Researchers tested whether adding a lot of fiber to the diet could help prevent colorectal cancer in Alaska Native people, who have higher rates of this disease. Participants took a supplement that added 44.5 grams of extra fiber daily for 4 weeks. The main side effect was increased gas and bloating, but fewer other stomach problems than expected. This study helps scientists understand whether people can actually stick with high-fiber supplements long enough for them to work, which is important before recommending them to larger groups.

The Quick Take

  • What they studied: Whether people can tolerate taking a large amount of extra fiber in supplement form, and what side effects they experience
  • Who participated: Alaska Native people participating in a cancer prevention study who took either a high-fiber supplement or a control supplement for 4 weeks
  • Key finding: The high-fiber supplement caused more gas than normal, but surprisingly caused fewer other digestive problems than researchers expected
  • What it means for you: If you’re considering high-fiber supplements for health, expect some gas and bloating for a while, but it may not be as uncomfortable as feared. However, this was a short 4-week study, so we don’t yet know if people can stick with it long-term or if it actually prevents cancer

The Research Details

This was a randomized controlled trial, which is one of the strongest types of research studies. Researchers randomly divided Alaska Native participants into two groups: one group received a supplement with 44.5 grams of extra fiber per day (including a special type called resistant starch), while the other group received a control supplement with only 1 gram of extra fiber. Both groups took their supplements for 4 weeks. The researchers then asked participants to report what side effects they experienced, like gas, bloating, stomach pain, or changes in bowel habits.

The study focused specifically on how well people tolerated the supplements—meaning whether they could handle taking them without too much discomfort. This is important because if a supplement causes too many problems, people won’t take it regularly, and it won’t help prevent disease. The researchers wanted to understand this before recommending high-fiber supplements to larger groups of Alaska Native people.

Understanding how people actually tolerate supplements is just as important as knowing whether they work. Even if a supplement could prevent cancer, it won’t help if people can’t stick with it because of side effects. This study gives real-world information about what to expect when taking high-fiber supplements, which helps doctors and patients make informed decisions.

This was a randomized controlled trial, which is a strong study design. However, the abstract doesn’t specify how many people participated, which makes it harder to judge the strength of the findings. The study was relatively short (only 4 weeks), so we don’t know if people could tolerate the supplements for longer periods. The study was conducted with Alaska Native people specifically, so results may not apply equally to other populations.

What the Results Show

The main finding was that the high-fiber supplement produced noticeably more gas (flatulence) than the control supplement. This is actually expected when people suddenly increase their fiber intake, because fiber is broken down by bacteria in the colon, which produces gas as a byproduct.

Interestingly, the researchers found fewer other digestive symptoms than they anticipated. While some participants likely experienced bloating or changes in bowel movements, these weren’t consistently reported across the group. This suggests that although gas was a common side effect, the overall digestive experience was more tolerable than many people might expect when taking a large amount of extra fiber.

The fact that participants were able to complete the 4-week study suggests that the side effects weren’t so severe that people quit. This is encouraging for future studies testing whether the fiber supplement can actually reduce cancer risk over longer periods.

The study focused primarily on tolerance and side effects rather than cancer prevention outcomes. The researchers noted that understanding how well people tolerate supplements is crucial for determining whether they’ll actually take them regularly in real life. If people experience too many uncomfortable side effects, they’re likely to stop taking the supplement, which would prevent it from having any protective effect against cancer.

The idea that fiber protects against colorectal cancer comes from observations made decades ago by researcher Denis Burkitt, who noticed that people in developed countries eating refined (processed) foods had much higher rates of colorectal cancer compared to people in less developed countries eating more whole foods with natural fiber. This study builds on that idea by testing whether adding fiber through supplements could help Alaska Native people, who currently have higher colorectal cancer rates and may have lower fiber intake in their diets.

The study only lasted 4 weeks, so we don’t know if people could tolerate the supplements for months or years. The abstract doesn’t specify the exact number of participants, making it difficult to assess how reliable the findings are. The study measured tolerance and side effects but didn’t measure whether the fiber supplement actually reduced cancer risk—that would require a much longer study. Results are specific to Alaska Native people and may not apply to other populations. The study doesn’t tell us whether people would actually take the supplement if it were available outside of a research setting.

The Bottom Line

If you’re considering high-fiber supplements for health reasons, expect to experience increased gas and bloating, especially when you first start taking them. This is normal and typically improves over time as your digestive system adjusts. Start with smaller amounts and gradually increase to help your body adapt. Drink plenty of water and stay physically active, as these can help reduce gas and bloating. However, this research doesn’t yet prove that fiber supplements prevent cancer—more long-term studies are needed. Confidence level: Moderate for tolerance information; Low for cancer prevention claims.

Alaska Native people and others with higher colorectal cancer risk should pay attention to this research. People considering high-fiber supplements for any health reason should know what side effects to expect. Healthcare providers working with populations at higher risk for colorectal cancer should consider this information when recommending dietary changes. People should NOT rely on this study alone to make decisions about cancer prevention—talk to your doctor about proven ways to reduce colorectal cancer risk, such as screening tests.

Gas and bloating from increased fiber typically peak within the first 1-2 weeks and often improve significantly by week 3-4 as your digestive system adapts. However, this study only tracked 4 weeks, so we don’t know what happens with longer-term use. If you’re considering fiber supplements, give yourself at least 2-3 weeks to adjust before deciding whether to continue.

Want to Apply This Research?

  • Track daily fiber intake (in grams) and rate gas/bloating severity on a scale of 1-10 each day. Note any other digestive symptoms like stomach pain, constipation, or diarrhea. This helps identify patterns and shows whether symptoms improve over time.
  • If using a nutrition app, gradually increase daily fiber intake by 5-10 grams per week rather than all at once. Set reminders to drink extra water throughout the day (fiber works best with adequate hydration). Log any digestive symptoms to share with your healthcare provider.
  • Over 4 weeks, track whether gas and bloating decrease as your body adapts. Monitor overall digestive comfort and whether you’re able to stick with the supplement consistently. If symptoms don’t improve after 3-4 weeks, discuss alternatives with your doctor. Continue tracking even after symptoms improve to ensure long-term tolerance.

This research describes tolerance to high-fiber supplements in a 4-week study and does not prove that fiber supplements prevent colorectal cancer. The findings are specific to Alaska Native participants and may not apply to other populations. Before starting any supplement, especially in large amounts, consult with your healthcare provider. This is particularly important if you have existing digestive conditions, take medications, or have other health concerns. Do not use this information to replace medical advice or proven cancer screening methods. Colorectal cancer prevention requires a comprehensive approach that may include screening, diet, exercise, and other lifestyle factors—discuss your individual risk and prevention options with your doctor.