Nutrition and Gut Health After Cancer Treatment
Featuring: Robert Thomas, MD
In short
Consultant oncologist Robert Thomas shares three decades of nutrition and lifestyle research to help cancer patients and survivors reduce the risk of recurrence, manage treatment side effects, and support gut health. The session covers what to eat more of (phytochemical-rich whole foods, fermented foods, prebiotic fibers), what to cut back on (burnt and processed meats, deep-fried foods, excessive sugar), and how gut health directly shapes how well treatments like immunotherapy and chemotherapy work.
- •Aim for 30 different fruits and vegetables per week and add fermented foods like kefir or kimchi regularly — variety in plant foods feeds a healthier gut microbiome.
- •Poor gut health can reduce immunotherapy effectiveness by up to 40%, so ask your care team whether a Lactobacillus probiotic and more prebiotic fiber (chicory, leeks, garlic, beans) make sense for you.
- •Whole foods outperform isolated supplements: phytochemicals from turmeric, broccoli, pomegranate, and green tea work together in ways that extracted single ingredients do not.
- •High-dose supplements of vitamin E, selenium, folic acid, and vitamin A carry real risks in cancer patients — bring any supplement you're considering to your oncologist before starting.
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Brad Power October 1, 2025 “The evidence now is becoming more and more convincing that it is worth helping yourself. After cancer, everybody benefits from self-help strategies, although you shouldn't blame someone or yourself if your cancer is progressing or comes back that you haven't tried hard enough. Because it's all about reducing the odds of progression and reducing the odds of your cancer coming back.
Meeting Summary
Cancer patients in the middle of treatment or navigating life after it are often fighting fatigue, low mood, joint pains, weight gain, and many other troublesome side effects and want to do things that will help them improve their quality of life and length of life.
Decades of clinical research confirm that structured lifestyle interventions - including personalized exercise, nutrition, and stress relief - are not “extras,” but evidence-based tools that can reduce treatment side effects, improve quality of life, and even lower the risk of recurrence. Yet if you look into complementary therapies, you face an uncertainty about what’s safe and effective.
You may struggle to find trustworthy guidance to make these practices part of daily life.
Professor Robert Thomas , MD, Consultant Oncologist Bedford & Addenbrooke’s Cambridge University Hospitals, Professor of Exercise & Nutritional Science University of Bedfordshire, Oncology Lead at The Royal London Hospital for Integrative Medicine and author of How to Live, is uniquely qualified to lead a discussion on nutrition and health after a cancer diagnosis.
He is a highly respected UK ‐based oncologist who combines expert cancer care with a strong focus on lifestyle nutrition, and integrative therapies. His clinical specialties include breast, prostate and bladder cancers, employing treatments such as chemotherapy, radiotherapy, hormone and biological therapies.
He also leads a Research Unit that reported that a nutritional intervention can help menopausal symptoms in women after breast cancer and led the UK's National Covid intervention study.
He recently present at ASCO Urology this year, the results of the world's largest nutritional intervention study for prostate cancer which found that boosting the diet with a phytochemical rich supplement called YourPhyto and gut health with a novel Lactobacillus probiotic, called Yourgutplus slowed prostate cancer progression, improved urinary symptoms, reduced markers of inflammation and increased grip strength.
Why should you learn about lifestyle interventions to manage your cancer care?
•Slow your cancer progression
•Reduce inflammation
•Improve treatment response and outcomes
•Reduce side effects
•Enhance overall health and well-being and your body's natural healing processes What lifestyle interventions should you consider?
•Diet: Consume a diet rich in phytochemicals from fruits, vegetables, and herbs; reduce processed and smoked meats; incorporate fermented foods like kefir and kimchi; eat whole foods instead of isolated supplements; consider targeted, evidence based supplements with phytochemicals and combinations like turmeric, pomegranate, broccoli, ginger, cranberry and green tea; and maintain balanced protein intake (3 times weekly meat, mostly plant-based proteins)
•Gut health: Take probiotics, especially lactobacillus; increase prebiotic fiber intake; consume foods that support healthy bacteria growth
•Lifestyle: Get regular exercise, maintain a healthy body weight, avoid smoking, try to manage stress What are the connections between nutrition, gut health, and cancer?
