Cutting carbohydrates from your diet just two days a week could lead to greater weight loss than adhering to a more traditional low-calorie diet, a new, preliminary study found. And those finding may also have implications for lowering breast cancer risk, by helping control levels of insulin -- a cancer-promoting hormone.
In new research being presented at the San Antonio Breast Cancer Symposium Thursday, researchers from England assessed the impact of three different diets on the weight and insulin blood levels in 115 women. A third of the participants followed a calorie-restricted, so-called Mediterranean diet every day, while another third went on a diet that restricted carbs in addition to calories, but for just two days a week. A third group followed a low-carb diet two days a week as well, but they were allowed to eat unlimited protein and healthy fats.
Both of the two-day, low-carb options resulted in greater weight loss than full-time dieting. On average, women on the so-called "intermittent" plans lost about 9 pounds, while women following the daily, calorie-restricted Mediterranean plan lost around 5 pounds.
Insulin resistance -- which decreases the ability of cells to transport glucose from the bloodstream -- also decreased more significantly among both low-carb groups, dropping by 22 percent among women on the low-calorie version, and by 14 percent on the unrestricted fat and protein plan. Women who adhered to daily calorie restriction saw a drop of only around 4 percent.
"The take home message is that this potentially a very interesting approach for anybody concerned about weight or insulin," said Dr. Michelle Harvie, Phd, a registered dietitian with the Genesis Prevention Center at the University Hospital in South Manchester, England. She cautioned, however, that the study is "quite preliminary" and relatively small.
Harvie also emphasized that participants who followed diet that restricted carbs but not calories two days-per-week were not just eating any type of fat or protein they wanted.
"We're not talking about Atkins here," she said. "Yes, they were restricted in carbohydrates [to around 50 grams per day], but we were encouraging that they eat lean, healthier proteins and healthy fats as well." Participants enjoyed foods like lean meats, olives and nuts.
According to the American Cancer Society, being overweight or obese has been found to increase women's breast cancer risk -- particularly after menopause. A 2002 study suggested that up to 18,000 deaths a year might be prevented if women over 50 maintained a Body Mass Index of under 25. (A BMI of 25 to 29.9 is considered overweight; 30 or greater is considered obese.)
Harvie added that any weight gain as an adult, regardless of overall BMI may also play a role, as it can impact cell metabolism, triggering changes in the body she said are not yet fully understood. On Wednesday, an exhaustive Institute of Medicine report weighing the potential impact of environmental factors on breast cancer risk listed "minimizing weight gain" as a promising preventive action, particularly for postmenopausal women.
Susan Brown, director of health education with Susan G. Komen for the Cure, which commissioned the IOM report, said that the strong point of the new study is that it suggests several possible methods that let women do exactly that -- and which might, in turn, offer some protection against breast cancer risk. She stressed that any possible associations are complex (research has suggested that being slightly overweight pre-menopause may offer some protection against breast cancer risk, for example) and more research is needed.
"The strength of the results is more closely tied to that weight loss [researchers found]," she said. "But there is no clear-cut answer in the body of evidence that any one specific diet is associated with breast cancer risk."
"In general, our message is to maintain a healthy weight," Brown continued. "But there are many other risk factors that contribute to a person developing breast cancer -- weight is just one of a whole litany."