Cancer and your weight: is it better to be fat or thin?

Your weight is an especially sensitive subject after a cancer diagnosis. Everyone knows that being overweight is linked to a higher risk of cancer but after diagnosis we are also told that it’s not a good idea to lose too much weight. I have found that the science around weight and cancer is not well understood, giving rise to all sorts of unhealthy advice. So what are the facts? 


There are plenty of studies to show that people who are overweight or obese have a higher risk of breast cancer; this seems to be particularly true pre-menopause. Being overweight tends to increase the action of aromatase enzyme which increases oestrogen production, especially in younger women. Excess body fat can also drive inflammation, another key factor in breast cancer development. The good news is that eating a healthy diet can help to reduce aromatase and inflammatory factors even if your weight doesn’t reduce as much as you would like.

Being bigger than the BMI charts say you should be isn’t always a problem: good health isn’t quite that easy to define. A bigger body size can still be metabolically healthy if you learn how to eat to control your insulin levels – which is an important part of the way I work with clients. And losing just 10% of your body weight if you are overweight is associated with better health outcomes.

Where you carry your weight can make a difference. A wobbly midriff with an ill-defined waist points to raised inflammatory molecules and hormones – a sign that you should pay attention to your diet, sleep and stress levels to find your hourglass again. Evenly-distributed chubbiness, or a lifelong pattern of heavy hips and thighs tends to be less of a worry.

Sometimes, a cancer diagnosis can exacerbate an existing weight problem. Stress has a major impact on your weight because it impacts metabolic pathways, affecting the way we make, use, and store energy. Some people lose weight when stressed and others tend to put it on, and if you’re prone to comfort eating, you’ll find it harder than ever to manage your diet. The right diet can support both stress and weight management and coaching can help you to manage stress in more effective ways.

Medical care tends to turn a blind eye to overweight and obese cancer patients because of the prevailing idea that you need to conserve your weight just in case things go wrong. That is a misguided notion and I’ll explain why.


The idea that we need to conserve our weight  – or even gain weight – after a cancer diagnosis is driven by a desire to avoid cachexia, a wasting condition which can affect people in advanced stages of cancer. I regularly meet cancer clients who have been thin all their lives and are advised to ‘put on a bit of weight’ by cancer nurses by ‘eating more stodge’ or by filling up on the sugary foods and drinks that are readily available in the cafés and vending machines in oncology units.

The belief that we can avoid cachexia by storing extra fat for a rainy day is a fundamental misunderstanding. Cachexia is not simply weight loss: it is a disordered metabolic state accompanied by uncontrollable inflammation which results in dramatic weight loss for you while supporting the growth of the cancer. Sadly, you cannot avoid cachexia by deliberately eating foods that make you fat. In fact sugary, processed foods drive insulin and inflammation and are more likely to lead to cachexia!

There is no evidence that lean people are at higher risk of cancer or have worse long term survival outcomes. So let’s drop the idea that you need to get fat to survive. A skinny body can be perfectly healthy and, while it can be a sign of a nervous disposition, it’s can also be a sign of a well-balanced metabolism.

If you want to put on weight in a healthy way you need to gently increase your exercise to build your muscle mass, not stuff yourself with junk food to build your fat mass!


If you follow a healthy diet (and find ways to manage your sleep and stress levels) your body will find its own healthy weight. It may not give you the perfect looks you crave but it will result in a healthier body composition and tissue microenvironment that helps to increase your chances of preventing the growth and spread of cancer.

A good anti-cancer diet should promote metabolic flexibility, keeping insulin at a healthy, low level which should prevent unwanted fat storage as well as helping to control cancer growth factors. When insulin levels are properly controlled it is easier for the body to manage other hormone levels too which should help to keep oestrogen and progesterone levels within a healthy range.

The diet programmes I design are always low in pro-inflammatory foods and packed full of anti-inflammatory nutrients that help to wake up your microbiome and your immune system, with the aim of restoring a healthy balance to your cell signalling and hormonal systems.

By contrast, the UK dietary guidelines are hopelessly unbalanced, encouraging overconsumption of starchy foods which are relatively low in cancer-fighting nutrients. Too much starch and sugar leads to too much insulin which causes inflammatory pressure and inappropriate growth signals (including excessive fat storage), both of which are linked to cancer. Ironically, while we can’t live without protein and fat, there is no absolute requirement for sugar and starch in the diet so it makes no sense to focus on these foods. Many experts think the advice to eat a lot of starchy food is the main factor driving the epidemics of cancer, diabetes, Alzheimer’s and obesity.