•Gut health impacts inflammation and immune response. A "leaky gut" can allow toxins to enter the body, triggering systemic inflammation that creates an environment conducive to cancer development.
•The gut microbiome plays a crucial role in digesting phytochemicals, absorbing vitamin D, detoxifying potential carcinogens, and supporting immune system function.
•Poor gut health can negatively affect cancer treatments by reducing the effectiveness of immunotherapy by up to 40%, increasing the risk of treatment side effects, and reducing the response to chemotherapy and radiotherapy.
•A diet rich in phytochemicals, prebiotics, and probiotics can reduce inflammation, improve the gut bacteria balance, slow cancer progression, and enhance overall treatment outcomes. What can you do to improve your nutrition and gut health?
•Eat diverse, colorful fruits and vegetables (e.g., 30 different vegetables and fruits per week)
•Eat fermented foods like kefir and kimchi
•Avoid processed foods and excessive sugar, especially processed sugar, omega-6 rich foods, and deep-fried foods
•Incorporate fiber-rich foods to support healthy gut bacteria
•Eat medicinal mushrooms (e.g., turkey tail, lion's mane, reishi)
•Eat prebiotic fibers (e.g., chicory, beans, leeks, garlic, nuts)
•Take probiotics, particularly lactobacillus
•Eat whole foods rich in phytochemicals
•Consider supplements with inulin, Vitamin D, Phytochemical-rich ingredients
•Introduce fiber slowly to allow gut bacteria to adapt
•Include herbs and spices with meals to enhance nutrient absorption How can you stick to a lifestyle program?
•Make gradual changes - introduce new foods slowly to avoid digestive issues
•Be patient with dietary changes, as your body needs time to adapt
•Remember that small, consistent improvements can make a significant difference in overall health How can you learn more about nutrition, gut health, and cancer tailored to your diagnosis and treatment?
•Consult with an integrative oncologist or nutritionist specializing in cancer care
•Attend support groups and patient education programs; find patient networks that share evidence-based nutritional information
•Review reputable sources like cancer research centers
•Work with your medical team to develop a personalized nutrition plan
•Participate in clinical trials focused on nutrition and cancer
•Stay updated on the latest research through medical conferences and publications
•For more from Professor Thomas, please see his blog: Keep-healthy.com, Youtube: ProfThomasMD, Instagram: @HealthNetUK, and LinkedIn: https://www.linkedin.com/in/profthomas/
•For notes and recordings from previous Cancer Patient Lab webinars on lifestyle and nutrition in cancer, please see:
•
•"A Patient’s View on Nutrition, Supplements, Integrative Oncology, and Complementary Therapies"
•The information and opinions expressed on this website or platform, or during discussions and presentations (both verbal and written) are not intended as health care recommendations or medical advice by Cancer Patient Lab, its principals, presenters, participants, or representatives for any medical treatment, product, or course of action. You should always consult a doctor about your specific situation before pursuing any health care program, treatment, product or other course of action that might affect your health. Meeting Notes KEYWORDS Nutrition, gut microbiome, cancer, prostate cancer, phytochemicals, probiotics, Omega-3, vitamin E, inflammation, dietary supplements, active surveillance, PSA progression, immunotherapy, prebiotic fibers, medicinal mushrooms. SPEAKERS Robert Thomas (87%), Brad Power (10%), Bruno Vinel (2%), Susanne Folkesson (1%) CHAT CONTRIBUTORS Allen Morris, Bruno Vinel, Russ Hollyer, Jessica, Elizabeth Clemmons, Rick Davis, Dianne Dowling, Ginny, Michael Penny, Hilary SUMMARY Professor Robert Thomas discussed the impact of nutrition and gut microbiome on cancer, particularly prostate cancer. He highlighted the importance of avoiding burnt meats and consuming a balanced diet rich in phytochemicals and omega-3. He emphasized the benefits of probiotics, especially Lactobacillus, and a supplement containing phytochemicals and organic ginger. His study showed that combining phytochemicals with probiotics significantly slowed PSA progression and improved urinary symptoms. He also noted the role of gut health in cancer treatment outcomes and the potential of medicinal mushrooms for inflammation reduction. OUTLINE Introductions
•Professor Robert Thomas has a focus on integrative oncology, nutrition, the gut microbiome, and cancer.
