Cancer is one of the leading causes of death worldwide (1).
Growing evidence points to certain dietary habits increasing or decreasing cancer risk.
What’s more, nutrition is thought to play an important role in treating and coping with cancer.
This article covers everything you need to know about the link between diet and cancer.
It’s difficult to prove that certain foods cause cancer.
However, observational studies have repeatedly indicated that high consumption of certain foods may increase the likelihood of developing cancer.
Sugar and Refined Carbs
Processed foods that are high in sugar and low in fiber and nutrients have been linked to a higher cancer risk (2).
In particular, researchers have found that a diet that causes blood glucose levels to spike is associated with an increased risk of several cancers, including stomach, breast and colorectal cancers (4, 5, 6, 7).
It’s thought that higher levels of blood glucose and insulin are cancer risk factors. Insulin has been shown to stimulate cell division, supporting the growth and spread of cancer cells and making them more difficult to eliminate (9, 10, 11).
In addition, higher levels of insulin and blood glucose can contribute to inflammation in your body. In the long term, this can lead to the growth of abnormal cells and possibly contribute to cancer (9).
This may be why people with diabetes — a condition characterized by high blood glucose and insulin levels — have an increased risk of certain types of cancer (12).
For example, your risk of colorectal cancer is 122% higher if you have diabetes (13).
To protect against cancer, limit or avoid foods that boost insulin levels, such as foods high in sugar and refined carbs (14).
Processed meat refers to meat that has been treated to preserve flavor by undergoing salting, curing or smoking. It includes hot dogs, ham, bacon, chorizo, salami and some deli meats.
Observational studies have found an association between consuming processed meat and an increased cancer risk, particularly colorectal cancer (16).
A large review of studies found that people who ate large amounts of processed meat had a 20–50% increased risk of colorectal cancer, compared to those who ate very little or none of this type of food (17).
However, these studies often don’t distinguish between processed meat and unprocessed red meat, which skews results.
Cooking certain foods at high temperatures, such as grilling, frying, sautéing, broiling and barbequing, can produce harmful compounds like heterocyclic amines (HA) and advanced glycation end-products (AGEs) (25).
Certain foods, such as animal foods high in fat and protein, as well as highly processed foods, are most likely to produce these harmful compounds when subjected to high temperatures.
These include meat — particularly red meat — certain cheeses, fried eggs, butter, margarine, cream cheese, mayonnaise, oils and nuts.
One study followed almost 4,000 men with prostate cancer. Results found that high intakes of whole milk increased the risk of disease progression and death (32).
More research is needed to determine possible cause and effect.
Theories are that these findings may be due to an increased intake of calcium, insulin-like growth factor 1 (IGF-1) or estrogen hormones from pregnant cows — all of which have been weakly linked to prostate cancer (33, 34, 35).
Other than smoking and infection, being obese is the single biggest risk factor for cancer worldwide (36).
It increases your risk of 13 different types of cancer, including of the esophagus, colon, pancreas and kidney, as well as breast cancer after menopause (37).
In the US, it’s estimated that weight problems account for 14% and 20% of all cancer deaths in men and women, respectively (38).
Obesity can increase cancer risk in three key ways:
- Excess body fat can contribute to insulin resistance. As a result, your cells are unable to take up glucose properly, which encourages them to divide faster.
- Obese people tend to have higher levels of inflammatory cytokines in their blood, which causes chronic inflammation and encourages cells to divide (39).
- Fat cells contribute to increased estrogen levels, which increases the risk of breast and ovarian cancer in postmenopausal women (40).
There is no single superfood that can prevent cancer. Rather, a holistic dietary approach is likely to be most beneficial.
Scientists estimate that eating the optimal diet for cancer may reduce your risk by up to 70% and would likely help recovery from cancer as well (2).
They believe that certain foods can fight cancer by blocking the blood vessels that feed cancer in a process called anti-angiogenesis (44).
However, nutrition is complex, and how effective certain foods are at fighting cancer varies depending on how they’re cultivated, processed, stored and cooked.
Some of the key anti-cancer food groups include:
Many vegetables contain cancer-fighting antioxidants and phytochemicals.
One review found that at least three servings of citrus fruits per week reduced stomach cancer risk by 28% (55).
For example, one study found that men with prostate cancer taking 30 grams — or about 4 1/4 tablespoons — of ground flaxseed daily experienced slower cancer growth and spread than the control group (58).
Similar results were found in women with breast cancer (59).
