How Cancer Treatments Disrupt the Gut Microbiome

Chemotherapy, radiation, long-term medications (like antibiotics or steroids), stress, and changes in appetite or eating patterns can significantly disrupt the diversity and balance of bacteria in the gut (PMID: 33081767).

This disruption is known as dysbiosis, and it’s extremely common during cancer treatment.

Common gut changes after treatment include:

• Bloating or abdominal discomfort

• Alternating constipation and diarrhoea

• Reduced appetite or early fullness

• Food intolerances

• Undesired weight gain

• Low energy and fatigue

But the impact goes deeper.

The Gut and Immunity

Around 70% of your immune system lives in your gut. If the gut microbiome is inflamed or imbalanced, it affects how the immune system responds, which matters a lot during recovery and long-term survivorship.

The Gut and Energy

Your gut bacteria help break down food and extract nutrients that your cells use to produce energy. When the microbiome is disrupted, even a healthy diet may not feel as nourishing.

The Gut and Weight Regulation

Hormones that influence appetite, metabolism, and fat storage are made and regulated in the gut. This helps explain why some survivors struggle with unexpected weight gain after treatment. Its not just about willpower, it’s physiology.

What Can Help? Practical Steps to Support Gut Healing

These strategies are gentle, well-researched, and suitable for most stages of recovery (but always personalised in clinical care).

1. Increase Plant Diversity

Aim for 30+ different plant foods per week. This includes vegetables, fruits, nuts, seeds, wholegrains, legumes, herbs, and spices. Each plant feeds different beneficial bacteria species and diversity builds resilience. You can find my 30+ Plant Food Planner here.

Simple ways to do this:

• Add a spoon of mixed seeds to breakfast

• Rotate your vegetables weekly. Instead of buying broccoli every week, choose cabbage, cauliflower, broccolini or bok choy instead

• Use fresh herbs generously

• Try new legumes like lentils, chickpeas, or black beans

2. Consider a Prebiotic Fibre Like PHGG

Partially Hydrolysed Guar Gum (PHGG) and Arabinogalactan are a gentle, clinically studied prebiotic fibres that supports beneficial bacteria, stool regularity, and gut lining repair without the bloating other fibres can trigger.

PHGG is particularly helpful for survivors experiencing alternating constipation and loose stools.

The key is to start with a low dose (1/4 teaspoon) and work your way up slowly to 1-2 tablespoons a day.

3. Reintroduce Probiotics Slowly and Strategically

Not all probiotics are the same and not all are helpful at every stage. Targeted strains can support immunity, repair gut lining, or help regulate mood and stress. Buying probiotics off the shelf at a supermarket, pharmacy or health food store without advice can cause more harm than good.

This is something I select very intentionally in clinic based on your individual needs, symptoms, treatment history and the latest research.

Your Gut Is Not an Afterthought. It’s Central to Recovery

Supporting your gut is about more than easing digestive discomfort. It’s about rebuilding your foundation: immune strength, energy, mental clarity, metabolic balance and emotional wellbeing.

Gut health is a cornerstone of my Cancer Survivorship Program.

If you're ready to feel supported, nourished, and understood, I’d love to support you.

👉 Click here to learn more and join the Cancer Survivorship Program.