•This presentation was delivered at the British Urology Group Conference.
•Topics covered include what to avoid, fish oils, vitamins, gut health, and phytochemical- rich foods.
•Diet and lifestyle are important in cancer treatment and prevention.
•Data from various studies and trials highlight conflicting evidence on certain nutritional supplements. What to Avoid in Diet
•You should avoid burnt and smoked meats, which are linked to cancer.
•"What's on the plate matters" – you need to consume meat with vegetables, fruits, herbs, and spices.
•The metabolization of nitrates in meats can lead to harmful nitrous amines, but the presence of phytochemicals can convert them into healthier nitric oxide.
•You should focus on the overall dietary approach rather than individual foods. Omega-3 and Fish Oil
•There is conflicting evidence on the impact of omega-3 on prostate cancer risk.
•Studies show both benefits and risks of omega-3 intake, including the CATFISH study presented at ASCO.
•The reduction of omega-6 rich foods, such as deep-fried foods, corn oil, and palm oil, may be more beneficial than increasing omega-3 intake.
•Oily fish and taking high-quality supplements should be consumed in limited amounts. Supplements and Vitamins
•There are potential risks of certain supplements, including vitamin E, selenium, folic acid, and vitamin A.
•High doses of direct antioxidants can interfere with the body's natural processes and increase cancer risk.
•Extracted phytochemicals, such as lycopene and soy isoflavones, may not have the same beneficial effects as whole foods.
•Consuming whole foods is important for their synergistic effects. Gut Health and Cancer
•Gut health has a role in cancer prevention and treatment.
•A leaky gut can have an impact on systemic inflammation, immune response, and cancer risk.
•The gut microbiome helps digest phytochemicals, absorb vitamin D, and detoxify carcinogens.
•Poor gut health is linked to worse outcomes in cancer patients undergoing immunotherapy, radiotherapy, and chemotherapy. Phytochemicals and Probiotics
•Phytochemicals can reduce cancer progression and improve urinary symptoms.
•Combining a phytochemical-rich supplements with a specific probiotic can enhance their effects.
•The study presented at ASCO showed that a combination of phytochemicals and probiotics led to significant reductions in PSA progression.
•The study also found improvements in markers of inflammation, grip strength, and testosterone levels. Active Surveillance and Lifestyle Interventions
•Lifestyle interventions can help men on active surveillance for prostate cancer.
•A study involved a phytochemical-rich supplement and a probiotic, with positive results in slowing PSA progression.
•The combination of phytochemicals and probiotics led to significant reductions in PSA progression and improvements in MRI findings.
•The study also showed improvements in urinary symptoms and markers of longevity. Future Research and Applications
•There is ongoing research on the use of phytochemical-rich supplements in women with side effects from cancer treatments.
•The potential benefits of these interventions include improving quality of life and reducing side effects.
Full transcript
Brad Power This is the Cancer Patient Lab. We're honored to have with us Professor Robert Thomas. He's going to be talking about nutrition, gut microbiome, cancer, prostate cancer, and a whole variety of things. Professor Thomas was introduced to me by a number of people, most notably Rob Newton, who's going to be speaking in another week or so on exercise and cancer. He recommended Professor Thomas for his work.
He will give his bio and introduce himself more thoroughly. First of all, this is medical information. It is not advice. We try to arm our patients with information they can take to their medical team. We ar are a nonprofit, 501(c)(3), and we depend on the kindness of donations. If you would be so inclined, we would appreciate it. There's a Donate button on our website.
