All or nothing? Mediterranean diet benefits reduced with unhealthy food consumption

11 Jan 2021 --- A new study has found that the benefits of a Mediterranean diet on cognitive health are diminished when unhealthy foods are also eaten. US researchers from the Rush University Medical Center are stressing the importance of limiting the consumption of processed and other unhealthy foods.

“Eating a diet that emphasizes vegetables, fruit, fish and whole grains may positively affect a person’s health,” says Dr. Puja Agarwal, a nutritional epidemiologist and assistant professor in the Department of Internal Medicine at Rush Medical College.

“However, when it is combined with fried food, sweets, refined grains, red meat and processed meat, the benefits of eating the Mediterranean part of the diet seem to be diminished.”

The Mediterranean diet includes daily consumption of fruit, vegetables, legumes, olive oil, fish, potatoes and unrefined cereals.Impacts on cognitive health
The examination of 5,001 older adults living in Chicago, US, found that participants with slower cognitive decline over the years of follow-up were those who closely followed a Mediterranean diet, along with limiting foods that are part of a Western diet.

In contrast, participants who ate more Western diet foods had no beneficial effect of healthy food components in slowing cognitive decline. 

There was no significant interaction between age, sex, race or education and the association with cognitive decline in either high or low levels of Western diet foods. The study also included models for smoking status, body mass index and other potential variables such as cardiovascular conditions and findings remained the same.

“Western diets may adversely affect cognitive health,” says Agarwal. “Individuals who had a high Mediterranean diet score compared to those who had the lowest score were equivalent to being 5.8 years younger in age cognitively.”

Assessing long-term effects
The observational study included adults who were part of the Chicago Health and Aging Project, an evaluation of cognitive health in adults over the age of 65 conducted from 1993 to 2012.

Every three years, the study participants completed a cognitive assessment questionnaire that tested basic information-processing skills and memory, and they filled out a questionnaire about the frequency with which they consumed 144 food items.

The researchers analyzed how closely the participants adhered to a Mediterranean diet, which includes daily consumption of fruit, vegetables, legumes, olive oil, fish, potatoes and unrefined cereals, plus moderate wine consumption. 

They also assessed how much each participant followed a Western diet, which included fried foods, refined grains, sweets, red and processed meats, full-fat dairy products and pizza. They assigned scores of zero to five for each food item to compile a total Mediterranean diet score for each participant along a range from zero to 55.

The researchers then examined the association between Mediterranean diet scores and changes in participants’ global cognitive function, episodic memory and perceptual speed.

Future studies on diet and cognition among the middle-aged population are needed to extend the findings of this study.Complementary results
Agarwal says that the results complement other studies showing that a Mediterranean diet reduces the risk of heart disease, certain cancers and diabetes and also support previous studies on Mediterranean diet and cognition.

The study also notes that most of the dietary patterns that have shown improvement in cognitive function among older adults, including the Mediterranean, MIND and DASH diets, have a unique scoring matrix based on the number of servings consumed for each diet component.

“The more we can incorporate green leafy vegetables, other vegetables, berries, olive oil, and fish into our diets, the better it is for our aging brains and bodies. Other studies show that red and processed meat, fried food and low whole grains intake are associated with higher inflammation and faster cognitive decline in older ages,” says Agarwal.

“To benefit from diets such as the Mediterranean diet, or MIND diet, we would have to limit our consumption of processed foods and other unhealthy foods such as fried foods and sweets.”

However, she notes that the study and its findings cannot be readily generalized. Future longitudinal studies on diet and cognition among the middle-aged population are needed to extend these findings.

Last week, a study found that following a traditional Mediterranean diet reduces the risk of secondary heart attacks in coronary heart disease patients more effectively than standard low-fat diets.

Meanwhile, a November investigation revealed the biomarkers explaining the longstanding link between Mediterranean diets and lowered risk of Type 2 diabetes.

Edited by Katherine Durrell