Researchers tested a new treatment called fecal microbiota transplantation (FMT)—essentially transferring healthy gut bacteria from donors to patients—in teenagers with obesity. After following 55 teenagers for 4 years, they found that those who received the treatment had improvements in body shape, fat levels, and markers of metabolic health compared to those who received a placebo. While overall weight didn’t change significantly between groups, the FMT group showed better cholesterol levels, less body fat, and reduced inflammation. The study suggests this bacterial transplant approach may help improve health in ways beyond just the number on the scale.

The Quick Take

  • What they studied: Whether transferring healthy gut bacteria from donors to teenagers with obesity could improve their weight, body composition, and overall metabolic health over a 4-year period.
  • Who participated: 55 teenagers with obesity (27 received the bacterial transplant, 28 received a placebo or fake treatment) who were part of a larger study that started years earlier.
  • Key finding: Teenagers who received the gut bacteria transplant had 10 cm smaller waist measurements, 4.8% less total body fat, better cholesterol levels, and 68% less inflammation in their blood compared to the placebo group, even though overall weight loss was similar between groups.
  • What it means for you: This research suggests that gut bacteria transplants may help improve body shape and health markers in teenagers with obesity, though it’s not a simple weight-loss solution. More research is needed before this becomes a standard treatment, and it should only be considered under medical supervision.

The Research Details

This was a long-term follow-up study based on a carefully designed experiment where teenagers were randomly assigned to receive either a fecal microbiota transplant (FMT) or a placebo treatment. Neither the participants nor the researchers initially knew who received the real treatment versus the fake one, which helps prevent bias. The researchers then tracked these teenagers for 4 years, measuring changes in their weight, body composition, blood markers, and gut bacteria using advanced genetic testing.

The study measured multiple health indicators including BMI (a weight-to-height ratio), waist circumference, body fat percentage, cholesterol levels, blood sugar control, inflammation markers, and the composition of bacteria in the gut. By looking at so many different measures, the researchers could see whether the treatment affected health in various ways, not just weight loss.

This research approach is important because it follows people for a long time (4 years) to see if benefits last, rather than just measuring short-term changes. The double-blind, randomized design means the results are more trustworthy because neither participants nor researchers knew who got the real treatment, reducing the chance that expectations influenced the results. By measuring gut bacteria composition using advanced genetic sequencing, researchers could confirm that the transplanted bacteria actually stayed in the recipients’ guts long-term.

This study has several strengths: it was published in a highly respected journal (Nature Communications), used a randomized controlled design (the gold standard for testing treatments), and included long-term follow-up data. However, only 63% of the original participants completed the 4-year follow-up, which means some people dropped out. The sample size is relatively small (55 teenagers), so results may not apply to all teenagers with obesity. The study was conducted in one country with specific populations, so results might differ in other groups.

What the Results Show

The most striking finding was that teenagers receiving the gut bacteria transplant showed significant improvements in body composition and metabolic health markers, even though their overall BMI (weight-to-height ratio) didn’t drop as much as expected. Specifically, the FMT group had waist circumference that was 10 centimeters smaller—an important measure because belly fat is linked to health problems. They also had 4.8% less total body fat, meaning the treatment helped them lose fat even if the scale didn’t show huge changes.

Blood tests revealed that the FMT group had much better inflammation levels, with a 68% reduction in a key inflammation marker (hs-CRP). This matters because chronic inflammation is linked to many health problems. The FMT group also had higher levels of HDL cholesterol (the “good” cholesterol that protects heart health), which increased by 0.16 mmol/L.

Perhaps most importantly, teenagers in the FMT group showed a significant improvement in metabolic syndrome severity score—a measure that combines several health risk factors. Their score improved by 0.58 points, suggesting their overall metabolic health improved substantially. The genetic testing showed that the transplanted bacteria persisted in the FMT group’s guts for the entire 4 years, meaning the treatment created lasting changes to their gut bacteria communities.

The study found no significant differences between groups in glucose control (blood sugar regulation) or most other lipid (fat) measurements besides HDL cholesterol. This suggests the treatment’s benefits were specific to certain health markers rather than improving everything. The sustained changes in gut bacteria composition and function suggest that the transplanted bacteria created a lasting biological change, not just a temporary effect.

This study builds on earlier research suggesting that gut bacteria play a role in obesity and metabolic health. Previous shorter-term studies hinted that FMT might help, but this 4-year follow-up provides much stronger evidence that benefits can last. The finding that body composition improved even when overall weight didn’t change as much as expected is interesting and suggests the treatment may work differently than traditional weight-loss approaches. This aligns with growing scientific understanding that gut bacteria influence how our bodies store and use energy.

The study had several limitations worth noting. Only 55 of the original 87 participants completed the 4-year follow-up, so we don’t know if those who dropped out had different results. The sample size is relatively small, making it harder to detect some effects and limiting how broadly we can apply the findings. The study was conducted in one country with a specific population, so results might differ in other groups. Additionally, the study didn’t measure some important factors like diet quality changes or physical activity changes in detail, which could have influenced results. Finally, while the study is long-term by research standards, 4 years is still relatively short for understanding lifelong health effects.

The Bottom Line

Based on this research, fecal microbiota transplantation shows promise as a potential treatment for improving metabolic health and body composition in teenagers with obesity (moderate confidence level). However, this should not yet be considered a standard treatment. It should only be pursued under close medical supervision as part of a research study or specialized medical program. It works best as part of a comprehensive approach that includes healthy eating and physical activity, not as a replacement for these lifestyle changes. More research is needed before widespread use can be recommended.

This research is most relevant to teenagers with obesity who have metabolic health problems (like inflammation or poor cholesterol levels), their parents, and healthcare providers treating adolescent obesity. It may be particularly interesting to those who haven’t had success with traditional weight-loss approaches. However, this treatment is not appropriate for everyone and should only be considered under medical guidance. People with certain medical conditions or those taking specific medications should not pursue this without consulting their doctor.

Based on this study, improvements in body composition and metabolic markers appeared to develop over months and were sustained over the 4-year follow-up period. However, this doesn’t mean changes happen overnight—metabolic improvements typically take weeks to months to become noticeable. Individual results would likely vary, and some people might see benefits while others don’t.

Want to Apply This Research?

  • Track waist circumference monthly and inflammation markers (if available through blood tests) quarterly, along with body composition changes through measurements or bioelectrical impedance analysis. These metrics showed the most significant improvements in the study and are more meaningful than weight alone.
  • Use the app to log dietary changes and physical activity consistently, as the study adjusted for these factors. Users could set goals for increasing fiber intake (which feeds beneficial gut bacteria) and track exercise minutes. The app could provide reminders about medication adherence if FMT is being pursued medically.
  • Establish a baseline of waist circumference, body fat percentage, and available blood markers before starting any treatment. Then track these metrics monthly for the first 6 months, then quarterly for at least 2 years. Create visual charts showing trends in these specific markers rather than focusing solely on weight, since the study showed improvements in these areas even when weight changes were modest.

This research describes an experimental treatment that is not yet approved for routine clinical use in most countries. Fecal microbiota transplantation for obesity should only be pursued under direct medical supervision as part of a clinical trial or specialized medical program. This article is for educational purposes and should not be considered medical advice. Anyone interested in this treatment should consult with their healthcare provider to discuss whether it might be appropriate for their specific situation. Results from this study may not apply to all individuals, and individual responses to treatment vary. This treatment should complement, not replace, healthy eating habits and regular physical activity. Always consult with a qualified healthcare professional before starting any new treatment.