Robert Thomas
I'm a consultant oncologist at Bedford and Cambridge University trusts.
I'm a head of integrative oncology at UCLH London, and I have run a lifestyle research lab for the last 30 years, looking at strategies to empower patients, to help them look after themselves during cancer treatments and afterwards, to reduce side effects and improve outcomes, mainly to produce research evidence, so we can first of all find out what to do, but also to persuade colleagues to take integrative and lifestyle medicine a bit more seriously.
I'm going to give a little bit of a talk which I presented to the British urology group conference a couple of weeks ago. But although this talk concentrates mainly on prostate cancer, a lot of what we do is not just for prostate cancer, so I'd welcome a discussion for any types of cancer. But a lot of this data does extrapolate to other tumor types. So next slide please.
Over the years, I've had some sponsorship companies, etc, but all the nutritional supplements used in this presentation were supplied free to the trials unit, so we got some benefit for the trust, but there's no individual financial connection to me or anyone on the trials unit. Next slide, please. So I'm just going to cover today, you know. So what to avoid? A bit about fish oils, because there was some presentation in ASCO urology this year.
Bit about vitamins, gut health, and the latest in phytochemical rich food supplement and intake. Next slide, please. So what to avoid? Well, I mean, there's lots of things we need to avoid. Smoking, not you know, sedentary lifestyle, but in terms of cancer, sort of burnt meats, or meats which are smoked seems to be number one on the naughty list. So anyone who likes their smoked barbecues should be feeling guilty right now next slide.
And it's not just about what we there's a famous chef in Britain called Dr rupee who always says, what's on the plate matters. So if you have, you know, some meat, for example, which has lots of health benefits but lots of risks.
If you have it on its own or with some sweet, you know, drink without any vegetables or fruit or herbs and spices, it tends the nitrates within them tend to get metabolized into nitrous amines, which is actually the thing which damages your DNA and causes mutations.
But if you have it with herbs, spices, vitamin C, phytochemicals, which you get in fruit and veg or herbs and spice, it tends to be metabolized into nitric oxide, which is actually healthy. It causes vasodilation and improved tissue diffusion. So. So yeah, it's about what's on your plate in general, rather than eating any individual thing. But next slide. I'd like to talk a bit about Omega three.
Now, we all know that we need a lot of Omega three in our diet, and omega six and other essential fatty acids. But there seemed to be a bit of confusion amongst patients whether we should be taking supplements, etc. Next slide.
So originally, but the health Stacey Canfield from the health professionals follow up study from California published a paper showing that men, for example, who had more fish and had more omega three in the diet had a lower risk of prostate cancer. So that seems quite obvious and beneficial. Next slide. The trouble is, since then, there was a Japanese study showing that people who have a lot of fish intake have a higher risk of prostate cancer.
The prostate prevention study which actually looked at finasteride or not, found that people who had more omega three had a higher risk of prostate cancer. The Select study which looked at vitamin E, selenium and against placebo, did a sub analysis and found that omega three correlated with an increased risk.
And the British biobank study recently showed the same thing, although it showed for breast cancer, taking supplements reduce the risk, but for prostate cancers actually increased risk. Next slide please. So you know, that's all a bit confusing. And then suddenly, in ASCO this year in San Francisco, the catfish study was presented, which shows that men who took a supplement of Omega three actually had a reduced risk of prostate cancer progression.
So if anyone can tell me what the answer is, I'll be all ears. My take on this data, which is very conflicting, and I can see why patients are confused, is that this study also looked at reducing Omega six rich foods, but they categorize these as deep fried foods, corn oil, palm oil, and things like this.
So my take on this is, is actually it's the reduction in these Omega six, rich, cheap oils which actually gave most of the benefit, rather than adding more omega three. And the reason is that omega three is usually preserved with vitamin E, and vitamin E in the Select study showed that it's too much of an antioxidant actually increases the risk of prostate cancer.
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