When we eat a more healthy balance of fats, proteins and carbohydrates we move to a more healthy metabolic state. Instead of being locked away by insulin, fat can be released from our body stores and used for energy. When insulin levels drop we lose our cravings for sweet or starchy foods and our energy levels become more dependable during the day. Burning fats for some of our energy can reduce oxidative stress and may even help to reduce cell replication for some cancers.

As long as you are not overeating foods laden with lots of fat AND sugar, there is no need to be afraid of eating fat if you have been diagnosed with cancer. It’s best to prioritise organic sources as fats have a particular affinity for xenoestrogens and other environmental toxins, then choose from saturated (animal and coconut), monounsaturated (olive oil and avocado) and omega 3 (oily fish, walnuts, flax oil and green veg) varieties. Try to minimise fats that are high in omega 6 which includes most refined and seed based oils (sunflower, safflower, maize/corn, rapeseed) as well as deep fried, hydrogenated and processed fats.  Fats are high in energy – so a little goes a long way – but they are also highly satiating, so they are great for alleviating hunger. All fats contain the same amount of energy whether they are solid or liquid at room temperature   – but butter and olive oil tend to be the most nutritious of the dietary fats, and there is some research to suggest that a higher olive oil intake may be associated with improved breast cancer survival.


Balancing your energy intake and output is an important part of an anti-cancer strategy. When we eat too much we give our bodies unwanted growth signals: if we eat too little we risk being deficient in important cancer-fighting nutrients.

A lot of people compensate for overeating by going to the gym to burn it off again. That’s not a good idea for cancer patients – it sends all the wrong signals to your cells. Exercise is important but your focus should be on gentle restorative exercise with occasional high intensity bursts, not regular body-bashing sessions at the gym to make up for dietary excess.

Looking at exercise in this way highlights the need to consume ‘just enough’ energy. Cancer is a disease of metabolic reprogramming. To put it simply, cancer cells have learned how to consume much more energy and commandeer more raw materials than healthy cells so that they can grow faster.

There are many theories around about how to starve cancer cells, and reducing your sugar and starch intake is an increasingly accepted way to do that, but unfortunately cancer cells are nothing if not adaptable – so reducing your sugar and following a ketogenic diet may not be enough.

Overeating anything – carbohydrates, fats or proteins – can give cancer cells an excuse to keep on growing. A good anti-cancer diet will seek to balance your energy intake to match your energy output.  If you’ve been taught that counting calories is the way to do that then now is a good time to abandon that idea. Low calorie diet foods leaving us tired and depleted, fuelling cravings and paving the way for metabolic disorders.

The drive to count calories has arguably been the single most damaging dietary change that has happened in our lifetime. The calorie theory been exploited by the diet industry to encourage us to eat low energy/low nutrient foods that may look appealing on the packet but actually leave us hungry and undernourished. When we eat smaller quantities of nutrient dense foods that satisfy the body’s sophisticated energy-sensing pathways in the gut and brain, appetite signals are shut down as nutrient requirements are met.


In summary, we are in a better position to overcome cancer when we are at a personal healthy weight, which will differ from one individual to another, but which comes from eating a nutrient-dense, energy-balanced diet designed to support healthy metabolism. The right diet should provide adequate nutrition while restoring insulin sensitivity. This results in immediate shedding of a few pounds for most people but it soon tails off if you are not overweight, allowing your body to find and maintain a healthy weight that is right for you. If that goal still remains elusive then it might be a good idea to get some professional nutritional advice.

I have struggled with my weight all my life and I know that maintaining a healthy weight is not always easy. If you need a higher level of support or a more personalised approach to the problem please book a follow-up appointment at



Onesti, J.K. & Guttridge, D.C., 2014. Inflammation Based Regulation of Cancer Cachexia. BioMed Research International, 2014, pp.1–7.

Paoli, A. et al., 2014. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European Journal of Clinical Nutrition, 68(5), pp.641–641.

O’Flanagan, C.H. et al., 2017. When less may be more: calorie restriction and response to cancer therapy. BMC Medicine, 15(1).

Mourouti, N., & Panagiotakos, D. B. (2016). The beneficial effect of a Mediterranean diet supplemented with extra virgin olive oil in the primary prevention of breast cancer among women at high cardiovascular risk in the PREDIMED Trial. Evidence Based Nursing, 19(3), 71-71.

Published by

Dawn Waldron

Highly experienced nutritional and nutrigenomic therapist helping people optimise diet, lifestyle and gene expression for health and happiness after breast cancer.