There is a growing body of scientific evidence and personal experience which demonstrates that the high content of sugar and refined carbohydrate foods is one of the main factors responsible for the rapidly increasing levels of obesity and diabetes. This in turn increases the risks of conditions such as heart disease, cancers and Alzheimer’s Disease. Conversely those who make adjustments to their diet in order to reduce the carbohydrates and increase the fat consistently find that they can achieve significant improvements in their health.
A recent paper has pulled together much of the relevant information and provides a valuable summary of the current state of knowledge (1).
There are 12 key points which are as follows:
- Hyperglycaemia is the most salient feature of diabetes. Dietary carbohydrate restriction has the greatest effect on decreasing blood glucose levels.It is universally accepted that dietary carbohydrate is the main dietary determinant of blood glucose and restriction shows the greatest reduction in blood glucose concentrations as well as HbA1c(Glycylated haemoglobin, which gives the average blood sugar level over the previous few months)
- During the epidemics of obesity and type 2 diabetes, caloric increases have been due almost entirely to increased carbohydrate. In the USA, there were increases in the carbohydrate content of the diet of about 7% of calories with concomitant reductions in the intake of fat between 1970 and 2000. Similar changes have been recorded for Great Britain
- Benefits of dietary carbohydrate restriction do not require weight loss. This is crucial because many diabetics are not overweight and many who are overweight are not diabetic. In fact the obsession with weight per se has not been particularly helpful because most people have great difficulty in losing weight by the conventional calorie control approach. Paradoxically the switch to a diet which is low in carbohydrates is often accompanied by weight loss even when this has not been a specific objective
- Although weight loss is not required for benefit, no dietary intervention is better than carbohydrate restriction for weight loss. In a British study it was found that those on a low carbohydrate diet were more successful in losing weight than a comparable group who followed a conventional Healthy Eating diet. On the other hand low fat diets have produced very poor results. In the Women’s Health Initiative (WHI) the low fat intervention group was encouraged to consume a diet with 20% fat, which was rich in fruits, vegetables and grains (2). Although they lost 2.2 kg in the first year, this was regained by the end of the 7-year study.
- Adherence to low-carbohydrate diets in people with type 2 diabetes is at least as good as adherence to any other dietary interventions and is frequently significantly better. In a study of The Active Low-Carber Forum, an on-line discussion group with over 150,000 members, a common assertion was that a low-carbohydrate regimen provides the greatest degree of satisfaction. Provided the carbohydrate reduction is maintained, there is no need to restrict total food intake, which is necessary on a low fat diet.
- Replacement of carbohydrate with protein is generally beneficial. Although it is generally recommended that carbohydrate is replaced by fat, a number of systematic studies have found that high-protein-low carbohydrate diets have a more favourable effect on weight loss and cardiovascular risk factors than fat reduced diets.
- Dietary total and saturated fat (SFA) do not correlate with risk of cardiovascular disease (CVD). Despite massive investigations it has not been possible to demonstrate that SFA is a risk factor for heart disease. One meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD (3,4). Although recommendations to lower SFA are an integral part of many national nutrition policies, the lack of evidence is now so compelling governments will eventually have make fundamental changes to official strategies.
- Plasma SFAs are controlled by dietary carbohydrate more than by dietary lipids. It is now becoming clear that the concentration of SFA in the blood is determined by the amount of carbohydrates rather than the SFA in the food. A diet low in carbohydrates is more effective in reducing the blood triglycerides than one which is low in fat.
- The best predictor of microvascular and, to a lesser extent, macro-vascular complications in patients with type 2 diabetes, is glycaemic control. In the United Kingdom Prospective Diabetes Study (UKPDS) it was found that the key controlling variable was HbA1c. As HbA1c increased, there was a corresponding increase in fatal and non-fatal myocardial infarction events. By contrast, there was a 14% decrease in myocardial infarction for every 1% reduction in HbA1c.
- Dietary carbohydrate restriction is the most effective method (other than starvation) of reducing serum triglycerides and increasing high-density lipoprotein (HDL). Compared with other diets, a low-carbohydrate diet achieved the greatest decrease in triglyceride, as well as decrease in weight, HbA1c and glucose and a greater increase in HDL.
- Patients with type 2 diabetes on carbohydrate-restricted diets reduce and frequently eliminate medication. People with type 1 usually require lower insulin. Dietary carbohydrate restriction, because of its increased effectiveness in glycaemic control, frequently leads to reduction and often complete elimination of medication in type 2 diabetes. Similarly, patients with type 1 typically require lower medication on low-carbohydrate diets.
- Intensive glucose lowering by dietary carbohydrate restriction has no side effects comparable to the effects of intensive pharmacologic treatment. It has been established that not only is the use of drugs to treat diabetes ineffective but there are also proven hazards. By contrast the change of diet definitely works and there are no known dangers.
When all the information is collated there is a very convincing case for choosing diets which are low in carbohydrates. It is becoming more and more obvious that the decision to advise a reduction in fat (and an increase in carbohydrates) was totally misguided. As a consequence huge numbers of people have developed chronic diseases. Unfortunately the wrong advice is still being promulgated in most countries. We have now reached the point where the evidence is overwhelming and that policies must be changed radically and without delay. The single exception is Sweden, where a recent official report clearly recognised the extensive benefits of a diet which is low in carbohydrates and high in fat. This topic will be covered in the next blog (5).