An NCI-designated Comprehensive Cancer Center
By Samantha Bonar | December 6, 2017
People have a lot of ideas these days about what might help prevent cancer: alkaline water, going vegan, a ketogenic diet, “bulletproof” coffee loaded with coconut oil or butter – even fasting.
None of these dieting trends are likely to have much of an effect on cancer risk, according to Elaine Siu, M.S., R.D., C.N.S.C., clinical dietician at City of Hope.
Working in a cancer hospital, we hear about a lot of diets,” Siu said. “Alkaline water, coconut water, coconut oil, going vegan, going vegetarian. There are a lot of nutrition myths.”
This is especially true in today’s society, which places such a high value on instant gratification.
“People are trying to find something fast, and there really is no magic to preventing or curing cancer,” Siu said. “The bottom line is eating a healthy, balanced diet and physical activity. There is no proof that any of these extreme diets work, or the hospitals would already be recommending them.”
Rather than focusing on what you eat, particularly gimmicky ingredients, the most important thing to do to prevent cancer is to stay within a healthy body weight, Siu said. “That’s more important than the specifics of your diet. Avoiding obesity is the key thing."
“We do recommend a diet that is higher in fruits and vegetables so that you get your phytonutrients from food rather than vitamins,” she said. “There is pretty good data to suggest that eating a plant-based diet is helpful in preventing cancer. And after cancer treatment, eating a plant-based diet has been shown to be helpful in keeping cancer from returning. What we recommend in general is a balanced diet that is more plant-based, but is not necessarily free of meat or dairy. ”
“Cutting down on animal protein is beneficial,” added colleague Dhvani Bhatt, M.S., R.D., C.D.E., also a clinical nutritionist at City of Hope. “There’s a lot of good data that shows a vegetarian diet is very healthy and helps to prevent a lot of chronic diseases, including heart disease and diabetes.”
We asked Siu and Bhatt to weigh in on some specific diet trends that purport to have cancer-preventing effects.
Alcohol intake: “Red wine has some phytonutrients and antioxidants, but more research is needed,” Siu said. "It also adds extra calories, which puts you at risk for obesity, which puts you at higher risk for cancer. Drinking alcohol may be good for your heart, according to some studies, but there is some data that shows it may actually increase your risk for head and neck and oral cancers. There’s no data to show that it helps with cancer prevention.”
Alkaline water: “A lot of my patients do the alkaline water. It’s basically just water that is slightly more alkaline,” Siu said. “There is no data at all that shows it is beneficial. It doesn’t change our body's pH level. Our body regulates the acid-base balance very well. For a healthy person, the body will just eliminate the alkaline water in the urine. Very small studies show that it might help with gastric acid. But that could put you more at risk for foodborne illness, because gastric acid helps kill foodborne pathogens.”
Ketogenic diet: “In the past it’s been used for seizure control in little kids, but more recently a lot of cancer patients are looking into it,” Siu said. “It’s really an extreme diet. It’s 90 percent fat, very little protein, minimal carbohydrates. Some research shows it might be beneficial for brain cancer. I think more research needs to be done; most of the studies are still preliminary.”
Avoiding sugar: “Sugar does feed cancer, but it feeds the rest of the cells as well,” Bhatt said. “It’s not the sugar itself that’s so bad, it’s the extra calories that turn into fat and obesity. It’s the total intake that’s important. Obesity is the real risk factor.”
Fasting:  “There are some studies going on about fasting during chemo treatment. It shows that it might help with chemo, reducing the stress on the healthy cells,” said Siu, while adding, “I wouldn’t recommend that any patient start fasting until they talk to their doctor. The risk is for patients who might already be malnourished — it might do more harm than good.”
Vegan diet: “I think being a vegan or eating a lot of fruits and vegetables and whole grains lowers people’s risk of developing cancer,” Siu said. “But it’s easy to become deficient in protein and B12 if you are on a vegan diet and you may need supplements, so you really need to consult with a dietician. Without careful meal planning, vegans can become nutrient deficient. We don’t recommend it for patients going through cancer treatment. They need protein to recover.”
Drinking coffee: “Chemicals in coffee may be beneficial,” Bhatt said. “Some small studies suggest that it can help with lowering your lipid profile, and it may lower your risk for prostate cancer. New dietary guidelines say that three to five cups of coffee a day are acceptable as part of a healthy diet pattern.”
Coconut oil: Adding coconut oil to your diet “is another thing that’s been really popular,” Siu said. “We have to remember it’s mostly saturated fat. It is still calories. A tablespoon is 120 calories. If you add calories, you end up gaining weight, and that puts you at risk for cancer. And eating a lot of saturated fat puts you at risk for heart disease. There is some data that shows consuming coconut oil increases the metabolic rate. But they are pretty small studies and they show that the metabolic rate goes back to normal after two weeks.”
In general, “With ketogenic and the alkaline diet and the Atkins diet, you eliminate a lot of fiber, fruits and vegetables and whole grains. This can open the door to cancer and other disease,” Siu said.
The bottom line, Bhatt said, is it’s not so much what you eat, it's avoiding extra pounds. There is no magic-bullet food or ingredient that will lower your overall cancer risk.
“Focus on eating a lot of fruits and vegetables and avoiding extra calories. It’s the extra weight and obesity that are the key factors for cancer risk,” she said.
This well-worn advice may not be as fun as putting gobs of butter in your coffee, but at least you will save money on fancy water.

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