by “So just to start with, we know that an overall healthy eating pattern has the potential to reduce cancer risk by 10% to 20%, which sounds a lot like mine.”
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 went on to ask questions of the three panel members, Edward Giovannucci: Professor of Nutrition and Epidemiology and Timothy Rebbeck: Vincent L. Gregory, Jr. Professor of Cancer Prevention, both TH Chan, and Eliza Leone: Registered Dietitian and Instructor in the Harvard Culinary Medicine and Nutrition Course.
Protein, fats, and carbohydrates came under scrutiny, with a nod toward lean meats, plant-based protein, plant fats, and whole grains. However, amidst the nutritional labyrinth, causality remains elusive, and hand-waving is more prevalent than concrete conclusions.
Here are the highlights
What is a healthy diet?
- Protein: Prioritize lean meat and plant-based protein sources such as beans and lentils.
- Fats: Emphasize plant-based fats such as nuts, avocados, olive oil, and minimize animal fats.
- Carbohydrates: Choose whole grains, vegetables and fruit over processed carbohydrates.
What is the diet link with cancer?
Most disease and nutrition studies have focused on diabetes and cardiovascular disease; less has been done in the field of cancer. However, two main risk factors cited by the panels were associated with all three diseases.
“Inflammation is not cancer, but it may set the environment in which cancer can develop.”
– Dr. Timothy Rebbeck, Professor of Cancer Prevention
Chronic inflammation a prolonged and dysregulated immune response is known to play a critical role in the initiation and progression of cancer. By creating a microenvironment that supports the survival and proliferation of cancer cells that release reactive oxygen and nitrogen species, which can damage DNA and promote genetic mutations. Dr. Giovannucci offered as an example the significant relationship between hepatitis, chronic inflammation of the liver, and subsequent liver cancer. Nutritional inflammation is more subtle and affects the whole body.
“Just by dividing a lot of cells, you’re more likely to get a mutation that will lead to cancer.”
– Dr. Edward Giovannucci, Professor of Nutrition and Epidemiology
Obesity is a significant risk factor for cancer and has clear links to our dietary intake. Specifically obesity is often accompanied by insulin resistance, which leads to elevated levels of insulin and insulin-like growth factor-1 (IGF-1) promoting the growth of cancer cells. In addition, obesity is associated with increased estrogen production in postmenopausal women, and elevated estrogen levels are linked to certain types of cancer, including breast cancer and endometrial cancer. Finally, adipose tissue is biologically active by producing and releasing 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, which stimulate and promote inflammation within the adipose tissue and beyond.
Unhealthy dietary patterns operate 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 is advised not to rely on supplements alone.
“There have been some long-term trials [of vitamins], randomized trials, and they see no harm. And after about 10 years of use, you start to see at least a hint of benefit. So there is some evidence for long-term use. … But I think there’s probably enough evidence to say it doesn’t hurt and maybe it will help.”
– Edward Giovannucci: Professor of Nutrition and Epidemiology
The two compounds that may offer some protection were Vitamin D, where the Harvard study showed a reduction in cancer mortality but no change in incidence, and a protective role for calcium in colon cancer. Also Mr Leone said there are no ‘magic bullets’ among vitamins and supplements
“Our bodies are able to absorb those nutrients more easily through food than we are through supplements. So any time we’re taking any supplements — nutritional supplements — these are meant to help fill in the gaps that we might be missing.”
What is the role of alcohol?
“I mean, [alcohol] it is likely to slightly increase your risk of cancer, especially in women because alcohol affects breast cancer. But diabetes and cardiovascular disease may have some benefits.”
Alcohol is a carcinogen, and cancers are linked to “high alcohol consumption patterns”. This particular message is difficult for people because it affects their lifestyles. But just as driving is a risk that can be mitigated with a seat belt, “you can make smart choices or limited choices when it comes to drinking alcohol.” For those who will not abstain, the panel fell back on the general US recommendation of one glass a day for women, two for men.
Does Exercise affect our risk of cancer?
Exercise emerged as a possible counterweight to a less-than-ideal diet. Although it is not carte blanche to abandon unhealthy eating habits, exercise can offset some negative effects, emphasizing the importance of energy balance.
“So I think exercise can – in a sense, … offset some of the negative effects that a poor diet can have. Now, I’m not saying you have a bad diet and exercise. But the other way to think about it is that the worst thing you can do is exercise and have a bad diet. So at least make one. It is best to do both. … I think it’s about energy balance.”
– Edward Giovannucci: Professor of Nutrition and Epidemiology
Are there any myths you would like to dispel?
Dr. Rebbeck with the view that eating refined sugar promotes cancer. He observed that the dysfunction of the mTOR metabolic pathway in cancers is driven by glucose in cells. However, it is wrong to interpret that eating refined sugar means feeding the tumor.
Ms. Leone pointed out that there is a lack of substantial evidence supporting its role in cancer prevention.
Do you have any practical advice on using your diet to reduce the risk of cancer?
– Learn how to cook simple, nutritious meals at home with controlled ingredients and portion sizes. Use calorie density, eat less caloric foods that have more volume and therefore more filling
– Prioritize plant-based diets to emphasize a higher intake of plant-based foods, including a variety of fruits, vegetables and whole grains, but do not completely exclude animal products.
– Make gradual, achievable, sustainable changes to dietary and lifestyle habits to reduce cancer risk.
Fun Fact: Dr. Rebbeck noted that he and his wife used smaller plates to make their portions seem larger and more filling – small plates, small glasses, to use the psychological effect of a small plate that makes it seem more on serving. That work, done by Dr. Brian Wansink from Cornell, has been called into question, and 15 of Dr. Wansink drew back on those psychological lines.
The only constant in the complex dance between diet and cancer seems to be a lack of clear answers. The journey through the nutritional maze requires greater understanding, emphasizing moderation, whole foods, and a mindful approach to lifestyle choices.
You can find a summary of evidence on nutrition and cancer here. Watch the video of the discussion here. And this article may be of more than passing interest. Is everything we eat linked to cancer? American Journal of Clinical Nutrition cookbook systematic review
