Athletes who train hard sometimes struggle with constipation because of intense exercise, irregular eating, and disrupted sleep schedules. Researchers tested whether a special fiber called konjac glucomannan could help elite Taekwondo athletes with constipation problems. Over 8 weeks, athletes who took this fiber supplement had significantly fewer constipation symptoms, better bowel movements, and improved quality of life compared to those taking a placebo. The fiber also changed the types of bacteria in their gut in ways that seemed to help with digestion. This suggests that this particular fiber might be a useful, natural way for athletes to manage constipation without medication.

The Quick Take

  • What they studied: Whether a special plant fiber called konjac glucomannan could reduce constipation symptoms and improve bowel health in competitive athletes
  • Who participated: Elite male Taekwondo athletes who had been diagnosed with functional constipation (difficulty having regular bowel movements without a medical cause)
  • Key finding: Athletes who took konjac glucomannan for 8 weeks had significantly better constipation symptoms, more regular bowel movements, and better quality of life compared to athletes taking a placebo pill. Their gut bacteria also changed in ways that appeared to support better digestion.
  • What it means for you: If you’re an athlete struggling with constipation, this fiber supplement may help improve your symptoms and bowel regularity. However, you should talk to your doctor before starting any new supplement, especially if you take medications or have other health conditions.

The Research Details

This was a double-blind randomized controlled trial, which is considered one of the strongest types of scientific studies. Double-blind means that neither the athletes nor the researchers knew who was getting the real fiber supplement and who was getting a fake pill (placebo) until the study ended. This prevents bias from affecting the results.

The study lasted 8 weeks. Elite male Taekwondo athletes with constipation were randomly divided into two groups: one group received konjac glucomannan (a soluble fiber from the konjac plant), and the other group received a placebo. Researchers measured constipation symptoms using standardized questionnaires, tracked bowel movement frequency, and analyzed stool samples to see how the gut bacteria changed.

The researchers used genetic testing (16S rRNA gene sequencing) to identify which types of bacteria were present in participants’ guts before and after the study. They also used computer analysis to predict how the bacterial changes might affect digestion and nutrient processing.

This study design is important because it removes bias and shows cause-and-effect relationships. By using a placebo group, researchers could prove that improvements came from the fiber itself, not from the athletes’ expectations or other factors. Testing the gut bacteria helps explain how the fiber actually works in the body, not just that it works.

This is a high-quality study because it used a randomized controlled trial design, which is the gold standard in nutrition research. The study was double-blind, meaning neither participants nor researchers knew who received the real supplement. The researchers measured multiple outcomes (symptoms, bowel function, and gut bacteria) to get a complete picture. However, the study only included male Taekwondo athletes, so results may not apply equally to female athletes, other sports, or non-athletes with constipation.

What the Results Show

Athletes who took konjac glucomannan showed significant improvements across all main measures of constipation. Their constipation symptoms decreased noticeably, and their quality of life improved compared to the placebo group. Bowel movement frequency increased, meaning they had more regular bathroom visits. Stool consistency also improved, becoming more normal according to the Bristol Stool Scale.

The most interesting finding was how the fiber changed the gut bacteria. The athletes taking konjac glucomannan developed a more diverse and balanced gut microbiota. Specifically, beneficial bacteria like Lactobacillus and Bacteroides increased, while bacteria associated with constipation problems (like Alistipes and Desulfovibrio) decreased.

These bacterial changes weren’t random—they directly correlated with symptom improvement. In other words, athletes whose gut bacteria changed the most also experienced the biggest improvements in constipation symptoms. This suggests the fiber works by feeding good bacteria and creating a healthier gut environment.

The computer analysis of bacterial genes showed that the fiber activated metabolic pathways related to nutrient production and processing, particularly biotin (a B vitamin) production. This may explain some of the digestive benefits.

Beyond the main constipation measures, the study found that the konjac glucomannan group experienced improved bowel function overall, as measured by the Bowel Function Index. The changes in gut bacteria composition were substantial and consistent across the group taking the supplement. The study also identified specific bacterial families (Prevotellaceae) that increased with the fiber, suggesting these bacteria may be particularly responsive to konjac glucomannan.

Previous research has shown that soluble fibers can help with constipation in general populations, but this is one of the first studies to specifically test konjac glucomannan in elite athletes. Athletes face unique constipation challenges due to dehydration, intense training, and irregular meal timing, so this targeted research fills an important gap. The findings align with other studies showing that dietary fibers work by changing gut bacteria composition, but this study provides more detailed information about which specific bacteria respond to konjac glucomannan.

The study only included male elite Taekwondo athletes, so the results may not apply equally to female athletes, recreational athletes, or people who don’t exercise intensely. The study lasted only 8 weeks, so we don’t know if the benefits continue long-term or if the gut bacteria changes persist after stopping the supplement. The study didn’t measure how much water participants drank or track other dietary factors that could affect constipation. Finally, the exact sample size wasn’t clearly reported in the available information, which makes it harder to assess the statistical power of the findings.

The Bottom Line

If you’re an athlete with constipation, konjac glucomannan appears to be a safe and effective option worth discussing with your doctor or sports nutritionist. The evidence from this study is moderately strong because it’s a well-designed randomized controlled trial, but more research in different populations would strengthen the recommendation. Start with a lower dose and increase gradually to minimize digestive discomfort, and drink plenty of water since fiber works best with adequate hydration.

This research is most relevant to competitive athletes, particularly those in sports with weight categories or intense training schedules. It may also help non-athletes with constipation, though the study didn’t test this. People with certain digestive conditions (like irritable bowel syndrome) should consult their doctor before trying this supplement. Pregnant women and people taking certain medications should also check with their healthcare provider first.

Based on this study, you can expect to see improvements in constipation symptoms within 2-4 weeks of starting konjac glucomannan, with more significant improvements by 8 weeks. However, individual responses vary, and some people may see benefits sooner while others take longer. Consistency is important—the supplement works best when taken regularly as directed.

Want to Apply This Research?

  • Track daily bowel movement frequency and consistency using the Bristol Stool Scale (a simple 1-7 scale where 1 is hard lumps and 7 is liquid). Log this daily in your app along with konjac glucomannan intake to see patterns over 2-4 weeks.
  • Set a daily reminder to take your konjac glucomannan supplement at the same time each day, paired with a glass of water. Also set reminders to drink water throughout the day, since fiber needs adequate hydration to work effectively. Track your water intake alongside the supplement.
  • Create a weekly summary view showing bowel movement frequency, stool consistency scores, and supplement adherence. After 4 weeks, review trends to see if symptoms are improving. If no improvement appears after 6-8 weeks, consult your healthcare provider. Continue tracking even after improvements to catch any changes and maintain consistency.

This research suggests konjac glucomannan may help with constipation in athletes, but it should not replace medical advice from your doctor. If you have chronic constipation, severe digestive symptoms, or take medications that affect digestion, consult your healthcare provider before starting any supplement. Konjac glucomannan can cause bloating or gas when first introduced—start with small amounts and increase gradually. People with swallowing difficulties or bowel obstruction should avoid this supplement. This summary is for educational purposes and does not constitute medical advice.