5 interesting studies: Artificial sweeteners, olive oil, and more

Welcome to the latest ZOE Nutrition Science Roundup. This series of features provides a snapshot of some recent nutrition science research that we’ve found interesting.

Below, we cover five new studies. We explain what the scientists did, what they found, and what it means for your health.

Up first, we’ve got an intriguing glimpse into legumes and longevity.

1. Can legumes lengthen your life?

At ZOE, we’re fans of legumes. From lentils, peas, and peanuts to a tasty range of beans, these plant foods are nutritious and delicious.

Thanks to legumes' impressive suite of nutrients, many scientists have investigated whether consuming them might reduce disease and mortality risk.

However, according to the authors of a recent paper, these “studies have shown varying results.” 

So, to set the record straight, they conducted a systematic review and meta-analysis. In other words, they compiled the findings from previous studies, pooled the data, and reanalyzed them to develop a clearer picture.

In particular, they wanted to understand the relationship between eating legumes and mortality risk.

What's 'mortality risk'?

Before we dive in, it’s worth explaining "mortality risk." It’s an unusual idea because, at the end of the day, we’re all going to die. So, everyone’s mortality risk is really 100%.

When scientists use the term, they mean the risk of a participant dying during a specific time frame — in this case, the duration of the study. 

As an example, imagine you ran a 10-year study, and your participants were healthy 20-year-olds at the start. The risk of them dying during the study would be low, so their mortality risk would be low. 

But if you planned the study to run for 80 years, the participants’ mortality risk would be much higher — close to 100%.

OK, back to the review.

What did they do?

The researchers combined the data from 31 studies, which included more than 1.1 million people total. 

What did they find?

Following their analysis, the researchers concluded:

“Higher intakes of legumes, compared with lower intakes, were associated with a reduced risk of mortality from all causes [...] and stroke.”

Specifically, they found that increasing legume intake by 50 grams a day was associated with a 6% reduced risk of all-cause mortality.

However, consuming more legumes wasn’t linked to a decreased risk of dying from cardiovascular disease, coronary heart disease, or cancer. 

Scientists still need to do more research. As the authors of the review write, the certainty of the evidence was only “low to moderate.”

What should you do?

Adding more legumes to your diet is probably not a bad idea. They’re rich in protein, fiber, B vitamins, potassium, magnesium, and a range of healthy phytonutrients. 

So, tuck in.

2. Can diet improve cognitive function in older adults?

As we age, many of us will experience a slow decline in our thinking ability. This is called called cognitive decline, and it's considered a normal part of aging.

But it doesn’t affect everyone. Some people maintain their mental agility well into old age.

Not everyone who experiences cognitive decline will develop dementia. But everyone who develops dementia experiences cognitive decline first.

So, scientists are keen to understand whether any lifestyle factors might reduce the risk of cognitive decline. And some are looking at dietary patterns.

To date, the results of studies investigating cognitive decline and dietary patterns have been inconclusive. So, a group of scientists recently published a systematic review and meta-analysis.

What did they do?

The researchers identified 22 relevant randomized controlled trials involving older adults. They reviewed all 22 and reanalyzed data from nine studies. 

These studies tested the effects of different dietary patterns on cognitive performance. Most patterns were a version of the Mediterranean diet. Some included:

  • the Mediterranean diet

  • an olive oil-rich Mediterranean diet

  • a fish-rich version of the Mediterranean-DASH Diet Intervention for Neurodegenerative Delay (the MIND diet)

  • the Modified Atkins diet

  • a walnut-rich diet

  • a Greek, high-phenolic, early harvest, extra virgin olive oil-rich Mediterranean diet

What did they find?

The authors write: “The results demonstrated that dietary patterns achieved a significant improvement on cognitive function outcomes.”

So, that’s encouraging. However, they also explain that many of the studies were small and short, so the overall quality of the evidence was low.

