What has ZOE’s research found about sleep?

ZOE is deeply rooted in science, and it’s something we’re very proud of. To date, we’ve published 20 studies in respected scientific journals, and we have more in the pipeline.

As Sleep Awareness Week draws to a close, we decided to recap what ZOE’s research has discovered about sleep so far.

While our research generally focuses on the links between nutrition and health, sleep is an important part of this equation, as you’ll see.

Metabolic responses and sleep

A paper ZOE published in 2020 investigated how responses to food varied between individuals. This was part of our PREDICT studies, the largest in-depth nutritional research program in the world.

Specifically, we analyzed how people’s blood sugar and blood fat levels responded to different meals.

After eating, your body breaks down carbohydrates into glucose, which then enters your bloodstream. There, the glucose circulates around your body before it’s used or stored for energy. After a couple of hours, your glucose levels return to baseline. 

It’s a similar story with fats — after a meal, levels of fat in your blood rise steadily — much slower than your glucose levels. After around 6 hours, the amount of fat in your blood returns to baseline, unless you’ve eaten something in the meantime.

These changes vary a lot among individuals. After the exact same meal, some people’s responses are much more pronounced than others.

Even identical twins, who are genetic clones, have very different metabolic responses.

Pronounced, “excessive” blood sugar and fat responses are linked to an increased risk of poorer health outcomes in the long term. 

So, in this study, we investigated which factors influence these responses.

We found that the macronutrient composition of a meal — how much fat, protein, and carbohydrate it contains — affects the size of blood sugar and blood fat responses.

It makes sense that a high-fat meal would cause a larger blood fat response, for instance.

What’s surprising is that sleep affected these metabolic responses about as much as the macronutrient content of the meal. 

Next, we’ll cover a paper we published in 2022, which investigated sleep’s influence further.

Sleep and blood sugar

Using data from PREDICT, we dug deeper into connections between sleep and blood sugar control.

The study included almost 1,000 people, 41% of whom were twins. We asked them to eat standardized meals, and we tracked their sleep. 

We found that people who went to bed late or had lower-quality sleep had more pronounced blood sugar responses to breakfast the next day. 

So, not getting the sleep you need has a measurable effect on how your body handles carbs the next morning.

The results also suggested that deviating from your normal sleep pattern is linked to poorer blood sugar responses the following day. Our next study dug deeper into this idea.

It’s well established that shift work negatively affects health. But what about smaller changes to sleep patterns? Do they also have an effect? To explore this, we investigated “social jet lag.”

What’s social jet lag?

Many of us go to bed early and wake up early Monday to Friday but go to bed later or wake up later on weekends. We call it “social jet lag” — relatively minor shifts in your daily sleep-wake cycle.

For this study, published in 2023, we used data from around 1,000 people. We looked at links between social jet lag, diet, the gut microbiome, and risk factors for heart and metabolic disease.

We found that social jet lag was associated with a poorer-quality diet. For instance, people with social jet lag ate more potatoes and sugar-sweetened beverages — and less fruits and veggies — than people who went to bed at the same time every night.

For people with social jet lag, there were also measurable differences in their gut microbiomes. And these were only partly explained by diet. Notably, there were more gut bacteria that researchers have deemed “unfavorable.”

This was the first study of its kind to identify these intriguing links between social jet lag, gut bacteria, and diet.

The final study we’ll cover today looked at factors that affect your alertness.

How to feel alert  

You might wake up feeling ready to face the day. Other times, you might feel like you haven’t fully woken up until lunchtime. Why is this?

To find out, we teamed up with Prof. Matt Walker, a sleep researcher and professor of neuroscience and psychology at the University of California, Berkeley.

The study included more than 800 people, aged 18–65, from our PREDICT study.

We found that your sleep habits, diet, exercise levels, and blood glucose responses to breakfast are all linked to how alert you feel when you wake up.

People who slept longer and had better sleep quality felt more alert than those who didn’t. This makes sense. 

More surprisingly, people who woke up a little later than normal — even if they slept for the same amount of time as usual — also felt more alert. 

Similarly, people who were more active during the day than usual tended to feel more alert the next day.

As part of the experiment, participants who had a high-protein breakfast felt less alert, and people who had a pure glucose breakfast felt even less alert. 

But carbs’ connection to alertness was a little unusual. People with good glucose control who ate a high-carb breakfast felt more alert. 

The researchers don’t know why this is, but it may relate to the other macronutrients — protein, fat, and fiber — in the breakfast. 

Alternatively, it might be because the breakfast contained sucrose rather than glucose, which produces a smaller blood sugar response.

Breakfast aside, we found that alertness increased with age — and people who reported feeling happier were also more alert. Finally, those who ate five or more times a day were less alert than those who ate less often.

The take-home

Clearly, sleep is intimately linked with your diet, health, and how you feel. Everyone is different, but no one can do without sleep. 

So far, it seems that having a regular sleep pattern is important. And getting enough good-quality sleep is linked to more healthy metabolic responses.

To improve your alertness, being active the day before and thinking about the macronutrient contents of your breakfast could help.

There’s still a lot to learn about sleep, so ZOE will continue to investigate.

We realize that not everyone finds it easy to get to sleep or stay asleep. For strategies and tips, listen to the ZOE Science & Nutrition podcast episode featuring Prof. Matt Walker.

Or, read this fascinating article on sleep and health.


Exploring the relationship between social jetlag with gut microbial composition, diet and cardiometabolic health, in the ZOE PREDICT 1 cohort. European Journal of Nutrition. (2023). https://link.springer.com/article/10.1007/s00394-023-03204-x 

Health consequences of shift work and insufficient sleep. The BMJ. (2016). https://www.bmj.com/content/355/bmj.i5210.abstract 

How people wake up is associated with previous night’s sleep together with physical activity and food intake. Nature Communications. (2022). https://www.nature.com/articles/s41467-022-34503-2 

Human postprandial responses to food and potential for precision nutrition. Nature Medicine. (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8265154/ 

Impact of insufficient sleep on dysregulated blood glucose control under standardised meal conditions. Diabetologia. (2022). https://pubmed.ncbi.nlm.nih.gov/34845532/