Breast cancer is the most common cancer affecting South African women. Being diagnosed, navigating treatment and trying to manage your weight all at once can feel overwhelming. Many women are surprised to find they gain rather than lose weight during chemotherapy — the opposite of what they expected. This guide is for South African women who want to understand why that happens, what they can safely do during treatment, how to tackle the excess weight after treatment, and where to find support from local organisations like CANSA and the Breast Cancer Foundation SA.
The relationship between body weight and breast cancer runs in both directions:
Excess body fat — particularly postmenopausal obesity — is a well-established risk factor for breast cancer. Adipose tissue contains aromatase, which converts androgens to oestrogen. In postmenopausal women (who no longer produce oestrogen from the ovaries), fat tissue becomes the primary source of circulating oestrogen. Higher oestrogen drives growth of oestrogen-receptor-positive (ER+) breast cancers, which represent about 75% of breast cancer diagnoses.
Research from the World Cancer Research Fund estimates that maintaining a healthy weight could prevent up to 17% of postmenopausal breast cancer cases globally. In South Africa, where overweight and obesity rates are among the highest in sub-Saharan Africa, this is a significant preventable fraction.
Counterintuitively, breast cancer treatment — particularly chemotherapy — frequently causes weight gain rather than loss. Average weight gain during adjuvant breast cancer chemotherapy is 2-6 kg, and some women gain significantly more. The mechanisms include:
During chemotherapy, radiation or other active treatment, the goal is to maintain your weight, eat nutritiously, manage side effects and stay as active as you safely can. This is not the time for aggressive dieting.
When corticosteroids are given on chemo days, hunger can become intense. Have healthy, filling foods pre-prepared so hunger doesn't lead to binge eating of high-calorie junk food. Protein-rich snacks (boiled eggs, Greek yoghurt, edamame, cottage cheese) are particularly helpful — protein is the most satiating macronutrient and helps preserve muscle mass during treatment.
This is one of the most evidence-supported interventions available — and it's free. Multiple large trials and meta-analyses show that exercise during breast cancer treatment:
If you have had axillary lymph node dissection or are at risk of lymphoedema, arm exercise requires care. Work with a physiotherapist or lymphoedema specialist before doing upper-body resistance training. Guidelines from the South African Oncology Consortium (SAOC) support supervised progressive resistance exercise for women with or at risk of lymphoedema — it does not worsen and may actually reduce lymphoedema severity.
No single food causes or cures cancer. But the overall pattern of what you eat over time significantly influences cancer risk, recurrence risk and survival outcomes.
The Mediterranean diet has the strongest evidence base for reducing breast cancer recurrence risk and improving survival. The DIANA-5 trial (the most rigorous dietary RCT in breast cancer) found that a Mediterranean-macrobiotic diet significantly reduced recurrence rates in hormone-sensitive breast cancer patients.
Key elements:
Alcohol is one of the most clearly established risk factors for breast cancer — and for recurrence in breast cancer survivors. Even moderate alcohol consumption (1 drink per day) increases breast cancer risk by 7-10%. There is no safe lower threshold. The South African oncology community, like CANSA, recommends complete alcohol abstinence for breast cancer patients and survivors.
Broccoli, cauliflower, Brussels sprouts, kale and cabbage contain sulforaphane and indole-3-carbinol, compounds that support oestrogen detoxification and have demonstrated anti-cancer properties in laboratory and observational studies. Include at least one serving daily.
Many breast cancer patients are told to avoid soy because of its phytoestrogen content. Current evidence does not support this — dietary soy (tofu, edamame, soy milk) does not worsen outcomes in breast cancer patients and may actually be protective in Asian populations who consume it regularly from childhood. High-dose isoflavone supplements are a different matter — discuss with your oncologist. Regular food-form soy is fine in moderation.
Vitamin D deficiency is associated with worse breast cancer outcomes. Have your GP check your 25-OH vitamin D level. Target: 75-100 nmol/L. Supplement with 2,000 IU D3 daily if deficient — particularly important in South Africa where indoor work means many people are paradoxically D-deficient despite abundant sunshine.
Once you have completed active treatment (chemotherapy, radiation, surgery) and your oncologist has cleared you, structured weight loss is appropriate and beneficial:
Research shows that post-treatment weight loss in overweight breast cancer survivors significantly improves survival outcomes. The WINS trial found that a low-fat dietary intervention reducing fat by 33g daily reduced relapse risk by 24% in ER-negative breast cancer patients.
If you're on tamoxifen or an aromatase inhibitor (letrozole, anastrozole, exemestane) for 5-10 years, long-term weight management requires understanding their specific effects:
Tamoxifen can cause fluid retention and some women report weight gain. Regular exercise and a low-salt diet help manage fluid. Tamoxifen is associated with fatty liver (NAFLD) in some patients — another reason to maintain a healthy weight and limit alcohol entirely.
AIs (used in postmenopausal ER+ breast cancer) cause joint and muscle pain (arthralgia) in up to 50% of patients — which severely limits exercise. Strategies:
You don't have to navigate this alone. South Africa has several excellent organisations supporting breast cancer patients:
Breast cancer is a prescribed minimum benefit (PMB) condition in South Africa. All registered medical aids must cover the diagnosis, treatment and management of breast cancer — including chemotherapy, radiation, surgery, hormone therapy and recommended follow-up. This includes oncology dietitian consultations, which are generally covered under the oncology PMB benefit. Keep records of all treatment and claim accordingly — and appeal if a claim is rejected, as PMB denials are often overturned.
Navigating breast cancer and managing your weight? You're not alone. CANSA's helpline (0800 22 66 22) is available weekdays, and ADSA's dietitian directory at adsa.org.za can connect you with an oncology dietitian who understands exactly what your body needs right now. Read our anti-inflammatory diet guide for more on Mediterranean eating patterns suited to South African tastes and budgets.
Yes — many breast cancer regimens cause 2-6kg average weight gain through steroid appetite stimulation, reduced activity, treatment-induced menopause and hormonal shifts. This is common and manageable with the right strategies.
Strict caloric restriction is not recommended during active chemotherapy or radiation — your body needs nutrition for treatment tolerance and healing. Focus on healthy eating and gentle activity during treatment. Structured weight loss is better pursued post-treatment with oncologist clearance.
A Mediterranean-style diet: abundant vegetables (especially cruciferous), fruits, whole grains, legumes, oily fish and olive oil. Limit red and processed meat, and eliminate alcohol entirely — even moderate alcohol intake is associated with increased breast cancer recurrence risk.
Yes — gentle exercise (walking, yoga, light resistance) is strongly recommended during chemotherapy. It reduces fatigue, improves mood, preserves muscle and helps limit treatment-related weight gain. Always check with your oncologist about timing relative to treatment days and blood count status.
CANSA at cansa.org.za (helpline 0800 22 66 22), ADSA at adsa.org.za for registered oncology dietitians, and the Breast Cancer Foundation SA at bcfsa.co.za. Oncology dietitian consultations are covered under the PMB oncology benefit by all registered medical aids.