Also, because of the range of dietary interventions, developing a clear overall picture was difficult. The team urges scientists to do longer, better-quality studies.

As it stands, there’s no effective treatment for cognitive decline or dementia. So, if dietary changes might reduce the risk — or slow the decline — it would be a huge win for society.

What should you do?

At ZOE, we know that having a varied, plant-heavy diet is important for your overall health. 

And the Mediterranean diet can fit the bill. It might not be the healthiest option for everyone — we’re all different — but it’s certainly better than the typical Western diet.

So, if you feel like following the Mediterranean diet, go for it. It might just look after your brain health as you age.

3. Artificial sweeteners, blood sugar, and hormones

Nutrition science has had its fair share of controversies over the years. And many have surrounded artificial sweeteners.

Despite decades of research, we still have unanswered questions: Are artificial sweeteners worse than sugar? Do they impact your gut microbiome? Do they really help you lose weight?

Meanwhile, some scientists are concerned that these sweeteners might influence how your blood sugar and hormone levels respond after you eat. 

Recently, a group of researchers conducted a review and meta-analysis to investigate.

What did they do?

The scientists pooled existing research on a range of artificial sweeteners. In particular, they wanted to know whether consuming sweeteners influenced people’s blood sugar responses or hormone levels.

In total, they scrutinized 36 carefully controlled trials involving a total of 472 healthy participants.

All the studies compared the effects of beverages containing artificial sweeteners with the effects of water, unsweetened drinks, or drinks containing caloric sugars (glucose, sucrose, or fructose).

What did they find?

The researchers concluded that none of the artificial sweeteners affected blood sugar or hormone levels. This was similar to water.

It's good news in general because many of us consume these sweeteners daily. But we have to take the findings with a pinch of salt. 

As the authors explain, the quality of the evidence is low to moderate. 

Also, the study received funding from the Low- And No-Calorie Sweeteners Scientific Committee of the Institute for the Advancement of Food and Nutrition Sciences. This body has a generally pro-artificial sweetener stance. 

It doesn’t mean we can dismiss the findings, but it’s worth keeping in mind.

What should you do?

If we take the results at face value, it seems that artificial sweeteners don’t influence your blood sugar or hormone responses.

But there’s more to your overall health than those factors. And we know that many of the foods that contain artificial sweeteners are ultra-processed. These foods should be enjoyed just once in a while.

ZOE knows that the healthiest diets contain a good selection of fresh, plant-based foods. If you opt for this type of diet, you’ll naturally reduce your intake of artificial sweeteners.

The debate surrounding these chemicals will no doubt rumble along for decades to come.

As it stands, we simply don’t know the effects of consuming artificial sweeteners every day for decades.

If you’d like to learn more, we have a feature on the sweetener aspartame

4. Olive oil, parent, and child

Having a healthy diet is always important. And it’s particularly important during pregnancy.

According to the authors of a recent review on olive oil, following the Mediterranean diet is “associated with a reduced risk of gestational diabetes, preeclampsia [high blood pressure before and just after giving birth], hypertension, and preterm birth.”

A recent review takes a closer look at one component of the Mediterranean diet — extra virgin olive oil (EVOO). 

The authors explored whether consuming EVOO was linked to having better outcomes during and after pregnancy.

What did they do?

The team reviewed nine studies conducted in Spain, Argentina, Denmark, Italy, and the United Kingdom.

The studies ranged in size from 30 participants to more than 35,000.

What did they find?

The authors concluded that participants who consumed more EVOO were less likely to have gestational diabetes and preeclampsia. 

They were also less likely to have certain cardiovascular risk factors, like elevated blood triglycerides — a measure of blood fat levels.

In addition, the scientists found that consuming olive oil was associated with less risk of having a baby that's smaller or larger than average.

What should you do?

The authors explain that we need more research to confirm the findings. In the meantime, adding EVOO to your diet is a healthy choice.

