It's most people's biggest health fear. But whether you get dementia, scientists now believe, is mostly a matter of lifestyle; it hinges on what you eat every single day. Here's a guide to making the choices that will preserve a healthy mind—starting right now!

When it comes to aging, life can be cruel. There's plenty to...well...let's come right out and say it: think about. What will happen to my looks? What will happen to my body?

Will I still be able to pursue my interests? What will happen to my mind?

That last question is now the second leading health concern (after cancer) among adults in at least four Western countries—France, Germany, and Spain, as well as the United States—according to a recent survey by the Harvard University School of Public Health and the Alzheimer Europe consortium. Fear of developing dementia would likely stir even more concern if Americans didn't mistakenly believe a cure for Alzheimer's disease exists (more than 45 percent of U.S. respondents think there is an effective treatment). Despite the lack of a cure, great progress has been made in the past three decades in understanding the disease.

The most common cause of dementia, or severe cognitive decline, and the sixth leading cause of death in the U. S., Alzheimer's disease is marked by difficulty storing new memories and recalling recent events, loss of ability to track day-to-day information, a disrupted sense of time and space, social withdrawal, irritability, and mood swings. The neurodegenerative condition typically manifests after age 60. Life expectancy in the U.S. is currently about 78 years and rising. The 5.4 million Americans who suffer from the illness include 13 percent of those over age 65.

Scientists attribute the debilitating disorder to the gradual accumulation between brain cells of a toxic protein, beta-amyloid, that blocks the transmission of information from cell to cell, wipes out synapses, and disrupts basic neuron function, leading to cell death. Inflammatory processes are also involved in memory loss.

The vast majority of Alzheimer's cases—over 99 percent—occur spontaneously; they are not linked to genetic factors. But they are linked to obesity. Researchers find that the same lifestyle choices that lead people to become obese or develop heart disease also increase the risk of developing dementia.

It comes down to this: Choices we make throughout life about what we put in our bodies may protect against Alzheimer's, or delay its onset. At the very least, says neuroscientist Gary Wenk, "We can slow down the time that it takes for someone to get symptoms." Professor of psychology, neuroscience, and molecular virology, immunology, and medical genetics at The Ohio State University, Wenk is author of the book Your Brain on Food.

Heading off dementia, he insists, starts with what we eat. Food should be thought of the same way as the drugs we put in our body. They're all made up of chemicals. Everything we consume prompts a reaction in the brain. Picking the right foods can minimize damage to neurons and preserve a healthy mind as you age.