Researchers studied 82 children in Brazil to see how eating ultra-processed foods (like packaged snacks and fast food) affects their gut bacteria and immune system. Kids who ate the most junk food had fewer healthy bacteria in their stomachs and more unhealthy ones. These changes were linked to higher levels of inflammation markers in their blood—basically, their bodies were more inflamed. The study suggests that eating too much processed food doesn’t just affect what we eat; it actually changes the tiny organisms living in our stomachs that help keep us healthy.

The Quick Take

  • What they studied: How eating ultra-processed foods (packaged snacks, fast food, sugary drinks) affects the bacteria living in children’s stomachs and whether it causes inflammation in their bodies.
  • Who participated: 82 children between 7 and 11 years old attending public schools in João Pessoa, Brazil. The study looked at kids from different economic backgrounds in the community.
  • Key finding: Children who ate the most ultra-processed foods had fewer healthy bacteria (like Ruminococcaceae) and more unhealthy bacteria in their guts. They also showed higher levels of inflammation markers in their blood, suggesting their immune systems were working overtime.
  • What it means for you: Eating lots of junk food may harm the good bacteria in your stomach that protect your health. This could lead to more inflammation and potentially weaker immunity. Eating more whole foods like fruits, vegetables, and whole grains may help keep your gut bacteria healthy. However, this is one study in one location, so more research is needed before making major changes.

The Research Details

This was a cross-sectional study, which means researchers looked at a group of children at one point in time rather than following them over months or years. They collected information about what the children ate using a 24-hour food recall (asking parents and kids what they ate the day before). They also took stool samples to analyze the bacteria living in each child’s gut using a special genetic test called 16S rRNA gene sequencing. Researchers measured inflammation by testing blood samples for specific immune chemicals called cytokines. They also recorded each child’s height, weight, and family’s economic situation.

This approach is useful because it shows us what’s happening right now in real children’s bodies. By looking at actual kids in their real communities (not a lab), the results are more likely to apply to everyday life. The genetic testing of gut bacteria is very accurate and can identify hundreds of different bacterial species. Measuring inflammation markers in the blood gives us real biological evidence that something is happening in the body, not just assumptions.

The study is relatively small (82 children), so the results may not apply to all children everywhere. Because it’s cross-sectional, we can see that junk food and unhealthy bacteria are connected, but we can’t prove that junk food causes the bacteria changes—other factors could be involved. The study was done in Brazil, so results might be different in other countries with different foods and populations. The researchers used well-established methods for measuring bacteria and inflammation, which is a strength.

What the Results Show

Children who ate the most ultra-processed foods had a very different diet compared to those who ate less junk food. The high-junk-food group got more calories from processed foods, more unhealthy trans fats, but less protein and copper (a mineral your body needs). Their gut bacteria were noticeably different: they had lower amounts of two types of healthy bacteria called Ruminococcaceae and Barnesiellaceae, while having higher amounts of potentially harmful bacteria like Monoglobaceae and Erysipelotrichaceae. These bacterial changes were statistically significant, meaning they weren’t due to chance. The study also found that specific bacteria were connected to inflammation markers in the blood. For example, bacteria called Faecalibacterium and Bifidobacterium were linked to lower inflammation, while other bacteria were linked to higher inflammation. This suggests the bacteria in your gut directly influence how much inflammation your body experiences.

Several specific bacteria showed strong connections to different inflammation markers. Dorea and Subdoligranulum bacteria were associated with immune chemicals IL-17A and IL-10. Agathobacter was linked to three different inflammation markers (IL-6, IL-10, and IFN-γ). Faecalibacterium showed connections to three markers as well (IL-10, IFN-γ, and TNF-α). Bifidobacterium and Fusicatenibacter were associated with IL-10, which is actually an anti-inflammatory marker (meaning it reduces inflammation). Roseburia was connected to TNF-α, a pro-inflammatory marker. These connections suggest that different bacteria have different effects on your immune system.

Previous research has shown that ultra-processed foods are linked to obesity, diabetes, and heart disease in children. This study adds important new information by showing the mechanism—how junk food actually changes the bacteria in your gut, which then affects inflammation. Other studies have shown that healthy bacteria like Faecalibacterium and Bifidobacterium are protective against inflammation and disease. This research confirms those findings in Brazilian children and shows that eating junk food reduces these protective bacteria. The findings align with growing evidence that gut bacteria are a key link between diet and health.

The study only included 82 children from one region of Brazil, so results may not apply to children in other countries or different environments. Because this is a snapshot in time, we can’t prove that junk food causes the bacteria changes—it’s possible that children with certain bacteria naturally prefer junk food, or that other factors (like stress, sleep, or infections) caused both the bacteria changes and the junk food eating. The study didn’t measure how long children had been eating this way, so we don’t know if short-term or long-term junk food consumption causes the changes. The researchers couldn’t control for all possible factors that affect gut bacteria, like antibiotic use, which could influence results.

The Bottom Line

Based on this research, children should eat fewer ultra-processed foods and more whole foods like fruits, vegetables, whole grains, and lean proteins. This may help maintain healthy gut bacteria and reduce inflammation. However, this is one study, so we should wait for more research before making it a strict rule. Parents should focus on gradually increasing whole foods rather than completely eliminating processed foods, which is often unrealistic. Confidence level: Moderate—the findings are interesting and supported by the biology, but more studies in different populations are needed.

Parents and caregivers of children aged 7-11 should pay attention to this research, especially if their children eat a lot of packaged snacks, fast food, or sugary drinks. Teachers and school administrators might use this to support healthier school lunch programs. Children with digestive problems, weak immune systems, or inflammatory conditions may benefit most from reducing junk food. However, this study doesn’t mean occasional treats are harmful—it’s about overall eating patterns. Children with severe food allergies or restrictions should work with a doctor before making major diet changes.

Changes in gut bacteria can happen relatively quickly—some studies show shifts within weeks of dietary changes. However, seeing improvements in inflammation markers and overall health typically takes 4-8 weeks of consistent eating better. Children may notice improved digestion, more energy, and better focus within 2-3 weeks. Long-term benefits like stronger immunity and better disease prevention develop over months and years of healthy eating habits.

Want to Apply This Research?

  • Track daily ultra-processed food servings (packaged snacks, fast food, sugary drinks, instant noodles) and whole food servings (fruits, vegetables, whole grains, nuts, beans). Set a goal to reduce processed foods by 25% each week while increasing whole foods. Use a simple tally or photo log to record meals.
  • Start by replacing one ultra-processed food item per day with a whole food alternative. For example: swap packaged chips for apple slices, replace sugary cereal with oatmeal, or trade soda for water. Make this change gradually so it feels manageable. Involve children in choosing and preparing healthier foods to increase buy-in.
  • Weekly check-ins on how many processed foods were eaten and how many whole foods were added. Track energy levels, digestion comfort, and focus in school as indirect measures of gut health. After 4-6 weeks, note any changes in overall well-being. Consider keeping a simple food and symptom diary to identify patterns between what’s eaten and how the child feels.

This research describes associations between ultra-processed food consumption and changes in gut bacteria in one group of Brazilian children. It does not prove that junk food causes these changes, and results may not apply to all children in all locations. This information is educational and should not replace professional medical advice. Parents concerned about their child’s diet, digestion, or immune health should consult with a pediatrician or registered dietitian. Children with diagnosed medical conditions, food allergies, or those taking medications should speak with their healthcare provider before making significant dietary changes.