Is the Sugar-Cancer Connection Just a Myth?

Is excess sugar by itself – in the absence of weight gain – a cancer risk?

Among popular beliefs about cancer risk is the one tying it with excess sugar. The depiction in popular media is that of cancer cells growing fast out of control when there’s plenty of sugar to feast on.

What’s already beyond doubt is that excess sugar can lead to weight gain. Obesity by itself, and type 2 diabetes, which is a common consequence of obesity, both increase the risk of cancer. But is excess sugar by itself – in the absence of weight gain – risky?

Cancer cells, like any other cell, need energy to grow and multiply. Due to their relative accelerated growth and the lack of oxygen inside a tumor, cancer cells may need even more energy, and sugar is the energy currency in our body. There are indeed treatments that try to starve cells of carbohydrates through diet, or through manipulation of insulin – which is necessary in order to get sugars inside cells. Other mechanisms that can make the sugar-cancer link suspect are the inflammatory and oxidative state caused by high sugar intake and insulin resistance.

So the sugar-cancer connection is plausible. Several past studies however were quite reassuring for those of us with a sweet tooth: A recent review of 37 studies didn’t find evidence of a link.

That’s why leading cancer research institutions such as the World Cancer Research Fund and the American Institute for Cancer Research don’t list sugar as a cancer risk at this point. But they do warn that “consumption of sugar-sweetened drinks is a cause of weight gain, overweight and obesity,” and being overweight or obese increases the risk of many cancers, and that greater glycemic load is a risk factor for endometrial cancer.

Sugar and breast cancer

A new study, however, finds a worrying link.

The study in the American Journal of Clinical Nutrition looks at a large cohort of more than 100,000 people, whose dietary intake was assessed every 6 months. Sugar intake was analyzed for total added sugar, as well as specific sugar types (table sugar, glucose, fructose, lactose etc.) and participants were followed for a median of about 6 years for cancer diagnosis.

And the results: In this large cohort sugar was associated with cancer, especially with breast cancer, even when weight status was accounted for. Total as well as added sugar quantity were associated with increased risk of breast cancer; sugars from fruit, however, were not associated with cancer risk. 

Excess added sugar is a well known risk factor for diabetes, heart disease and fatty liver disease. This study links sugar with cancer, especially to breast cancer, and clearly further proof is needed; but since the recommendation is to limit added sugar to no more than 6 teaspoons for women, 9 teaspoons for men for heart-health reasons, the suspected cancer link just adds further motivation for what’s a difficult task. Very few people manage to stick to the eat-less-sugar recommendations. Sugar is added to many processed foods – from breads to condiments to breakfast cereals – and just one serving of sugary drinks already puts you over the top. Sugar limits are easily exceeded on a highly processed food diet even without the joy of the occasional dessert.

Cutting excess added sugar in your diet is one of the most important steps towards improving overall diet quality and reducing the risk of weight gain and chronic diseases, and the easiest way to achieve that is through reducing the amount of sugar in drinks – sweetened drinks are the major contributor of added sugars in the American diet and the easiest to cut – and limiting highly processed foods.

Dr. Ayala