The debate over whether carbohydrates are a positive or a negative part of a healthy diet has been heated in recent years. It’s helpful to know that the primary role of “carbs” is to provide energy. Understanding the role of carbohydrates in a healthy diet is particularly important for cancer patients because cancer cells require a lot of energy. Effectively managing your body’s intake of its preferred fuel—carbohydrates—will also help control the fuel available for cancer cells.
Carbohydrates: Structure and Functions in the Body
Carbohydrates are created by plants as a way of storing energy from the sun. They are composed of one or more sugar molecules. Two examples of carbohydrates that are a single sugar molecule are glucose, the sugar found in the blood, and fructose, which comes from fruit. Complex carbohydrates are multiple sugar molecules that are connected into a chain.
The main function of carbs is to provide energy. Glucose is the main energy currency that the body uses. Carbohydrates that enter the body as sugar chains must first be broken down into glucose to be used by the cells for energy.
Carbohydrates and Cancer
Cancer cells require a lot of glucose for energy—more than normal cells. This is because cancer cells metabolize, or break down, sugars using a different and less efficient process than that of normal, healthy cells. Cells typi cally use oxygen to burn glucose for energy. Because cancer cells grow in excess and become densely packed, however, they often survive in a low-oxygen environment and have adapted to breaking down sugars in the absence of oxygen—a process called anaerobic metabolism. Unfortunately, anaerobic metabolism is much less efficient than breaking down sugars aerobically, or with oxygen. As a result, cancer cells may need as much as 40 times more glucose than normal cells that function with sufficient levels of oxygen to generate the same amount of energy.1
To supply the excessive sugars that the cancer demands, the liver breaks down proteins and fats to make more glucose. If inadequate carbohydrates are consumed, the body resorts to using protein from muscles and stored fats to meet energy demands. Thus the high-energy demands of the cancer may explain why cancer patients often experience weight loss and fatigue.
One purpose of nutritional therapy for cancer is to limit the amount of excess glucose available to the growing cancer while providing enough energy for the brain and other vital functions. A practice that can help accomplish this is maintaining even blood sugar levels and avoiding spikes in glucose, which provide extra sugars that can be used by the cancer.
There are several tools for managing blood sugar. Using the glycemic index and following a low-carbohydrate diet are both well-known options, but a whole-foods diet may be easier and more effective.
Approaches for Controlling Blood Sugar: Glycemic Index, Low-carb Diets, and Whole-foods Diet Glycemic Index
The glycemic index (GI) is a measure of how fast the carbohydrates in food increase blood sugar levels. It is a scale from 1 to 100; 100 corresponds with pure glucose. Foods with a higher glycemic index are those that cause blood glucose levels to rise more quickly. Foods with a GI of 70 or more are considered high-GI foods. Foods with a GI of 55 or less are considered low-GI foods. The carbohydrates in a low-GI food do not cause a large spike in blood sugar.
While the glycemic index does help explain how different foods affect blood sugar, it does have the following limitations.
Limited foods tested. Only a small number and variety foods have been tested for their glycemic index.
Food combinations. The GI is based on how foods affect blood sugar when consumed alone, but most people do not eat one food at a time. Combining foods changes how those foods affect blood sugar. For example, meals that include fiber or fat will have a less dramatic effect on glucose.
Food preparation. The same food prepared in different ways can have very different affects on blood sugar. For example, more-processed foods increase glucose more dramatically.
Individual variability. The response to a food varies from person to person and from day to day.
These problems underscore the fact that the glycemic index can be difficult to use in the real world because so many factors alter the affect of foods on blood sugar.
Another way to control glucose levels is to follow a low-carb diet. These diets have been around since the 1800s and go in and out of favor. A woman on a low-carb diet usually gets 40 percent of her calories from carbohydrates and the remaining 60 percent from equal proportions of protein and fat.
Like the glycemic index, low-carb diets are difficult to follow even when you are healthy because food choices are so limited. When you are not feeling well, following such a diet may be impossible. Also, low-carb diets often do not contain foods rich in the antioxidants, vitamins, and minerals the body needs to fight cancer.
An alternative to a low-carb diet for controlling blood sugar is the whole-foods diet, which is rich in whole grains, legumes, fruits, vegetables, and fiber and also happens to have a low glycemic index. There are no charts to interpret, and, unlike the low-carb diet, a bounty of food choices is available.
To follow a whole-foods diet, avoid foods that are overly processed and/or refined, foods that are high in added sugar, and those that are made with refined flour. By following this cardinal rule of the whole-foods diet, you will get most of your calories from slow-burning, unrefined carbohydrates.
Here are a few more tips for controlling blood sugar with a whole-foods diet:
- Always eat a balanced meal with mixed foods. A meal rich in complex carbohydrates and fiber will slow the release of food from the stomach, thereby slowing the release of glucose from the meal.
- Avoid eating or drinking anything that tastes sweet on an empty stomach. This includes sweet-tasting fruit and vegetable juices, fruit, soda, sweetened refined cereals, honey, or any liquid sweetened with any form of sugar.
- Eat sweet whole foods such as fruit only with meals.
- Drink diluted or low-sugar fruit and vegetable juices only with fat-containing meals.
Bongaerts GPA, van Halteren HK, Verhagen CAM, Wagener DJ. Cancer cachexia demonstrates the energetic impact of gluconeogenesis in human metabolism. Medical Hypotheses. 2006;67(5):1213-1222.