Lifestyle and cancer: My 6M system

Your overall health affects how well you tolerate cancer treatment, how quickly you recover, and how strong you feel while you are living with and beyond cancer. Chemotherapy, radiotherapy, surgery and immunotherapy are often incredibly effective, but at the same time, they place real demands on the body: on energy, appetite, immunity, sleep, mood, muscle, and blood sugar regulation. When your body is already under strain, side effects hit harder and recovery takes longer. When your body is supported, you are more likely to stay on track with treatment, maintain quality of life, and get a better outcome.

This is not about being a perfectionist, and it is not about blaming anyone for their diagnosis. Cancer is complex: no lifestyle intervention can promise a particular outcome, and it’s important to be crystal clear that changing your diet is not a substitute for standard cancer treatment. What you absolutely can do, however, is improve the terrain in which treatment takes place. That means keeping weight and muscle in a safe range, smoothing out big swings in blood sugar, reducing avoidable inflammation, and supporting sleep and mental resilience.

I take a scientific approach to this, just as I do to the choice of chemotherapy or the way radiotherapy is planned. The approach below is a structured way to think about your lifestyle alongside your cancer treatment. I call it my 6M system: Metabolism, Movement, Microbiome, Maintenance, Mindset, and Momentum. It’s what worked for me when I had to navigate cancer as a patient, and it is designed to help you focus on what is achievable in the here-and-now.

The six domains are separate for clarity, but they interact constantly. Poor sleep makes glucose control harder. Anxiety can suppress appetite and reduce activity. Antibiotics may alter the gut microbiome, which can influence inflammation and bowel function. Muscle loss reduces insulin sensitivity and worsens fatigue. The point of a framework like this is not to make you do everything; it is to help you identify which levers matter most at a given stage.

The priority is often to achieve stability: maintaining nutrition, preserving muscle, staying safely active. After treatment, the focus can shift towards rebuilding fitness and improving long term metabolic health. Sometimes having come through to the other side of cancer treatment is a transformational moment that changes, for the better, how people approach life. For those living with incurable cancer, the goals may be different but no less important: maintaining strength and independence, limiting treatment interruptions, maximising effectiveness, and protecting long-term health while systemic therapy does its work.

Like many of the people I treat, I am sceptical of big claims and magical thinking. What tends to work best is consistent, evidence-informed support, delivered in a way that respects the reality of fatigue, stress, and uncertainty.

When people hear ‘metabolism’ they often think of weight alone. In cancer care, it is broader than that. Metabolism includes how your body handles glucose, how much insulin it needs to do so, where your body stores fat, how much muscle you carry, and how inflamed your system is day-to-day.

A key concept is insulin resistance. If the body becomes resistant to insulin, it needs higher hormone levels to keep glucose stable. High insulin and unstable glucose are linked to fatigue, cravings, reduced fitness, and a general sense that the body is not coping. This can be amplified by steroid medications (commonly used alongside chemotherapy as anti-sickness or anti-allergy premedication). In some patients, that may include modern diabetes and weight-management medicines such as GLP-1 receptor agonists (for example Ozempic or Mounjaro), which can improve glucose regulation and reduce appetite and weight gain — but they are not right for everyone during cancer treatment, and the decision needs to be individual and discussed with your doctor.

Another concept that matters more than most people realise is body composition, not just weight. Two people can have the same body mass index (BMI), but one may have robust muscle reserves and the other may have low muscle mass hidden under normal weight or even excess fat. This matters because muscle is not cosmetic. Muscle is a metabolic organ. It helps regulate glucose, supports immune function, protects mobility and balance, and buffers you against the stress of treatment.

Low muscle mass, often called sarcopenia, is common in cancer and is linked to higher treatment toxicity. In colorectal cancer, for example, studies have found a strong association between sarcopenia and severe chemo side effects. That link is one reason I pay attention to strength, protein intake, and functional capacity early rather than waiting until the end of treatment. There is also cancer cachexia, which is different from simple weight loss. Cachexia is a metabolic syndrome driven by the body’s inflammatory response to the cancer. People can lose weight and muscle even if they are eating. The right response is not guilt or a magic diet, but instead, it is early, expert support: input from the dietitian who works with me, symptom management, and a plan that prioritises protein and energy in a realistic way.

For most patients, the metabolic goal during treatment is not dramatic weight loss. It is avoiding a spiral of poor intake, muscle loss, worsening fatigue, and treatment delays. If weight reduction is appropriate, it is usually a post-treatment goal, done slowly, while preserving muscle and function.

Movement is medicine! It influences fatigue, mood, insulin sensitivity, muscle preservation, constipation, sleep quality, and confidence in your body. A personalised exercise programme improves all of this at once, with essentially no side effects. Guidelines consistently recommend that people with cancer avoid inactivity and aim for a blend of aerobic activity and strength work when feasible. Ideally, this means 150 minutes a week of moderate activity, and strength work at least twice weekly, adapted to the individual.

The most important part of that sentence is ‘adapted to the individual’. For someone in the middle of chemotherapy, 150 minutes can feel out-of-reach. That is fine. The goal is not to hit a number; it is to build a habit of movement that respects your energy and symptoms. Ten minutes of walking after meals, a few gentle resistance exercises with a band, or sitting-to-standing repetitions in the kitchen can be a meaningful start. The dose can increase as you stabilise.

Strength training deserves special mention. Cancer and its treatments can quietly erode muscle. Resistance exercise is one of the most reliable ways to protect it. Preserving muscle helps with balance, reduces falls risk, improves glucose control, and often reduces the sense that your body is shrinking around you. It also supports long-term independence, which matters whether your aim is cure, long-term control, or living well with metastatic disease.

