Sugar, insulin and breast cancer: separating myth from mechanism

A common fear after a breast cancer diagnosis is that eating sugar will feed the cancer and make it grow faster. This idea comes partly from how PET scans work, where cancer cells take up a glucose-based tracer because they use a lot of energy. It is true that all cells, including cancer cells, use glucose for fuel. However, the body tightly controls blood sugar levels, releasing insulin and using stored energy, so eating a sweet does not directly feed a tumour, and cutting out all sugar does not starve cancer cells. Even without dietary sugar, the body makes glucose from other foods. The more important link is indirect. Diets high in added sugars and refined carbohydrates can lead to weight gain, high insulin levels and insulin resistance, and these are associated with higher breast cancer risk and possibly poorer outcomes. High insulin and related growth factors may encourage cell growth, and excess body fat raises oestrogen after menopause. Diabetes and poorly controlled blood sugar are also linked with more complications during cancer treatment. So the sensible approach is not to fear every grain of sugar, but to limit added sugars, sweets, sugary drinks and refined foods, choose whole grains and fibre-rich foods, stay active and maintain a healthy weight. Enjoying an occasional sweet at festivals is fine.

Sugar does not directly feed tumours

The body regulates blood sugar regardless of what you eat.

Insulin and weight matter

Diets high in sugar can raise insulin and weight, which are linked to risk.

Balance, not fear

Limit added sugars while enjoying occasional treats.

Blood sugar control matters for overall health and treatment.

During chemotherapy

Steroids can raise blood sugar. Tell your team about thirst or frequent urination.

If you have diabetes

Your diabetes medicines may need adjusting during treatment.

After treatment

Regular checks for diabetes are sensible, especially if you gained weight.

Everyday habits

Regular meals with fibre and protein, and daily activity, help steady blood sugar.

Carbohydrates are an important source of energy, especially during and after treatment. The aim is to choose carbohydrates that release energy slowly and come with fibre, rather than cutting them out.

Whole grains and millets

Whole wheat atta, brown or hand-pounded rice, ragi, jowar, bajra and oats contain more fibre and nutrients than refined flour and polished rice, and raise blood sugar more gradually.

Pulses and legumes

Dal, chana, rajma and moong combine carbohydrate with protein and fibre, helping keep blood sugar steady and supporting fullness.

Vegetables first

Starting a meal with vegetables or salad and filling half the plate with them slows the rise in blood sugar.

Watch portion size

Even healthy carbohydrates add up. A smaller mound of rice or fewer rotis, balanced with dal and vegetables, suits most people.

Pair carbohydrates with protein

Adding curd, eggs, paneer or dal to meals reduces blood sugar spikes and keeps energy stable.

Limit refined snacks

Maida-based biscuits, namkeen, white bread and bakery items are best kept occasional.

Hidden sugars

Check labels on packaged foods, sauces, health drinks and flavoured curds, which often contain added sugar.