Experts caution on dietary advice purporting to show fat is good

The international media response to a BMJ opinion piece claiming to debunk the "myth" of saturated fat as a cause of coronary heart disease could undermine public confidence in lifestyle changes that have resulted in appreciable health benefits, say a group of experts in public health and nutrition representing a number of New Zealand health-related organisations.

They have also expressed concern regarding recent promotion in New Zealand of exceptionally low carbohydrate/high fat diets aimed at weight loss and reduced risk of some chronic diseases.

The group's spokesman, University of Otago Professor in Human Nutrition Jim Mann, says avoiding and treating obesity is central to advice about food and physical activity for people of all ages aimed at reducing chronic diseases, including several of the most commonly occurring cancers in New Zealand; type 2 diabetes, coronary heart disease and stroke.

WHO has commissioned studies, also published in the BMJ, that have confirmed the importance of total fat reduction (typically also involving a reduction in saturated fat) as well as the reduction of sugars in helping to reduce overweight and obesity. "There is no evidence that this is achieved in the long term by very low carbohydrate- high fat diets," says Professor Mann.

In western countries a reduction in saturated fats has occurred in parallel with a reduction in blood cholesterol levels and coronary heart disease.

Professor Mann adds that although heart disease has many causes, in western countries coronary heart disease risk is directly related to cholesterol levels.

"In New Zealand the reduction in fat consumption from more than 40% towards 30% (and saturated fat towards 10%) since the 1970's has been associated with a reduction in coronary heart disease death rates by more than two thirds," he says.

"In parts of Sweden the trend towards reducing cholesterol levels has been reversed in association with the promotion and adoption of high fat diets."

Most people tend to think of what they eat in terms of foods rather than nutrients and the expert group supports the concept that different dietary patterns are compatible with calorie balance, a healthy body weight and reduced risk of type 2 diabetes, coronary heart disease and several cancers.

However, the group suggests that those who advocate for radical new dietary approaches have a responsibility to provide convincing peer-reviewed evidence of long term benefit as well as absence of harm. Such evidence does not exist for diets high in saturated and total fat, and very low in carbohydrate.