Some test-tube and animal studies have found that cinnamon may have anti-cancer properties and prevent cancer cells from spreading (60).
Additionally, curcumin, which is present in turmeric, may help fight cancer. One 30-day study found that 4 grams of curcumin daily reduced potentially cancerous lesions in the colon by 40% in 44 people not receiving treatment (61).
Beans and Legumes
One study in over 3,500 people found that those eating the most legumes had up to a 50% lower risk of certain types of cancers (63).
For example, one study in more than 19,000 people found that those who ate more nuts had a reduced risk of dying from cancer (66).
Many studies show a link between olive oil and reduced cancer risk (67).
One large review of observational studies found that people who consumed the highest amount of olive oil had a 42% lower risk of cancer, compared to the control group (68).
There’s evidence that eating fresh fish can help protect against cancer, possibly due to healthy fats that can reduce inflammation.
A large review of 41 studies found that regularly eating fish reduced the risk of colorectal cancer by 12% (73).
The type and amount of dairy consumed are important.
For example, moderate consumption of high-quality dairy products, such as raw milk, fermented milk products and milk from grass-fed cows, may have a protective effect.
The reasons behind these results aren’t fully understood but may be due to hormones present in milk from pregnant cows or IGF-1.
Plant-Based Diets May Help Protect Against Cancer
Higher intake of plant-based foods has been associated with a reduced risk of cancer.
In fact, a large review of 96 studies found that vegetarians and vegans may have an 8% and 15% lower risk of cancer, respectively (80).
However, these results are based on observational studies, making it difficult to identify possible reasons.
The Right Diet Can Have Beneficial Effects for People With Cancer
Malnutrition and muscle loss are common in people with cancer and have a negative impact on health and survival (1).
While no diet has been proven to cure cancer, proper nutrition is vital to complement traditional cancer treatments, aid in recovery, minimize unpleasant symptoms and improve quality of life.
Most people with cancer are urged to stick to a healthy, balanced diet that includes plenty of lean protein, healthy fats, fruits, vegetables and whole grains, as well as one that limits sugar, caffeine, salt, processed foods and alcohol.
Good protein sources include lean meat, chicken, fish, eggs, beans, nuts, seeds and dairy products.
Side effects of cancer and its treatment can sometimes make it difficult to eat. These include nausea, sickness, taste changes, loss of appetite, trouble swallowing, diarrhea and constipation.
If you experience any of these symptoms, it’s important to speak to a registered dietitian or other health professional who can recommend how to manage these symptoms and ensure optimal nutrition.
Additionally, those with cancer should avoid supplementing too heavily with vitamins, as they act as antioxidants and can interfere with chemotherapy when taken in large doses.
A Ketogenic Diet Shows Some Promise for Treating Cancer, but Evidence Is Weak
Animal studies and early research in humans suggest that a low-carb, high-fat ketogenic diet may help prevent and treat cancer.
High blood sugar and elevated insulin levels are risk factors for cancer development.
Several pilot and case studies in people have also indicated some benefits of a ketogenic diet, including no serious adverse side effects and, in some cases, improved quality of life (94, 95, 96, 97).
There seems to be a trend in improved cancer outcomes as well.
For example, one 14-day study in 27 people with cancer compared the effects of a glucose-based diet to those of a fat-based ketogenic diet.
Tumor growth increased by 32% in people on the glucose-based diet but decreased by 24% in those on the ketogenic diet. However, the evidence is not strong enough to prove correlation (98).
A recent review looking at the role of a ketogenic diet for managing brain tumors concluded that it could be effective in enhancing the effects of other treatments, such as chemotherapy and radiation (99).
Yet no clinical studies currently show definitive advantages of a ketogenic diet in people with cancer.
It’s important to note that a ketogenic diet should never replace treatment advised by medical professionals.
If you decide to try a ketogenic diet alongside other treatment, be sure to speak to your doctor or a registered dietitian, as veering from strict dietary rules can lead to malnutrition and negatively influence health outcomes (100).
Though there are no miracle superfoods that can prevent cancer, some evidence suggests that dietary habits can offer protection.
A diet high in whole foods like fruits, vegetables, whole grains, healthy fats and lean protein may prevent cancer.
Conversely, processed meats, refined carbs, salt and alcohol may increase your risk.
The Bottom Line
Though no diet has been proven to cure cancer, plant-based and keto diets may lower your risk or benefit treatment.
Generally, people with cancer are encouraged to follow a healthy, balanced diet to preserve quality of life and support optimal health outcomes.