Poor health literacy, and not a lack of motivation, could be the main reason patients have difficulty overcoming obesity issues, UNSW research says.

Many Australian GPs wrongly assume that obese patients are not sufficiently motivated to lose weight, a new study says.

The real issue could be their "poor health literacy" - a lack of understanding of their own wellbeing, of what they can do to improve it and of what help the healthcare system can offer them.

Very few of the 61 health staff surveyed said they assessed a patient's health literacy, only 15 per cent reported success in treating obese patients and only 26 per cent enjoyed treating them.

The UNSW research, presented at the Primary Health Care Research Conference in Adelaide on Friday, examined how GPs and practice nurses managed overweight and obese patients with low health literacy in 20 practices in disadvantaged areas in Sydney and Adelaide.

The study found while more than half those surveyed reported regularly assessing diet, physical activity and Body Mass Index (BMI), goal setting and referral to other services were less frequently reported.

One in five Australians have very low health literacy, putting them at higher risk of ill-health as they are more likely to delay seeking care, less likely to receive preventative care and have difficulty navigating between services and providers.

"The problem is they are also more likely to have a weight problem so you have a sort of double whammy there," UNSW researcher Professor Mark Harris told AAP.

Clinicians should use techniques such as asking patients in their own words what they have understood, agree on specific clear goals, and explain and arrange for them to attend lifestyle programs, he said.