Many cancer survivors fail to get adequate exercise and nutrition following their diagnosis, putting them at risk of health problems and their cancer returning, finds a new study.

"Even small changes can make a difference for patients, such as including a moderate amount of exercise and healthy eating in their treatment and recovery period, if and when they can," said Dr. Kerry Courneya, professor and Canada Research Chair at the University of Alberta, in a release.

Researchers at the university looked at self-reported data gleaned from a 2005 Community Health Survey that showed that of the 114,000 adults studied, only 21 per cent of cancer survivors are physically active. In general, 25 per cent of Canadians are physically fit.

Eighteen per cent of cancer survivors are obese — versus 15 per cent of Canadians in general. Male cancer survivors (62 per cent) were more likely to be overweight or obese than female cancer survivors (47 per cent).

Middle-aged survivors — those aged 40 to 66 — were less likely to be active than those under 40.

Colorectal cancer, breast cancer and female melanoma survivors were the least likely to participate in physical activity while the highest levels of activity — and lowest levels of obesity — were reported by prostate cancer survivors and skin cancer survivors.

Physical activity is defined as walking for one hour a day, according to the study. Obese refers to a body mass index of 30 or more.

"We know that physical inactivity and obesity are risk factors for developing cancer," said Courneya.

The study recommends that community-based programs be introduced to encourage cancer survivors to develop more active lifestyles.

The study, published Monday in the journal Cancer, was supported by the Canadian Cancer Society.