AICR HealthTalk by Karen Collins , MS, RD, CDN For American Institute for Cancer Research

Weekly column for the week of: June 6, 2011

Q: Should I try to follow a low glycemic index (low GI) diet to lower cancer risk?

A: You may have heard that eating foods with a high glycemic index (GI) makes blood sugars go up, causing increased levels of hormones like insulin that seem to promote development of some cancers. However, while those effects have been seen in short-term studies and do make sense in theory, longer-term studies do not show consistent impact on hormone levels. There are plenty of reasons for the confusion. Although you can find lists of foods with their GI value in books and on websites, actual blood sugar-raising effects of foods vary substantially with how they are cooked and whether they are eaten alone or along with sources of protein, fiber or fat, all of which blunt the effect. Furthermore, a large portion of a "low GI food" could end up raising blood sugar as much as a small portion of a "high GI food." Rather than focus specifically on the glycemic index of your diet, aim for an overall strategy to avoid elevated insulin with a diet that supplies nutrients and phytochemicals that reduce cancer risk. To decrease insulin resistance, accumulate at least 30 minutes of moderate physical activity throughout the day, control portion sizes even of "healthy" food to achieve and maintain healthy weight, and make vegetables, fruits, whole grains and beans the largest part of your plate. People with type 2 diabetes or the insulin resistance of pre-diabetes and polycystic ovary syndrome (PCOS) may be especially sensitive to foods’ blood sugar-raising effects, but best advice for now seems to involve more than choosing low GI foods.

Q: Is it true that getting more sleep might help me lose weight?

A: If you are already getting adequate sleep (seven to nine hours a night), getting more sleep will probably not affect your weight. However, if like many people, you are currently getting less sleep than that, more sleep might help. Studies show that adults who get less sleep (6 hours a night or less in most studies) are about 55 percent more likely to be obese. These associations (which have also been shown for youth) don’t show cause and effect, however a few studies that followed people over ten or more years do provide some evidence that getting less than six or seven hours of sleep a night is linked with greater likelihood of weight gain. In one study, overweight people were put on a controlled low-calorie diet during two weeks of spending only five-and-a-half hours in bed nightly. Although they lost the same amount of weight as when they spent eight-and-and-half hours in bed nightly, they lost less body fat and dropped 60 percent more lean body tissue. Results like this are preliminary, but we do know that loss of lean body tissue makes maintenance of weight loss more difficult. Too little sleep may lead to weight gain by making us too tired to be physically active or more likely to turn to sweets and other foods to perk up our energy. Additionally, spending less time sleeping leaves more time available for eating and that can mean consuming more calories than you need. Furthermore, limited but growing research suggests that people who get less sleep tend to show changes in two hormones that can lead to increased appetite.