According to Gram Research analysis, maternal L-citrulline supplementation significantly improved fetal growth in nutrient-restricted animals, with lambs born 10-15% heavier and showing larger pancreases, brains, and livers compared to controls. This 2026 study suggests L-citrulline could help babies develop better when mothers face nutritional challenges during pregnancy, though human clinical trials are needed before medical recommendations can be made.
When pregnant animals don’t get enough food, their babies can be born smaller and face health problems later. Scientists found that adding a nutrient called L-citrulline to the mother’s diet during pregnancy helped babies grow bigger and develop healthier organs. This research matters because L-citrulline works better in animals with multiple stomachs than a similar nutrient called arginine. The study followed baby lambs from birth through two months old and found they weighed more and had larger pancreases—the organ that controls blood sugar—when their mothers received the supplement. These findings suggest L-citrulline could be a practical way to help babies grow better when mothers face nutritional challenges.
Key Statistics
A 2026 animal study published in Amino Acids found that lambs born to mothers supplemented with L-citrulline were significantly heavier at birth and maintained greater weight through 60 days of age compared to control lambs, despite both groups’ mothers receiving only 50% of normal nutrition.
Maternal L-citrulline supplementation increased pancreatic mass per gram of body weight in lambs by a statistically significant margin, with the pancreas, brain, liver, and small intestine all showing greater absolute weights in the supplemented group compared to controls.
Lambs from L-citrulline supplemented mothers showed elevated circulating insulin at birth and increased blood glucose by day 60, suggesting improved pancreatic function and metabolic programming during fetal development in a 23-animal controlled study.
The Quick Take
- What they studied: Whether giving pregnant sheep a nutrient called L-citrulline helps their babies grow bigger and develop better when the mother doesn’t eat enough food.
- Who participated: 23 baby lambs born to 23 pregnant sheep. The mothers were fed only half the nutrition they normally need to create growth problems, similar to what happens with malnourished pregnant women.
- Key finding: Baby lambs whose mothers received L-citrulline were heavier at birth and at two months old. Their pancreases, brains, livers, and intestines were all larger and better developed compared to lambs whose mothers received a different supplement.
- What it means for you: This research suggests L-citrulline could help babies grow better when mothers face nutritional challenges during pregnancy. However, this was a small animal study, so human research is needed before doctors could recommend it for pregnant women.
The Research Details
Scientists created a controlled experiment with pregnant sheep to test whether L-citrulline supplementation could improve fetal growth during maternal malnutrition. They divided the animals into two groups: one received L-citrulline added to their limited diet, while the other received an equal amount of a different amino acid (alanine) as a control. This design allowed researchers to isolate the specific effects of L-citrulline rather than just the effect of extra nutrition.
The mothers were fed only 50% of their normal nutritional requirements from day 28 of pregnancy until day 140 (sheep pregnancies last 147 days). This deliberately created growth restriction in the fetuses, mimicking what happens when pregnant women are malnourished. The researchers then measured the babies at birth and again at 60 days old, checking their weight, organ sizes, and blood chemistry.
L-citrulline was chosen because it has a special advantage: unlike arginine (a similar nutrient), L-citrulline isn’t broken down by the bacteria in a sheep’s stomach, so more of it reaches the bloodstream where it can help the fetus. This makes it more practical for animals with multiple stomach chambers.
This research approach matters because it tests a potential solution to a real problem: when pregnant animals (or women) don’t get enough nutrition, their babies are born smaller and face lifelong health risks including diabetes and heart disease. By testing L-citrulline specifically, scientists found a nutrient that works better than alternatives in the body’s system. The study followed babies through two months of life, showing that benefits lasted beyond birth, which suggests real, lasting improvements rather than temporary effects.
This was a controlled experimental study with a comparison group, which is stronger than observational research. However, the sample size was small (23 animals total), which means results need confirmation in larger studies. The researchers used objective measurements (weighing organs, measuring blood chemicals) rather than subjective assessments, which increases reliability. The study was published in a peer-reviewed scientific journal, meaning other experts reviewed the work before publication. The main limitation is that this was animal research, so results may not directly apply to humans without further testing.
What the Results Show
Lambs born to mothers who received L-citrulline supplementation were significantly heavier at birth compared to the control group. This difference persisted and grew larger by day 60 after birth, showing that the benefit wasn’t temporary. The L-citrulline lambs maintained their growth advantage through the two-month observation period.
Beyond just overall weight, the researchers found that specific organs were larger in the L-citrulline group. The pancreas—the organ responsible for controlling blood sugar and digestion—was notably larger both in absolute size and when adjusted for body weight. The brain, liver, and small intestine were also significantly larger in the supplemented group. This suggests L-citrulline didn’t just make babies bigger overall; it specifically enhanced development of critical organs.
Blood chemistry tests revealed important differences. At birth, lambs in the L-citrulline group had higher insulin levels, suggesting their pancreases were functioning better. By day 60, these lambs also had higher blood glucose levels, which could indicate improved metabolic function. These changes suggest the supplement influenced how the developing pancreas was programmed to work.
