Plant-heavy Mediterranean diet may help reduce risk

The authors looked at multi-country ecological studies (which look for associations between factors and disease occurrence in populations) and prospective and cross-sectional observational studies (in which participants are assessed without any intervention by researchers) to determine the effects of different diets on Alzheimer’s risk.

In ecological studies, the researchers found that meat consumption was most strongly correlated with increased numbers of people with Alzheimer’s. They concluded that meat consumption was the single most important dietary risk factor for Alzheimer’s.

William B. Grant, Ph.D., study author and independent researcher, director of Sunlight, Nutrition and Health Research Center in San Francisco, told Medical News Today why meat might have this effect:

“Red and processed meat have a number of mechanisms by which they increase the risk of Alzheimer’s including having iron that increases oxidative stress, [and] methionine, which increases homocysteine, a very important risk factor for Alzheimer’s. Cooking meat at high temperature produces advanced glycation end products (AGEs), which explain many neuropathological and biochemical features of Alzheimer’s such as extensive protein crosslinking, glial induction of oxidative stress, and neuronal cell death. Red meat is also an important source of Arachidonic acid, which is pro-inflammatory.”

— Dr. William B. Grant, study author

The observational studies looked at a range of dietary patterns, including:

The Western diet is characterized by a high intake of foods that are high in energy and low in nutrients, such as fast foods, soft drinks, and highly processed foods. These foods are also high in added sugars, salt, and saturated fats.

The Mediterranean diet emphasizes intake of grains, legumes, vegetables, fruit, nuts, and fish, plus small amounts of meat, eggs, dairy, and alcohol.

The DASH diet is similar, but encourages intake of low-fat dairy products as well. Both advise people to limit intake of saturated fats, red meat and sugars.

The MIND diet is an adaptation of these 2 eating systems, but it focuses on daily and weekly recommendations for the different food groups.

The Mediterranean diet reduced Alzheimer’s risk the most, with a relative risk 46% of the Western diet. For the MIND diet, relative risk was 47%, and for the DASH diet it was 61%.

“The study suggests that adopting a diet similar to the Mediterranean diet, which emphasizes fruits, vegetables, legumes, nuts, whole grains and de-emphasizes red meat, saturated fats and ultra-processed foods, is associated with a lower risk of Alzheimer’s disease,” Dr. Emer MacSweeney, CEO and consultant Neuroradiologist at Re:Cognition Health, told MNT. Dr. MacSweeney was not involved in the research.

Plant-rich diets are known to benefit the gut microbiome.

Dr. Heather M. Snyder, Ph.D., Alzheimer’s Association vice president of Medical and Scientific Relations, who was not involved in the study, explained how this might affect Alzheimer’s risk:

“Many studies have shown that bacteria living in the gut may play a key role in how well a person’s immune system functions. People with higher levels of beta-amyloid in their brain — which is a hallmark of Alzheimer’s disease — tend to also have higher levels of bacteria in their gut that are associated with brain inflammation. However, it is not yet known whether these changes relate to declines in thinking and memory that occur as Alzheimer’s progresses. More research is needed in this area.”

Inflammation has been called a central mechanism for Alzheimer’s.

Research suggests that inflammation contributes to both β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs), both of which are key factors in Alzheimer’s.

“Inflammation leads to an accumulation of amyloid beta plaque aggregates and tau hyperphosphorylation, resulting in neuronal loss,” Dr. Grant explained. “Inflammation increases in old age in a process called Inflammaging: systemic chronic low-grade age-related inflammation.”

However, diets high in plant-based foods reduce inflammation, which may explain the findings of this study, as Dr. MacSweeney noted.

“Foods like green leafy vegetables, colorful fruits and vegetables, legumes, nuts, omega-3 fatty acids and whole grains are protective against Alzheimer’s disease,” MacSweeney said.

“These foods contain anti-inflammatory components and antioxidants, which may help mitigate the risk factors associated with Alzheimer’s.”

The authors identified several other risk factors, including oxidative stress, insulin resistance, and obesity, all of which they suggest can be addressed by modifying diet along the same lines.

Although this study has identified diet as a key factor in Alzheimer’s risk, other modifiable lifestyle factors can also help to reduce the risk of developing this form of dementia.

“Improving diet is the first line of defense for our brain,” Dr. Steve Blake, study author and director of Nutritional Neuroscience at the Maui Memory Clinic, told MNT.

“Continuing to learn keeps our brain sharper. Physical exercise improves brain-derived neurotrophic factor to help with short-term memory. Reducing stress and anxiety can improve cognition,” Dr. Blake added.

And Dr. MacSweeney agreed: “It’s important to note that while diet appears to be a significant factor, other lifestyle factors such as physical activity, cognitive engagement, and social connections also play roles in overall brain health and may influence the risk of Alzheimer’s disease.”

However, she stressed the importance of consulting healthcare professionals for personalized advice based on individual health conditions and needs before undertaking any diet and lifestyle changes.