August 6, 2013 | 4 minute read

Sugar and cancer: it’s a hot topic these days and this week it made headlines again. A new study in fruit flies suggests that a high-sugar diet may explain why people with type 2 diabetes and obesity are at a higher risk for cancer.

The study was published in Cell and here is the abstract. Basically, the study found that when fruit flies consumed a high-sugar diet it changes the signaling pathways of two human genes that can cause cancer called oncogenes, Ras and Src. That, in turn, caused tumor progression and metastasis.

Articles on the study have honed in on the dangers of a high-sugar diet for cancer risk, so we spoke with our nutrition advisor Karen Collins, a registered dietitian and expert on diabetes and cancer risk. Here, Karen talks about the study and says that when it comes to eating for lower cancer risk and good health, it’s not all about the sugar.

Q: This study focuses on metabolic disorders seen in type 2 diabetes and some cancers. Why is this important?

A: The research shows that people with type 2 diabetes and obesity are at increased risk of developing several cancers, such as postmenopausal breast and pancreatic. A metabolic environment in the body with inflammation and high levels of insulin and insulin-like growth factors is common to both type 2 diabetes and several types of cancer, and seems to be part of what promotes their development.

Q: What did you take away from this study?

A: This is a very interesting study; it shows how interconnected the pathways are in metabolism. However, the whole point of fruit fly studies is that it is an easy way to look at these pathways, but we can’t make the jump from fruit flies to humans.

One thing is that these fruit flies were given a diet extremely high in sugar: the high dietary sugar condition was more than six times the amount of the control diet. I think that is important. People get nervous when they think sugar increases cancer risk but there’s sugar in peaches and other healthy foods and that’s not the amounts of sugar given in this study. It would be like comparing what we consider a modest to low amount of added sugar – 10 percent of a day’s calories [about a can of sugary soda with little other food with added sugar] – to someone who drank eight cans of sugary soda a day. It’s a lot.

Q: Yet the fruit flies consuming the high-sugar diet did have increased tumor growth, correct?

A: Yes, in giving the fruit flies this super high sugar intake the researchers created a metabolic environment seen in people with type 2 diabetes. They created a model that showed insulin resistance, high blood sugar, and excess body fat. Then they looked at changes in the metabolic pathways. What you see is that indeed, this metabolic state of insulin resistance and high blood sugar does strongly effect tumor formation, which research has shown.

Just like in people, high blood sugar leads to insulin resistance. In this study, when the fruit flies where fed a high-sugar diet and the researchers blocked the insulin signals promoting cell growth, it did not increase cancer development in the fruit flies. It’s the insulin resistance not just the sugar itself.

Q: And for people, you’re saying the link to increased risk is insulin resistance?

A: If focusing on sugar alone, we miss the point of all the research in reducing risk of diabetes and cancer. It’s not just sugar intake, it’s excess body weight and a sedentary lifestyle pushing people towards elevated insulin levels and insulin resistance.

Limiting added sugar is good for weight control and excess amounts do seem to increase risk for diabetes, but sugar alone is not the demon. We need to focus on reducing insulin resistance.

Q: In this study, a high-fat diet did not affect tumor growth like the high-sugar diet. Can you talk about the research on dietary fat and cancer and diabetes risk?

A: The study does not specify the type of fat used. But what is known is that total high fat intake is not associated with insulin resistance, diabetes risk or cancer risk. And eating a Mediterranean diet, with healthy fats in the context of a plant-based diet does not increase the risk of diabetes or cancer. A high intake of saturated fat could increase insulin resistance.

Q: For people who want to eat to lower diabetes and cancer risk, what does the research say?

A: Eat a predominately plant-based diet focusing on vegetables, fruits, and whole grains. Limit the amount of red and proceeded meats along with refined starchy foods. We have tons of data in humans: its weight reduction, regular physical activity and this dietary pattern. It’s not just the sugar, it’s the insulin resistance.