Vegetables and Fruits Are Great, but Just Eating Them May Not Help You Fight Cancer

Is it healthy to eat a diet consisting only of vegetables and fruits? Not necessarily. suriyachan/Shutterstock

Modern nutritional science recognizes fruits and vegetables as healthy foods that can reduce the risk of cancer, and most people agree with the saying “an apple a day keeps the doctor away.” But can we fight cancer effectively by eating only fruits and vegetables? Is it healthy to eat only fruits and vegetables? Well, not necessarily.

Fruits and Vegetables Can Fight Cancer, but There Is a Limit to Their Effectiveness

Fruits and vegetables may reduce cancer risk because they are rich in fiber, vitamins, minerals, antioxidants, and phytochemicals that help boost the body’s ability to fight cancer in many ways. Conversely, low fruit and vegetable consumption is associated with an increased risk of death from cancer.

A meta-analysis of 95 studies showed that adding 200 grams of vegetables and fruits to the diet was associated with a 10 percent reduction in all-cause mortality. A daily intake of 550 to 600 grams of fruits and vegetables combined, fruits, and vegetables, was associated with 14 percent, 8 percent, and 12 percent reductions in the relative risk of total cancer, respectively. It also reported that cruciferous and green-yellow vegetables were associated with a significant reduction in total cancer risk.

However, the study also found that increasing intake beyond 550 to 600 grams of fruit and vegetables per day did not lead to further reductions in risk.

Another meta-analysis showed a similar result: The protective associations for humans did not increase beyond 300 grams per day of fruit and vegetable intake.

In a randomized clinical trial, participants with low intake of fruit, juice, and vegetables were randomized into two groups. One group’s participants maintained their usual diet, while the other group received an additional 480 grams of fruit and vegetables and 300 milliliters of fruit juice per day for 12 weeks. The results showed that people in the group who consumed additional fruits and vegetables had a 35 percent increase in plasma vitamin C levels, a 15 percent increase in folate, and a significant increase of 50 to 70 percent in certain carotenoids. However, there were no significant changes in the body’s antioxidant capacity, DNA damage in lymphocytes, and markers of vascular health, all of which are indicators associated with diseases.

A critical review also found that, in several large cohort studies, the effect of vegetable and fruit intake on cancer was detectable only if there were large differences in vegetable and fruit consumption between the groups, and it could be that effects only appeared in cases of high carcinogen (such as smoking) exposure.

In other words, there is a limit to the effectiveness of increasing the intake of fruits and vegetables to fight cancer.

Some people choose to switch their diets to only fruits and vegetables in hopes of minimizing their risk of cancer and diseases. This is not necessarily wise, though, and carries certain risks.

Eating Only Vegetables and Fruits Carries Risks

1. High blood sugar level increases the risk of cancer

In 2013, actor Ashton Kutcher simulated Steve Jobs’ diet to get into character for the role. After months of following a strict diet consisting of only fruits, nuts, and some grain seeds, he was admitted to the hospital with severe damage to his pancreas.

Eating too much fruit can lead to a high blood sugar level, which can damage the pancreas and increase cancer risk.

A study published in the Cell Metabolism journal in 2019 showed that a high blood sugar level can induce a series of metabolic changes, and pancreatic cells can become starved of raw materials to repair DNA, resulting in a doubling of the mutation rate. Ninety percent of pancreatic cancers have been proven to have this gene mutation, which can lead to canceration of pancreatic islet cells. The study also mentioned that DNA damage in pancreatic tissue was significantly higher in diabetics than in nondiabetics. Hence, the researchers proposed that high blood sugar is the major culprit that causes DNA damage in the pancreatic cells.

Another clue that high blood sugar level can cause cancer is that it can lead to a decrease in 5-hydroxymethylcytosine (5hmC), an important epigenetic marker on DNA, and it can greatly increase cancer risk; decreased 5-hmC in DNA indicates cancer progression.

2. Nutritional imbalance

A diet consisting of only fruits and vegetables can lead to nutritional imbalance. Fruits and vegetables are rich sources of vitamins, minerals, and fiber, but are low in protein and fat. A deficiency of these two essential macronutrients can affect human health. Without the sources of nutrients that fuel the body, we lose muscle and strength. This can put the body into starvation mode, slowing the metabolism to conserve energy.

Moreover, fruits and vegetables are also missing some important nutrients, such as vitamin B12, vitamin D, calcium, and zinc. Deficiencies in these nutrients can lead to anemia, fatigue, lethargy, and immune system disorders.

Therefore, this diet should not be followed in the long term for most people.

3. Interferes with drug absorption

Studies have found that components in grapefruit juice can interact with various drugs and affect the body’s metabolism, leading to abnormal drug levels in the blood, which can exacerbate side effects and reduce drug efficacy. More than 85 drugs are predicted to interact with grapefruit; of these, 43 have interactions that can result in serious adverse effects.

4. Other risks

Additionally, some fruits and vegetables are high in oxalate, which can lead to kidney stones if consumed in large amounts over a long period. Fruits and vegetables are also high in fiber, which can lead to gas or bloating if consumed in excess. Lastly, some fruit and vegetable sources are prone to contamination with pesticides, chemicals, and other substances—and the hazards cannot be completely removed by washing and peeling the fruits and vegetables.

A Balanced Intake

A balanced intake of fruits and vegetables should be included in the diet. Lex0077/Shutterstock

Certain amounts of fruit and vegetables are part of a healthy and well-balanced life. Most nutritionists will agree that balanced diets are important no matter what your goals are.

Healthy people who wish to detoxify and cleanse their colons can try to follow a diet of only fruits and vegetables for a short period, but the duration should not exceed a few days.

Generally, fruit intake should be kept at no more than 25 to 30 percent of the diet to avoid nutritional imbalances.

The 2020–2025 Dietary Guidelines for Americans recommends that adults should consume the equivalent of 1.5 to 2 cups of fruit and 2 to 3 cups of vegetables per day as part of healthy dietary patterns.

Otis Brawley, a professor of oncology and epidemiology at the Johns Hopkins Bloomberg School of Public Health, emphasized in an interview with The Epoch Times that “carcinogenesis and cancer risk reduction are long-term processes.” Just as years of smoking can increase your risk of many different cancers, it takes years of consistent healthy eating habits to lower your risk of cancer.

Brawley also stated that he does not advocate a diet that only eats fruits and vegetables without protein; instead, he recommends choosing a balanced diet that is rich in fruits, vegetables, and protein (from plants or animals). However, he emphasized that “when we say a diet high in fruits and vegetables, we do not mean fruits with added sugar.”

Meat Consumption Can Be Important for Cancer Patients

Patients who have been diagnosed with cancer or are undergoing cancer treatment (such as radiotherapy or chemotherapy) need to pay more attention to the calories and nutrients in their diets to ensure that they have the strength to fight cancer.

Cynthia Wong, a registered dietician at Memorial Sloan Kettering Cancer Center, said in an interview with The Epoch Times that many normal cells are killed during chemotherapy and radiation therapy, so protein and adequate nutrition are needed to promote recovery.

Common high-protein foods include red meat, fish, poultry, eggs, beans, dairy products, and nuts.

She also mentioned that patients often lose their appetite and lose a lot of weight due to the side effects of treatment, so “whatever they can eat at this stage is good for them.”