Research shows that guanidinoacetic acid and 5-hydroxytryptophan supplements successfully stimulated muscle cell growth in laboratory conditions, but a 28-day study in 15 sheep found these supplements did not increase weight gain, food intake, or muscle size compared to controls. According to Gram Research analysis, while guanidinoacetic acid altered genes involved in muscle metabolism, the supplements failed to produce measurable muscle-building results in living animals, suggesting lab success doesn’t guarantee real-world effectiveness.
Scientists tested whether three special supplements could help muscles grow better. They studied how these supplements affected muscle cells in the lab and then gave them to young sheep for four weeks. According to Gram Research analysis, two of the supplements showed promise in lab tests by helping muscle cells multiply or mature. However, when the sheep actually took the supplements, the results were mixed—the supplements didn’t make the animals gain weight faster or build more muscle, but they did change how the body processes amino acids, which are the building blocks of muscle. This research suggests these supplements might work differently than expected and need more study.
Key Statistics
A 2026 study published in Muscles journal found that 5-hydroxytryptophan and quercetin increased muscle cell proliferation in laboratory cultures, while guanidinoacetic acid enhanced muscle cell differentiation at doses of 12.5 to 50 micromoles per liter.
In a 28-day trial with 15 sheep, guanidinoacetic acid and 5-hydroxytryptophan supplementation at 2.5 mg per kilogram of body weight daily produced no significant changes in weight gain, food intake, or muscle area compared to control animals.
Guanidinoacetic acid supplementation altered muscle gene expression to promote amino acid metabolism and energy pathways linked to muscle protein synthesis, despite producing no measurable increase in muscle growth over 28 days.
A 2026 research article in Muscles found that 5-hydroxytryptophan supplementation elevated plasma 5-hydroxyindoleacetic acid levels, confirming the supplement was absorbed and metabolized, but did not translate to increased muscle development in sheep.
The Quick Take
- What they studied: Whether three dietary supplements (guanidinoacetic acid, 5-hydroxytryptophan, and quercetin) could help muscle cells grow and multiply, and whether they would help young sheep build bigger muscles.
- Who participated: First, muscle cells from sheep were grown in laboratory dishes. Then, 15 young Texel sheep weighing about 73 pounds each were divided into three groups and given either a control treatment or one of two supplements daily for 28 days.
- Key finding: In lab tests, two supplements successfully made muscle cells multiply or mature better. However, when sheep actually received the supplements for four weeks, the supplements didn’t increase weight gain or muscle size, though they did change how the body’s genes worked to process amino acids.
- What it means for you: These supplements show potential in laboratory conditions but didn’t produce the expected muscle-building results in living animals during this short study. More research with longer treatment periods and larger groups is needed before these supplements can be recommended for muscle growth.
The Research Details
The researchers conducted two separate experiments. In the first experiment, they grew muscle cells from sheep in laboratory dishes and exposed them to different amounts of three supplements to see which ones helped cells multiply (proliferate) or mature (differentiate). Based on these lab results, they selected the two most promising supplements for the second experiment.
For the second experiment, they worked with 15 young sheep that weighed about the same. They divided the sheep into three equal groups: one group received no supplement (control), one received guanidinoacetic acid, and one received 5-hydroxytryptophan. Each sheep got its assigned supplement every day for 28 days, given under the tongue before feeding. The researchers measured how much the sheep ate, how much weight they gained, and examined their muscle tissue and blood samples.
This approach allowed the scientists to first identify promising supplements in controlled lab conditions, then test whether those same supplements would actually work in living animals.
Testing supplements in both lab cells and living animals is important because something that works in a dish doesn’t always work in a real body. The lab tests help identify which supplements are worth testing further, while the animal tests show whether those supplements actually produce real-world benefits. This two-step approach saves time and resources by eliminating supplements that don’t work before expensive human studies are conducted.
This study has both strengths and limitations. The strength is that it combined lab and animal testing, which provides more complete information. However, the study used only 15 sheep, which is a relatively small number, making it harder to detect real effects. The study also lasted only 28 days, which may not be long enough to see muscle growth changes. The researchers measured important markers like gene expression and blood chemistry, which adds credibility to their findings.
What the Results Show
In the laboratory experiment, muscle cells treated with 5-hydroxytryptophan and quercetin multiplied more than control cells, while guanidinoacetic acid made cells mature better. These results suggested that all three supplements had potential to support muscle growth through different mechanisms.
However, when the supplements were given to living sheep for 28 days, the results were disappointing. The sheep that received either supplement gained weight at the same rate as the control group, ate the same amount of food, and developed muscle tissue at the same rate. The muscle area measurements showed no significant difference between groups.
Interestingly, the genetic analysis revealed that guanidinoacetic acid did change how genes were expressed in muscle tissue, specifically affecting pathways related to amino acid metabolism and energy production. This suggests the supplement was having some effect at the cellular level, even though it didn’t translate to visible muscle growth. The 5-HTP group showed elevated levels of a metabolite (5-HIAA) in the blood, confirming the supplement was being processed by the body.
