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Research Theme Park: Foodland

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Blueberries, walnuts, tea, salt, and the Mediterranean diet are featured in this playful but practical stroll through the latest research on food and the brain.

Published On: 5/25/20

Duration: 10 minutes, 1 seconds

Diet for Depression: Vegetables (5 servings per day), fruits (2–3 per day), wholegrain cereals (3 per day), protein (lean meat, poultry, eggs, tofu, legumes; 3 per day), unsweetened dairy (3 per day), fish (3 per week), nuts and seeds (3 tablespoons per day), olive oil (2 tablespoons per day), spices (turmeric and cinnamon; 1 teaspoon most days). Decrease refined carbohydrate, sugar, fatty or processed meats and soft-drinks.

Test your Diet: A score of 57 or more was considered a poor enough diet to get you into this study.

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The Research Theme Park is a magical place in the Carlat Psychiatry Podcast that showcases papers that are practical, playful, and reveal a little bit about human nature. Today we’ll stop for lunch with a motley cast of characters in Foodland.

A 13-minute intervention for diet and depression
The studies keep rolling in that a Mediterranean style diet treats depression, but how do you teach this diet? In the pivotal trial of 2018, it was taught through individual weekly sessions with a dietician. The next trial used an educational group. This new study pared it down even further, and taught the Mediterranean diet through a single session video. 

Like the first two trials, this randomized controlled trial took place in Australia. It enrolled 76 college students who were eating a poor diet, heavy in processed foods, sugar, and saturated fats, which is also known as the typical Western Diet. They were not specifically diagnosed with DSM-5 major depression, but they had moderate-to-high depression on the Depression, Anxiety and Stress Scale-21 Depression subscale.

The intervention was a 13-minute video that taught them to increase vegetables, fruits, wholegrain cereals, protein, unsweetened dairy, fish, nuts, seeds, olive oil, spices (that was 1 teaspoon of turmeric and cinnamon; 1 teaspoon on most days). And there were a few foods to decrease: Refined carbohydrate, sugar, fatty or processed meats and soft-drinks.  If you didn’t get all that, it’s in the podcast notes along with the daily servings for each food group.

We’ve also put the diet test they used in this study in those notes. Try it yourself. Unless you’re consciously trying to eat healthy in this Western Diet World, there’s a good chance you would have qualified for this study.

They were also given a basket of health ingredients, gift cards to buy more, and followed up with two 5 minute phone calls throughout the 3 week study.

One weakness of this study is that the other group didn’t even get so much as a placebo. There were simply assessed and asked to return after 3 weeks for follow up, which makes them more like a wait list control.

In the end, depression improved in the dietary group, with a p value of 0.007 and a medium effect size of 0.65.

Francis HM, Stevenson RJ, Chambers JR, Gupta D, Newey B, Lim CK. A brief diet intervention can reduce symptoms of depression in young adults – A randomised controlled trial. PLoS One. 2019;14(10):e0222768. Published 2019 Oct 9.

Diet for Depression: Vegetables (5 servings per day), fruits (2–3 per day), wholegrain cereals (3 per day), protein (lean meat, poultry, eggs, tofu, legumes; 3 per day), unsweetened dairy (3 per day), fish (3 per week), nuts and seeds (3 tablespoons per day), olive oil (2 tablespoons per day), spices (turmeric and cinnamon; 1 teaspoon most days). Decrease refined carbohydrate, sugar, fatty or processed meats and soft-drinks.

Test your Diet: A score of 57 or more was considered a poor enough diet to get you into this study.


Salt and cognition

Sugar, saturated fats, and processed foods. Each of these are bad for the heart and the brain, and each has been linked to poor cognition and low mood. But what about salt? A new study in Nature found that a high-salt diet impairs cognition and contributes to dementia through effects on vascular health. Researchers at the Weill Cornell School of Medicine found that mice fed a high-salt diet had lower levels of nitric oxide, which is essential for maintaining vascular health. Nitric oxide widens and relaxes blood vessels. It also affects the stability of tau proteins which play a role in dementia, and this new study found that the high salt diet was causing hyperphosphorylation of tau proteins.

The research builds on a 2018 study where mice were fed a high salt diet. That study had striking results the mice became unable to complete daily living tasks such as building their nests and had problems passing memory tests. At the time it was thought that the salt was impairing brain function through its known effects on vascular health, and this study suggests that more than one mechanism may be at plan, adding hyperphosphorylation of tau proteins to the list.

