In a previous column I discussed the brain-healthy effects of brief, periodic fasting. Happily, there is an alternative to going hungry every few days. An increasing body of evidence suggests that you can also eat your way to better brain health. For several years, researchers have been publishing evidence that certain foods contain nutrients that slow processes in the cells of the body that lead to degeneration and disease in both research animals and human populations. Numerous studies have shown that people who consume foods that make up a “Mediterranean diet” had reduced risk of memory impairment or dementia from Alzheimer’s disease. (Singh B et al. Journal of Alzheimer’s Disease 2014; January 1:39:2:271-82) The Mediterranean diet relies on olive oil as the main dietary fat, with high consumption of green, leafy vegetables, legumes, fruits, nuts and fish. Previous studies of the Mediterranean diet provide evidence of an association of diet and better performance on cognitive tests in older adults, but they do not prove cause and effect. For example, people who eat more fruits and vegetables may also exercise more, have more education, smoke less or have other reasons to be healthier in old age. We’ve been waiting for studies that don’t just look at diet and current cognitive function, but instead look at diet and memory and cognition over time while controlling for the other variables beside diet that might affect brain aging.
The Mediterranean diet had previously been shown to preserve cognitive function over time in one randomized, prospective trial, but the effect was slight and the study was not designed to detect reduced risk of dementia. (Martinez-Lapiscina EH et al. Journal of Neurology Neurosurgery Psychiatry 2013; 84:1318-25) We now have a study that provides more convincing evidence. Martha Clare Morris and colleagues at Rush University Memory and Aging Project in Chicago have recently published the results of one of the first prospective studies of diet and development of dementia. (Morris MC et al. Alzheimer’s & Dementia 2015; 11:1007-1014) They followed 923 participants (ages 58 to 98 years) for an average of 4.5 years and analyzed how well their diets conformed to either a Mediterranean diet or a diet designed to control high blood pressure. Based on previous work, they knew that if a person reported more consumption of brain healthy foods on a validated questionnaire, they performed better on cognitive tests. In this new study, they actually followed people over time to see who developed cognitive decline and dementia due to Alzheimer’s disease. Whether or not a person’s cognitive decline or dementia was caused by Alzheimer’s disease (AD) was determined by well-validated criteria.
The Rush University Memory and Aging Project group did not randomly assign people to a certain type of diet, but rather assessed how closely participants’ diets conformed to either the Mediterranean diet, a high blood pressure diet called Dietary Approaches to Stop Hypertension (“DASH”), or a combination of the two. The DASH diet had previously been shown to improve both cognitive function and coordination when combined with a weight loss program in people with high blood pressure who were both sedentary and obese. The participants’ diets were characterized as conforming to either the Mediterranean style diet or the “DASH” diet for hypertension based on questionnaires. They called the combination of Mediterranean and hypertension diet, “MIND”, an acronym of Mediterranean-DASH Intervention for Neurodegenerative Delay and they analyzed the relative benefits of either diet alone or combined on subsequent risk of cognitive decline while controlling for other important variables that may affect risk for dementia from Alzheimer’s disease.
Before this Rush University study, neither the Mediterranean nor DASH diets had been shown to reduce risk of developing dementia. In this study, people who followed the MIND diet either very closely or moderately closely, had the lowest chance of developing dementia from Alzheimer’s disease; only 47% risk compared to those with very low compliance scores. The MIND or combined diet seemed to provide more benefit than either of the Mediterranean or DASH diet alone; only those who had very high compliance for either Mediterranean or DASH diet alone had lower dementia risk. They conclude that strict adherence to any of the three diets reduced risk of cognitive decline, but that even moderate adherence to the combined diet (MIND) reduced risk as well.
The risk reduction found in this study was fairly profound and needs to be confirmed in subsequent studies. I want to repeat that this was not a randomized study and does not prove cause and effect. A person could still argue that people who take better care of themselves in other ways or are better educated would be more likely to follow these healthier diets, although these results held true even when the investigators statistically controlled for other variables that could affect cognitive aging: age, sex, education level, genes (APOE4), degree to which people participated in cognitively stimulating activities and physical activity. The slowing in cognitive decline of MIND diet was estimated to be equivalent to being 7.5 years younger with respect to risk of dementia. The benefits of the diets are thought to be due to their rich concentrations of nutrients with antioxidant and anti-inflammatory effects. There are theoretical reasons to believe these mechanisms are important to brain aging and to development of dementia from Alzheimer’s disease, but are not specific for Alzheimer’s disease. It is likely that these diets reduce risk of developing vascular disease that is another common cause of cognitive decline and dementia. I should also mention that these diets have shown benefit in reducing heart disease and depression as well as cognitive decline.
The components of the MIND diet used in the Rush University study are shown in the table below:
|Brain Healthy Foods|
|Green leafy vegetables||≥ 6 servings/wk|
|Other vegetables||≥ 1 serving/day|
|Berries||≥ 2 servings/wk|
|Nuts||≥ 5 servings/wk|
|Olive oil||Primary oil used for cooking|
|Whole grains||≥ 3 servings/day|
|Fish (not fried)||≥ 1 serving/wk|
|Beans||≥ 3 meals/wk|
|Poultry (not fried)||≥ 2 servings/wk|
|Less Healthy Foods|
|Butter or margarine||< 1 tblspn/day|
|Cheese||< 1 serving/wk|
|Red meat||< 4 servings/wk|
|Fast or fried foods||< 1 serving/wk|
|Pastries or sweets||< 5 servings/wk|
Table adapted from Melanie V. Betz, MS RD. Geriatric Medicine 2015; 8:6: 24-5.
Conclusions: I’m looking forward to future studies in which people are randomly assigned to a particular diet and followed over several years to see what happens to memory, cognition, walking speed and other measures of brain “aging”. But I think the evidence we now have is sufficiently strong to make some recommendations about diet. I work in the “Mood and Memory Clinic” for older adults at Acadia Hospital. We always make a point of discussing “brain healthy habits” with our patients and families. We encourage getting adequate sleep, increasing physical activity, engaging in challenging mental activities and practicing stress-reduction techniques. There is growing evidence that all these habits may slow brain ageing and help preserve memory, mood and mobility. We have always spent a few moments discussing “brain healthy” diets with our patients, but with these data from the Rush University Memory and Aging Project, we will have to make this more of an emphasis. I encourage you to take your questions about diet and your health to either your primary care provider or a registered dietician.