5 interesting studies: Chocolate, nuts, plant prescriptions, and more

Welcome to the seventh edition of the ZOE Nutrition Research Roundup. In this series, we pick five recent studies from the realm of nutrition science that we think are fascinating.

We’ll tell you what the scientists did, what they found, and what it means for your health.

Among other topics, we touch on weight loss, vitamin D, brain health, and chocolate.

1. High-fiber diets and weight loss

Eating foods high in fiber, like fruits and vegetables, supports your gut microbiome and protects your gut health.

But could these fibrous foods also help you manage your weight? According to a recent, tightly controlled study, they might.

What did they do?

The scientists recruited 17 young participants with healthy weights. They measured their energy intake, how much energy they burned off, and how much energy came out in their poop and urine.

Some participants followed a Western diet, and the rest followed a Microbiome Enhancer Diet (MBD). This includes nutrients that feed gut bacteria, like fiber and resistant starch.

Importantly, the scientists made sure that the Western diet and the MBD contained similar amounts of energy, fat, carbs, and protein.

What did they find?

The scientists found that people following the MBD excreted, on average, 116 more calories than those on the Western diet. 

In other words, those eating the high-fiber diet absorbed less energy into their bodies. 

What should you do?

Although this study was tightly controlled, it was small. So, experts need more research to understand whether a high-fiber diet can help promote weight loss in the long term.

However, we already know that a high-fiber diet is good for your gut and overall health.

So, whether it helps you lose weight or not, adding more fiber-rich foods to your diet is certainly a good idea. ZOE has a handy list of high-fiber foods to add to your next shopping list.

2. Vitamin D and IBS

The symptoms of irritable bowel syndrome (IBS) include stomach pain, cramps, diarrhea, constipation, and bloating.

Though IBS affects around 5–10% of people, scientists are still figuring out precisely why and how it develops. 

Because of this knowledge gap, current treatments aren’t effective for everyone — there’s a real need for better options. And some experts are looking at vitamin D. 

Recently, scientists carried out a meta-analysis to see whether vitamin D might be effective against IBS. In this type of research, they pool data from a selection of existing studies. 

What did they do?

The researchers reanalyzed data from six randomized controlled trials, including 572 participants in total.

What did they find?

The team concluded that compared with a placebo, vitamin D did reduce the severity of IBS symptoms. 

However, when the participants filled out the study questionnaires, they didn’t report improved quality of life.

Also, the authors acknowledge that we need more research — they could only identify a handful of studies that had explored this approach to treatment.

What should you do?

If you have IBS, a vitamin D supplement might be worth a try. However, it’s not guaranteed to work, and you should speak with your doctor before you take any new supplement.

Your skin produces vitamin D when it’s exposed to sunlight. So, being outside can help make sure your body produces enough. 

For people who live in colder regions, getting enough sun can be challenging. So, if this is you, a supplement might be useful.

You can also get vitamin D from foods, including oily fish, egg yolks, mushrooms, and peppers. For more information, check out ZOE’s podcast on vitamin supplements.

3. Chocolate and thinking skills

It’s almost impossible not to love chocolate. And if you choose minimally processed dark chocolate — with at least 70% cocoa — it can be a relatively healthy treat.

But can it improve your thinking, also called your cognitive skills? Maybe.

What did they do?

A group of researchers recently carried out a meta-analysis of studies looking at links between eating chocolate and cognitive performance.

They identified seven relevant randomized controlled trials and pooled the data to look for a trend.

What did they find? 

The team found that eating chocolate before completing tasks helped participants think more quickly. Their thinking and language skills also improved significantly.

However, this analysis only included data from a handful of small studies. And the studies were all run differently, making comparisons difficult.

Also, there was a risk of bias: Some of the research was funded by or supported by chocolate manufacturers, who have a vested interest in finding the benefits of chocolate.

What should you do?

This study certainly doesn’t provide enough of an excuse to fill your shopping cart with chocolate. But if you feel like eating a couple of squares before an exam or a job interview, it likely won’t do you any harm.

And eating moderate amounts of dark chocolate might even have some health benefits.

4. Plant prescriptions and heart health

At ZOE, we know that a plant-filled diet supports good health. But not everyone has easy access to fruits and veggies.

The lead author of a recent study, Dr. Kurt Hager, explains:

“We know that food insecurity impacts health through several important pathways, including overall dietary quality, but also through stress and anxiety, mental health, and trade-offs between paying for food and other basic needs such as housing costs, utilities, and medications.”

So, could “produce prescriptions” be the way forward?

What did they do?

Produce prescriptions allow you to access free fruits and veggies or to buy them at a discounted rate. 