What’s the clinical message? When patients buy packaged foods, advice them to choose the item with the lowest amounts of salt, added sugar, and processing i.e. chemical ingredients.

Faraco G, Hochrainer K, Segarra SG, et al. Dietary salt promotes cognitive impairment through tau phosphorylation. Nature. 2019;574(7780):686‐690.  

Tea drinkers have long been known to have lower rates of dementia and depression, and a new study  though not controlled   found that people who drank green tea, oolong tea, or black tea at least four times a week for about 25 years had brain regions that were interconnected in a more efficient way on imaging studies.

One of those “more efficient” regions was the default mode network, which is the seat of the ruminative style of thinking so common in depression and anxiety.

Li J, Romero-Garcia R, Suckling J, Feng L. Habitual tea drinking modulates brain efficiency: evidence from brain connectivity evaluation. Aging (Albany NY). 2019;11(11):3876‐3890. doi:10.18632/aging.102023


Walnuts help memory…. maybe

Also in the news is a 2-year study that randomized over 600 older adults to a walnut-enriched or a regular diet. The results were a little disappointing – no difference overall – but in a subgroup – the ones who smoked and started out with poor cognitive functioning the walnuts had a mild protective effect. Walnuts contain omega-3 fatty acids and polyphenols, which have previously been found to counteract oxidative stress and inflammation, both of which are drivers of cognitive decline. 

The main limitation of this finding is that it was only positive on post-hoc analysis, otherwise known as data fishing.  A few years ago walnuts were also put through a randomized controlled trial of depression – unfortunately the omega-3 rich nuts made no difference.

Sala-Vila A, Valls-Pedret C, Rajaram S, et al. Effect of a 2-year diet intervention with walnuts on cognitive decline. The Walnuts And Healthy Aging (WAHA) study: a randomized controlled trial. Am J Clin Nutr. 2020;111(3):590‐600.  


Blueberries and Mood

Randomized controlled trials usually involve pills. But these two used blueberries to treat depression,  which raises the question – what do you do for a placebo?

The brain benefits of blueberries are pretty well known,  so these studies wouldn’t mean much if people knew that they were getting a daily dose of BB instead of the placebo.  Here’s how they did it. ? They didn’t actually give blueberries, they gave an extract with all the blueberry brain friendly ingredients,  while the controlled group got a powder that tasted like blueberries. 

And the result? Blueberry extract improved mood shortly after eating it, and those improvements also built up over a 4 week trial. So far good news for the blueberry council who sponsored this study.

But now let’s talk about the limitations – these studies were small. The first involved 64 children aged 12 to 17 years old ……these kids didn’t have major depressive disorder – they just had depressive symptoms. So we don’t know if Blueberries will help people in a deep depression, but they may just lift mood when depression is mild. 

This new crop of blueberry trials was done in children and adolescents with mild depressive symptoms, but we should mention that the humble Blueberry already has a pretty good track record in older adult with cognitive decline. Last year a systematic review of those studies improved cognition in older adults, and in the young as well. At least 1 of those studies was done in 8 year olds. Some of these studies used Blueberry juice others extract and others the real thing. But If you are planning to try this at home we’ll leave you with this dosing strategy. The various doses equate to about 1 half to 1 cup of blueberries a day. 

Fisk J, Khalid S, Reynolds SA, Williams CM. Effect of 4 weeks daily wild blueberry supplementation on symptoms of depression in adolescents. Br J Nutr. 2020;1‐8. 

Khalid S, Barfoot KL, May G, Lamport DJ, Reynolds SA, Williams CM. Effects of Acute Blueberry Flavonoids on Mood in Children and Young Adults. Nutrients. 2017;9(2):158. Published 2017 Feb 20. doi:10.3390/nu9020158

Travica N, D’Cunha NM, Naumovski N, et al. The effect of blueberry interventions on cognitive performance and mood: A systematic review of randomized controlled trials. Brain Behav Immun. 2020;85:96‐105.  

You can find references to all these studies in the show notes for this episode. And now, as you exit the park, we’d like to thank you for helping us reach a new milestone. The Carlat Psychiatry podcast is now ranked #1 on Apple podcast among all mental health podcasts. If you like the show, share it with a friend – you can text it to them with the button in your podcast player. There’s nothing wrong with doing that, and it helps us stay free of industry support.


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