When older people stay in the hospital for a long time, they lose muscle mass very quickly, which makes them weaker and less able to move around. Researchers wanted to see if drinking high-protein supplements could help rebuild that muscle and change the bacteria in the gut in helpful ways. They studied 43 older adults (ages 60-90) who had low muscle mass. For three months, everyone drank protein shakes with 36 grams of protein daily, then stopped for three months. The results showed that men who drank the protein shakes gained muscle mass, and their gut bacteria changed in ways that seemed to support muscle growth. This suggests that protein supplements might help fight muscle loss in hospitalized older people, especially men.

The Quick Take

  • What they studied: Can drinking high-protein shakes help older hospital patients rebuild muscle and change their gut bacteria in healthy ways?
  • Who participated: 43 older adults between ages 60 and 90 who were hospitalized and had low muscle mass. They were studied for 6 months total—3 months with protein shakes and 3 months without.
  • Key finding: Men who drank the protein shakes gained muscle mass (from 6.0 to 6.3 kg/m²) after 3 months. Their gut bacteria also changed in ways that appeared to support muscle growth. Women showed less dramatic changes.
  • What it means for you: If you’re an older man in the hospital dealing with muscle loss, protein supplements may help you rebuild strength. However, this was a small study, so talk to your doctor before starting any supplement. Results were stronger for men than women, so women may need different approaches.

The Research Details

This study used a self-controlled design, which means each person served as their own comparison. All 43 participants went through two phases: first, a 3-month period where they received 36 grams of high-protein supplement daily (made from casein and whey proteins—common types found in milk), and second, a 3-month period where they received regular hospital care without the protein supplement. Researchers measured muscle mass and analyzed gut bacteria samples at the beginning, after 3 months, and after 6 months.

The researchers used special lab tests to identify which bacteria were present in each person’s gut and how the bacterial communities changed over time. They also looked at what functions these bacteria performed, particularly focusing on how they helped produce amino acids (the building blocks of protein).

This type of study design is useful because it allows researchers to see how the same person changes with and without the intervention, reducing the effect of individual differences.

Understanding how protein supplements work isn’t just about building muscle—it’s about understanding the connection between what we eat, the bacteria in our gut, and our physical strength. This ‘gut-muscle axis’ is a newer area of research that could lead to better treatments for older people who lose muscle during hospitalization. By identifying which bacteria help with muscle growth, doctors might eventually be able to target these bacteria specifically.

This study has some strengths: it measured both muscle mass and gut bacteria, it followed people over 6 months, and it was published in a peer-reviewed medical journal. However, there are important limitations to consider: the sample size was small (43 people), there was no control group receiving a placebo, and the results were different for men and women, which wasn’t fully explained. The study was conducted in China, so results may not apply equally to all populations.

What the Results Show

The most important finding was that men who received the protein supplement showed an increase in muscle mass index from 6.0 to 6.3 kg/m² after 3 months of supplementation. However, when the protein supplement was stopped and they returned to regular care, their muscle mass declined slightly to 6.1 kg/m² by the 6-month mark. This suggests the protein supplement helped build muscle, but the gains weren’t permanent once supplementation stopped.

Women in the study showed much smaller changes in muscle mass compared to men, which was unexpected. The researchers noted this sex difference but didn’t fully explain why it occurred. This is an important finding because it suggests that protein supplements may work differently in men versus women.

The gut bacteria analysis revealed significant changes in bacterial diversity and composition during the protein supplementation phase. Males specifically showed an increase in bacteria that were associated with muscle growth and muscle mass. These beneficial bacteria appeared to enhance pathways related to amino acid synthesis—essentially, they helped produce the building blocks needed for muscle protein.

The metabolic pathway analysis showed that certain bacteria species, particularly Blautia wexlerae and Corynebacterium dentalis, were positively linked with muscle growth in men. These bacteria became more abundant during the protein supplementation phase and appeared to be actively producing amino acids. The researchers also found that the overall structure of the gut bacterial community changed, with some bacteria becoming more common and others becoming less common during supplementation.

This research builds on previous studies showing that gut bacteria influence muscle health, but it’s one of the first to specifically examine this relationship in hospitalized older adults receiving protein supplements. Previous research has shown that muscle loss during bed rest is a serious problem, but effective treatments have been limited. This study suggests that protein supplementation combined with the resulting changes in gut bacteria might be a promising approach. However, the sex differences found here contradict some previous research suggesting protein works equally well in men and women.

Several important limitations should be considered: First, the study had no control group receiving a placebo or standard care, making it harder to know if the protein supplement itself caused the changes or if other factors were responsible. Second, the sample size was relatively small (43 people), which limits how much we can generalize these findings to all older hospitalized patients. Third, the study lasted only 6 months, so we don’t know if the benefits would continue longer or if the muscle loss would continue after supplementation stopped. Fourth, the dramatic differences between men and women weren’t fully explained, raising questions about whether these results apply equally to both sexes. Finally, all participants were hospitalized with low muscle mass, so results may not apply to healthier older adults or those in other settings.

The Bottom Line

Based on this research, high-protein supplementation (around 36 grams daily) may help older men in the hospital rebuild muscle mass that’s lost during bed rest. The evidence is moderate—this is promising but not definitive. Women should not assume the same benefits apply without further research. Any older person considering protein supplements should discuss this with their doctor or a registered dietitian, especially if they have kidney disease or other health conditions. The protein should come from quality sources like milk-based proteins (casein and whey).

This research is most relevant to: older men (60+) who are hospitalized and experiencing muscle loss; hospital care teams looking for ways to prevent muscle wasting; and older adults concerned about maintaining strength during recovery. This research is less clear for: women, as the results were less dramatic; people with kidney disease, as high protein intake requires careful monitoring; and younger adults, as this study focused on older populations. People should not use this as a reason to take excessive protein supplements without medical guidance.

Based on this study, you might expect to see measurable increases in muscle mass within 3 months of consistent protein supplementation combined with whatever physical activity is possible. However, the gains appear to decline once supplementation stops, suggesting ongoing supplementation may be needed to maintain benefits. Realistic expectations are modest improvements—not dramatic muscle building, but meaningful gains for someone recovering from hospitalization.

Want to Apply This Research?

  • Track daily protein intake (target 36+ grams) and log it in the app, noting the source (shakes, food, etc.). Also track any measurements of muscle mass or strength if available from your doctor (such as grip strength tests or muscle mass scans). Record weekly how you feel physically—energy levels, ability to move, and any improvements in daily activities.
  • Set a daily reminder to consume your protein supplement at the same time each day (such as with breakfast or lunch). Use the app to log when you’ve completed this, creating a habit streak. If you’re able to do any light physical activity (walking, gentle exercises), log those too, as protein works best when combined with some muscle use.
  • Check in monthly with measurements of muscle mass or strength if your doctor can provide them. Track your protein intake consistently in the app to ensure you’re meeting the 36-gram daily target. Monitor how your energy and physical function change over 3-month periods. If you notice improvements, continue the supplementation; if not, discuss with your healthcare provider about adjustments.

This research is preliminary and based on a small study of 43 hospitalized older adults. The findings, while promising, should not be considered definitive medical advice. Before starting any protein supplement regimen, especially if you have kidney disease, diabetes, or other chronic conditions, consult with your doctor or registered dietitian. This study showed different results for men and women, so individual responses may vary. Protein supplements are not a substitute for medical treatment or physical rehabilitation. The muscle gains observed in this study declined after supplementation stopped, suggesting ongoing use may be necessary. Results from this Chinese study may not apply equally to all populations. Always discuss supplement use with your healthcare provider before beginning.