The facts about sugar consumption and cancer

By Heather Knutson, MS, RD, CSO, LD May 02, 2017

Sugar! We know it’s bad for us, right? But in the cancer community rumor mill, one that consistently circulates is that eating sugar “feeds” your cancer, making it worse. As with most rumors, this one sounds possible, but the fact is there is nothing that definitively links sugar consumption to worsening cancer. At a time when you may be facing a lot of anxiety and many lifestyle changes, trying to eliminate sugar completely from your diet is another potential stressor. More stress can increase the production of hormones that raise blood sugar levels and decrease your body’s immune function. You don’t want that either.

How sugars work in your body
Carbohydrates in food are digested into simple sugars and absorbed into the blood. Almost every cell in your body requires glucose, the form of sugar the body uses for fuel — including healthy cells and cancer cells. Strictly in that sense, some might say that sugar “feeds” cancer. However, your healthy cells also need energy from sugar. Both cancer and healthy cells need energy from sugar, but cancer cells use the glucose faster because they do everything at a faster pace. This helps doctors identify them on PET scans.

Since you can’t control which cells get sugar, trying to avoid it completely can deplete healthy cells. Even if you were to completely eliminate carbohydrates from your diet, your body would respond, going into a “survival” mode and making sugar from other sources like proteins and fats. Removing carbohydrates from your diet entirely would also make it difficult to maintain weight, something that is already a challenge when dealing with cancer and the side effects of treatment.

Research shows it is sugar’s relationship to insulin and related growth factors that influences the growth of cancer cells over time. All carbohydrates are broken down to simple sugars in the intestine, where they increase blood sugar levels after being absorbed into the blood. In response, the pancreas releases insulin, which performs several important jobs making the body function properly as it travels through the bloodstream.

Too much insulin can tell cells to grow too much — the origin of the “sugar makes cancer worse” rumor. Research shows wise carbohydrate consumption helps keep your glycemic index (blood sugar level) in normal range. But there is no evidence indicating that eliminating sugar and carbohydrates from your diet slows the growth of tumors.

A high-sugar diet can also lead to unwanted weight gain, possibly causing changes in your body’s levels of hormones. Obesity may also increase your risk of several cancers.

Confused? Here’s what to do
We know a normal part of metabolizing food is our body producing insulin to process sugar. When you eat too much sugar or carbohydrates, a large amount of insulin is produced. If you are able to eat normal amounts of food and maintain your weight, it may be beneficial to limit excessive intake of simple carbohydrates — especially by themselves. Don’t eat carbohydrates on an empty stomach. Adding fat and fiber to carbohydrate intake lowers the overall glycemic index. Adding protein also helps avoid low blood sugar levels.

Avoid processed carbohydrates because these foods are more easily broken down, making them more likely to raise blood sugar levels. When your stomach empties more slowly, your blood sugar levels are more stable and you feel more satisfied.

Complicated? Not really
You may feel it’s too complicated to figure out what you should and shouldn’t eat when it comes to protein, carbohydrates, fat and fiber. Research has done the complicated work for you. While there is no proof sugar causes cancer growth, we know for a fact that a healthy diet and regular physical activity reduce cancer risk and help people with cancer diagnoses better manage their disease. We also know too much sugar is unhealthy for our bodies. When it comes to simple-sugar foods, the keys are smart eating and moderation.

Simple-sugar foods are carbohydrates based on white sugar, brown sugar, honey and syrups (cookies, cakes, candy, desserts, for example). It’s better to get most of your carbs from complex carbohydrates like whole grains, vegetables, fresh fruits, dried beans and peas.
Start by minimizing simple sugars:

  • Eliminate sodas and sweetened or sugar-added drinks and avoid drinking fruit juice
  • Limit desserts and other high-calorie, low-nutrition snacks to no more than two to three times per week — if possible, eliminate them completely and replace them with healthy ones
  • Don’t add sugar or sweeteners to the food you eat; if you can’t give up sugar in your coffee or on your cereal, reduce it as much as you can
  • If you must have something sweet, choose dark chocolate with 70 percent or greater cocoa — it tastes decadent and delivers antioxidants that help the body

Practice healthy habits every day:

  • Eat plant-based carbohydrates that protect you from disease and do good things for your body. Focus on whole, healthy, unprocessed food, including vegetables, fruit, whole grains, nuts, seeds and legumes (beans, lentils and peas).
  • As much as possible, avoid processed foods — those that are already prepared in a box or sack, ready to eat right off the shelf. Processed foods raise blood sugars and insulin levels more rapidly, especially when eaten alone.
  • Avoid eating carbohydrates by themselves. Eat them in conjunction with foods that are good sources of protein, fat and/or fiber. Include a protein-rich and fiber-rich food with each meal and snack. This slows the way your stomach empties, allowing carbohydrates to be released into your body more gradually, steadying blood sugar levels.
  • Practice balance and moderation. If you really crave sweets, occasionally allow yourself small amounts. But also look for healthy replacements, like fruit, that can satisfy that craving.
  • Reducing your cancer risk encompasses all aspects of your lifestyle. Stay well-hydrated. Regularly engage in walking and other physical activity. Get adequate rest and sleep and find ways to manage stress.

Continue on? Here are good resources
Harvard Health offers a good explanation of the glycemic index and how foods compare. This information increases your understanding of the impact of different foods on blood glucose levels.

The American Institute for Cancer Research offers a wealth of nutrition knowledge, including specific information on how to plan and implement healthy eating, as well as recipes to help you enjoy your healthy eating.

Your primary care provider, dietitian, oncologist and oncology team members are also excellent sources of information and guidance. They have a personal interest in your health and well-being. Feel free to ask them for advice and direction as you continue your journey toward becoming cancer-free.

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