The authors of the study believe that insulin and the related hormone, insulin related growth factor-1 (IGF-1), are the key players in reducing the brain protein amyloid-beta, an indicator of Alzheimer's disease
"You might say that fat is the bomb, and insulin (from carbohydrate) is the fuse," says Richard Feinman, editor of Nutrition and Metabolism, that published the study this week.
The research, by Samuel Henderson at US pharma firm Accera, runs counter to previous studies suggesting a negative effect of fat on Alzheimer's disease.
Feinman explains why this latest research has thrown up a new angle.
"Most studies of the deleterious effects of fat have been done in the presence of high carbohydrate. If carbs are high, dietary fat is not oxidised and is instead stored as body fat."
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 observed reduction 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 AD who were given a diet that raised ketone bodies.
"Although it is too early to tell how the results will fit into the treatment of AD, the implication for diet in general is also important," underlines Feinman.
The primacy of insulin as a control element is the basis of popular weight-loss diets based on carbohydrate restriction, he adds.
Such diets, he adds, allow dieters to regulate fat and calorie intake by appetite alone as long as carbohydrate intake remains minimal.
"Henderson's effort is one of several recent studies that point the way to understanding metabolism beyond the issues surrounding simple fat reduction, " says Feinman.
There are nearly 18 million people with dementia in the world and the most common cause of this dementia is Alzheimer's disease. By 2025 this figure is expected to rise to 34 million, with 71 per cent of these likely to live in developing countries.
Today research continues to investigate how the diet may slow down, or prevent, the development of dementia.
Several studies have found an association between intake of omega-3s - the fatty acid found in high quantities in oily fish - and reduced risk of dementia, although a recent trial failed to link the presence of these fats in the diet with slower cognitive decline.
This trial, on elderly men and women living in Chicago, did find however that those who reported eating fish at least once a week had a slower decline in mental function than peers who did not eat fish as often - about 10 per cent less per year.