According to the Mayo Clinic, around 5.8 million people over the age of 65 in the United States are diagnosed with Alzheimer’s Disease (AD) [1]. Neurons in the brain atrophy, leading to an impairment in thinking, cognitive and social skills. Additionally, AD is the leading cause of dementia; of the 50 million people around the globe with dementia, 60-70% of them have AD. The fact that AD is so common and detrimental only underscores the need for medical prescribers and physicians to advise their patients – current and prospective – on how to reduce their risk of developing AD or increasing the impairment of their symptoms. One major lifestyle choice that can be a risk or protective factor is diet.
Solfrizzi and colleagues, in their review of diet as a risk and preventative factor for AD, recommend a diet with a high consumption of fats from fish, vegetable oils, vegetables, and nuts, the same recommendations to decrease the risk of obesity [2]. These monounsaturated and polyunsaturated fatty acids have been associated with a lower risk of cognitive decline and dementia. Similarly, a light-to-moderate alcohol consumption and a Mediterranean diet have been correlated with decreased cognitive decline and risk for AD. Paradoxically, lower consumption of dairy products and consumption of whole-fat dairy products have been associated with reduced cognitive function. They reason that the vitamin D, calcium, phosphorus and magnesium in dairy products like milk, cheese, and yogurt have anti-inflammatory effects and contribute to better vascular health, which in turn, reduces risk of cognitive decline. On the other hand, whole-fat dairy products contribute to obesity, which has been associated with increased cognitive decline.
In a review of longitudinal and epidemiological research, Profenno and colleagues investigated the effect of factors related to diet (body mass, diabetes, metabolic syndrome, and glucose and insulin levels) on the risk for AD [3]. They found that obesity and diabetes significantly and independently raise the risk of developing AD, the reason being that these comorbid conditions result in physiological changes that facilitate AD.
Based on the current research, a Mediterranean diet shows promise in being a protective factor for AD. This diet involves high intake of plant food consumption in the form of fruits, vegetables, breads, legumes, potatoes, beans, nuts and seeds; fresh fruit as the typical dessert; olive oil as the main source of monounsaturated fatty acids; dairy products (mainly cheese and yogurt); a low-to-moderate consumption of fish depending on the proximity of the sea; a low-to moderate consumption of poultry; less than four eggs per week; and low-to-moderate amounts of red meat and wine [3].
Even modified versions of the Mediterranean diet provide protection against the development of dementia [4]. In a longitudinal research study, Morris et al. (2015) tested whether a hybrid of the Mediterranean and DASH (Dietary Approaches to Stop Hypertension) diet could be associated with the risk of developing incident AD. In their study, participants were scored on this MIND (Mediterranean-DASH Intervention for Neurodegenerative Delay) diet on the basis of 10 brain healthy food groups (green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, fish, poultry, olive oil, and wine) and five unhealthy food groups (red meats, butter and stick margarine, cheese, pastries and sweets, and fried/fast food). After controlling for age, physical activity, depressive symptoms, diabetes history, etc., they found that modest to greater adherence to the MIND diet was significantly associated with a lower risk of developing AD when compared to modern adherence to the DASH and Mediterranean diets. Interestingly, the same lower risk was only found in the greatest adherence to the DASH and Mediterranean diets.
However, a meta-analysis of research in this domain has warned of insufficient research to draw conclusions. Moreover, data gathered from randomized controlled trials with the Mediterranean diet have been inconsistent and the general inability to determine its efficacy could be complicated by confounding factors like age, disease stage, other dietary components, cooking processes, and other methodological issues [5]. Furthermore, scientists deem the mechanism by which certain nutrients protect the human brain from AD as unknown; this mechanism could be direct or indirect via the vascular system.
There has also been research conducted on whether the Ketogenic diet, a diet popular for weight loss, was associated with a reduced risk of developing AD [6]. In the diet of the participants of this pilot study, 70% of energy was derived from fat, 20% of energy from protein, and carbohydrates were restricted to less than 10% of energy input. Additionally, researchers provided daily multivitamin, vitamin D, calcium, and phosphorus supplements to participants to prevent any possible micronutrient deficiencies. Over the course of 3 months, only 1 of the 10 participants showed significant cognitive decline. Therefore, the researchers concluded that a ketogenic diet could be beneficial and feasible for reducing the risk of cognitive decline. However, they remain unsure of the mechanisms of this and caution readers that the side effects may hinder implementation and that more research needs to be done to draw definitive conclusions.
Furthermore, based on the research at hand, medical officers can aid their current and potential patients in helping them feel more secure about their own risk for developing AD and increased cognitive decline by advising them to adhere to anti-obesity diets like the Mediterranean Diet, DASH Diet and MIND Diet.
References
- Mayo Clinic Staff. (2020, December 29). Alzheimer’s disease. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/symptoms-causes/syc-20350447.
2. Solfrizzi, V., Panza, F., Frisardi, V., Seripa, D., Logroscino, G., Imbimbo, B. P., &, Pilotto, A. (2011). Diet and Alzheimer’s disease risk factors or prevention: the current evidence. Expert Review of Neurotherapeutics, 11(5), 677–708. https://doi.org/10.1586/ern.11.56
3. Profenno, L. A., Porsteinsson, A. P., &, Faraone, S. V. (2010). Meta-Analysis of Alzheimer’s Disease Risk with Obesity, Diabetes, and Related Disorders. Biological Psychiatry, 67(6), 505–512. https://doi.org/10.1016/j.biopsych.2009.02.013
4. Morris, M. C., Tangney, C. C., Wang, Y., Sacks, F. M., Bennett, D. A., &; Aggarwal, N. T. (2015). MIND diet associated with reduced incidence of Alzheimer’s disease. Alzheimer’s & Dementia, 11(9), 1007–1014. https://doi.org/10.1016/j.jalz.2014.11.009
5. Otaegui-Arrazola, A., Amiano, P., Elbusto, A., Urdaneta, E., &; Martínez-Lage, P. (2013). Diet, cognition, and Alzheimer’s disease: food for thought. European Journal of Nutrition, 53(1), 1–23. https://doi.org/10.1007/s00394-013-0561-3
6. Taylor, M. K., Sullivan, D. K., Mahnken, J. D., Burns, J. M., &; Swerdlow, R. H. (2017). Feasibility and efficacy data from a ketogenic diet intervention in Alzheimer’s disease. Alzheimer’s & Dementia: Translational Research & Clinical Interventions, 4(1), 28–36. https://doi.org/10.1016/j.trci.2017.11.002
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