In a recent study published in the European Journal of Clinical Nutrition, researchers report that protein intake from plant sources may improve sleep quality. In contrast, increased animal protein intake worsens sleep quality.

Study: Protein intake and its association with sleep quality: results from 3 prospective cohort studies. Image Credit: sivaleela . v / Shutterstock.com

How does diet affect sleep?

High-quality sleep at night is necessary for a healthy living. Changes in metabolic rate, blood circulation, hormonal secretion, and immune regulatory functions occur during sleep, all of which are needed to maintain homeostasis within the body.

An adult requires seven to eight hours of sleep daily to reduce the risk of chronic diseases and mortality. However, a significant reduction in sleep duration in the general population has been reported in recent decades, with many individuals reporting difficulty initiating and maintaining sleep and waking up multiple times at night and early morning. The prevalence of both sleep disturbances and disorders has also risen, which can lead to daytime functional impairments and an increased incidence of numerous chronic diseases.

Poor diet quality, characterized by a higher intake of saturated fats, refined carbohydrates, and processed foods, can impair sleep quality and duration. Studies have provided mixed results regarding the impact of protein intake on sleep quality, which could be due to different ratios of specific amino acids across different protein sources.

About the study

In the current study, scientists investigate the impact of total protein intake and intake of different protein sources on sleep quality. To this end, dietary intake data and sleep quality measures were collected from three ongoing prospective cohort studies among United States health professionals, including the Nurses’ Health Study (NHS), NHS2, and Health Professionals Follow-up Study (HPFS).

In these cohort studies, the participants’ dietary intake was assessed every four years using validated food-frequency questionnaires. Sleep quality was evaluated using the original or modified version of the Pittsburgh Sleep Quality Index.

Data obtained from a total of 32,212 and 51,126 women from the NHS and NHS2 studies, respectively, as well as 14,796 men from the HPFS, were analyzed to determine the association between protein intake and sleep quality.

Important observations

In all three cohorts, participants with the highest protein intake exhibited higher body mass index (BMI) values and a greater prevalence of pre-existing health conditions than those with the lowest protein intake. Over 65% of study participants reported seven to eight hours of sleep each night.

Regular use of sleep medication was reported by 5-6% of study participants. The presence of sleep apnea was more common among participants with the highest protein intake, with the prevalence of this condition higher among males than females.

Study participants with better sleep quality were associated with slightly lower BMI values, higher physical activity, better diet quality, higher consumption of alcohol, and less pre-existing health conditions. Comparatively, those who reported higher consumption of animal protein were more likely to have a higher BMI, lower physical activity, and more pre-existing health conditions. These factors were more favorable among participants with higher intake of plant protein intake.

Association between protein intake and sleep quality

The current study did not identify any association between total protein intake and sleep quality. Although total animal protein intake was not associated with sleep quality, a higher intake of plant protein was associated with better sleep quality.

Among different animal protein sources, dairy protein intake had divergent associations. While no association between dairy protein intake and sleep quality was observed in the NHS and HPFS cohorts, a position association was observed in the NHS2 cohort.

Among different meat sources, intakes of processed and unprocessed red meat and poultry were associated with worse sleep quality. This type of association was not observed for fish intake.

Conclusions

The current study did not identify any association between total protein intake and sleep quality among men and women; however, a positive association was observed between plant protein intake and sleep quality. After adjusting for potential confounding factors, this association was less prominent in men and weak in women.

Protein-rich plant sources are often rich in carbohydrates and fiber, both of which have been shown to improve sleep quality. Comparatively, processed red meat and poultry, which are higher in fat, may also lead to worse sleep quality, as observed in the current study.