But a new study out of Japan says unhealthy eating can be linked to Alzheimer's.
Researchers tested the cholesterol levels of nearly 2,600 people between the ages of 40 and 79 who had no signs of Alzheimer's.
Ten to 15 years later researchers performed autopsies on 147 people from the study group who had died. They found 34 percent had been diagnosed with dementia.
The autopsies showed plaques and tangles, which represent protein buildup in the brain.
The key finding: 86 percent of people with high cholesterol had brain plaques.