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Many questions remain about link between sugar intake and cancer
Elevated levels of blood glucose are linked to an increased risk for a number of cancers, including breast and colorectal cancers.
Blood glucose levels generally are controlled by the hormone insulin, and the hallmark of diabetes — a disease in which cells become resistant to the actions of insulin — is elevated blood glucose.
Dietary ingestion of sugar can increase blood glucose levels among individuals with diabetes. However, the potential cause-and-effect relationship between sugar consumption and cancer risk is not well understood.
HemOnc Today spoke with Jennifer Ligibel, MD, associate professor of medicine at Harvard Medical School and senior physician at Susan F. Smith Center for Women’s Cancers at Dana-Farber Cancer Institute, about the sugar-cancer connection, the ongoing research in this area, and the ways in which physicians can help patients use nutrition and physical activity to help prevent cancer and disease recurrence.
Question: Can you summarize the available evidence regarding the potential link between sugar and cancer?
Answer: We know that people who have higher levels of glucose seem to have a higher risk for developing certain cancers. This is particularly true for breast cancer and colorectal cancer. The main determinant of blood glucose when someone has diabetes is their body weight; however, it is not necessarily the sugar that one consumes. Sugar has a lot of calories and it certainly contributes to obesity but, for people who are leaner in general, the body maintains a tight level of blood glucose. When someone starts to become insulin resistant, they begin to experience higher levels of blood glucose. Insulin is a growth factor, but it is also the hormone that controls your blood glucose. When people become obese and start to develop diabetes, they become less sensitive to insulin. Insulin levels have to go up in order to keep blood glucose down. There has been some question about whether higher levels of blood glucose or higher levels of insulin place obese people at higher risk for cancer. The studies showing the relationship between obesity and cancer risk are primarily population-based studies rather than randomized trials, so we cannot establish a firm cause and effect.
Q: Is there sufficient evidence to warrant recommendations about sugar consumption for individuals already diagnosed with cancer?
A: Not at this point. There are very few studies looking at links between sugar and cancer recurrence among people with cancer. A few studies in colon cancer surveyed patients regarding dietary patterns, including intake of sugary foods. The investigators showed a link between higher sugar intake and higher risk for cancer recurrence, but only among people who were obese. Therefore, I would say there is not enough evidence on the link between sugar and cancer among people to develop guidelines at this point. There are a number of preclinical studies in yeast models or rodents evaluating the impact of sugar on cancer development and growth, but almost nothing in humans.
Q: What would you tell a patient at average risk for a first cancer regarding sugar consumption?
A: The American Cancer Society has developed guidelines about nutrition and physical activity for cancer prevention. They focus on keeping weight in a good range. There is a strong link between obesity and increased risk for developing 13 different cancer types based upon evaluation by the International Agency for Research and Cancer. The guideline also suggests trying to consume a diet that is more plant-based with lower levels of meat consumption, as studies have shown a link between the consumption of red meat and colon cancer. In fact, the guideline recommends against consumption of a lot of processed foods, as there are associations between certain types of preserved meats and stomach cancer, for example. Regular exercise is also recommended due to the relationship between exercise and reduced risks for breast, prostate and colon cancers. Another recommendation is to limit alcohol consumption to one glass per day for women and two glasses per day for men, as there are links between higher levels of alcohol consumption and cancer risk. However, the guidelines do not specifically make a statement about cancer and sugar. I think that is borne out by the evidence that we have in humans. I tell people to be aware of their weight and to be aware of the nutritional content of foods they are eating, as it is certainly clear that sugar has a lot of calories and not much nutritional value.
Q: Is it likely that sugar is the driving factor, or could it be that elevated sugar consumption leads to obesity and that, in turn, elevates cancer risk?
A: The data we have so far suggest a much stronger link between obesity and cancer risk than it does specifically for any type of specific nutritional intake.
Q: How much remains unanswered about the sugar-cancer connection?
A: There is still much that we do not know about the link between sugar intake and cancer. Most of the research we have in humans is based on observational studies. Additionally, the tools we use to measure diet are crude and rely on self-report. People often underreport the amount of fat and sugar they consume in an effort to appear more health-conscious. This obviously adds a lot of uncertainty and messiness to dietary studies.
Q: What type of research is underway?
A: The research that will give us more definitive information about the effects of weight, diet and exercise primarily is taking place in cancer survivors rather than in people at risk for developing cancer. The large-scale Breast Cancer Weight Loss Study will evaluate the effect of a weight-loss intervention for women who are overweight or obese when they are diagnosed with breast cancer.
Q: Is there anything else that you would like to mention?
A: When we think about preventing cancer or cancer recurrence, overall balance is key. At this point, having a diet that focuses on good nutrition and keeps the body in a normal weight range appears to be most important. We want to make sure people are getting all the nutrients they need from the food they eat. When an individual consumes a diet that provides enough vitamins, minerals and fiber, there are not a lot of calories left over for sugar. On the flipside, it is important to realize that — for a person at risk for cancer or someone who has been diagnosed with the disease — eating an occasional brownie or cookie should not give them a sense of guilt that they have done something that will cause them harm. Good nutrition is something that requires balance over many months and years. – by Jennifer Southall
For more information:
Jennifer Ligibel, MD, can be reached at Dana-Farber Cancer Institute, 450 Brookline Ave., Boston, MA 02215.
Disclosure: Ligibel reports no relevant financial disclosures.