Deciphering the Link Between Diet and Cancer | American Science and Health Council

"So for starters, we know that an overall healthy diet has the potential to reduce cancer risk by 10% to 20%, which seems like a lot to me."

Those were the opening words of Gabrielle Emanuel, senior reporter at WBUR and moderator of Harvard's TH Chan School of Public Health discussion on "Reducing Cancer Risk Through Nutrition."

Ms. Emmanuel then asked questions of the three panelists, Edward Giovannucci: Professor of Nutrition and Epidemiology and Timothy Rebbeck: Vincent L. Gregory, Jr. Professor of Cancer Prevention, both from TH Chan, and Eliza Leone: Registered Dietitian and Instructor in the Culinary Medicine and Harvard Nutrition.

Proteins, fats and carbohydrates came under the microscope, with a nod to lean meat, vegetable proteins, vegetable fats and whole grains. Yet causality remains elusive amid the nutritional labyrinth, and hand gestures are more common than concrete conclusions.

Here are the highlights

What is a healthy diet?

• Protein: Prioritize lean meats and plant-based protein sources such as beans and lentils.
• Fats: Emphasize plant-based fats such as nuts, avocados and olive oil and minimize animal fats.
• Carbohydrates: Choose whole grains, vegetables and fruits over processed carbohydrates.

What is the link between diet and cancer?

Most of the research into disease and nutrition has focused on diabetes and cardiovascular disease; Less has been done in the field of cancer. However, two major risk factors mentioned by the panelists were associated with all three diseases.

Chronic infection A prolonged and dysregulated immune response is known to play a crucial role in both the initiation and progression of cancer. By creating a microenvironment that supports cancer cell survival and proliferation, releasing reactive oxygen and nitrogen species that can damage DNA and promote genetic mutations. Dr. Giovannucci gave as an example the significant relationship between hepatitis, a chronic inflammation of the liver, and subsequent liver cancer. Dietary inflammations are more subtle and affect the entire body.

Obesity is a known risk factor for cancer and has clear links to our dietary intake. More specifically, obesity is often accompanied by insulin resistance, leading to increased levels of insulin and insulin-like growth factor-1 (IGF-1) that promote cancer cell growth. In addition, obesity is associated with increased production of estrogen in postmenopausal women, and increased estrogen levels have been linked to certain types of cancer, including breast and endometrial cancer. Finally, adipose tissue is biologically active and produces and releases pro-inflammatory molecules such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and adipokines such as leptin. These substances act as signaling molecules and cause and maintain inflammation in the fatty tissue and beyond.

Unhealthy diets work through these two mechanisms.

What are the roles of vitamins and supplements?

Vitamins and supplements, touted by many as potential saviors, offer a mixed bag of results. There are no magic bullets among vitamins and caution should be taken not to rely solely on supplements.

The two compounds that might provide some protection were vitamin D, which a Harvard study showed a reduction in cancer mortality but no change in incidence, and a protective role for calcium in colon cancer. In addition to pointing out that there are no "magic bullets" among vitamins and supplements, Ms. Leone went on to say

"Our bodies can absorb these nutrients more easily through food than through supplements. So every time we take supplements - nutritional supplements - they are meant to fill in the gaps of what we may be missing."

What is the role of alcohol?

"I mean, [alcohol] probably increases your risk of cancer somewhat, especially in women, because breast cancer is affected by alcohol. But there may be some benefits in diabetes and cardiovascular disease."

Alcohol is a carcinogen, and cancer has been linked to "patterns of alcohol consumption that are high." People find this particular message difficult because it disrupts their lifestyle. But just as driving is a risk that can be mitigated by wearing a seat belt, "you can make smart choices or limited choices about alcohol consumption." For those who do not want to abstain, the panel fell back on the general US recommendation: one drink per day for women, two for men.

Does exercise affect our cancer risk?

Exercise emerged as a potential counterbalance to a less-than-ideal diet. While it is not carte blanche to indulge in unhealthy eating habits, exercise can offset some of the negative effects, highlighting the importance of energy balance.

Are there any myths you would like to debunk?

Dr. Rebbeck spoke about the belief that eating refined sugar fuels cancer. He noted that dysfunction of the mTOR metabolic pathway in cancer is caused by glucose in cells. However, it is wrong to interpret this as how eating refined sugar feeds the tumor.

Ms. Leone pointed out that intermittent fasting has no substantial evidence to support its role in cancer prevention.

Do you have any practical advice on using your diet to reduce your risk of cancer?

- Learn to prepare simple, nutritious meals at home to control ingredients and portion sizes. Take advantage of calorie density, eat fewer calories of food that has a larger volume and is therefore more filling

- Prioritize plant-based diets to emphasize a higher intake of plant foods, including a variety of fruits, vegetables and whole grains, but don't completely exclude animal products.

- Make gradual, achievable, sustainable changes in diet and lifestyle to reduce the risk of cancer.

Fun fact: Dr. Rebbeck noted that he and his wife used smaller plates to make their portions appear larger and presumably more filling - small plates, small glasses, to take advantage of the psychological effect of a small plate making a portion seem larger. That work of Dr. Brian Wansink of Cornell has been questioned and fifteen of Dr. Wansink's articles in this psychological sense have been retracted.

The one constant in the complicated dance between diet and cancer seems to be the lack of clear answers. The journey through this nutritional maze requires a nuanced understanding, focusing on moderation, whole foods and a conscious approach to lifestyle choices.

A summary of the evidence on diet and cancer can be found here. Watch the video of the discussion here. And you may find this article more than just interesting. Is everything we eat associated with cancer? A systematic cookbook review American Journal of Clinical Nutrition