Researchers studied 65 adults with systemic sclerosis (a disease affecting connective tissue) to see how ultra-processed foods affect their digestive health. They found that people who ate more processed foods like packaged snacks, fast food, and sugary items experienced worse stomach problems and had changes in their gut bacteria. The study suggests that reducing ultra-processed foods might help improve digestive symptoms in people with this condition. While the results are promising, more research is needed to confirm whether changing eating habits can actually reduce symptoms.

The Quick Take

  • What they studied: Whether eating ultra-processed foods (like packaged snacks, fast food, and processed meals) affects stomach problems and gut bacteria in people with systemic sclerosis, a disease that hardens skin and connective tissue.
  • Who participated: 65 adults with systemic sclerosis, mostly women (about 85%), with an average age of 54 years. Researchers collected stool samples and asked participants about their eating habits and digestive symptoms.
  • Key finding: People who ate more ultra-processed foods reported significantly more stomach problems. The study also found that higher ultra-processed food intake was linked to changes in the types of bacteria living in their gut.
  • What it means for you: If you have systemic sclerosis and experience digestive issues, eating fewer ultra-processed foods might help reduce symptoms. However, this study shows a connection, not proof that changing diet will definitely help—more research is needed before making major dietary changes. Talk to your doctor before making significant changes to your diet.

The Research Details

This was an observational study where researchers collected information from 65 people with systemic sclerosis at one point in time. Participants provided stool samples (which researchers analyzed to identify gut bacteria) and completed two questionnaires: one about their diet over the past year and another about their digestive symptoms. Researchers used advanced DNA testing to identify which bacteria were present in each person’s gut and in what amounts.

The researchers then looked for patterns between how much ultra-processed food each person ate and their digestive symptoms. They used statistical methods to account for other factors that might affect gut bacteria, such as body weight, medications people were taking, and whether they had bacterial overgrowth in their small intestine.

Ultra-processed foods were identified using a standard food classification system that includes items like packaged snacks, sugary drinks, instant noodles, mass-produced baked goods, and fast food—basically foods that have been heavily modified from their original form and contain many additives.

This research approach is important because it looks at real-world eating patterns and their actual effects on people’s health, rather than just studying bacteria in a lab. By analyzing gut bacteria directly from stool samples, researchers could see exactly which types of bacteria changed with different eating habits. The study also carefully controlled for other factors that might affect results, making the findings more reliable.

Strengths: The study used advanced DNA technology to accurately identify gut bacteria, included detailed dietary information, and adjusted for multiple factors that could affect results. Limitations: The sample size was relatively small (65 people), the study only shows association (not cause-and-effect), and all participants had the same disease, so results may not apply to people without systemic sclerosis. The study was also conducted at a single point in time, so we don’t know if these patterns continue over time.

What the Results Show

The main finding was clear: people who ate more ultra-processed foods reported significantly more digestive symptoms, including issues like bloating, stomach pain, and other GI problems. On average, participants consumed about 2,400 grams (roughly 5.3 pounds) of ultra-processed food per week.

The study also found that ultra-processed food consumption was linked to changes in specific types of gut bacteria. Some bacteria that are generally considered beneficial (like Limosilactobacillus fermentum) were less abundant in people who ate more processed foods. Meanwhile, other bacteria associated with digestive problems were more common in high ultra-processed food consumers.

Importantly, these patterns remained even after researchers accounted for other factors known to affect gut health in people with systemic sclerosis, such as medications, body weight, and other digestive conditions. This suggests that ultra-processed food consumption itself may be driving these changes.

The study identified six different bacterial species whose abundance was associated with digestive symptom severity. This suggests that ultra-processed foods don’t just cause general changes to gut bacteria—they specifically affect bacteria that may be connected to how bad digestive symptoms become. The research also found that the relationship between ultra-processed foods and symptoms was independent of whether people were taking probiotics or stomach acid-reducing medications, suggesting these interventions don’t fully counteract the effects of processed food consumption.

Previous research in the general population has shown that ultra-processed foods harm gut bacteria and increase inflammation. This study extends those findings to people with systemic sclerosis, a group that already has known problems with gut bacteria and digestive health. The results align with existing knowledge that diet significantly shapes which bacteria live in our gut and that processed foods tend to reduce bacterial diversity and promote harmful bacteria.

This study shows that ultra-processed food consumption and digestive problems are connected, but it doesn’t prove that processed foods cause the problems—other unmeasured factors could be involved. The study included only 65 people, mostly women, so results may not apply equally to men or to people without systemic sclerosis. The study captured eating habits at only one moment in time, so we don’t know if these patterns are consistent or how they change over months or years. Finally, the study relied on people’s memory of what they ate, which can be inaccurate.

The Bottom Line

For people with systemic sclerosis experiencing digestive problems: Consider reducing ultra-processed foods and eating more whole foods like fruits, vegetables, whole grains, and minimally processed proteins. This recommendation has moderate confidence based on this study combined with existing research. However, make dietary changes gradually and discuss them with your healthcare provider, especially if you have systemic sclerosis, as this condition requires specialized medical care.

This research is most relevant for people with systemic sclerosis who experience digestive symptoms. It may also be interesting to people with other autoimmune diseases affecting digestion. The findings are less directly applicable to people without systemic sclerosis, though the general principle that ultra-processed foods affect gut health applies broadly. Anyone considering major dietary changes should consult their doctor first.

If you reduce ultra-processed food intake, you might notice improvements in digestive symptoms within 2-4 weeks, though some people may take longer. Changes in gut bacteria composition typically take several weeks to become established. Full benefits may take 8-12 weeks or longer. Results vary significantly between individuals.

Want to Apply This Research?

  • Track weekly ultra-processed food consumption in grams and rate digestive symptoms daily on a scale of 1-10. Record specific symptoms (bloating, pain, etc.) to identify patterns. Compare symptom severity to processed food intake from the previous week.
  • Set a goal to replace one ultra-processed food item per week with a whole food alternative. For example: swap packaged snacks for fresh fruit, instant meals for home-cooked dishes, or sugary drinks for water or herbal tea. Track which swaps feel easiest and most sustainable.
  • Create a weekly dashboard showing ultra-processed food grams consumed and average symptom severity. Use a 4-week rolling average to identify trends rather than daily fluctuations. Set monthly reduction goals (e.g., decrease processed food intake by 10% each month) and monitor corresponding symptom changes.

This research shows an association between ultra-processed food consumption and digestive symptoms in people with systemic sclerosis, but does not prove that processed foods directly cause these symptoms. This information is for educational purposes only and should not replace professional medical advice. People with systemic sclerosis should consult their rheumatologist or gastroenterologist before making significant dietary changes, as this condition requires specialized medical management. Individual responses to dietary changes vary greatly. Always discuss new dietary approaches with your healthcare provider, especially if you take medications or have other health conditions.