In natural health circles, people often trade lists of foods, herbs, and supplements said to “fight cancer.” Most of those claims rest on test tubes or wishful thinking. But one natural, free, side-effect-light intervention now has some of the strongest evidence in all of cancer care: regular exercise.
In 2025, the New England Journal of Medicine published the results of a 15-year international trial called CHALLENGE. It was the first large randomized study to show that a structured exercise program, started after treatment, helps people with colon cancer stay cancer-free longer and live longer. Oncologists called it a turning point. Here is what it found and what it means for you.
Key Takeaways
- The CHALLENGE trial followed 889 colon cancer survivors for a median of almost eight years.
- Those in a three-year guided exercise program had a 28% lower risk of cancer returning, a new cancer, or death.
- Eight years out, 90% of the exercise group were alive, compared with 83% of the comparison group.
- The program built up gradually and relied mostly on brisk walking.
- Exercise complements medical treatment. It does not replace surgery, chemotherapy, or follow-up care.
Why This Study Matters So Much
For decades, observational studies hinted that active cancer survivors tend to do better. The problem is that those studies cannot prove cause and effect. Maybe people who feel healthier simply move more. To know whether exercise itself makes the difference, you need a randomized trial, where chance decides who gets the program. That is very hard and expensive to do with exercise, which is why it took so long.
The CHALLENGE trial, led by Dr. Kerry Courneya of the University of Alberta and run through the Canadian Cancer Trials Group, took on that challenge. It enrolled patients at 55 centers across six countries between 2009 and 2024.
How the Trial Worked
All participants had stage II or III colon cancer and had finished surgery and chemotherapy within the previous two to six months. They were randomly split into two groups:
- Health education group (444 people): received printed materials encouraging physical activity and healthy eating.
- Structured exercise group (445 people): received the same materials plus three years of support from a trained coach.
Coaches met with the exercise group regularly, often in supervised sessions early on, then gradually less often. Participants chose their own activities, but most simply walked briskly. The goal was to add about 10 MET-hours of activity per week. In everyday terms, that is roughly three to four brisk 45 to 60 minute walks a week, or about 150 minutes of moderate exercise.
The Results
CHALLENGE Trial at a Glance
| Outcome | Exercise group | Education only |
|---|---|---|
| Cancer-free at 5 years | 80.3% | 73.9% |
| Alive at 8 years | 90.3% | 83.2% |
| Muscle or joint complaints | 18.5% | 11.5% |
Source: Courneya et al., New England Journal of Medicine, 2025.
Put simply, over about eight years, for every 16 people who joined the exercise program, roughly one additional cancer recurrence, new cancer, or death was prevented. The overall risk of those events fell by 28 percent, and the risk of death fell by 37 percent.
The main downside was more minor aches and strains, which is what you would expect when people start exercising more. These were generally manageable.
How Might Exercise Fight Cancer?
Scientists are still working out the details, but several mechanisms are likely at play:
- Lower insulin and blood sugar. High insulin levels can act as a growth signal for some tumors. Exercise improves insulin sensitivity.
- Less chronic inflammation. Regular activity lowers inflammatory markers linked to cancer growth.
- A stronger immune response. Exercise mobilizes natural killer cells and other immune cells that patrol for abnormal cells.
- Faster gut transit. For colon cancer specifically, movement may reduce how long the bowel is exposed to harmful compounds.
- Healthier body composition. More muscle and less visceral fat change the hormonal environment in favorable ways.
Does This Apply to Other Cancers?
The trial studied colon cancer, so we cannot assume identical results elsewhere. However, a large body of observational research links physical activity with better outcomes in breast and prostate cancer too, and earlier reports have tied walking and yoga to a lower risk of cancer spreading or returning. Major cancer organizations already recommend that survivors aim for the same activity levels as the general population. Read our earlier coverage of how walking and yoga may cut the risk of cancer returning.
Exercise also helps with prevention. Regular activity is linked with lower risk of at least seven cancers, including colon, breast, endometrial, and kidney cancer.
How to Get Started Safely
- Talk to your oncology team first, especially if you are still in treatment, have a port or ostomy, low blood counts, bone involvement, or neuropathy.
- Start small. Ten-minute walks count. Add a few minutes each week.
- Aim for about 150 minutes a week of moderate activity, where you can talk but not sing.
- Add strength training twice a week. Simple bodyweight moves or resistance bands help rebuild muscle lost during treatment.
- Find support. The coaching in CHALLENGE was a big part of its success. Ask about cancer exercise programs at your hospital, YMCA, or a qualified cancer exercise trainer.
- Listen to your body. Fatigue is real. Gentle movement often helps it, but rest on hard days.
Movement benefits your mind as well. Research shows that walking, yoga, and strength training all help ease depression, which is common after a cancer diagnosis.
A Word of Caution About “Natural Cures”
Exercise works alongside proven treatment, not instead of it. Studies have found that people who choose alternative medicine in place of standard cancer treatment have a much higher risk of dying. The CHALLENGE participants all received surgery and chemotherapy first. The most powerful approach combines the best of medicine with healthy, natural habits.
The Bottom Line
For colon cancer survivors, a steady program of brisk walking and activity now has proof from a gold-standard trial that it improves survival. It is free, widely available, and good for nearly every other part of your health. If you or someone you love has been through cancer treatment, ask the care team about building exercise into the recovery plan.
Frequently Asked Questions
Is it safe to exercise during chemotherapy?
For many people, light to moderate exercise during treatment is safe and helps with fatigue. Your oncology team can tell you what is right for your situation.
Do I need a gym?
No. Most CHALLENGE participants walked. Bands, bodyweight exercises, gardening, and cycling all count too.
What if I was inactive before my diagnosis?
That describes many trial participants. They started slowly and built up over months.
Can exercise prevent cancer from developing in the first place?
Being active is linked to a lower risk of several cancers, though it cannot guarantee prevention. Combine it with not smoking, limiting alcohol, a fiber-rich diet, and recommended screenings.
Sources
- Courneya KS, Vardy JL, O’Callaghan CJ, et al. Structured Exercise after Adjuvant Chemotherapy for Colon Cancer. New England Journal of Medicine, 2025;393(1):13-25.
- Campbell KL, et al. Exercise Guidelines for Cancer Survivors: Consensus Statement from International Multidisciplinary Roundtable. Medicine & Science in Sports & Exercise, 2019.
- Johnson SB, et al. Use of Alternative Medicine for Cancer and Its Impact on Survival. Journal of the National Cancer Institute, 2018.
This article is for educational purposes and is not medical advice. Always discuss exercise plans with your healthcare team, especially during or after cancer treatment.
