Diet and cancer: what nutritional prevention can provide
IRIS Prévention
8 July 2026
Approximately 40% of cancers are preventable: and diet plays a direct role in this prevention.
Cancer is a reality that affects one in two families in France. This is a subject that deserves to be approached with rigor and respect, without false promises or alarmist speeches. What I know for certain is that scientific research in nutritional oncology has made considerable progress over the past twenty years. According to the World Cancer Research Fund (WCRF) and the International Agency for Research on Cancer (IARC), approximately 30 to 40% of the most common cancers are preventable through lifestyle changes, including diet. This article offers you a rigorous and nuanced synthesis of what science is establishing today - to act on what is actionable, without feeling guilty about what is not.
1. What science establishes with solidity
It is important to distinguish the levels of evidence in nutritional oncology. The IARC uses a rigorous classification: group 1 (definite carcinogen), group 2A (probable), group 2B (possible), group 3 (unclassifiable). Here are the best established associations:
Factor food
IARC Level of Evidence
Cancers concerned
Deli meats and processed meats
Red meat (>500g/week)
Group 2A - Likely
Colorectal cancer. The risk increases with regular and heavy consumption.
Alcohol
Group 1 - Certain
Mouth, throat, larynx, esophagus, liver, colon-rectum, breast. The risk exists from the first consumption.
Overweight and obesity
Group 1 - Certain
13 types of associated cancers including breast, colorectal, endometrial, kidney, pancreas.
Dietary fibers (protective effect)
Fruits and vegetables (protective effect)
Probable evidence
Digestive cancers, lung, throat. Via antioxidants, fibers and phytochemicals.
Aflatoxins (mold on food)
Group 1 - Certain
Liver cancer. Contamination of poorly preserved cereals and legumes.
Salt and very dirty foods
2. Mechanisms: how diet influences carcinogenesisUnderstanding the mechanisms by which diet influences the development of cancer allows us to better understand why these associations are biologically plausible:
●Oxidative stress and free radicals: free radicals can damage the DNA of cells, a key step in the initiation of the cancer process. Food antioxidants (vitamins C' and E, polyphenols, carotenoids) neutralize these free radicals and protect the integrity of DNA.
●Chronic inflammation: persistent systemic inflammation creates an environment favorable to abnormal cell proliferation. Omega-3 fatty acids, fiber (via butyrate production) and polyphenols reduce this inflammation.
●N-nitrose compounds and heterocyclic amines: cooking meat at high temperatures (grilling, frying) generates heterocyclic amines and polycyclic aromatic hydrocarbons (PAH), potentially mutagenic compounds. The salting and smoking of cold meats generates nitrosamines, established carcinogenic compounds.
●The microbiota-cancer axis: the intestinal microbiota plays an increasingly recognized role in the prevention or promotion of certain cancers, particularly colorectal. A diverse microbiota rich in butyrate-producing species exerts a protective effect on the colonic mucosa.
●Overweight and hormones: excess adipose tissue produces estrogens, insulin and growth factors (IGF-1) which promote cell proliferation. This is the main mechanism linking obesity to hormone-dependent cancers (breast, endometrial, prostate).
3. Recommendations from the World Cancer Research Fund
The WCRF regularly publishes a synthesis of scientific evidence in the form of practical recommendations. The 2018 report, covering more than 51 million people included in the studies analyzed, makes 10 recommendations:
●Maintain a healthy body weight, within the normal BMI range
●Be physically active on a daily basis and limit a sedentary lifestyle
●Eat whole foods: whole grains, legumes, fruits and vegetables as a basis of the diet
●Limit high-calorie foods, fast foods and sugary drinks
●Limit red meat to 350-500 g per week and cold meats as much as possible
●Limit alcohol - and if possible not consume it at all in terms of cancer risk
●Limit salt consumption and foods preserved in salt
●Do not use food supplements to protect against cancer (unless medically indicated)
●Breastfeed infants if possible (maternal protection against breast cancer)
●After a diagnosis of cancer, follow these recommendations as part of oncological follow-up
4. What protects: foods and habits to favor
Beyond risk factors, nutritional prevention of cancer also involves positively protective eating habits:
●Dietary fiber: this is the best supported recommendation. Each increase of 10 g of fiber per day is associated with a 10% reduction in the risk of colorectal cancer according to several meta-analyses. Legumes, whole grains and vegetables are the champions. Objective: 25 to 30 g of fiber per day.
●Crucifers: broccoli, cabbage, Brussels sprouts, cauliflower, arugula, radishes. They contain glucosinolates which transform into isothiocyanates when chewed - compounds with antiproliferative properties documented on many types of cancer cells in in vitro and epidemiological studies.
●Cooked tomatoes and lycopene: lycopene, released by cooking tomatoes with olive oil, is associated with a reduction in the risk of prostate cancer in several prospective studies. The bioavailability of lycopene is much higher in cooked tomatoes.
●Green tea and polyphenols: regular consumption of green tea is associated in epidemiological studies with a reduction in the risk of certain digestive cancers. The EGCG in green tea inhibits the proliferation of cancer cells in vitro.- Vitamin D: several meta-analyses suggest an inverse association between vitamin D levels and risk of colorectal and breast cancer. The mechanisms involve the regulation of cell differentiation and apoptosis.
5. What nutritional prevention cannot and what it can
It is essential to be honest about the limits of nutritional cancer prevention:
●No food cures cancer or provides complete immunity. Nutritional prevention reduces probabilities, it does not guarantee.
●Cancer is a multifactorial disease: genetics, environment, biological hazard and lifestyle all contribute. Diet is one factor among others.
●Non-dietary factors are also determining factors: tobacco (1st preventable risk factor), sedentary lifestyle, occupational exposure, infections (HPV, Helicobacter pylori).
●Nutritional prevention is part of a global healthy lifestyle approach, not in the search for a miracle food or an anti-cancer diet.
What nutritional prevention can do: significantly reduce the risk of several common cancers (colorectal, breast, endometrial, stomach) through well-established eating habits. 30 to 40% of preventable cancers is tens of thousands of fewer cases each year in France if the recommendations were followed.
💡 tips to remember
30 to 40% of common cancers are preventable through lifestyle: it is a real and documented lever for action, not a promise.
I limit cold meats as much as possible: processed meat is classified as a definite carcinogen for colorectal cancer by the IARC. The objective is not zero but a significant reduction.
I aim for 30 g of fiber per day: each +10g is associated with -10% risk of colorectal cancer. Legumes, whole grains and vegetables are my main allies.
Alcohol is carcinogenic from the first consumption: 7 types of cancer are linked to alcohol. Reducing consumption directly reduces the risk.
I eat cruciferous vegetables regularly: broccoli, cabbage, Brussels sprouts contain isothiocyanates with documented antiproliferative properties.
Overweight is linked to 13 types of cancer: maintaining a healthy weight through diet and physical activity is one of the most powerful prevention actions.
No food alone cures or prevents cancer: it is the overall quality of the diet over the long term that counts, not a miracle superfood.
