June 13, 2018
Recently, researchers have explored the connection between diet and a healthy brain. Such studies focus on Alzheimer’s Disease (AD) and dementia, but several have attempted to look at concentration and performance on tests or other intellectual tasks. While some results point to low or high consumption of a single nutrient such as omega-3 fats or vitamin B12, or a single food, such as olive oil or fish, the reality is that people eat foods in combination. The food we eat may have additive synergistic effects or even negative effects on health. Looking at the overall dietary intake, or dietary patterns, is important when seeking the best approach for issues that are multifactorial, such as cognition or dementia.
In particular, the Mediterranean diet has been linked to lower risk of cognitive decline and dementia. The Mediterranean diet (MeDi) is characterized by a high intake of plant-based foods such as vegetables, whole grains, fruits; legumes and nuts; healthy fats such as olive oil; moderate dairy, fish and poultry; and low intake of red meat, butter and other animal fats. A study of the Mediterranean Diet and Alzheimer’s Disease in the elderly observed that those with better adherence to the MeDi had less brain atrophy, with an effect similar to five years of aging. They concluded that higher fish and lower meat intake might be the two key food elements that contribute to the benefits of the MeDi on brain structure.[i] Another similar study of older individuals following a Mediterranean-like diet (NU-AGE) demonstrated that better adherence to the diet could slow down age-related cognitive decline, helping to prevent cognitive impairment and dementia. Most recently the MIND diet, a combination of the Mediterranean and DASH diets (DASH diet was developed to lower blood pressure), was used to develop a score of healthy foods and unhealthy foods from the food records of the Nurse’s Health Study (more than 100,000 participants followed over 14 years). The MIND diet includes many of the same dietary components as in the Mediterranean and DASH diets, such as emphasis on plant-based foods and limited animal and high saturated fat foods, but uniquely specifies food component servings that reflect diet-dementia study findings, such as berries and green leafy vegetables. Long-term adherence to the MIND diet was moderately associated with better verbal memory in later life.[ii] Finally, a Dutch study suggested that the effect of nutrition on neurodegeneration may act via brain structure and showed that better diet quality is associated with larger brain tissue volumes[iii].
Overall, studies have found associations between higher intake of fruits, vegetables, fish, whole grains, dairy (low-fat) and nuts, and lower intake of meat, saturated fats, alcohol and sugar-containing beverages and larger brain volumes such as gray matter volume and hippocampal volume.
And it’s not just older folks. Long-term adherence to a healthy diet promotes healthy brain aging later in life, such that maintaining ideal levels of cardiovascular health in young adulthood is associated with greater whole brain volume in middle age.[iv] A study of Korean youth looked at detailed diet intake and various memory tests. Healthy diet components correlated with better memory and reaction times, whereas refined grains, sugar-sweetened beverages, snacks and fast food had negative correlations.[v]
Another connection between diet and brain health is the gut-brain connection. Multiple studies have demonstrated an association with a healthy gut and better memory and cognition. Higher intake of vegetables and fruit may also contribute more brain protective nutrients: fiber, vitamin D, zinc and polyphenols, which promote growth of probiotic gut microbes. Healthy fats from fish, nuts and seeds also appear protective. In a Danish Health Study, diets and lifestyles that were characterized by abstinence from alcohol, smoking and meat showed lower incidence of dementia and Alzheimer’s disease. Furthermore, the polyphenols that are good for our brain are absorbed and then metabolized in the gut by bacteria, further emphasizing the importance of a healthy gut.
The gut microbiota (collection of bacteria) also influences psychological processes such as the stress response and cognition.[vi] The mechanisms are not clear, but we do know that we make many neurotransmitters in the gut.
