Does the MIND diet help against dementia and cognitive decline?

The MIND diet combines elements of the Mediterranean diet and the DASH diet, with an emphasis on green leafy vegetables, berries, nuts, legumes, whole grains, fish, poultry and olive oil, while limiting red meat, butter, cheese, pastries and fried food. Observational studies, including a cohort study of 960 older adults followed for an average of 4.7 years, found that people who adhered most closely to the MIND diet showed substantially less cognitive decline than those who adhered least. The difference was equivalent to being 7.5 years younger in age. A meta-analysis of 11 cohort studies totalling more than 224,000 participants showed that a higher MIND diet score was associated with a 17 percent lower chance of developing dementia (hazard ratio 0.83). These are observational associations: other healthy lifestyle habits among people who follow this diet may (partly) explain the observed benefit.

The only large randomised controlled trial published to date, however, showed no effect. In that study, 604 older adults with a familial risk of dementia were followed for three years. Half followed the MIND diet (with mild calorie reduction), while the other half also ate a mildly calorie-restricted diet but without a specific MIND prescription. The difference in cognitive test scores between the two groups was minimal (0.035 standard deviations, p=0.23) and not clinically meaningful. MRI measurements of brain volume, hippocampus and white matter lesions also did not differ. Both groups even improved slightly, which makes it harder for the study to detect an effect in people who were already eating relatively healthily.

Multiple review studies conclude that the MIND diet, together with the Mediterranean and DASH diets, is associated with a lower risk of Alzheimer's disease and cognitive decline. Some review articles suggest that the MIND diet may be more effective than the individual parent diets, but this has not been demonstrated in an RCT. The authors of those reviews themselves acknowledge that the available research is limited and partly contradictory.

In summary: the observational studies consistently point in a favourable direction, but the only large RCT to date does not confirm that benefit. One possible explanation is that the control group in that RCT also ate fairly healthily, making a difference difficult to detect. Whether the diet itself is protective, or whether other factors associated with healthy eating provide the explanation, remains uncertain. Anyone who wishes to try the MIND diet takes little risk in doing so: the dietary pattern falls within generally recognised guidelines for healthy eating.