Masticatory Movement With Whey Peptide Supplementation Inhibits the Decrease of Masseter Weight in Protein Malnourished Rats.

Background: The importance of continued mastication to maintain oral function has been suggested, but whether atrophy of the masseter muscle can be inhibited with a combination of mastication and protein intake is not known.

Objective: This study aimed to clarify the molecular mechanism for inhibiting masseter atrophy, and the effects of mastication and protein intake were examined in a rat model of masseter muscle atrophy.

Methods: Male Wistar rats were divided into a group given a solid purified diet with normal (20%) protein content and administered a sugar solution and groups given solid or powdered purified diets with low (2.5%) protein content, each of which was given a whey peptide solution or a sugar solution for 3 weeks. On the final day, the animals were sacrificed 1 h after being administered each of the solutions, and blood and masseter muscles were collected.

Results: Masseter weight decreased in all of the groups given the low-protein diet compared with the normal protein content diet, but that decrease was inhibited the most in groups fed a solid diet and administered whey peptide. When animals were given a solid diet and administered whey peptide, the expression levels of ULK1 (Unc-51-like kinase 1) and phosphorylated ULK1 (Ser757) proteins, which are associated with protein degradation, were markedly elevated compared with other conditions.

Conclusion: The decrease in masseter weight was inhibited in protein malnourished rats in which mastication was encouraged and whey peptide was administered. The results suggest that the molecular mechanism for this is attributable to the control of autophagy.