5 interesting nutrition studies you should know about

At ZOE, we’re fascinated by nutrition, as you may have noticed. So, we like to keep abreast of recent research.

We also love sharing the latest science with others, and that’s where this article comes in.

Below, we briefly outline five studies from the last few months that we think are worth talking about. We’ll cover ultra-processed foods, chocolate, caffeine, and more. So, let’s jump in.

1. Ultra-processed food and cognitive decline

As we age, many of us will experience a reduction in our thinking abilities. This is called cognitive decline, and it’s a normal part of aging.

However, cognitive decline affects everyone differently, with some people keeping their cognitive dexterity for longer than others.

As the population ages, scientists are keen to understand why some people’s thinking abilities decline more rapidly. And many researchers are looking at the role of food. 

In a recent study, including 568 older adults with type 2 diabetes, the scientists zeroed in on ultra-processed foods: Could they influence brain health as we age?

They found that a higher intake of ultra-processed meats, oils, and spreads was associated with a faster decline in overall thinking ability and executive function.

Executive function is a set of mental skills that includes planning, following instructions, and self-control. 

If you’d like to learn more, we have a feature on the relationship between ultra-processed food and brain health.

And we’ve also written about links between these foods and mental health.

What should you do?

ZOE holds a dim view of ultra-processed foods. Realistically, it would be difficult to give them up entirely. It’s your overall eating pattern that matters most. 

So, cut them out when possible, and try to replace them with plants and other whole foods. 

2. Chocolate and death risk

A recent study set out to investigate whether eating chocolate was linked to a reduced risk of mortality. In other words, they asked whether people who ate chocolate were less likely to die during their study.

To investigate, they followed more than 84,000 postmenopausal women for an average of 19 years.

Perhaps surprisingly, they found that eating more chocolate was linked to a reduced risk of dying during the study. 

They also found that people who ate 1–3 servings of chocolate each week were slightly less likely to die from cardiovascular disease and dementia during the follow-up period.

And, before you ask, no, the study wasn’t sponsored by Hershey’s.

What should you do?

Chocolate is delicious; there’s no getting around it. But much of it is ultra-processed, containing a wide range of additives. 

And according to the authors, this study is the first to identify a relationship between eating chocolate and mortality. So, before you stock up, other scientists need to replicate these findings.

With that said, it's best to opt for minimally processed dark chocolate.

This contains 70% cocoa or more, which doesn't leave room for a lot of added sugar and other additives.

Plus, dark chocolate contains beneficial compounds, like antioxidants, polyphenols, and flavonoids. Read more about the health benefits of dark chocolate here.

3. Caffeine and depression

As one of the most popular drinks on the planet, coffee has been the subject of a fair bit of research.

Overall, drinking a moderate amount of coffee seems to be generally healthy. Among other nutrients, it contains a good dose of fiber, and it may protect your gut health.

In fact, ZOE's own research has found that people who drink coffee have more diverse gut microbiomes.

A recent meta-analysis of 29 studies explored whether coffee might be linked to depression risk. It included data from 422,586 adults.

Overall, they found that higher coffee and caffeine intakes were linked to a lower risk of depression.

But, interestingly, tea didn’t seem to affect depression risk. So, scientists need to carry out more research to understand whether the relationship between coffee, caffeine, and depression risk is causal. 

What should you do?

At ZOE, we know that everyone responds differently to foods and drinks, including coffee.

Caffeine makes some people anxious and disrupts their sleep. If this is you, don’t worry about upping your coffee intake.

However, if you enjoy drinking coffee, you can take this as good news. 

Also, it’s worth noting that the studies in this meta-analysis were observational. This means that they can’t prove cause and effect. 

In other words, the results might stem from other factors that the scientists couldn’t control in the study.

So, we can’t conclude that coffee directly causes a reduced risk of depression. As ever, we need to do more research.

If you’d like to know more about the possible health effects, ZOE has a podcast episode on coffee.

4. Mediterranean vs. keto Mediterranean

A small study recently tested two diets in people with overweight or obesity. All the participants also had diabetes or prediabetes.

Each participant adopted either a very-low-calorie Mediterranean diet or a very-low-calorie ketogenic Mediterranean diet for 30 days.

