Research reviewed by Gram suggests that genetically predicted liking for foods like roast chicken, red meat, and lentils may be linked to birth weight, but no food link passed strict statistical testing. A 2026 study in Medicine found that placenta size signals overlapped with birth weight signals on chromosomes 5 and 12, hinting at the placenta as a possible pathway.
Gram Research analysis of a 2026 study in the journal Medicine asked whether the foods people like and eat, as shaped by their genes, are linked to how much babies weigh at birth. The researchers used a genetic method called Mendelian randomization, which uses natural differences in genes to test cause and effect more fairly than simple surveys can. Liking foods such as roast chicken, red meat, lentils and beans, healthy foods, and porridge showed hints of a link to birth weight. However, none of these links passed the strict statistical test needed to rule out chance. The study also found that the placenta, the organ that feeds the baby, may be part of the picture, since some gene signals for placenta size overlapped with signals for birth weight. The authors describe these results as a starting point for future research, not proof that diet changes birth weight. Pregnant people should continue following standard prenatal nutrition advice from their healthcare team.
Key Statistics
A 2026 Mendelian randomization study published in the journal Medicine tested 187 food-liking traits and 38 food-consumption traits against birth weight, and none of the food links met the corrected statistical threshold.
In a 2026 study published in Medicine, placenta-weight and birth-weight gene signals on chromosome 12 showed a 97.9% probability of sharing a common genetic cause, suggesting a biological link worth further study.
Liking for roast chicken, red meat, lentils and beans, healthy foods, and porridge showed suggestive links to birth weight with P values from about 0.0004 to 0.012, though none survived multiple-testing correction in the 2026 Medicine analysis.
The Quick Take
- What they studied: Researchers asked whether genetically influenced food preferences and eating habits are connected to a baby’s birth weight, and whether the placenta, the organ that supplies the baby with nutrients, helps explain any connection.
- Who participated: The paper reports 450 as the number of statistical tests run, not the number of people. The analysis used large genetic databases from earlier genome studies of food preferences, food intake, placenta size, and birth weight. The exact number of people in those source studies is not given in the summary.
- Key finding: Five food-liking traits showed weak hints of a link to birth weight, but none held up after strict correction for the many tests run. Placenta-related gene signals did overlap with birth-weight gene signals on two chromosomes, with a probability of 97.9% and 99.3% that they share a common genetic cause.
- What it means for you: This study does not show that eating specific foods will change your baby’s birth weight. It suggests that the placenta may play a role worth studying further. Pregnant people should focus on proven steps such as balanced meals, adequate calories, and regular prenatal visits.
The Research Details
The researchers used a method called bidirectional two-sample Mendelian randomization. This approach uses genetic variants that people are born with as a natural experiment. Because genes are assigned at conception, they are less likely to be shaped by the lifestyle and income factors that often confuse ordinary diet studies.
The team tested 187 food-liking traits and 38 food-consumption traits against two measures of birth weight. Because so many comparisons were made, they set a strict cutoff to reduce the chance of false alarms. This correction method, called Bonferroni correction, is a common safeguard but also makes it harder to find real effects.
The team also looked at placenta weight and used a statistical tool called colocalization to check whether two traits appear to share the same genetic cause in the same region of DNA. Some steps, including the placenta pathway analysis, were labeled secondary or exploratory, meaning they were added to explore possibilities rather than to confirm a main hypothesis.
Most nutrition studies rely on people remembering what they ate, which can be inaccurate. Genetic methods avoid many of those memory and lifestyle problems, so they offer a different and useful way to examine diet and pregnancy. They can point researchers toward biological pathways worth testing in larger, more direct studies.
The study uses a modern, carefully designed genetic method and reports its statistical corrections openly, which is a strength. However, the main food findings did not pass the strict threshold, and the placenta pathway analysis was conditionally selected, which weakens how firmly its results can be read. The authors themselves call the findings hypothesis-generating. Readers should treat the study as an early step, not a final answer.
What the Results Show
The main test looked at 187 food-liking traits and 38 food-consumption traits. Liking roast chicken, red meat, lentils and beans, healthy foods, and porridge each showed a suggestive link to birth weight. The statistical strength of these links ranged from about 0.0004 to about 0.012, which is weaker than the strict cutoff the researchers used.
Because none of these food links met the strict cutoff, the researchers could not claim that any specific food preference reliably affects birth weight. Results that fall just short of a strict threshold can still be due to chance, especially when many tests are run at once.