Although scientists have investigated this before, most studies have focused on small produce prescription programs.

So, in the latest study, the researchers pooled data from nine of these smaller groups, which included 3,881 children and adults in total. 

What did they find?

The team found that produce prescriptions encouraged fruit and vegetable intake: Adults consumed almost 1 cup more each day, and children ate around an extra quarter cup per day.

The prescriptions were also linked to improvements in food insecurity and self-reported health among both adults and children.

And in the adults — all of whom were at risk of cardiovascular disease — the produce prescriptions were associated with improved blood sugar levels, blood pressure, and body mass index.

What should you do?

This study provides more evidence that a plant-rich diet can benefit your health. ZOE’s Scientific Co-Founder Prof. Tim Spector recommends eating 30 different plants each week

And as this research shows, even adding just one extra portion of plants per day might help improve certain health measures for some people.

5. Nuts and brain health

Earlier research has suggested that nuts might help protect your cognitive function as you age.

However, many of the earlier studies were short and didn’t focus on how nuts might protect brain health. A new investigation has set out to fill these gaps.

What did they do?

The 16-week study included 28 people with an average age of 65. Half of the group ate a handful of mixed nuts each day for 8 weeks, then went 8 weeks without nuts. 

The other half had 8 weeks without nuts, followed by 8 weeks with a handful each day.

The researchers measured blood flow in the participants’ brains before and after each 8-week period. And they had the participants do cognitive tests.

What did they find? 

The scientists found that after the participants had eaten the mixed nuts for 8 weeks, blood flow in some important brain regions had improved. 

This included parts of the frontal lobe, which is essential for more complex thinking. 

And after the 8 weeks of nut consumption, scores in some (but not all) of the cognitive tests had improved.

What should you do?

At ZOE, we love nuts — they’re nutrient-dense and delicious. Even if they don’t improve your cognitive skills, they’re a healthy addition to your diet. 

If you’d like to learn more, we have a podcast dedicated to the wonders of nuts.

The takehome

So, what have we learned from this edition’s collection of nutrition science studies? Here are the main takeaways:

  1. Adding fiber to your diet might help you manage your weight. And if it doesn’t, it’ll likely benefit your health in other ways.

  2. Vitamin D supplements might improve IBS symptoms. And if they don’t, this vitamin is still important for good health.

  3. Chocolate might improve your thinking skills. And if it doesn’t, consuming moderate amounts of dark chocolate containing at least 70% cocoa might have other health benefits.

  4. Produce prescriptions seem to improve measures of health in people at risk of cardiovascular disease. Upping your plant intake, even by a small amount, may improve your health.

  5. Nuts might protect your thinking skills as you age. And if they don’t, they’re still a healthy addition to your diet.


Benefits in cognitive function, blood pressure, and insulin resistance through cocoa flavanol consumption in elderly subjects with mild cognitive impairment. Hypertension. (2012). https://www.ahajournals.org/doi/full/10.1161/HYPERTENSIONAHA.112.193060 

Effects of chocolate on cognitive function in healthy adults: A systematic review and meta-analysis on clinical trials. Phytotherapy Research. (2023). https://pubmed.ncbi.nlm.nih.gov/37211619/ 

Host-diet-gut microbiome interactions influence human energy balance: A randomized clinical trial. Nature Communications. (2023). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10232526/ 

Impact of produce prescriptions on diet, food security, and cardiometabolic health outcomes: A multisite evaluation of 9 produce prescription programs in the United States. Circulation: Cardiovascular Quality and Outcomes. (2023). https://www.ahajournals.org/doi/10.1161/CIRCOUTCOMES.122.009520 

Irritable bowel syndrome (IBS). (n.d.). https://gi.org/topics/irritable-bowel-syndrome/ 

Longer-term mixed nut consumption improves brain vascular function and memory: A randomized, controlled crossover trial in older adults. Clinical Nutrition. (2023). https://pubmed.ncbi.nlm.nih.gov/37296019/ 

Prescription for fruits, vegetables linked to better heart health, food security. (2023). https://www.eurekalert.org/news-releases/999299 

Reasoning, learning, and creativity: Frontal lobe function and human decision-making. PLOS Biology. (2012). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3313946/ 

The effect of flavanol-rich cocoa on the fMRI response to a cognitive task in healthy young people. Journal of Cardiovascular Pharmacology. (2006). https://journals.lww.com/cardiovascularpharm/fulltext/2006/06001/the_effect_of_flavanol_rich_cocoa_on_the_fmri.18.aspx 

Vitamin D improves irritable bowel syndrome symptoms: A meta-analysis. Heliyon. (2023). https://pubmed.ncbi.nlm.nih.gov/37260904/