On both diets, participants lost weight and fat mass. However, those on the ketogenic version lost more fat mass and reduced their waist and hip circumferences. 

The keto version also significantly improved measures of blood sugar control, but the very-low-calorie Mediterranean diet didn’t.

What should you do?

This study was small — just 80 participants. So, scientists need to do more research to check the results. In fact, the paper's authors are now planning a larger trial.

Also, the existing study only lasted for 30 days. So, we don’t know how the participants’ weights and blood sugar responses changed after that point.

At ZOE, we know that calorie counting isn’t an effective strategy for long-term weight maintenance. And the same goes for the keto diet.

Because they’re so restrictive, most people find them incredibly difficult to follow for the long haul. 

And although blood sugar control and weight are two measures of health, they’re not the only measures.

Plus, there are health risks associated with the keto diet.

Still, there's good evidence that the Mediterranean diet is a healthy way to eat. Although it's not a weight loss diet, it may help reduce your heart disease risk.

5. Fiber and dementia risk 

Fiber is great for your health, particularly your gut health. But can adding it to your diet influence your dementia risk?

A recent paper looked for links between consuming fiber and the risk of developing dementia that requires care. The authors refer to this as “disabling dementia.”

They took data from more than 3,700 adults in Japan who were aged 40–64 at the start of the study. And they followed them for an average of 20 years. 

The scientists found that people who ate the most fiber, especially soluble fiber, were significantly less likely to develop disabling dementia.

Specifically, those who ate 18–65.3 grams of fiber each day had a 26% lower risk than those who ate 2.2–10.6 g a day.

What should you do?

A fiber-rich diet is linked to a range of health benefits, like better gut and heart health, weight loss, improved blood sugar control, and more. 

However, in the United States and United Kingdom, many of us don't eat enough fiber.

For instance, experts recommend that we consume 25–38 g of fiber each day. And on average, people in the U.S. only consume 10–15 g daily.

So, although scientists need to carry out more research to confirm fiber’s protective effects against dementia, adding more fiber to your diet is a good idea.

For more information, ZOE has an article outlining high-fiber foods to add to your diet and a podcast episode on the wonders of fiber.

The takeaways

Nutrition science is an ongoing voyage of discovery. Researchers add to our knowledge with every study that’s published. 

Over time, we develop an ever-clearer understanding of how food influences our health.

And if you want some actionable takeaways from today’s research, here they are:

  1. Try to reduce your intake of ultra-processed foods: It might reduce your dementia risk and will likely improve your overall health.

  2. Eat some dark chocolate a few times a week: It might reduce your mortality risk if you're postmenopausal, and it will certainly be delicious.

  3. Drink coffee if you like it: It might reduce your risk of depression, and drinking 4–5 cups a day may also have other health benefits. But if caffeine makes you jittery or unwell, listen to your body.

  4. Try the Mediterranean diet: It’s sustainable in the long run and linked to various health benefits.

  5. Eat more fiber: It might reduce your risk of developing dementia, but it will certainly benefit your gut and beyond.


Association between dietary caffeine, coffee, and tea consumption and depressive symptoms in adults: A systematic review and dose-response meta-analysis of observational studies. Frontiers in Nutrition. (2023). https://www.frontiersin.org/articles/10.3389/fnut.2023.1051444/full 

Chocolate consumption in relation to all-cause and cause-specific mortality in women: The Women’s Health Initiative. Journal of the Academy of Nutrition and Dietetics. (2022). https://www.sciencedirect.com/science/article/pii/S2212267222012564 

Consumption of ultra-processed food and cognitive decline among older adults with type-2 diabetes. (2023). https://pubmed.ncbi.nlm.nih.gov/35305016/ 

Dietary fiber intake and risk of incident disabling dementia: The Circulatory Risk in Communities Study. Nutritional Neuroscience. (2022). https://www.tandfonline.com/doi/full/10.1080/1028415X.2022.2027592 

Italian ketogenic Mediterranean diet in overweight and obese patients with prediabetes or type 2 diabetes. Nutrients. (2022). https://www.mdpi.com/2072-6643/14/20/4361