The researchers also found that several placenta-weight traits were associated with birth weight in secondary analyses. In some of these analyses, the steps linking food preference, placenta growth, and birth weight pointed in the same direction, which is consistent with a possible placenta pathway. These steps were selected based on earlier results, so they should be considered tentative.
The strongest biological signals came from two regions of DNA, on chromosome 12 and chromosome 5. In both regions, the gene signals for placenta weight and birth weight appear to share a common cause. The chromosome 12 region contains a gene called SLC38A4, which helps move nutrients such as amino acids across cell membranes and is a reasonable candidate for future research.
The placenta findings are the most notable secondary result. Placenta size and birth weight appear to be influenced by overlapping genetic factors. This matters because the placenta is the bridge that delivers nutrients from mother to baby, so a biological link through it would make sense. Still, this is an association found in genetic data, not direct proof that the placenta changes birth weight in a specific way.
Earlier observational studies have often found that the mother’s diet is linked to birth weight. This new genetic study adds a more cautious view, since it suggests that the picture is more complicated than simple food choices. Its placenta findings fit with a growing body of research pointing to the placenta as a key player in how babies grow before birth.
Genetic studies can only examine the patterns they are given, and the food preference data come from self-reports, which can be imprecise. The main food findings did not pass correction for multiple testing, so they could be chance results. The placenta pathway analysis depended on earlier choices about which results to follow, which can overstate the apparent strength of a link. The study also cannot tell us how these genetic factors play out in individual pregnancies, and it does not account for every factor such as income, health conditions, or medications. Larger and more direct studies are needed.
The Bottom Line
Confidence is low that any specific food preference changes birth weight, based on this study alone. Confidence is moderate that the placenta is worth studying as a pathway, since the genetic overlap signals were consistent across analyses. Pregnant people should continue with established advice, which includes eating a varied diet with enough total calories, protein, iron, and folate, and attending regular prenatal care.
Pregnant people, healthcare providers, and researchers studying pregnancy nutrition may find this study interesting. People who are not pregnant and those looking for a quick diet fix for birth weight should not apply these findings directly. Anyone with a medical condition affecting pregnancy should follow advice from their own doctor or midwife.
This study is research for future work, so no immediate changes to a pregnancy are expected from it. Larger studies, including direct tests of nutrition and placenta health, could take several years to produce clearer answers. Anyone planning or managing a pregnancy should rely on current prenatal guidance while that research develops.
Frequently Asked Questions
Does eating more red meat or lentils during pregnancy increase birth weight?
A 2026 genetic study in Medicine found only weak hints that liking red meat, lentils, and beans may be linked to birth weight. None of these links passed strict statistical testing, so the study cannot confirm that eating these foods changes birth weight.
What role does the placenta play in a baby’s birth weight?
The placenta delivers nutrients and oxygen from mother to baby. A 2026 study in Medicine found that gene signals for placenta weight overlapped with birth weight signals on chromosomes 5 and 12, suggesting the placenta may be an important pathway that deserves further research.
Can genetics research tell us how diet affects pregnancy outcomes?
Mendelian randomization uses naturally assigned genetic differences to test possible cause and effect, which avoids some problems of diet surveys. However, results from this 2026 Medicine study are hypothesis-generating and do not prove that diet causes changes in birth weight.
What should pregnant people do about nutrition based on this study?
This study does not change current advice. Pregnant people should follow established prenatal guidance, including a varied diet with adequate calories, protein, iron, and folate, and should discuss any concerns about baby growth with their healthcare provider.
Want to Apply This Research?
- Log daily servings of protein foods, vegetables, whole grains, and fluids, along with total calorie intake, using a simple 1 to 5 rating for how well each day met general prenatal nutrition goals. Track prenatal appointment dates and any weight gain reported by your care team.
- Set a reminder to include a protein source, such as lean meat, lentils, beans, or eggs, at two or more meals each day. Pair this with a vegetable or fruit at each meal. These steps match standard prenatal guidance and do not depend on the uncertain findings of this study.
- Review your weekly nutrition logs with your healthcare provider at each prenatal visit. Note any changes in appetite, food cravings, or energy levels, and bring questions to appointments. Keep your provider informed about dietary changes so they can track fetal growth in the context of your full health picture.
This article summarizes a genetic research study and is for general information only. It is not medical advice and does not replace guidance from your doctor, midwife, or other healthcare provider. The study’s findings are preliminary and do not show that any food or diet changes a baby’s birth weight. If you are pregnant or planning a pregnancy, speak with your healthcare team before making changes to your diet.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.