Making a choice that leads to better health is not always easy. Otherwise, we would have many more ex-smokers and far fewer holiday pounds to shed. We would have no need for nicotine gum and patches, or Weight Watcher's meetings. So if it's that difficult, why bother? For years, physicians have told the American public that reducing your calorie intake, eating a diet low in salt/sugar/saturated fat, and exercising 3-5 days per week will reduce your risk for heart disease and diabetes. Now, new information has shown that the benefits of a healthy lifestyle are even more far reaching than initially thought -- diet and exercise can affect our minds. About 5-8% of people over the age of 65, and nearly 50% of people in their 80's, show signs of dementia. As the baby-boomer generation increases the population of the 55-64 age group in the U.S. from 29 to 40 million by 2014 , and their life expectancy continues to rise, the number of people affected by dementia is poised to increase as well. Recent studies have shown that regular exercise may prove to be a potent mediator of dementia and Alzheimer's Disease. In one study, those who exercised 3 or more days per week had a 32% risk reduction in developing dementia compared to those who exercised less. Exercise has also been linked in similar studies to moderate cognitive improvements in adults who are at risk for Alzheimer's Disease, as well as a lower occurrence of vascular dementia.
Recent pre-clinical results have shown that diet is also tied to brain health. A 2002 study revealed that rats fed a diet high in saturated fat and refined sugar for 2 years exhibited changes in both gene expression in the brain, as well as performance on a memory task (finding its way through a water maze). This fast-food type diet decreased the levels of brain-derived neurotrophic factor (BDNF), which is a versatile molecule that mediates brain cell formation, function, and survival. Both BDNF gene expression (mRNA) and BDNF protein production in the hippocampus, an area crucial for short-term memory, were significantly reduced in the animals fed the high-fat and refined sugar diet, compared to those on a low-fat, complex carbohydrate diet. Although the experiment lasted for 2 years, and the greatest effects were seen at the end of the experiment, changes in gene expression were seen in as little as 6 months after the rats began downing cheeseburgers. Even more striking, the rats had a significant deficit in the water maze memory task after only 3 months on the high fat/sugar diet, which shows that the "McDiet" led to a change in behavior in the mice.
Nevertheless, the research presented here had limitations. The studies that looked at the effects of exercise on dementia were conducted in relatively small, non-diverse human populations and were not completely controlled against other "good health" factors that tend to occur when people exercise. For example, exercisers are much more likely to do other healthy things, such as eating right, quitting smoking, getting quality sleep, or maintaining target weight. The fast-food diet study was well controlled to show that decreased BDNF was not related to hypertension, atherosclerosis, obesity, and changes in activity level -- but the results must be taken at face value since it was conducted in rodents, not humans.
So what does all of this mean? The idea of eating right and getting more exercise is nothing new. We've known for years that changing our health behaviors can stave off heart disease, and potentially let us live longer. The studies mentioned here really highlight the positive-feedback nature of our actions -- behavior changes (diet and exercise) cause physiological and molecular changes in the body, which in turn alter another behavior (memory). This relationship tells us that our behavior choices no longer only determine life or death, but they also can impact our quality of life. It's true that the results don't make a direct link between diet/exercise and brain health, but rather, a loose correlation between the two that requires further study. But in my mind, it doesn't really matter what keeps the brain healthy -- my point isn't that diet and exercise are the end-all cure for disease, but rather, that they are an extremely important part of an overall healthy lifestyle that will allow us to make the most of our golden years.