Researchers found that mice fed meals similar to those of the original Atkin's Diet had brains five per cent lighter than all the others.
They also found that the hippocampus part of the brain, which is responsible for memory, were less developed in those rodents on the high protein diet.
Scientists say the findings, published in the journal Molecular Neurodegeneration, suggest that the ravages of dementia "might be slowed or avoided through healthy eating."
Previous research has discovered Mediterranean-style low-calorie, low-fat diets rich in vegetables, fruits, and fish may delay the onset or slow the progression of Alzheimer's disease.
Researchers used mice specially-bred to develop alzheimer's.
The animals were fed either a regular diet, a high fat-low carbohydrate diet, a high protein-low carb version or a high carb-low fat option.
The researchers then looked at the brain and body weight of the mice, as well as plaque build-up associated with Alzheimer's.
They were surprised by the smaller brains of those given the high protein-low carb diet.