broccoli & peppers may prevent parkinson's disease; eating a 'mediterranean' diet may only slow cognitive decline if you don't also eat lots of 'western' food (spoiler: not really)  

original articles: Agarwal et al., 2021 (Alzheimer's and Dementia), Hantikainen et al., 2021 (Neurology), reported in: The Daily Mail by Ryan Morrison on 7th January 2021 & The Daily Mail by Stacy Liberatore on 11th January 2021 image source

this story was in episode 1 #broccoli #vegetable #brain #degeneration

the error bar says

a pair of papers claim that brain degeneration can be prevented by the foods we eat.

in the first paper - which was not freely available online - the claim is that vitamins c and e found in peppers and broccoli help prevent the degenerative disease parkinsons's disease.

the second paper looks at the historical food reports of 10000 people in the USA, along with how they performed on follow-up cognitive tests every three years.

only half of the 10000 volunteers' data were used - some had died, and others hadn't filled in the food questionnaires correctly. somewhat suspiciously, people who reported eating too little or too much food, or had poor mental state scores, were removed from the analysis.

the headline-grabbing claim is that a mediterranean-style diet with lots of fruit and vegetables is only good for your brain if you also don't eat lots of western food on the side

when exactly are vegetables good for your brain?

the claim is that mediterranean food is only good for you if you don't also eat lots of western food. but that's not actually what the study found. it's more subtle and contextual than that.

as is common in studies like this, there are lots of possible variables to take into account - the age, sex, ethnic group, and pre-existing health conditions. for example, people with a high western style diet were more male, and those with a high mediterranean diet also took more exercise.

but let's just examine the central claim. if you eat lots of mediterranean food, that is always a good thing - cognitive test scores were higher and declined less slowly. and if you eat lots of western food, then you were a little worse off overall. but these two trends were totally unrelated to each other - not what the headline claims.

the researchers then divided the western diets into a 'high' and a 'low' diet and did analyses on each part separately. this 'median split' is a common tactic - divide the data into slices and look at each slice separately.

in the low-western slice they found slightly stronger relationships than in the high western slice. but the direction and size of these relationships was quite comparable. so, while the conclusions were that a mediterranean diet is only good for you if you don't also eat lots of western food, actually, the benefit of eating lots of mediterranean foods was always about 6 years' additional brain health, for both high and low western diets


eat a balanced diet, lots of fresh fruit and vegetables, exercise lots, stay mentally active; don't believe everything you read in retrospective food questionnaire studies


The Daily Mail: fudge - scientific story distorted