Sugar and Breast Cancer

The three macronutrients that are essential to the body’s proper functioning are carbohydrates, proteins and fats. Carbohydrates include:

1. Sugars:
   • Sugars that are naturally present in many foods: simple sugars (glucose, fructose and galactose), and compound sugars such as lactose (glucose + galactose) contained in milk and certain dairy products, maltose (glucose + glucose) contained in barley or corn, or sucrose (fructose + glucose) contained in fruits and vegetables.
   • Sugars added to foods and beverages during processing, preparation or at the table: table sugar (sucrose extracted from sugar beets or sugar cane) and all its derivatives (granulated sugar, powdered sugar, brown sugar, etc.), sweeteners (honey, molasses and syrups).
   • Free sugars refers to all foods and beverages that contain added sugar as well as those naturally present in fruit juices. 
2. Starches: These are long chains of simple sugars that don’t taste sweet and are naturally present in foods such as cereals, legumes, tubers (potatoes, sweet potatoes, cassava), bananas, as well as their derivatives. Starches are the body’s main source of energy.
3. Fibre: Although it is not digested or absorbed by the body, it plays a crucial role in gut health, as well as slowing down the digestion of sugar and reducing the absorption of cholesterol. Learn more about dietary fibre by watching our educational video here.

Every cell in the body prefers to burn glucose. Most sugars and starches are broken down into glucose during the digestion process. Once absorbed into the bloodstream, it raises blood sugar levels. The body closely controls blood sugar levels at all times to keep them within a normal range.

Insulin, a hormone secreted by the pancreas in response to rising blood sugar levels, is responsible for lowering blood sugar levels. It does this by redistributing excess glucose to:

• Cells, to provide them with energy;
• The liver and muscles, to build up easily accessible reserves; and
• Fat cells, in the form of fat for later.

The more carbohydrates you eat, the more insulin your body has to produce to stabilize blood sugar levels. If your intake is often greater than your needs, your fat reserves increase.

On the other hand, if your diet doesn’t contain enough carbohydrates, your body may first draw on reserves and then convert proteins into glucose to continue functioning. This process can lead to unwanted loss of muscle mass during breast cancer treatment.

If the absence of glucose is prolonged, the body may, as a last resort, convert fat into molecules called ketone bodies (also called ketones), which are an alternative source of energy.

Cancer cells, just like all cells in the human body, prefer to use glucose for energy. Since they’re fast-reproducing cells, they require more glucose than healthy cells. This is the basis of positron emission tomography (PET) imaging, which uses a radioactive compound associated with glucose to highlight areas of the body with high metabolic activity.

Since cancer cells use glucose to grow and multiply, it’s legitimate to ask whether sugar causes breast cancer, contributes to its growth and spread or increases the risk of its recurrence. Following this same logic, you may also wonder if it’s possible to prevent or stop cancer growth by eliminating sugar from your diet.

Breast cancer is a multifactorial disease. No single food or food component, including sugar, causes breast cancer. However, an unbalanced diet containing too much free sugar  over the long term may have an indirect impact on the risk of developing the disease and on prognosis.

Specifically, we know that an excess of foods containing free sugars at the expense of more nutritious foods can, in the long run, contribute to an increase in body fat. Research shows that being overweight or obese after menopause increases the risk of breast cancer and impacts survival and the risk of recurrence after diagnosis.

What’s more, although cancer cells use glucose as a source of energy, glucose itself doesn’t make cancer cells grow faster.

Cancer cell metabolism is complex, and researchers are trying to better understand how they use nutrients to obtain energy, as well as the impact of diet, particularly sugar intake, on the development and progression of breast cancer. It’s difficult to conduct studies and establish clear links between diet and breast cancer, especially since we consume thousands of food components every day, and there are many individual variabilities. Some studies tend to show a link between excessive consumption of free sugars and the risk of breast cancer or prognosis. This said, studies are limited, results are mixed and mechanisms are unclear.

At this time, there’s no evidence that excluding all sugars is effective and safe in the treatment of breast cancer. Furthermore:

• The body is able to produce glucose, regardless of dietary intake;
• Although cancer cells prefer glucose, they can use other nutrients as a source of energy;
• Glucose comes from many different foods, and it would be very difficult to avoid them all without having a restrictive diet; and
• It’s not advisable to undertake a restrictive diet without the recommendation and guidance of a health professional as it could be detrimental to health and lead to harmful nutritional deficiencies during breast cancer treatment.

A better understanding of these mechanisms could lead to the development of new therapeutic strategies, which would involve depriving cancer cells of their energy sources while continuing to provide the body with everything it needs to function properly.

After a breast cancer diagnosis, it’s advisable to adopt a healthy and appropriate diet, which includes foods that naturally contain sugar, but should not include a significant proportion of foods containing free sugars. In fact, both the World Health Organization (WHO) and Canadian health agencies recommend that less than 10% of calories consumed daily come from free sugars. Ideally, this intake should even be less than 5%.

For a diet of about 2,000 calories per day, 10% is around 50 grams of table sugar, or 12 teaspoons. Depending on your habits, following these recommendations could be a challenge. Below are some tips on how to do so while avoiding complicated calculations.

Tips to limit your intake of free sugars:

• Eat sugary processed foods less often and in smaller portions: candy, cookies, cakes, baked goods, pastries, ice cream, flavoured yogurts, granola bars, etc.
• Avoid sugary drinks: fruit juices, energy drinks, sweetened teas and coffees, sweetened flavoured waters, store-bought smoothies, sodas, flavoured milks and plant-based drinks, cocktails (with or without alcohol), etc.
• Limit the addition of certain condiments: sugars are usually hidden in sauces (ketchup, barbecue, honey mustard, etc.). Opt for homemade sauces with no added sugar and use spices and aromatic herbs.
• Opt for whole foods: which naturally contain sugar, but also other components such as fibre (e.g., fruit), vitamins, minerals and other elements that are beneficial to the body. Opt for healthier alternatives more often; for example, choose whole fruit rather than fruit juice. For more information, we invite you to watch our educational video on food quality.
• Avoid “sugar cravings”:
  • Eat until you feel full at meals and avoid skipping meals.
  • Plan healthy and satisfying snacks ahead of time.
  • Plan healthy and satisfying snacks ahead of time.
• Learn how to read labels to find out the amount of sugar per serving and recognize added sugars in the ingredient list. Ingredients that end in “ose” are usually sugars (dextrose, sucrose, trehalose, fructose, maltose, etc.). Added sugar can also be masked under various names: nectar, brown sugar, syrup, evaporated cane juice, cane juice extract, fruit purée, honey, fruit juice, molasses, etc.
• Get used to not having sugar: 
  • Gradually reduce the amount of sugar you add to your foods and beverages (tea, coffee, yogurt).
  • Limit foods and beverages containing artificial sweeteners (aspartame, acesulfame potassium, cyclamate, saccharin, sucralose stevia, sorbitol, xylitol, mannitol, lactitol, isomalt and erythritol), which may maintain the appeal of sugary products. Sweeteners can be found in beverages such as “diet” or “zero” sodas. In addition, aspartame is suspected of being carcinogenic.

Nutritional needs vary from person to person. A nutritionist can tell you how much sugar you should be consuming and offer personalized advice on how to adopt a healthy diet suited to your needs.

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