Researchers show that pea protein combined with the fiber inulin increases muscle mass, inhibits gene activity for muscle breakdown, and enhances the function of the cell powerhouse — mitochondria — in muscle of aged rats.
Sarcopenia — muscle loss and deterioration — constitutes a common affliction in aged people, beginning after age 40. To counteract sarcopenia, people often supplement with proteins such as plant-based pea protein, an environmentally friendly alternative to proteins from animals. Interestingly, gut health has also been shown to influence muscle synthesis and breakdown. For this reason, researchers have questioned whether combining supplemental plant protein with prebiotics — nutrients for healthy gut bacteria — such as the fiber inulin can enhance muscle mass during aging.
Published in Nutrients, Walrand and colleagues from the Université Clermont Auvergne in France show that combining inulin and pea protein increases muscle mass more than pea protein supplementation alone in aged rats. The researchers also show that the protein and prebiotic combination reduces gene activity for MuRF1 — a protein involved in muscle breakdown — in fast-twitch muscle. Additionally, the nutrient combination enhances activity for two muscle mitochondria enzymes with roles in generating energy, citrate synthase and 3-hydroxyacyl-CoA dehydrogenase (HAD). These findings suggest that consuming a prebiotic like the plant fiber inulin can enhance muscle building when added to pea protein supplementation.
To find whether inulin improves muscle mass when added to pea protein, Walrand and colleagues fed aged rats either pea protein alone or pea protein with inulin and measured their effects on muscle mass. They found that the addition of inulin significantly increased muscle mass in fast-twitch muscle — the muscle type that deteriorates the most with age — but not in slow-twitch muscle. These results suggest that inulin enhances the muscle building effects of supplementing with pea protein.
To get a better grasp on how adding inulin to pea protein increases muscle mass, Walrand and colleagues measured gene activity for MuRF1, a protein involved in muscle breakdown. They found that inulin with pea protein almost cut in half MuRF1 gene activity compared to pea protein alone following a meal. These results suggest that adding inulin to pea protein increases muscle mass by inhibiting gene activity for muscle breakdown.
To find whether, in addition to increasing fast-twitch muscle mass, inulin improves muscle cell energy, Walrand and colleagues measured the activity of mitochondrial enzymes with key roles in energy production in fast twitch muscle. They found that, compared to pea protein supplementation alone, pea protein with added inulin significantly increased two mitochondrial enzymes involved in energy generation — citrate synthase and HAD. These findings support that inulin improves muscle function when added to pea protein by increasing muscle cell energy production.
“These findings provide promising insights into the potential benefits of combining pea protein with inulin for muscle health in older people,” said Walrand and colleagues. “While more research is needed to fully understand the additional or even synergistic effects of plant-derived compounds such as proteins and fibers on muscle health during aging, there is already enough evidence to recommend combining intake of a high-quality protein with a sufficient fiber intake to protect muscle mass and function, and thus extend the autonomy of older people.”
The findings show that the plant fiber with prebiotic properties, inulin, increases muscle mass when consumed with pea protein in aged rats. Moreover, by increasing the activity of mitochondrial enzymes involved in energy generation, inulin and pea protein may enhance muscle function. How inulin confers these benefits needs further examination.
Inulin’s promotion of muscle mass may come from potential anti-inflammatory effects stemming from improved gut health. Age-related muscle loss can be partially explained by inflammation driving muscle decline. Along those lines, higher concentrations of beneficial gut bacteria in the gut from inulin supplementation may reduce inflammation. However, the study didn’t examine inulin’s effects on inflammatory molecules in blood or muscle, which may have helped explain its benefits, a major limitation.
Additionally, the study didn’t examine how inulin changes gut bacteria composition. Finding what specific bacterial species increase and drop in abundance with inulin supplementation could help to better explain inulin’s muscle-enhancing effects. For example, research has shown that the gut bacterial species Lactobacillus and Bifidobacterium influence gut-muscle communication and regulate muscle size. If either of these two gut bacterial species increased in concentration with inulin supplementation, this could provide some explanation for how inulin contributes to increased muscle mass.
Model: Twenty-month-old male Wistar rats
Dosage: A diet containing 14% pea protein or a diet containing 14% pea protein with 7.5% inulin content for 16 weeks