Plant-based proteins may promote better sleep

Dietary protein seems to have positive effects on sleep duration in middle-aged and older adults, especially when looking at the amino acid tryptophan (Trp) and its ratio with large neutral amino acids (LNAA), according to a recent Singapore study.

“Developing strategies to improve the sleep is of importance, especially in older adults who are more susceptible to poorer sleep quality,” the researchers said. “We found an association between a higher total dietary Trp:LNAA intake with a better sleep duration. In addition, we observed that the source of the protein may influence their association with sleep quality.”

The current cross-sectional analysis included 104 healthy participants (aged 50–75 years, 57 percent women) from whom dietary data were collected using a 3-day food record. Protein intake was further broken down into Trp and LNAA composition. Sleep quality parameters, including sleep duration, global sleep score (GSS), and sleep efficiency, were also measured using the Pittsburgh Sleep Quality Index (PSQI).

The average protein intake per day was 18.7 percent of total energy intake (E%), most of which came from animal rather than plant sources (10.4 vs 7.9 E%). Broken down, this corresponded to an average intake of 0.870 g Trp, of which 0.351 and 0.517 g came from plant and animal sources, respectively. [Front Nutr 2022;doi:10.3389/fnut.2022.832341]

Moreover, the mean dietary Trp:LNAA ratio was 0.047. When considering only plant and animal proteins, the resulting ratios were 0.05 and 0.045, respectively.

Multiple linear regression analysis revealed that daily total protein intake was significantly, strongly, and inversely correlated with sleep duration (β, –23.648; p=0.038), as was daily Trp consumption (β, –5.166; p=0.017). Meanwhile, plant-sourced Trp (β, 2.653; p=0.020) and plant protein Trp:LNAA ratio (β, 54.006; p=0.008) were significantly and positively associated with sleep duration.

Independent t-test analysis confirmed that participants who slept for ≥7 hours per night consumed a significantly lower amount of Trp than those with <7 hours of sleep (0.029 vs 0.057 g; p=0.009). Meanwhile, dietary protein was significantly lower among participants with sleep efficiency >85 percent vs ≤85 percent (0.7 vs 1.2 E%; p=0.033).

Aside from intake, regression analysis showed that plasma levels of amino acids significantly affected sleep quality. The Trp:LNAA ratio was significantly and inversely correlated with sleep duration (β, –19.522; p=0.014), such that its plasma value was significantly lowered in participants with ≥7 vs <7 hours of sleep (0.72 vs 0.80; p=0.005).

“Sleep duration in middle-aged and older adults in Singapore is positively associated with dietary Trp and Trp:LNAA, in particular when obtained from plant sources. This suggests that the source of protein, for example, plant protein, may matter in its ability to improve sleep quality,” the researchers said.

Important study limitations included its cross-sectional design, the use of US-based standards for dietary intake estimation, and the risk of food underreporting. Future randomized studies, as well as more locally adopted diet databases, are needed to confirm the present findings.