How a vegan diet can help prevent and manage cancer, and the foods to focus on

From scmp.com

Experts talk about the links between diet and disease and why one of the best reasons to eat a plant-based diet is to help prevent cancer 

The benefits of a vegan diet are well documented. From promoting a healthy weight and reducing our risk of heart disease and type 2 diabetes, to improving gut health and lowering blood pressure, countless studies have found good reason to consume more plant foods such as fruits, vegetables, whole grains, legumes, nuts and seeds.

Veganuary, the global January campaign, encourages people to go meat-free or reduce their intake of animal products such as dairy for the month. Besides promoting animal welfare and environmental protection, the campaign aims to raise awareness of the health advantages of consuming more plant foods.

One of the strongest reasons to switch to a plant-based diet is cancer prevention.

A study published in 2023 in the journal Nutrients suggests that the phytochemicals in plant foods help to inhibit cancer growth. Examples of phytochemicals include sulforaphane, found in cruciferous vegetables like broccoli, kale, bok choy and cabbage; and carotenoids, found in carrots, tomatoes and squash.

“Phytochemicals are found only in plants. These compounds fight harmful cell growth and reduce the risk of many types of cancer,” says Noah Praamsma, a dietitian at the Physicians Committee for Responsible Medicine, a non-profit health organisation based in Washington.

“They often do this by acting as antioxidants – compounds that stop harmful molecules, known as free radicals, from damaging DNA and other parts of your cells.”

The fibre in whole plant foods may also reduce our cancer risk. It helps to remove carcinogenic compounds from the gut, promotes a healthy community of gut bacteria that makes cancer-fighting compounds, and helps us maintain a lower body weight, Praamsma says. Being overweight is linked to greater inflammation in the body, which may heighten the risk of developing cancer.

A 2025 review by Chinese researchers published in the journal Food & Nutrition Research found that higher dietary fibre intake from plant sources is associated with a lower risk of developing and dying from several types of cancer, particularly cancers of the digestive and reproductive systems.

The researchers noted that increasing daily fibre intake – from about 7g (0.25oz) to 36g a day – could significantly reduce colon cancer risk.

As plant-centred diets tend to be higher in dietary fibre, rich in micronutrients and phytochemicals, and lower in calories, processed foods and saturated fat, they may also help cancer patients manage treatment side effects, recover more quickly and improve their long-term health.

“Some observational data suggest that plant-forward patterns may support faster recovery and fewer complications, largely because of better metabolic health and inflammation control,” says Karthika Thirugnanam, a clinical nutritionist and dietitian at Tucker Medical in Singapore who works with cancer patients.

However, she emphasises that during chemotherapy, radiation or post-surgery recovery, it is essential for people with cancer to consume adequate calories and protein.

“A poorly planned vegan or vegetarian diet that is too low in energy or protein can worsen outcomes through malnutrition and potential lean-mass loss,” she says.

When planning a plant-focused diet to support cancer treatments, Thirugnanam says to emphasise nutrient density, protein adequacy and energy sufficiency, and not merely plant exclusivity.

She recommends focusing on the following core foods:

• Legumes (beans, lentils, chickpeas, soy foods): These provide fibre, protein, iron and zinc, support glycaemic (blood sugar) control, and optimise gut health by improving microbiome diversity.

• Whole grains: These are associated with reduced colorectal cancer risk and improved insulin sensitivity. Examples include brown rice, oats, quinoa, and wholewheat bread and pasta.

• Vegetables and fruits: These supply folate, potassium, antioxidants and phytochemicals linked to lowering overall inflammation. Choose a variety of colours: they contain various phytonutrients that offer different health benefits.

• Nuts and seeds: Eaten in appropriate amounts, these provide healthy fats and minerals and have been associated with lower cancer mortality in observational studies.

• Healthy fats: Fat is necessary for calorie adequacy and absorption of fat-soluble vitamins and is particularly important during treatment when appetite is poor.

Choose fruit and vegetables in a variety of colours: they contain various phytonutrients that offer different health benefits. Photo: Shutterstock

It may be challenging for many people to give up meat, poultry, seafood, eggs and dairy products at once in favour of a completely plant-based diet. In this case, start by trying to fill your plate with as many plant foods as possible.

“If you are new to a whole food, plant-based diet, I recommend stocking your fridge with whatever foods you’re most likely to eat,” says Praamsma.

“The ‘perfect’ diet isn’t perfect if your taste buds aren’t on board and you start skipping the meals you planned in favour of food with animal products. Start by finding vegan recipes that you enjoy and that are sustainable for you right now.”

Avoid or minimise ultra-processed snacks like crisps and heavily refined mock meats, deep-fried food like French fries, and refined carbohydrates including sugary packaged cereals, white bread, pastries and cakes, Thirugnanam says.

These foods tend to be devoid of important nutrients while being high in fat, calories, sugar and sodium. They may also increase cancer risk. A study published in 2023 in the journal Clinical Nutrition found a consistent significant association between the intake of ultra-processed foods and the risk of overall and several cancers, including colorectal, breast and pancreatic cancer.

Louis Yap, a senior dietitian at Mount Elizabeth Novena Hospital in Singapore, stresses the importance of supplementation if you are considering eliminating animal products from your diet.

“A strict vegan diet may lead to deficiencies in vitamin B12, iron, zinc and calcium. Supplementing your diet, or incorporating nutrient-dense fortified cereals, can help,” he says.

Patients undergoing cancer treatment may experience side effects that affect their appetite and nutrient intake, Yap says.

“While a vegan diet offers antioxidant benefits, it tends to be lower in calories, which can increase the risk of weight loss and loss of muscle mass. This can significantly affect treatment outcomes, recovery and long-term survival.”

The degree of dietary restriction should be based on the patient’s condition and nutritional needs. Yap suggests consulting a dietitian to understand how to manage your dietary needs during specific phases of cancer treatment.

Yap, 38, is himself a cancer survivor. At 20, he was diagnosed with Hodgkin’s lymphoma, and his cancer journey inspired him to pursue a career in dietetics.

He is now cancer-free, and while his diet is not plant-based, he does consume plenty of fruits, vegetables and whole grains every day. He also snacks on nuts and popcorn, and makes sure that any animal protein he eats is first removed of its fat and skin. He enjoys the occasional treat, like bubble tea without sugar.

“I strongly believe in the connection between diet and disease. Eating too many unhealthy foods can increase the risk of disease, while consuming more vegetables and fruits can help reduce that risk,” he says.

“At the same time, I believe food should be enjoyed. The key is moderation – pair balanced eating with regular exercise, stay mindful of your mental health, and seek support when you need it.”

Thirugnanam adds that for a plant-based diet to be most protective, it should provide nourishment.

“That means it helps you meet your calorie needs, get enough protein, cover key micronutrients and support healthy body composition and metabolic health, especially during cancer treatment or recovery.”

She adds that nutritional adequacy and overall diet quality consistently matter more than dietary labels alone.

“That nuance is essential to understand if you want plant-based eating to be both effective and sustainable.”

https://www.scmp.com/lifestyle/health-wellness/article/3340828/how-vegan-diet-can-help-prevent-and-manage-cancer-and-foods-focus