Timothy Rebbeck (from left), Eliza Leone, Edward Giovannucci, and Gabrielle Emanuel explored the connection between diet and cancer at the Harvard Chan Studio panel discussion.
We all know that we are what we eat. Unfortunately, the rule extends to cancer.
Research increasingly shows that diet not only affects risk for obesity, diabetes, and heart disease, but cancer as well, according to experts who convened for a panel Monday at the Harvard T.H. Chan School of Public Health.
“Having chronically high levels of inflammation and insulin — and probably some lipids are cancer-promoting — that’s the biggest impact of diet on cancer.”
Edward Giovannucci, professor of nutrition and epidemiology
Ultra-processed foods — think chips, sweets, and meals that come from the factory rather than the field — make up a large part of the U.S. diet and have been implicated in cancer rates. Other problem foods include processed meats such as bacon, hot dogs, and common deli items. And, despite the ongoing debate over whether alcohol is good or bad for heart health, when it comes to cancer, the effects of booze are pretty clear. It’s a carcinogen, noted Timothy Rebbeck, the Chan School’s Vincent L. Gregory Jr. Professor of Cancer Prevention.
The biological mechanisms behind different cancers vary, but a common culprit is inflammation. When low-level inflammation triggered by diet becomes chronic, the stress put on cells can lead to disease.
“Chronic inflammation happens over years and years and the cells become dysregulated, mutated,” Rebbeck said. “That’s the kind of inflammation that we think diet and nutrition — as well as other things — may have an impact on and would be very important in cancer causation.”
The “other things” include high levels of insulin circulating in the body, as occurs with obesity and in the early stage of Type 2 diabetes, and certain fats.
“Having chronically high levels of inflammation and insulin — and probably some lipids are cancer-promoting — that’s the biggest impact of diet on cancer,” said Edward Giovannucci, a professor of nutrition and epidemiology at the Chan School.
As with people focused on heart health and blood sugar, those looking to reduce cancer risk should maintain a diet heavy on fruits and vegetables, together with whole grains and healthy proteins, the panelists said. Cut down on red and processed meats, they added.
“It’s generally known that a plant-forward diet is very helpful for long-term health,” Leone said. “That’s a lot of plants, but not only plants.”
The Harvard Healthy Eating Plate is 50 percent fruits and vegetables, she pointed out. The rest is split between whole grains and healthy proteins.
While panelists urged consumers to be cautious of health claims about supplements, they noted that studies have suggested that vitamin D has cancer-fighting properties. Findings from the VITAL study, led by investigators at Harvard Medical School and Brigham and Women’s Hospital, showed that vitamin D supplements taken over six years lowered rates of cancer death.
“One of the most important things you can do to enhance the nutrition in your life is to become more comfortable in the kitchen — all of these nutrition recommendations come down to what you eat.”
Eliza Leone, registered dietitian
Giovannucci said that folate, typically sold as folic acid, may be beneficial against the disease. He cautioned against megadosing, however, since some compounds, like selenium and zinc, can promote the disease in very high doses.
Panelists also covered the benefits of exercise, including as a measure against bladder, breast, colon, endometrial, esophageal, stomach, and kidney cancers. The anti-inflammatory power of physical activity is one key reason, Giovannucci said.
Intermittent fasting has gained popularity in recent years, but there isn’t much evidence the method lowers cancer risk. (Weight control does.) The problem with the regimen, Leone said, is that people often feel justified eating whatever they want, including highly processed foods, when they’re not fasting. In addition, she said, most diets are not sustainable for the long term and it’s better to focus on healthy choices and portion control.
That kind of discipline isn’t always easy, the panelists acknowledged. More time in the kitchen is a good first step.
“One of the most important things you can do to enhance the nutrition in your life is to become more comfortable in the kitchen — all of these nutrition recommendations come down to what you eat,” Leone said. “With all the research out there, it’s overwhelming. Just start somewhere. Pick one thing that is achievable for you and do that.”
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