SAN ANTONIO -- Limiting carbohydrate intake just two days a week can mitigate some risk factors for breast cancer by burning body fat and improving insulin sensitivity, researchers said here.

Over three months, eating fewer carbohydrates alone or combining that reduction with severe caloric restriction two days per week was associated with significant changes in body fat and insulin resistance, Michelle Harvie, PhD, of Genesis Prevention Center at University Hospital in South Manchester, U.K., reported during a poster session at the San Antonio Breast Cancer Symposium.

"Both diets showed improvement in insulin sensitivity, compared with a regular calorie-restriction diet alone," Harvie told MedPage Today. "It's an interesting finding, but we need more research. This isn't ready to be recommended to patients yet."

Action Points This study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Limiting carbohydrate intake just two days a week can mitigate some risk factors for breast cancer by burning body fat and improving insulin sensitivity.

Three months of the low-carbohydrate diets also led to better weight loss and lower levels of insulin, both risk factors for breast cancer, compared with standard caloric restriction.

In an earlier study, Harvie and colleagues demonstrated that two days per week of calorie restriction was comparable to daily calorie restriction in terms of weight loss, but it wasn't any easier for patients to follow because the choice of food was limited to fruit and vegetables on restricted days.

The present study allowed for more food choices during calorie restriction, Harvie explained.

They randomized 115 overweight or obese patients who, based on their weight were at risk of breast cancer, to one of three diets over a three-month period:

A calorie-restricted (600 kcal), low-carbohydrate (less than 40 g) diet for two days a week A low-carbohydrate diet for two days per week, plus an ad-lib Mediterranean (healthy fats, fruits, and vegetables) diet the other five days A daily calorie-restriction Mediterranean diet (1,500 kcal) all week

Harvie told MedPage Today that enforcing the diet two days per week, rather than three days, or one week on and one week off, was "just pragmatic; two days is achievable."

The women met monthly with a dietitian and had bi-weekly motivational phone calls. Eighty-eight of them completed the three-month trial, plus an additional month of follow up to assess whether restricting carbohydrates one day a week could help maintain weight and metabolic changes.

Harvie and colleagues found that after three months, patients on either of the low-carbohydrate diets had significantly greater declines in insulin resistance as measured by HOMA-IR (P=0.023) and in body fat (P=0.004) compared with those who just restricted their calories every day.

Those declines were maintained over an additional month of limiting carbohydrate intake to just one day per week, Harvie said.

Three months of the low-carbohydrate diets also led to better weight loss and lower levels of insulin, both risk factors for breast cancer, compared with standard caloric restriction. Those changes were maintained after an additional month, Harvie added.

"Weight loss and reduced insulin levels are required for breast cancer prevention, but are difficult to achieve and maintain with conventional dietary approaches," Harvie said.

None of the diets, however, had any effects on several other metabolic parameters, including adiponectin, insulin-like growth factor-1, interleukin-6, or TNF-alpha.

Harvie said the diets did reduce the levels of leptin, which is the hormone that tells the brain that the body is satiated, but not significantly so.

Overall, she called the intermittent low-carbohydrate diets a possible alternative to full-blown calorie restriction "for potentially reducing the risk of breast cancer and other diseases."

The researchers reported no conflicts of interest.