Dr Peter Brukner OAM

Ask a doctor: Low carb or low calorie?

2 mins read

A really important research paper was published recently. The paper was a systematic review of randomised control trials (RCTs) – the highest form of scientific evidence – and published in the Journal of Nutritional Science.

We know that there are two ways that people can lose weight and improve the management of type 2 diabetes. The first is a low-energy diet (LED), also known as an ultra low-calorie diet, of less than 800-1200 cals/day. The other is a low carbohydrate diet (LCD), defined as less than 130 g/day of carbohydrate, or in the case of a very low carbohydrate or ketogenic diet, less than 50 g/day.

A number of randomised controlled trials (RCTs) have been published demonstrating the effectiveness of both these types of diet in reducing weight and improving blood glucose management for people living with type 2 diabetes.

What has been the subject of much debate is whether a low energy diet or a low carbohydrate diet is more effective for weight loss and type 2 diabetes management.

This important study examined whether restricting calorie intake as well as reducing carbohydrates is an advantage over a low carbohydrate diet with unlimited calories.

What did the study involve?

The paper looked at 15 RCTs which met the inclusion criteria. Nine of the 15 studies used LCDs with moderate or unrestricted calorie intake. The remaining six studies used LED diets with less than 1200 calories per day. All but one included meal replacements as part of their weight loss program.

Both types of diets produced significant weight loss and decreased HbA1c in their trials. Interestingly, after 12 and 24 months, the trials that restricted calories did not deliver better results than those that allowed unlimited calories while following a low carb diet. The two studies reporting the largest changes after 12 and 24 months involved low carbohydrate diets with unrestricted or moderate calorie restriction. The most effective? A ketogenic diet with unlimited calorie intake.

What can we learn from this study?

The main message from this study of low calories versus low carbs is that restricting calorie intake in the context of a low carbohydrate diet is of no added advantage. This has enormous consequences as it means that reducing carbs does not have to be associated with calorie restriction.

It can be extremely difficult to stick to a low calorie diet of just 800 cals/day due to the feeling of constant hunger. It is why so many of us struggle with traditional low calorie diets. The second issue is that all but one of the low-calorie diets examined consisted of meal replacements, which again is not sustainable in the long term.

So this systematic review shows that restricting carbohydrate intake is sufficient for weight loss and type 2 diabetes management without restricting calorie intake and using meal replacements. A real food diet restricting carbohydrate intake by focusing on meat, fish, vegetables, eggs, dairy, nuts, seeds and fats is the most effective way of achieving weight loss and improving management of type 2 diabetes. In many cases, such an approach can even send type 2 diabetes into remission.

This is very encouraging for the team at Defeat Diabetes. After all, this is exactly the program that we provide to members.

Source: Nicholas, A., Soto-Mota, A., Lambert, H., & Collins, A. (2021). Restricting carbohydrates and calories in the treatment of type 2 diabetes: A systematic review of the effectiveness of ‘low-carbohydrate’ interventions with differing energy levels. Journal of Nutritional Science, 10, E76. doi:10.1017/jns.2021.67

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