Animal or plant protein: Which has the best effect on sleep?

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• Good quality sleep is essential for staying physically and mentally healthy.
• An adult should aim to get 7-8 hours of quality sleep a night for maximum benefit, but many people struggle to achieve this.
• Studies investigating the effect of diet on sleep quality have not drawn firm conclusions, but suggest that a healthful diet, such as the Mediterranean diet, could improve sleep in some people.
• Now, a study has found that plant proteins may improve sleep quality, while animal proteins can have the opposite effect.

People need to sleep to stay healthy, and the Center for Disease Control and Prevention (CDC) recommends that adults get a minimum of 7 hours of quality sleep a night.

During sleep, a person’s blood pressure and heart rate fall, their metabolism changes, their hormones are balanced, they breathe less often and less deeply, and their learning and memory is enhanced.

Inadequate, or poor quality sleep increases the risk of chronic diseases, obesity, an impaired immune system and problems with memory and thinking.

To improve sleep quality doctors advise:

• going to bed and waking up at the same time every day, including weekends
• developing a relaxing bedtime routine
• ensuring the bedroom is dark, quiet, not too warm, and the bed is comfortable
• to stop using electronic devices 2 hours before bedtime
• avoiding caffeine, nicotine, and alcohol
• exercising regularly
• managing stress, using relaxation techniques if necessary.

Several studies have investigated whether diet may affect sleep quality, but have found little conclusive evidence.

Now, researchers in Ireland and the United States have examined whether protein affects sleep quality. They found that while overall protein intake had no effect, protein from plant sources may improve the quality of a person’s sleep, while protein from animal sources can impair sleep quality.

The study appears in The European Journal of Clinical Nutrition.

Kelsey Costa, M.S., R.D.N., a registered dietitian nutritionist and founder of Dietitian Insights, not involved in this study, explained to Medical News Today:

“The lack of association between total protein intake and sleep quality, juxtaposed with the weak association observed for plant protein intake, underscores a nuanced understanding of how different types of proteins might influence sleep.”

Looking at the link between sleep and protein sources

The researchers collected data from three different cohorts of U.S. health professionals: the Nurses’ Health Study (NHS) and NHS2 — both in women — and the Health Professionals Follow-up Study (HPFS), which only included men.

They analyzed data from 83,338 women and 14,796 men from the three cohorts.

They assessed dietary intake using a validated food-frequency questionnaire that included more than 130 different food items. Participants had to report their consumption of each food from “never or less than once per month” to “more than six times per day”, based on standard U.S. food portion sizes.

The researchers then calculated intake of different types of protein — total, animal, dairy and plant — as percentages of total energy consumption.

In all three cohorts, participants completed the Pittsburgh Sleep Quality Index, or a similar survey that assessed sleep time/duration, sleep latency (the amount of time taken to fall asleep), sleep efficiency (the ratio of total sleep time to total time in bed), sleep disturbance, subjective sleep quality, sleep medication use, and daytime dysfunction due to sleep problems. They completed this just once during the study period.

Plant protein may improve sleep quality

Total protein intake had no effect on sleep quality in any of the three cohorts.

However, when the researchers looked at the different categories of protein, they found some small differences.

The study found that women who consumed higher amounts of plant protein reported better sleep quality, but there was not a clear trend in men. After the researchers adjusted for variables, they found the association in women was weakened.

When the researchers analyzed meat subgroups, they found that higher consumption of processed red meat and poultry was associated with poorer sleep quality, while unprocessed red meat adversely affected sleep in women only.

Dairy protein was associated with better sleep in the NHS2 cohort, but not in either of the others. Fish consumption had no effect on sleep quality.

Dr. Janine Wirth, first author of the study and research project manager in the Bump2Baby and Me team at University College Dublin, in Ireland, told MNT that:

“The most important finding is the fact that not the amount of protein seems to be of importance but the type of protein might make a difference for sleep quality.”

Costa further noted that the relationship between sleep quality and protein source was more complex than this study could determine.

“The weak association observed specifically with plant protein intake suggests that the quality and source of protein, along with the presence of other nutrients in plant-based foods, may play a more pivotal role in affecting sleep quality than the quantity of protein ingested,” she told us.

“This insight highlights the complexity of diet-sleep interactions, and it implies that factors beyond protein content, such as the accompanying nutritional matrix of foods, might be at play,” she added.

Why might diet affect sleep?

One review of studies found that high-carbohydrate diets, and foods containing tryptophan, melatonin, and phytonutrients, were linked to improved sleep outcomes.

Tryptophan is an amino acid found in several foods, which is essential for the production of serotonin and melatonin in the body. Good sources include milk/dairy products, poultry, oily fish, dark green leafy vegetables, eggs, soy products, and nuts and seeds.

Costa explained why tryptophan might promote good sleep:

“Tryptophan, a crucial amino acid found in both plant and animal proteins, is a precursor for serotonin and melatonin, neurotransmitters that promote sleep. The higher levels of tryptophan in plant proteins potentially enhance sleep quality through its positive effect on the tryptophan to large neutral amino acids (LNAA) ratio.”

“This ratio is critical as it influences tryptophan’s ability to cross the blood-brain barrier. Plant proteins often present a slightly superior ratio conducive to better sleep quality.”

Observational study cannot prove causation but intervention studies are tricky

Costa highlighted that other factors, such as overall diet quality, meal timing, caffeine intake, alcohol consumption, exercise and stress levels also impact sleep quality, adding that, “[w]hile the present study considered some of these factors, further studies that explore these complexities will help provide a more comprehensive understanding of the relationship between diet and sleep quality.”

“Nevertheless,” she told MNT, “this study contributes to the growing body of literature on diet-sleep interactions, emphasizing the importance of a balanced and varied plant-based diet in promoting better sleep quality and optimal health.”

Dr. Wirth cautioned that their study could not show a causative effect of diet: “Like other types of observational studies, cohort studies can suggest associations between an exposure and a health outcome but cannot prove causality. Residual confounding cannot be ruled out.”

She emphasized the need for further research to verify the findings: “To investigate causality, targeted intervention studies would be the method of choice.”

“Conducting well-designed intervention studies examining nutrition and sleep is not easy. Studies with carefully determined sleep quality using objective methods are rare, as are well-selected intervention groups and control groups that allow a correct comparison,” she added.