June 20, 2025, 1:48 pm | Read time: 5 minutes

Want to sleep well tonight? Then you should follow a simple dietary rule, according to a recent study from the U.S. FITBOOK author Friederike Ostermeyer explains what it’s all about and which foods should be on your menu in the coming hours.

You Are What You Eat, Even in Sleep?

The team wanted to find out how daytime nutrition specifically affects sleep the following night. They aimed to pinpoint which foods have an immediate positive impact on sleep quality and which might be counterproductive. The focus was on the following products:

• Fruits and vegetables (a handful counts as one serving)
• Whole grain or white flour products
• Red meat and processed meats like sausage and ham
• Sugar

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Study with 34 Young, Healthy Adults

Thirty-four healthy adults (average age: 28 years, without clinical sleep disorders) were asked to keep a 24-hour dietary log using an app over eight days. They were to record every snack, down to a glass of water. The app calculated not only the food groups but also the macronutrients (carbohydrates, proteins, fats, and fiber) and sleep-relevant micronutrients (magnesium, vitamin B6, vitamin D, calcium, sodium, and zinc) consumed. Since only light or non-drinkers were allowed in the study, alcohol, known as one of the strongest sleep disruptors, was not included.

How Sleep Was Measured

At the same time, participants wore a sleep tracker on their wrist. This allowed researchers to objectively measure sleep patterns. They specifically examined “sleep fragmentation,” an indicator of sleep disturbances that shows how often someone wakes up during the night or shifts from deep sleep to light sleep. The lower the index, the more restful the sleep. Additionally, self-reported sleep quality information was included. By the end of the trial period, the research team had 201 detailed data sets.

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Which Dietary Rule Improves Sleep Quality

What did the scientists conclude? It became clear that the type of diet had a significant impact on sleep as soon as the following night. Specifically, it was the amount of fruits and vegetables consumed by the participants. Those who followed the well-known “5 a day” dietary rule and ate five servings throughout the day had a measurable 16 percent better sleep quality than those who didn’t. To recall: A serving is roughly the amount that fits in a palm. “Sixteen percent is a highly significant difference,” said study leader Esra Tasali in a university statement.² “It’s remarkable that such a significant change could be observed in less than 24 hours.”

Whole grain bread or oatmeal also performed better compared to white bread, while red meat and sausage had a slightly negative effect. Interestingly, sugar had no clear impact on sleep quality. According to this study, a bedtime treat seems to still be allowed.

More Fruits and Vegetables Instead of Complex Sleep Techniques

Researchers suspect that fiber, complex carbohydrates, polyphenols, and magnesium found in fruits and vegetables play an important role in sleep health. Other nutrients, such as those found in tomatoes and cherries, may help the brain produce or release the sleep hormone melatonin better in the evening. The exact connections are to be explored in future studies. However, researchers are already convinced that there is a direct link between the “5 a day” dietary rule and improved sleep quality: “Even small changes in diet can affect sleep. That’s encouraging–you have control over your recovery.”

Study Author to FITBOOK: “Our Results Could Be of Great Benefit to People with Real Sleep Disorders”

The strength of the work lies in the combination of free everyday conditions with measurement by tracker–a rarity in nutrition studies. However, the study also has weaknesses.

The sample size was limited and predominantly male and young; therefore, the results cannot be immediately applied to women or older groups. Additionally, the observation phase per participant lasted only about six days, leaving long-term effects open. Study author Dr. Marie St-Onge admits to FITBOOK: “We would even expect our results to be of even greater benefit to people with real sleep disorders, as there is more room for improvement.”

“Even Small Changes Pay Off”

Diet was self-reported; under- or overestimations are possible, which could have distorted the data on micronutrient intake. However, St-Onge notes to FITBOOK: “Even small changes pay off. Replacing a piece of fruit for breakfast, an afternoon snack, or a side dish with vegetables would be a good start.” Occasionally replacing white flour products with whole grain versions also has its effect. The closer you get to the “5 a day” rule, the better–even if it doesn’t always succeed. Nonetheless, factors like stress or spontaneous physical activity were not systematically recorded.

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Conclusion

The present study provides remarkable insights into the potential impact of diet on sleep–which apparently occurs immediately. Participants could apparently notice the positive effect just hours later. This further underscores the health importance of five servings of fruits and vegetables daily. However, the study’s weaknesses should also be considered in its evaluation. Nutrition is certainly an important lever for good sleep, but not the only one. A conducive sleep hygiene, limiting screen time, and reducing disruptive light sources are also important, to name just a few.