It contains “good” fats and a range of healthy compounds, like vitamin E and polyphenols.

If you’d like to learn more, we have a podcast on fats and oils. We also have a podcast on which cooking oils to use.

5. Exercise and sleep

We all know that exercise is good for our overall health. And as we age, exercise can help keep us healthier for longer.

Similarly, getting enough quality sleep also plays a part in healthy aging.

However, many older adults don’t get the exercise they need. And sleep disorders, like insomnia, are particularly common at this time of life.

According to the authors of a recent review, insomnia medications for older adults aren’t always the safest option.

So, they wanted to find out whether a structured exercise routine might improve sleep instead.

What did they do?

The researchers reviewed 13 studies, including data from 2,612 older adults. The studies had investigated whether different exercise routines improved measures of sleep.

The teams had looked at a range of exercise interventions, including yoga, pilates, walking, and cycling.

What did they find?

Compared with older adults who didn’t exercise, those who followed the exercise plans had measurable improvements in their sleep quality and efficiency. 

"Sleep efficiency" refers to how much time you're actually asleep after going to bed.

What should you do?

Although the authors of the review call for more research, previous reviews have also concluded that exercise is linked to better sleep in adults.

And even if it doesn’t help you sleep, getting regular exercise is a wise choice.

If you’re thinking of trying a new exercise routine, start slowly and build up to it. All types of movement count, and there’s no rush.

The takeaways

OK, what have we learned from today’s selection of studies? Here are today’s five takeaways:

  1. Eating more legumes might reduce your risk of dying from all causes and stroke. And if it doesn’t, legumes are healthy, so upping your intake is probably a good idea.

  2. Following the Mediterranean diet might improve older adults’ thinking ability. And if it doesn’t, it’s still healthier than a standard Western diet.

  3. Artificial sweeteners might not affect your post-meal blood sugar or hormone levels. But if they do, you can avoid these sweeteners and other additives by having a plant-based diet and reducing your intake of ultra-processed foods.

  4. Consuming EVOO might improve health outcomes for pregnant people and their offspring. And if it doesn’t, it’s still a healthy addition to your diet.

  5. Regular exercise might help older adults get better sleep. And if it doesn’t, physical activity is still vital for maintaining good health, so keep active when you can.


A good night’s sleep. (2020). https://www.nia.nih.gov/health/good-nights-sleep 

Effect of dietary patterns on cognitive functions of older adults: A systematic review and meta-analysis of randomized controlled trials: Dietary patterns on cognition of older adults. Archives of Gerontology and Geriatrics. (2023). https://www.sciencedirect.com/science/article/pii/S0167494323000468 

Effects on sleep quality of physical exercise programs in older adults: A systematic review and meta-analysis. Clocks & Sleep. (2023). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10123754/#B3-clockssleep-05-00014 

Exercise and older adults. Clinics in Geriatric Medicine. (2018). https://pubmed.ncbi.nlm.nih.gov/29129214/ 

Exercise and sleep: A systematic review of previous meta-analyses. Journal of Evidence-Based Medicine. (2017). https://onlinelibrary.wiley.com/doi/full/10.1111/jebm.12236 

Legume consumption and risk of all-cause and cause-specific mortality: A systematic review and dose-response meta-analysis of prospective studies. Advances in Nutrition. (2023). https://www.sciencedirect.com/science/article/pii/S2161831322013114 

Lo- and no-calorie sweeteners. (n.d.). https://iafns.org/our-work/nutrition/low-calorie-sweeteners/ 

Olive oil consumption confers protective effects on maternal-fetal outcomes: A systematic review of the evidence. Nutrition Research. (2023). https://www.sciencedirect.com/science/article/pii/S0271531722001543 

The effect of non-nutritive sweetened beverages on postprandial glycemic and endocrine responses: A systematic review and network meta-analysis. Nutrients. (2023). https://www.mdpi.com/2072-6643/15/4/1050