Researchers testing diets to see how they affect Alzheimer's disease said they found that a high-protein diet seems to lead to a smaller brain.

The team from the U.S., Canada and the United Kingdom had been checking for how plaque formed in the brains of mice.

The scientists were checking into the formation of a protein known as APP, which is used to generate the amyloid plaques typical in Alzheimer's disease, according to a news release from the researchers.

The mice either got a regular diet; a high-fat, low-carbohydrate diet; a high-protein, low-carb diet; or a high-carb, low-fat option.

Researchers said the mice on the high-protein, low-carb diet had brains 5 percent lighter than the others. They said they were surprised and not sure what caused the change or whether it was associated with Alzeimer's disease plaques.

They also did not say if the lighter brains had any effects on the animals' cognitive abilities or if that was tested.

"Given the previously reported association of high protein diet with aging-related neurotoxicity, one wonders whether particular diets, if ingested at particular ages, might increase susceptibility to incidence or progression of (Alzheimer's disease)," said lead author Sam Gandy of the Mount Sinai School of Medicine in New York City.

The study was published in BioMed Central's open access journal Molecular Neurodegeneration.