The study found that guanidinoacetic acid altered the muscle’s genetic activity in ways that theoretically support muscle growth through improved protein synthesis and energy metabolism. This is important because it shows the supplement was working at a molecular level, even if the overall muscle growth wasn’t visible. The elevated 5-HIAA in the 5-HTP group confirmed that this supplement was being absorbed and metabolized by the sheep’s bodies, ruling out absorption problems.
Previous research suggested that these supplements could enhance muscle growth by supporting the activity of satellite cells, which are muscle stem cells responsible for muscle repair and growth. This study confirmed that the supplements do affect satellite cells in laboratory conditions, supporting earlier findings. However, the failure to see muscle growth in living animals suggests that the lab results don’t automatically translate to real-world benefits, which is common in supplement research. The findings align with other studies showing that supplements effective in cells don’t always produce measurable results in whole organisms.
The study had several important limitations. First, only 15 sheep were used, which is a small sample size that makes it harder to detect real effects. Second, the study lasted only 28 days, which may not be long enough for muscle growth changes to become obvious. Third, the supplements were given at relatively low doses, which might not have been enough to produce visible effects. Fourth, the study used young sheep, so results might differ in older animals or humans. Finally, the researchers didn’t measure muscle protein synthesis directly, which is the actual process of building muscle tissue.
The Bottom Line
Based on this research, these supplements cannot yet be recommended for muscle growth in humans or animals. While the lab results are promising, the animal study showed no real-world benefits. People interested in building muscle should focus on proven strategies: eating enough protein, doing strength training, and getting adequate sleep. If considering these supplements, consult a healthcare provider first, as this research is preliminary and conducted in sheep, not humans.
Athletes and people trying to build muscle should be aware of these findings, as they show that supplements working in lab tests don’t automatically work in real life. Farmers raising livestock for meat production might be interested in future research if these supplements prove effective with longer treatment periods. Healthcare providers should know about these results when patients ask about muscle-building supplements.
This study used only a 28-day treatment period, which is quite short for measuring muscle growth. Real muscle growth typically takes weeks to months to become noticeable. If these supplements were to be studied further with longer treatment periods (8-12 weeks or more), results might be different. Anyone considering these supplements should expect to wait at least 8-12 weeks to see any potential benefits, and should combine supplementation with proper nutrition and exercise.
Frequently Asked Questions
Do amino acid supplements actually help build muscle?
Some amino acid supplements show promise in laboratory tests by stimulating muscle cell activity. However, a 2026 study found that guanidinoacetic acid and 5-hydroxytryptophan didn’t increase muscle growth in sheep over 28 days, suggesting lab results don’t always translate to real-world benefits. Proven muscle-building strategies remain proper nutrition, strength training, and adequate rest.
What supplements help muscle growth the fastest?
This 2026 research found that supplements effective in lab cells didn’t produce faster muscle growth in living animals. The most evidence-based approaches for muscle growth are adequate protein intake (0.7-1 gram per pound of body weight), consistent strength training, and sufficient sleep—not supplements alone.
How long does it take for muscle supplements to work?
This study tested supplements for only 28 days and found no muscle growth benefits. Real muscle development typically requires 8-12 weeks of consistent training and nutrition to become noticeable. Any supplement study should run at least this long to produce meaningful results.
Can 5-HTP help you build bigger muscles?
While 5-hydroxytryptophan increased muscle cell multiplication in laboratory conditions, a 2026 animal study found it produced no increase in muscle size or weight gain over 28 days. More research with longer treatment periods is needed before this supplement can be recommended for muscle building.
Is guanidinoacetic acid effective for muscle growth?
Guanidinoacetic acid altered muscle genes involved in protein synthesis and energy metabolism, but a 2026 study found it didn’t increase actual muscle growth in sheep over 28 days. The supplement showed cellular effects without producing measurable muscle development, suggesting longer studies are needed.
Want to Apply This Research?
- If users are interested in muscle-building supplements, they should track weekly body weight, muscle soreness, and strength measurements (like how much weight they can lift) over at least 8-12 weeks. This provides concrete data to determine if a supplement is actually working.
- Users could log their daily protein intake, strength training sessions, and any supplements taken. The app could send reminders to maintain consistent exercise and nutrition habits, which are proven to build muscle, while tracking whether added supplements provide additional benefits.
- Establish a baseline of current muscle mass (using body composition measurements if available), strength levels, and weight. Then track these metrics weekly for at least 12 weeks while maintaining consistent exercise and nutrition. Compare results between weeks with and without supplementation to determine actual effectiveness.
This research was conducted in sheep over a 28-day period and has not been tested in humans. These supplements are not FDA-approved for muscle growth and their safety and effectiveness in people are unknown. Do not use these supplements without consulting a healthcare provider, especially if you have existing health conditions or take medications. This article is for informational purposes only and should not replace professional medical advice. Always consult with a doctor or registered dietitian before starting any supplement regimen.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.