Low-carbohydrate diet shown to have considerable potential to protect against type 2 diabetes

By Dr John Briffa on 4 July 2014 in Diabetes/Metabolic Syndrome, Healthy Eating, Low-Carbohydrate

Type 2 diabetes is a condition characterised by generally elevated levels of blood sugar (glucose), usually as a result of ‘insulin resistance’ (insulin not doing its blood sugar-lowering job very well). Between a state of health and type 2 diabetes, the medical profession has defined a state known as ‘impaired glucose tolerance’ (IGT). Here, insulin functioning tends to be impaired and blood sugar levels on the high side, but not so bad as for the criteria of type 2 diabetes to be met.

In some respects, IGT can be thought of as a potential stepping stone between health and type 2 diabetes: 25 – 75 per cent of people with IGT go on to develop type 2 diabetes within a decade, apparently.

If someone was to give three words of advice for someone with IGT they would undoubtedly be ‘cut the carbs’. Cutting back on sugar and starch in the diet is what I have found works best for improving blood sugar control and perhaps retaining some insulin sensitivity. There are other things that might be considered too (such as physical activity, if this is not currently a feature of someone’s life), but scaling back carbohydrate intake would be my number one piece of advice.

I was therefore interested to read a recent study in which a ‘low carbohydrate diet’ (LCD) was trialled in a group of 72 individuals with IGT [1]. Half were educated about low-carbohydrate eating and encouraged to adopt this diet for a year. The other half of the group was left to its own devices. For a free pdf of this article, click here.

Here is a description of the intervention for the ‘LCD’ group.

The LCD group was admitted to hospital for 7 days to participate in an educational program. On the first day of the program, a physician gave a lecture about the LCD using slides that lasted for 60 minutes. On the second day, the subjects received individual lessons from nutritionists, pharmacologists, and nurses. After that, they ate the LCD every day and studied the diet using a textbook that was given to them. In compliance with the LCD, rice (the main dish) was offered at lunchtime only. The target was a total intake of 1,300 kcal per day. The nutritional composition of the food was 30% carbohydrates, 25% protein, and 45% fat. On the fifth day, the subjects completed some tests on the LCD (30 questions, true/false test), and discussed their diet with nutritionists, nurses, and physicians at a lunch meeting on the LCD. After that, they reviewed the diet and were discharged from hospital.

The individuals in this group were instructed to aim for a maximum daily intake of carbohydrate of 120 grams (a higher threshold than popular low-carbohydrate diets).

At the end of study, 12 months, the LCD group saw significant improvements in practically every parameter measured by the investigators, including:

Body weight
Fasting blood glucose level
HbA1c (measure of blood sugar control over approximately the last 3 months)
Fasting insulin level
Measures of insulin sensitivity
‘Healthy’ HDL cholesterol level
Triglyceride levels

Crucially, about 70 per cent of the group saw a return on blood sugar levels to normal, compared to only about 8 per cent in the control group. Not one person in the LCD group developed diabetes during the study, compared to 5 (14 per cent) in the control group.

The results clearly show that compared to ‘doing nothing’, restricting carbohydrate helps people with IGT. One might argue that perhaps another sort of diet (e.g. a low fat one) would work even better. However, as the authors point out, other studies have found that in those with IGT, low-fat eating leads to a one-year incidence of type 2 diabetes of between 2.0 and 12.5 per cent. This does not compare so favourably the 1-year incidence of 0 per cent found in LCD eaters in this study.

References:

1. Maekawa S, et al. Retrospective study on the efficacy of a low-carbohydrate diet for impaired glucose tolerance. Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy 2014:7 195–201