From the extreme Atkins Diet to the more modest Zone Diet, low carbohydrate diets are all the rage, embraced by celebrities and the general public alike as a quick way to lose weight. These diets claim to reduce the risk of diabetes, heart disease and other chronic diseases as well as to promote general good health.
Indeed, so great has been the promotion of such diets that food companies, supermarkets, restaurants and some airlines are offering a range of food products and meals which are exceptionally low in carbohydrate. And now, at this weekend's NZ branch of the Australasian Society for the Study of Obesity conference in Auckland, a new range of low-carb products is about to be launched.
But what is the scientific evidence for the benefit of such diets?
Researchers at the University of Otago have carried out a series of studies in New Zealand which will provide some of the answers and those are due to be published in major international scientific and medical journals in the near future. However, the New Zealand Dietetic Association and Otago researchers have examined in depth the various research papers published to date and offer the following interim recommendations based on the best available evidence.
- The Atkins (extremely low carbohydrate) diet does appear to promote short-term weight loss, but studies which have continued for at least six months to one year do not confirm long-term benefit compared with other weight loss programmes in terms of weight loss and risk factors for diabetes and heart disease. In some people these diets increase cholesterol levels. Other risk factors for heart disease may also be adversely affected.
- Diets which are higher than average in protein, lower than usually recommended in carbohydrate and have moderate amounts of fat can lead to weight loss with minimal risk. However, for weight loss to occur, these diets need to ensure that the amount of energy consumed (caloric intake) is less than the amount of energy a person uses. These diets are relatively low in saturated fat and are otherwise compatible with guidelines for healthy eating (e.g. contain plenty of vegetables and fruit, a variety of foods and at least some whole grain breads and cereals). However, higher protein diets are not recommended for those with diabetes who have features of kidney disease.
- Diets which are relatively high in carbohydrate, low in fat and moderate in protein are suitable for most patient groups and those who wish to reduce the risk of diabetes and many other chronic diseases. But for weight loss, these diets must reduce caloric intake, and ensure that most of the carbohydrate is derived from high fibre, low glycaemic index foods, and not from sugar, sugary beverages and foods rich in sugars and starches. Plenty of vegetables and fruit and whole grain cereals are important. Carbohydrates have received a bad press largely because so-called experts do not appreciate the difference between the "good" and the "not so good" carbohydrate.
"Thus there is no one best-bet or wonder diet that's going to solve obesity in this country," says Dr Kirsten McAuley, a senior research fellow with Otago's Department of Human Nutrition and the Edgar National Centre for Diabetes Research. "We need to consider a variety of options for different people who have different eating habits and preferences.
"But as long as diets have all the essential nutrients and provide a balanced eating pattern, they're going to be acceptable. All this focus on 'carbs' is getting away from what is really important – the quality and quantity of the food we eat."