Diets that are heavy in vegetables, whole grains and fiber are associated with healthier guts; whereas consumption of a protein-rich animal-based diet (higher in meat, dairy, saturated fats) shows a significant increase in a gut-specific bacterium associated with colitis and a variety of irritable bowel disease in mice.[vii] Studies with germ-free mice (void of gut bacteria) demonstrate anxiety, mood disorders and learning and memory problems. Additionally, people with anxiety or depression have a higher likelihood of having gastrointestinal disorders related to gut health. These findings are consistent with the hypothesis that diet-induced changes to the gut microbiota may contribute to the development of inflammatory bowel disease.[viii]
Most scientifically supported lifestyle factors for Alzheimer’s disease are also known factors for cardiovascular diseases and diabetes.
What about seafood specifically? There is evidence that at least one serving/week of seafood can protect against dementia and AD.[ix] In a recent study of 45-70 year olds, fatty fish and marine omega-3 fatty acid consumption was associated with a reduced risk, and the intake of cholesterol and saturated fat with an increased risk of impaired cognitive function—memory, flexibility, speed of reaction.[x] In addition to providing vascular protection, the omega-3 fatty acids contained in fish oils could reduce inflammation in the brain and may have a specific role in brain development and regeneration of nerve cells.
Is meat good or bad? Rather than a direct relationship, it appears that heavy meat consumption fits in a more harmful pattern of eating that also includes more sugars, refined grains and saturated fats. Meat is likely to be protective early in life and provide important nutrients for brain development early in life and in cases of undernutrition, but a Western dietary pattern that is heavy in red and processed meats appears to be detrimental to the long-term health of our brain.
So, while miracle foods may be interesting to pursue, there is still no substitution for a healthy diet pattern when it comes to memory and cognition. And, consuming a diet that is good for your heart is good for you brain too. That includes a lot more vegetables, nuts, beans, whole grains and fruit and a lot less red meat. That means more foods from plants, less food from animals (except fish). And even better, this plant-focused diet patter is also more sustainable, less resource intensive, and better for the climate.
Image: Illustration from “The Home and School Reference Work, Volume I” (1917), courtesy of Flickr user Sue Clark
[i] Mediterranean diet and brain structure in a multiethnic elderly cohort
Yian Gu, Adam M. Brickman, Yaakov Stern, Christian G. Habeck, Qolamreza R. Razlighi, José A. Luchsinger, Jennifer J. Manly, Nicole Schupf, Richard Mayeux, Nikolaos Scarmeas
Neurology Nov 2015, 85 (20) 1744-1751; DOI: 10.1212/WNL.0000000000002121
[iii] Better diet quality relates to larger brain tissue volumes
Pauline H. Croll, Trudy Voortman, M. Arfan Ikram, Oscar H. Franco, Josje D. Schoufour, Daniel Bos, Meike W. Vernooij. Neurology May 2018
[iv] Cardiovascular health in young adulthood and structural brain MRI in midlife
Michael P. Bancks, Norrina B. Allen, Prachi Dubey, Lenore J. Launer, Donald M. Lloyd-Jones, Jared P. Reis, Stephen Sidney, Yuichiro Yano, Pamela J. Schreiner
[v] Kim JY, Kang SW. Relationships between Dietary Intake and Cognitive Function in Healthy Korean Children and Adolescents. Journal of Lifestyle Medicine. 2017;7(1):10-17. doi:10.15280/jlm.2017.7.1.10
(Dinan et al. 2015).
[viii] David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505(7484):559-563. doi:10.1038/nature12820. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3957428/
[ix] Barberger-Gateau Pascale, Letenneur Luc, Deschamps Valérie, Pérès Karine, Dartigues Jean-François, Renaud Serge et al. Fish, meat, and risk of dementia: cohort study BMJ 2002; 325 :932 https://www.bmj.com/content/325/7370/932.short
[x] Dietary intake of fatty acids and fish in relation to cognitive performance at middle age
- Kalmijn, M. P.J. van Boxtel, M. Ocké, W. M.M. Verschuren, D. Kromhout, L. J. Launer
Neurology Jan 2004, 62 (2) 275-280; DOI: 10.1212/01.WNL.0000103860.75218.A5