Anyone who has been a reader of this newsletter for any period of time knows that I’m not all that impressed with the data on any particular dietary interventions and tend to be an agnostic when it comes to nutrition.
So when the New England Journal of Medicine publishes a new trial on the impact of a Mediterranean-DASH hybrid diet to prevent cognitive decline, my strong prior is to expect an unimpressive result.
Dementia is probably the most feared illness in medicine, and at least some dementia is probably preventable through lifestyle intervention, we just don’t know what those interventions might be.
The MIND diet trial is an attempt to try to understand this question a bit better.
Why did I say some dementia is preventable?
The most common form of dementia is Alzheimer’s disease, and most experts in the field think that Alzheimer’s disease is partly preventable.
Some of the major risk factors for Alzheimer’s are things that overlap as risk factors for cardiovascular disease and that impact general health: diabetes, hypertension, alcohol, poor sleep, smoking, and many others.
If you get into the weeds on this, you’ll see research discussing the vascular hypothesis of Alzheimer’s disease and a hypothesis that Alzheimer’s dementia may actually be “type 3 diabetes.”
This concept - that Alzheimer’s may be preventable - isn’t written on a stone tablet, but it’s still strongly suggested by the evidence that we have.
Lower the risk of diabetes and cardiovascular disease through lifestyle modifications, and you’re likely to lower the risk of Alzheimer’s as well.
Enter the MIND diet.
What is the MIND diet?
From the paper:
“The Mediterranean–DASH Intervention for Neurodegenerative Delay, known as the MIND diet, is a hybrid of the Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet, with modifications to include foods that have been putatively associated with a decreased risk of dementia.”
In other words, sounds like the type of diet that would generally have a connotation of being healthy.
The trial design was interesting
The authors took overweight patients who had risk for cognitive decline (family history of dementia) and a poor diet at baseline, and then randomized them to the MIND diet with mild calorie restriction versus their usual diet with “mild calorie restriction for weight loss.”
This is an important point, and one that we’ll come back to later.
They followed people for 3 years and collected data on them every 6 months, which included cognitive assessments and brain MRIs:
Support for the participants was pretty rigorous
You’ve probably read stories about blueberries, olive oil, or nuts being linked to a lower risk of dementia.
The authors of the MIND trial tried to test that hypothesis by providing people randomized to this diet foods that have been suggested to lower dementia risk.
They actually gave out free stuff here - the trial group received berries, olive oil, ad nuts, while the comparison group received gift certificates to test the idea that free food is actually the important intervention:
“The MIND-diet group received a monthly supply of blueberries (2.5 cups, or 15 oz [425 g], per week), mixed nuts (5 oz [142 g] per week), and extra virgin olive oil (14 tablespoons, or 7 fl oz [207 ml] per week) that was donated by nonprofit food-grower organizations. The participants in the control-diet group received $30 gift cards at the same frequency that the MIND-diet group received food.
This was also a trial where a lot of support was provided to participants in both groups, and this became about community, not just diet adherence:
“All the participants had at least five opportunities to connect with other members in their assigned trial group in group sessions that took place at months 3, 9, 18, and 30 to cultivate social support. Group sessions included education about their assigned diet, tips to promote mild weight loss, and other motivational activities such as cooking sessions, trivia games, competitions, and holiday celebrations.”
They even measured diet adherence by looking at biomarkers of fruit and vegetable intake like beta carotene and lutein.
All in all, a pretty rigorous study design.
What do you think they found?
The end result of this trial was pretty neutral, as you might expect.
Global cognition scores were the same in both groups:
So were brain MRI findings:
And if you look at the baseline characteristics of the two groups, you’ll see that the control diet group may even have been at higher risk for Alzheimer’s based on some genetic testing looking at apolipoprotein E4, which increases risk of Alzheimers:
So what do we learn from a trial like this?
You can look at this data in a few different ways. Here are a handful of potential take home points:
If you’re overweight, a calorie restricted diet may lead to an increase in global cognition, so we should emphasize mild calorie restriction for anyone overweight regardless of risk for Alzheimer’s disease
Free blueberries, nuts, and olive oil aren’t better at preventing cognitive decline than getting a monthly check for $30
A 3 year long trial doesn’t tell us anything about a disease that takes decades to unfold
The Standard American Diet is bad, and any persistent intervention that takes people away from that is a net positive
I think any of these conclusions are reasonable to draw here. Ultimately, it’s reassuring to see that older adults can have improvements in global cognitive function.
The other big takeaway I have is that doing a little bit better probably makes a difference when it comes to diet.
Too many of my patients are concerned about optimizing when it comes to things like this.
“How many blueberries should I eat?”
“How often should I eat fish and how many ounces should I have? Is tuna as good as salmon ”
“Do all leafy greens work as well as spinach? Is raw better than cooked?”
A trial like this tells me that optimization is likely a waste of energy unless you enjoy the process of doing it.
Trying to eat a little bit better is probably good, and we shouldn’t let the perfect be the enemy of the good.