An overweight man measures his waist with measuring tape.During the past several decades, the percentage of overweight and obese adults in this country has increased markedly, putting them at higher risk for a variety of medical conditions.

According to the results of a study, recently published in The Lancet Oncology, nearly half a million new cases of cancer each year worldwide are also linked to being overweight, defined as having a body mass index of at least 25.

The relationship between being overweight and developing certain cancers appeared strongest in women, largely attributed to endometrial (womb/uterus) and post-menopausal breast cancers. High BMI was associated with 345,000 new cancer cases in women and 136,000 new cases in men. Among heavier men, colorectal and kidney cancers were most common.

Several possible mechanisms have been suggested to explain the association of extra weight with increased risk of cancer:

  • Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers.
  • Obese people often have increased levels of insulin and insulin-like growth factor in their blood, which may promote the development of certain tumors.
  • Fat cells produce hormones that may stimulate or inhibit cell growth.
  • Fat cells may also have direct and indirect effects on other tumor growth regulators.
  • Obese people often have chronic low-level inflammation, which has been associated with increased cancer risk.

“Excess fat in the body functions like an organ producing its own hormones,” said Christy McFadden, a board-certified oncology dietitian and educator with the Spectrum Health Cancer Center. “This corrupts normal body chemistry and does lead to increased inflammation.”

However, a loss of just 5 to 10 percent of excess body weight is effective in lowering risks for disease, including cancer. The best way to achieve weight loss is the tried and true advice: eat more fruits and vegetables, whole grains and low-fat animal foods along with increased physical activity.

“Plant-based foods are actually our best defense against disease, including cancer,” McFadden said. “Much of our diet should consist of vegetables, fruits, beans, nuts and whole grains. Fats from plants–avocados, vegetable oils, nuts–are good fats and most of us could use more of them.”

She also noted that physical activity–even without weight loss–can help restore healthier body chemistry.