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A sugar-laden diet is recognized as a key risk factor for obesity, heart disease and Type 2 diabetes. And cutting back on sugary foods, especially sugary drinks, can mitigate that risk.

The evidence linking sugar intake to cancer, however, has been limited and inconsistent.

Now, a large study suggests that consuming too much sugar – both total sugar and added sugar – increases breast cancer risk.

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About the study

The findings, published online this month in the American Journal of Clinical Nutrition, come from the NutriNet-Santé study, a continuing study investigating the link between nutrition and health outcomes among adults living in France.

The latest analysis examined the relationship between cancer risk and sugar intake. Researchers tracked the habits and health status of 101,279 healthy adults for six years. Sugar intake was assessed at baseline and again every six months until study completion.

A high intake of total sugar was tied to a modest increase in overall cancer risk, but this was mainly driven by breast cancer. Among specific cancers, only breast cancer risk was associated with a higher sugar intake.

Women who consumed the most added sugar a day (50 grams or 12.5 teaspoons worth) were 47-per-cent more likely to be diagnosed with breast cancer during the study compared with those who consumed the least (21 g or five teaspoons worth). Added sugars are those added to foods at home and during processing.

When the researchers look at food sources of sugar, a higher intake of sugars from sugary drinks (e.g., soft drinks, pure fruit juice), dairy products and milk-based desserts (e.g., sweetened yogurt, pudding, milkshakes) were linked to a greater breast cancer risk. Naturally occurring sugars from whole fruit were not.

A high intake of “free” sugars was also tied to an increased breast cancer risk. Free sugars include added sugars plus the sugars naturally present in fruit juice, fruit juice concentrates, honey and syrups.

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The study controlled for other lifestyle-related cancer risk factors including physical activity, dietary factors, alcohol intake, body weight and weight gain during the study.

Strengths, caveats, plausibility

Credits to the study include its large sample size, frequent dietary assessments and adjustments for many diet and lifestyle risk factors for cancer.

There are limitations, of course. This was an observational study and, as such, it doesn’t prove that eating lots of sugar directly increases cancer risk.

Also, the six-year period is likely too short to investigate the dietary factors for cancers that can take decades to develop.

Still, there are biologically conceivable reasons why eating too much sugar could increase cancer risk.

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Excessive sugar intake can lead to increased body fat and obesity, a known risk factor for postmenopausal breast cancer as well as a number of other cancers.

Even in the absence of excess weight, a high sugar intake may increase cancer risk by promoting inflammation in the body and free radical damage to cells. It can also lead to insulin resistance, which is thought to play a role in breast cancer.

Reducing sugar intake

Sugar intake guidelines, released by the World Health Organization in 2015, recommend that adults and children reduce their intake of free sugars to less than 10 per cent of daily calories.

Cutting sugar to less than 5 per cent of daily calories is thought to provide additional health benefits. Based on a 2,000 calorie diet, that’s no more that 25 g of free sugars a day (about six teaspoons worth).

Replace sugar-sweetened beverages (e.g., pop, iced tea, energy drinks, fruit juice) with water, herbal tea or unsweetened green or black tea. Buy unsweetened products such as yogurt, non-dairy milks and canned fruit.

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If you’re in the habit of eating sugary desserts, try satisfying your sweet tooth with fresh fruit, a couple of dates or a small square of dark chocolate. Set a goal to reduce how often you eat sweets.

If you add sugar to coffee or tea, cut back gradually. Ditto for maple syrup or honey added to oatmeal, yogurt and smoothies. Your taste buds will adjust to a less sweet taste.

Leslie Beck, a Toronto-based private practice dietitian, is Director of Food and Nutrition at Medcan.

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