The researchers found that mice bred with the mouse version of Alzheimer's disease showed improvements in their condition when treated with a high-fat, low-carbohydrate diet.

The recently published report showed that a brain protein, amyloid-beta, which is an indicator of Alzheimer's disease, was reduced in mice on the so-called ketogenic diet.

The finding by Samuel Henderson, from Accera, Inc., Colorado and colleagues from Belgium, contradict previous studies suggesting a negative effect of fat on Alzheimer's disease.

The authors say their work supports the premise that key aspects of Alzheimer's disease can be altered by changes in metabolism, and also highlights the 'interaction of dietary components and how such components influence the metabolic state'.

The authors believe that insulin and the related hormone, insulin-related growth factor-1 (IGF-1), are the key players.

Insulin, which is often regarded as a storage hormone, since it promotes deposition of fat, may also work to encourage amyloid-beta production.

According to Richard Feinman, editor of the journal Nutrition and Metabolism, who explains the relation between nutrients, that if fat is the bomb, then insulin (from carbohydrate) is the fuse.

Most studies of the harmful effects of fat have been done in the presence of high carbohydrate.

If carbs are high, dietary fat is not oxidized and is instead stored as body fat.

However when carbohydrates are very low and fat is high, compounds called ketone bodies are generated (ketosis) and these compounds may play a role in the reduction seen in amyloid-beta.

In association with a group from the University of Washington, led by Dr. Suzanne Craft, Henderson has previously shown cognitive improvement in patients with mild Alzheimer's disease who were given a diet that raises ketone bodies.

Feinman also says, in an accompanying editorial, that although it is too early to tell how the results will fit into the treatment of Alzheimer's disease, the implication for diet in general is also important.

The importance of insulin as a control element is the basis of popular weight-loss diets based on carbohydrate restriction, and such diets allow dieters to regulate fat and calorie intake by appetite alone as long as carbohydrate intake remains minimal.

Feinman says that the study by Henderson and colleagues is one of several recent studies that point the way to understanding metabolism beyond the issues surrounding simple fat reduction.

he study is reviewed in the journal Nutrition and Metabolism.