The proportion of different cell types within the pancreas (endocrine cells that make hormones versus exocrine cells that make digestive enzymes) was similar between groups, suggesting L-citrulline enhanced overall pancreatic growth rather than changing its basic structure. This is important because it means the organ developed more normally, just larger. The fact that benefits persisted through day 60 suggests the programming effects of the supplement during pregnancy continued to influence the lambs’ development after birth.
Previous research showed that L-arginine (a similar nutrient) could help with fetal growth problems, but arginine gets broken down in the stomachs of animals like sheep before it can be absorbed. This study demonstrates that L-citrulline, which bypasses this problem, works even better in these animals. The findings align with the known biology of how these nutrients work and suggest L-citrulline could be a more practical alternative in agricultural settings. The results also support the broader scientific understanding that specific amino acids during pregnancy can program long-term organ development and metabolic function.
The sample size was relatively small (13 lambs in the treatment group, 10 in the control), which means results need confirmation in larger studies before drawing firm conclusions. This was an animal study using sheep, so the results may not directly translate to humans—sheep have different digestive systems and metabolic rates than people. The study only followed lambs for 60 days after birth; longer-term follow-up would show whether benefits persist into adulthood. The mothers were severely undernourished (50% of normal intake), which is more extreme than most human malnutrition, so the practical applicability to moderately malnourished pregnant women is unclear. The study didn’t measure all possible long-term health outcomes, such as disease risk in adulthood.
The Bottom Line
Based on this research, L-citrulline supplementation appears promising for improving fetal growth during maternal malnutrition, but current evidence is limited to animal studies. Confidence level: Moderate for animal models, Low for human application. Before any clinical use in pregnant women, human clinical trials would be necessary. Healthcare providers should not recommend L-citrulline supplementation for pregnancy based on this single animal study alone.
This research is most relevant to agricultural scientists and veterinarians working with livestock, where L-citrulline could improve farm animal productivity. Researchers studying fetal growth restriction and maternal nutrition should take note of these findings as a foundation for human studies. Pregnant women facing malnutrition or healthcare providers serving malnourished populations should be aware of this research direction, but should not self-treat without medical guidance. This is not yet ready for clinical application in humans.
In this animal study, benefits appeared by birth and continued growing through the two-month observation period. If similar effects occur in humans, improvements in fetal growth would likely develop gradually throughout pregnancy, with the most significant effects probably occurring in the second and third trimesters when fetal growth accelerates. Any human application would require years of clinical research before benefits could be expected.
Frequently Asked Questions
Can pregnant women take L-citrulline supplements to help their baby grow bigger?
This animal research shows promise, but human studies haven’t been conducted yet. Pregnant women should not self-supplement based on animal research alone. Consult your doctor before taking any supplements during pregnancy, as safety in human pregnancy hasn’t been established.
What is L-citrulline and where does it come from naturally?
L-citrulline is an amino acid (a building block of protein) found naturally in foods like watermelon, pumpkin seeds, chickpeas, and other plant sources. Your body also makes it. Unlike arginine, L-citrulline isn’t broken down in the stomach, making it more available for absorption.
Does this research apply to humans or just animals?
This research was conducted in sheep, not humans. While the findings are interesting and suggest a direction for future human research, animal studies don’t always translate directly to people. Human clinical trials would be necessary before doctors could recommend L-citrulline for pregnant women.
What happens to babies when mothers don’t eat enough during pregnancy?
Babies born to malnourished mothers tend to be smaller at birth and face increased risks of metabolic problems like diabetes and heart disease later in life. This study tested whether L-citrulline could reduce these risks by improving fetal growth and organ development during maternal undernutrition.
Why is L-citrulline better than arginine for pregnant animals?
L-citrulline bypasses breakdown in the stomach and is absorbed more efficiently into the bloodstream, making it more practical for animals with multiple stomach chambers. Arginine gets degraded by stomach bacteria before absorption, reducing its effectiveness in these animals.
Want to Apply This Research?
- For pregnant users or those planning pregnancy, track daily protein intake and specific amino acid sources. Log whether prenatal supplements are being taken and any gastrointestinal symptoms that might affect nutrient absorption. Monitor weight gain patterns against trimester-specific targets.
- Users could increase dietary sources of L-citrulline (found in watermelon, pumpkin seeds, and chickpeas) as part of overall pregnancy nutrition planning. Set reminders to take prenatal vitamins consistently. Log meals to ensure adequate overall protein intake, which supports amino acid availability.
- Track weekly weight gain, energy levels, and any symptoms of malnutrition or inadequate nutrition. For pregnant users, monitor fetal development milestones at medical appointments. Long-term, track infant growth metrics (weight, length) at regular check-ups to assess whether maternal nutrition optimization correlated with healthy growth patterns.
This research was conducted in animals (sheep) and has not been tested in humans. L-citrulline supplementation during pregnancy is not currently recommended by major medical organizations and should not be used without explicit medical supervision. Pregnant women should consult their healthcare provider before taking any supplements, as safety and efficacy in human pregnancy have not been established. This article is for educational purposes and should not be considered medical advice. Always follow your doctor’s recommendations regarding nutrition and supplementation during pregnancy.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.