How diet can help—or harm—your cognitive fitness.
Before you cut into a big T-bone steak with French fries, here is some food for thought: Research suggests that what we eat might have an impact on our ability to remember and our likelihood of developing dementia as we age.
Take that steak you're about to slice into, for example. It's loaded with saturated fat, which is known to raise blood levels of unhealthy low-density lipoprotein (LDL) cholesterol. Other kinds of fats, such as trans fats, do the same thing to LDL.
LDL cholesterol builds up in, and damages, arteries. "We know that's bad for your heart. There is now a lot of evidence that it's also bad for your brain," says Dr. Francine Grodstein, associate professor of medicine at Harvard Medical School and associate epidemiologist at Brigham and Women's Hospital.
Beta-amyloid plaque in the brain
Diets high in cholesterol and fat might speed up the formation of beta-amyloid plaques in the brain. These sticky protein clusters are blamed for much of the damage that occurs in the brains of people with Alzheimer's.
The diet and memory connection
As evidence of this effect are the results of a study conducted by researchers at Brigham and Women's Hospital, published online May 17 in the journal Annals of Neurology. Women in the study who ate the most saturated fats from foods such as red meat and butter performed worse on tests of thinking and memory than women who ate the lowest amounts of these fats.
The exact reason for the connection between diets high in saturated and trans fats and poorer memory isn't entirely clear, but the relationship may be mediated by a gene called apolipoprotein E, or APOE. This gene is associated with the amount of cholesterol in your blood, and people with a variation of this gene, called APOE e4 are at greater risk for Alzheimer's disease. "About 65% of individuals who wind up with dementia due to Alzheimer's disease in their 60s and 70s have that gene," says Dr. Gad Marshall, assistant professor of neurology at Harvard Medical School.
How does the APOE e4 gene contribute to dementia? Researchers aren't exactly sure, but they have discovered that people with this genetic variation have a greater number of sticky protein clumps, called beta-amyloid plaques, in the brain. These plaque deposits, which are associated with the destruction of brain cells, are a hallmark of Alzheimer's disease.
The connection is a little clearer when it comes to memory loss that's related to blood vessel damage. The buildup of cholesterol plaques in brain blood vessels can damage brain tissue, either through small blockages that cause silent strokes, or a larger, more catastrophic stroke. Either way, brain cells are deprived of the oxygen-rich blood they need to function normally, which can compromise thinking and memory.
Other ways to protect memory as you age
Diet isn't the only way to preserve memory. If you want to keep your brain sharp as you get older, follow these recommendations:
Control your cholesterol, blood sugar, and blood pressure levels with diet, exercise, and medicines such as statins or beta-blockers if you need them.
Quit smoking. One review of studies associated smoking with a significantly higher risk for Alzheimer's disease.
Get outside for a brisk daily walk. Exercising three or more times a week has been linked to a lower risk for dementia.
Work with your doctor to keep your weight in a healthy range for your height. A body mass index (BMI) between 18.5 and 24.9 is considered normal.
Foods for memory
If saturated and trans fats are the food villains, then mono- and polyunsaturated fats may be the heroes in the dietary battle to preserve memory. In particular, the Mediterranean diet, with its menu of foods that are high in healthy unsaturated fats (olive oil, fish, and nuts) has been linked to lower rates of both dementia due to Alzheimer's disease and mild cognitive impairment (MCI)—the stage of memory loss that often precedes dementia.
The Mediterranean diet includes several components that might promote brain health:
Fruits, vegetables, whole grains, fish, and olive oil help improve the health of blood vessels, reducing the risk for a memory-damaging stroke.
Fish are high in omega-3 fatty acids, which have been linked to lower levels of beta-amyloid proteins in the blood and better vascular health.
Moderate alcohol consumption raises levels of healthy high-density lipoprotein (HDL) cholesterol. Alcohol also lowers our cells' resistance to insulin, allowing it to lower blood sugar more effectively. Insulin resistance has been linked to dementia.
Sample Mediterranean diet
Roasted salmon with tomato-olive tapenade, saut�ed spinach with pine nuts and raisins, poached pears OR
Broiled chicken with garlic and lemon, asparagus
Can food preserve memory?
Although certain foods do seem to protect memory, our experts say research on the subject is still too preliminary to recommend any specific memory-enhancing foods. "The truth is, we still don't know a lot," Dr. Grodstein says. "So I don't think we're ready yet to identify a brain-healthy diet in the way we are a heart-healthy diet."
Yet doctors are finding that what's good for the heart may also be good for the brain. Protecting the blood vessels by following a heart-healthy diet might just protect the mind too. "A lot of the cardiovascular risk factors have been shown to be risk factors for dementia, including dementia due to Alzheimer's disease," Dr. Marshall says. When you eat a heart-healthy diet that is low in saturated fat, you reduce your risk for high blood pressure, diabetes, and obesity, all of which are believed to contribute to memory loss.
So what are the components of a heart-healthy diet? They're very similar to the ingredients in the Mediterranean diet, which so far carries the strongest evidence of any diet-related intervention for preserving memory, Dr. Marshall says.
The Mediterranean diet includes
fruits and vegetables
whole-grain breads and cereals
beans and nuts
very limited red meat
no more than four eggs per week
moderate wine consumption (one glass a day for women).
Supplements and memory
A number of dietary supplements claim to improve memory, concentration, and focus. These products often contain blends of supposedly memory-boosting ingredients such as antioxidants and omega-3 fatty acids—some of which are found in the Mediterranean diet.
The trouble with these products is they're largely untested. "There's a lot of information out there on supplements that isn't evidence-based," Dr. Marshall says. "And it's not to say some of them might not work. We just need better proof." Many supplements that have been studied against a placebo (inactive pill) have not been shown effective for treating or preventing dementia due to Alzheimer's disease.