Diet & Cancer: A Conversation

Can changes to diet and lifestyle stave off cancer?

According to the American Cancer Society Nutrition and Physical Activity Guidelines Advisory Committee for most Americans who do not use tobacco, the most important cancer risk factors that we have control over are body weight, diet, and physical activity. The World Cancer Research Fund estimates that about 20% of all cancers diagnosed in the U.S. are related to body fatness, physical inactivity, excess alcohol consumption, and/or poor nutrition, and thus may also be prevented.

Although our genes influence our risk of cancer, most of the difference in cancer risk between people is due to factors that are not inherited. Avoiding tobacco products, staying at a healthy weight, staying active throughout life, and eating a healthy diet may greatly reduce a person’s lifetime risk of developing or dying from cancer. Yet the evidence is not definitive. Published results are either inconsistent and the methods of studying nutrition and chronic disease in human populations continue to evolve. Randomized controlled clinical trials, the gold standard, are a challenge to conduct and they over simplifying the complexity of foods, dietary patterns, and the large variations in nutritional status among human populations. Therefore, the complex interrelationships between body weight, physical activity, diet, and cancer risk are based, for the most part, on a combination of shorter-term clinical trials and observational studies coupled with the advancement of our understanding of the biology of cancer. It is imperative to understand that no diet or lifestyle pattern can guarantee full protection against any disease; the potential health benefit represents a decreased likelihood that the cancer will occur, not a guarantee of total protection.

Yet we still want to do everything we can to improve our overall health and decrease our risk of cancer. The 2015–2020 Dietary Guidelines for Americans, published by the Department of Health and Human Services provides us with guidelines that leave us still looking for answers.

1. Follow a healthy eating pattern across the lifespan.
2. Focus on variety, nutrient density, and amount.
3. Limit calories from added sugars and saturated fats and reduce sodium intake.
4. Shift to healthier food and beverage choices.

The government even provides us with ‘imagery’ to help us follow these guidelines such as “My Plate”

As a Professor of Nutrition at the University of California, San Diego, I believe in these guidelines but know that without education the average individual is still helpless when it comes to wandering through the grocery store and making food choices. Do you know what the 6 essential nutrients are and what nutrient density means?

Three Provide Energy (calories):

1. Carbohydrates: 4 cal/gram
2. Proteins: 4 cal/gram
3. Fats (lipids): 9 cal/gram

Three Do NOT Provide Energy (calories):

1. Vitamins: water and fat soluble vitamins
2. Minerals: macro- and micro-minerals
3. Water

Nutrient density refers to the amount of nutrients per calorie. The guidelines help us select foods that have a high nutrient density by providing us with recommendations on what to decrease and what to increase.

We should decrease or consume less of those foods that are nutrient deficient and calorie dense. For example, foods with added sugars and solid fats provide a lot of calories but few of the essential nutrients. These foods include sugar-sweetened beverages, processed snack foods, and desserts. Calories add up fast with these calorie-dense foods, which not only can lead to weight gain but leaves little room for more healthful, potentially cancer-preventive foods. We should also limit but not eliminate our alcohol consumption and salt intake (sodium).

We should increase or consume more fruits and vegetables, including beans. Plant foods contain powerful micronutrients, such as flavonoids and carotenoids, which studies have shown to be strong antioxidants. They counter damaging reactions (oxidation) from biological processes that can harm or kill cells. Plant nutrients also reduce inflammation, which is associated with the development of cancer, and some can stop or even kill cancer cells. Like healthy cells, tumor cells need nutrients, which are delivered through a network of tiny blood vessels. Tumors can actually initiate the growth of new blood vessels through a process called angiogenesis. Some compounds in plant foods may prevent angiogenesis and thereby starve the cancer cells.

What about supplements? Whole foods are your best bet for reducing your risk of cancer. Research suggests that the synergy between nutrients found naturally in foods offers a protective effect. The best sources of nutrients for cancer prevention are nutrient-rich whole foods and healthful beverages. However, it is often difficult to consume enough nutrient dense foods without consuming too many calories. Therefore, supplements may be an appropriate addition to your daily regime. Talk to your health care provider before taking any supplements.

What about superfoods? Blueberries, beetroot, broccoli, garlic, green tea… the list goes on. We have all searched thousands of websites that claim that a certain ‘superfood’ will prevent cancer. However ‘superfoods’ is a marketing term used to sell products and has no scientific basis. That’s not to say you shouldn’t think about eating these foods. As we stated above, some foods are clearly healthier than others. Stocking up on fruits and vegetables is a great idea as is eating a wide variety of vegetables.

Conclusion:

Many diet myths distort sensible dietary advice. Yet nobody is saying that eating a healthy diet doesn’t matter when it comes to cancer. You can read about the scientific evidence on diet and cancer on this website. But remember, there is a difference between the role of diet in preventing or reducing your risk of cancer and the role of diet in curing cancer. We will discuss this later in this series.

Dietary advice must be based on nutritional and scientific fact. When it comes to offering diet tips to reduce cancer risk, research shows that the same boring healthy eating advice still holds true. Fruit, vegetables, fiber, white meat, and fish are good. Too much fat, salt, sugar, red or processed meat, and alcohol are less so. It seems so simple — but true.

Despite the fact that we lack randomized, controlled clinical trials, evidence remains strong that obesity is a significant risk factor for several types of cancer. According to the National Cancer Institute, it has been associated with a higher risk for breast, colon and rectum, endometrial, esophageal, and pancreatic cancers, among others. Remember it’s not just what you eat — it is how much!