Feb. 6, 2024 — Nutritionists are sounding the alarm on just how much your dietary consumption can affect your risk — or lack thereof — for cancer. 

A whopping 25% of the 18 million cancer cases in the U.S. could be prevented by improving your nutrition, according to research out of the Harvard T.H. Chan School of Public Health. Being overweight or obese can put you at risk for a slew of cancers, including cancer of the breast, liver, and colon, among a handful of others, according to the American Cancer Society. 

A healthy diet can help offset these diseases by reducing risks linked to obesity – most notably chronic inflammation, according to Harvard experts who spoke at a news conference Monday. Developing inflammation from a poor diet causes your insulin levels to spike, which can lead to IGF-1 insulin-like growth factors, said Edward Giovannucci, MD, professor of nutrition and epidemiology at Harvard University. These insulin growth factors tell your cells that ample nutrients are around and these cells should continue growing.

She gives the example of the “Harvard Healthy Eating Plate.” This means that your plate should be 50% fruits and vegetables, 25% whole grains/grains/starches, and 25% protein. Proteins could include animal proteins (like eggs, dairy, lean meats) or plant-based proteins (such as tofu, beans, nuts). Overly processed meats, such as deli meat, and red meat should be eaten sparingly. 

“Inflammation, insulin, and obesity sort of go together, and processed foods that are high in refined carbohydrates (e.g., white breads) and probably saturated fats all contribute to excess energy (calorie) intake to begin with,” Giovannucci said. “Chronic inflammation is important for cancer. So I think processed foods are definitely an important part of the equation.”

A good majority of your diet should be whole foods, like those from the ground, and you should be very aware of your portion sizes, Rebbeck said. Whole foods include foods like rice, potatoes, beans, fruits, and vegetables versus processed foods like breads, cookies, and pastas. 

Supplements and Cancer 

It’s important also to remember that supplements and vitamins are supposed to be in addition to, not replacement for, a health-promoting diet. This is largely due to the fact that our bodies can take in nutrients through food far more efficiently than it can through supplements, said Leone. 

Furthermore, most vitamins and supplements may not be all that necessary, Giovannucci said. In fact, some research shows that particularly high doses of vitamins like zinc and selenium can actually increase your risk for certain cancers. 

The vitamins that may actually help stave off cancers are calcium, multivitamins, and vitamin D. One Harvard study found that 2,000 international units of vitamin D greatly lowered risk of cancer death after 6 years. Other research has shown that calcium is a great preventative measure for colon cancer, according to Giovannucci. “If people don’t take or eat a lot of dairy products, it may not be a bad idea to have some supplementary calcium,” he said. 

Debunking Cancer and Nutrition Myths

Social media posts spreading “dietary advice” to the masses should be scrutinized due to various misleading, and downright dangerous, claims surrounding nutrition and cancer prevention, Rebbeck said. One of the most harmful myths circulating is that certain vitamins and minerals can be used as a substitute for life-saving chemotherapy medicines and vaccines, he says.

“I see a lot of misinformation or sometimes disinformation out there that supplants well-established, scientifically determined practice and tries to replace it with something like ‘just take this pill, just eat this vegetable, just drink this juice, and you don’t need your chemotherapy,’” Rebbeck said. “Those are the [myths] that I think are the most dangerous.”

For more information on cancer and health-promoting nutritional practices, click here.