. However, a recent systematic review of the evidence shows little or no benefit of low carb diets compared to balanced carb diets when it comes to both weight loss and cardiovascular disease risk factors.

The Cochrane review combined the findings of 61 randomised controlled trials involving close to 7000 people. The participants were all overweight and some also had type 2 diabetes and/or heart disease or associated risk factors. The studies ranged from 3 months to 2 years duration.

While there is no widely accepted definition of a low carbohydrate diet, these diets generally restrict grains, legumes, fruit and starchy vegetables, along with other carbohydrate containing foods, and replace them with foods high in fat and/or protein such as meat, chicken, fish, eggs, cheese, butter, cream and oil. The carbohydrate content of the low carb diets included in this review varied from less than 50 g/day (less than 10% of total energy) up to 150 g/day (45% of energy or less).

Balanced carbohydrate diets were described in this paper as diets containing moderate amounts of carbohydrates, fats and protein, in line with healthy eating advice from health authorities. When used for weight loss, these diets encourage a reduction in portion size and making healthy food choices.

The researchers found little to no difference in weight loss between people following a low carbohydrate weight loss diet compared to a balanced carbohydrate weight loss diet, in both the short-term (3-6 months) and longer term (1-2 years).

They also found no difference between the diets when it came to changes in heart disease risk factors including blood pressure, LDL (“bad”) cholesterol and HbA1c (a measure of average blood glucose levels over the past 2-3 months). These findings were the same in people with and without type 2 diabetes.
The researchers say that they were unable to make any conclusions about negative effects of low carb diets as these were reported in very few of the trials.

Considering that many carbohydrate foods (including minimally processed wholegrains, legumes, fruits and vegetables) have been shown to have benefits for cardiometabolic health, and the lack of evidence for a benefit of low carb diets, research to date suggests focusing on quality of carbohydrate over quantity, and healthy dietary patterns rather than macronutrients (i.e., fat, protein and carbohydrate).

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Dr Kate Marsh is an is an Advanced Accredited Practising Dietitian, Credentialled Diabetes Educator and health and medical writer with a particular interest in plant-based eating and the dietary management of diabetes and polycystic ovary syndrome (PCOS).

Contact: Via her website www.drkatemarsh.com.au