Weight gain on endocrine therapy: cause and management

Many women gain weight during and after breast cancer treatment, and hormone therapy is often blamed. The picture is more complicated. Large studies of tamoxifen and aromatase inhibitors have generally not shown that the tablets themselves cause large weight gain. Instead, weight tends to rise because of several things happening together: menopause or a sudden drop in oestrogen, which shifts fat towards the waist; less physical activity during treatment; tiredness; joint pain that makes exercise harder; steroids given with chemotherapy; comfort eating during a stressful time; and a slower metabolism with age. The good news is that these causes can usually be addressed.

Why weight matters after breast cancer

Keeping to a healthy weight supports heart health, blood sugar, joints, energy and mood. Some studies suggest that weight gain after diagnosis is linked with a higher chance of recurrence for some women, which is one more reason to take it seriously, without blame.

What helps most

A combination of regular physical activity, especially walking and strength training, a balanced diet with sensible portions, good sleep and support from family or a dietitian works better than any single strict diet.

When to look for another cause

Rapid weight gain, swelling of the legs or face, breathlessness or feeling very tired and cold may point to fluid retention, thyroid problems or other conditions, and should be checked.

Losing weight after breast cancer treatment is genuinely harder for many women than it was before, because of changes in hormones, muscle, energy and routine. Slow, steady progress is realistic and far more lasting than rapid dieting.

Crash diets can backfire

Very low-calorie diets can cause muscle loss, tiredness and rebound weight gain. They can also leave you short of nutrients your body needs while recovering.

Stopping hormone tablets is not the answer

Because the tablets are rarely the main cause of weight gain, stopping them usually does not solve the problem, and it can reduce protection against recurrence. Talk to your team before making any change.

Health improves even with modest weight loss

Losing even a small amount of weight, and becoming more active, improves blood pressure, blood sugar, joint pain and energy, even if you never reach a so-called ideal weight.

What this page cannot tell you

It cannot tell you what is behind your own weight change. Ask your team to review your medicines, thyroid and other possible causes.

Tiredness and joint pain can make exercise feel impossible, yet gentle activity usually improves both. The key is to start small and build gradually.

Begin with short walks

Ten minutes after meals, two or three times a day, is a good start and also helps blood sugar. Increase the time a little each week.

Strength without a gym

Sitting and standing from a chair, wall push-ups, light water bottles as weights and resistance bands build muscle at home.

Choose what you enjoy

Yoga, dancing, gardening, swimming or walking with a friend are all helpful. Enjoyment is what keeps people going for years.