Safety matters. There are times to dial exercise down, particularly if you have fever, uncontrolled pain, significant dizziness, unstable bone metastases, or severe anaemia. There are also times when gentle movement is exactly what helps: fatigue, stiffness, low mood, mild nausea, constipation, and sleep disruption often improve with light activity. If you are unsure, ask. This should be part of supportive care, not an extra burden you carry alone.

The microbiome is the community of bacteria living in your gut. It affects digestion, immune regulation, inflammation, and metabolism. It matters because it can influence how people feel during treatment, how their bowels behave, and potentially how the immune system responds to certain therapies. The science is moving quickly. Research shows that the gut microbiome can influence antitumour immunity and response to immunotherapy drugs. Gut health is worth protecting.

In general, a diverse diet that includes plant foods, adequate protein, and sensible fibre (tailored to symptoms) supports gut health. If you have diarrhoea or bowel inflammation, the answer is not simply ‘eat more fibre’ but ‘eat what you can tolerate, and treat the underlying cause’. Sometimes that means short-term low residue diets. Sometimes it means anti-diarrhoeal medication and hydration. Sometimes it means stool tests and antibiotics if infection is suspected. Microbiome-informed care is not DIY. It is careful, symptom-led, and individual.

Probiotics are a common question. They can be helpful in some contexts and unhelpful in others, particularly in immunosuppressed patients. If you are considering them, it is worth discussing first. The foundations tend to matter more: food variety where possible, symptom control, and avoiding unnecessary antibiotics.

Cancer treatment can disrupt sleep in different ways. Steroids can make people wired. Anxiety can make the mind race at 3 am. Pain can wake you. Reflux can flare when appetite changes. Hot flushes can appear after hormonal changes. When sleep becomes fragmented, everything else becomes harder: glucose control, mood regulation, appetite, exercise, concentration, and coping.

Sleep is not a luxury. It is maintenance therapy for the whole system. Research repeatedly links sleep disturbance with worse quality of life, higher fatigue, and increased emotional distress. What helps is rarely dramatic. It is often a combination of symptom control and behavioural structure. If pain is waking you, pain control needs improving. If steroids are the culprit, we can often modify timing or tapering. On the behavioural side, careful sleep hygiene has value and cognitive behavioural therapy for insomnia (CBT-I), which can be delivered in person or digitally, has a strong evidence base in people with cancer.

Supplements are another common area of confusion. Most patients do not need a cupboard full of pills, but targeted correction of deficiencies is useful. Vitamin D, iron, B12, folate or magnesium can be appropriate depending on blood tests – we take care of this for you. What is usually unhelpful is high-dose supplementation without a clear reason, particularly when it risks interactions with other drugs.

Mindset is often mishandled in cancer conversations. It can sound like people are being told to ‘stay positive’ as if optimism is a treatment in itself, but the obvious truth is that your mind and body interact, and understanding how can help you strengthen both.

The autonomic nervous system automatically controls vital functions such as heart rate, blood pressure, breathing, digestion, and the body’s stress response. It has two broad settings: a threat mode (fight-or-flight) and a restorative mode (rest-and-digest). Cancer treatment pushes many people towards ‘threat mode’ for understandable reasons. When that happens, appetite drops, sleep fragments, digestion changes, and inflammation can increase. The body becomes less efficient at recovery.

Autonomic regulation is therefore a practical tool. It can be as simple as a breathing technique used twice a day, a short guided meditation or spiritual practice such as prayer, or spending time in nature. The goal is not to become a hippie—it’s to give your nervous system repeated signals of safety, which can improve sleep, appetite, and emotional stability. This then has knock-on positive effects on your physical wellbeing.
Many people find that they need more than this. Counselling and psychotherapy have a key role to play here. We can arrange this for you.

You probably already know quite a lot about what you ‘should’ do – the problem is having the time, energy and mental space to develop a personalised plan, and deliver it consistently. My team and I will do the first part with you, and then help you to put it into action.

The first principle is choosing the smallest viable action. If you are deeply fatigued, it isn’t as simple as summoning the willpower to do something really strenuous but it might mean walking to the end of the road and back on good days, or doing two minutes of resistance band work while the kettle boils.
The second principle is linking habits to existing routines. For example: “after I brush my teeth, I do two minutes of breathing exercises,” or “after lunch, I walk for 30 minutes.” These are simple ‘if-then’ plans that reduce decision fatigue. They are particularly effective when treatment cycles make motivation fluctuate.
The third principle is re-designing your environment: the resistance band stays visible, your walking shoes stay by the door, you keep high-protein snacks where you can reach them. None of this is glamorous, or difficult, but it works because it reduces friction. It can also mean bigger changes: changing the way you approach work, for example.

The fourth principle is tracking progress. Gaining muscle, or seeing a reduction in inflammation in your blood tests, is feedback you will find profoundly motivating. Many people find that a simple record helps them keep going during the weeks when everything else feels uncertain.
Momentum also includes knowing when to pause. During severe side effects, infection, or recovery from major surgery, pushing harder can be counter-productive. Part of momentum is returning gently when the sudden storm passes.

‘More easily said than done’ is a phrase that might spring to mind now you’ve read through all this! And you’re correct. Getting this right requires careful personalisation by my team and me, and consistent effort from you. It can also be the thing that makes all the difference, so I discuss all of this in detail with people who choose to have a long course of treatment with me at one of the private hospitals where I offer chemotherapy and other drug treatments. If you’re under the care of another doctor, you should bring it up with them. This stuff is central to good cancer care, not a distraction from it.