Australia's peak body for dietitians is urging people to share a meal with older relatives, friends and neighbours this festive season to fend off malnutrition.

'Tis the season to be jolly and tackle the hidden health issue of malnutrition among older Australians, says the peak body for dietitians.

The Dietitians Association of Australia is urging people to enjoy a meal with their older relatives, friends and neighbours this festive season to fend off malnutrition through meaningful connection.

"One of the major risk factors for under-nutrition in our older generation is social isolation and loneliness. We know from studies that when older people are living alone, their diet often suffers," said Joel Feren, an accredited practising dietitian and spokesman for the DAA.

"Elderly people often eat alone, and many lack the ability or motivation to prepare and cook balanced and nutritious meals. Some people call this the 'tea and toast syndrome'. But the good news is that improving people's social ties can lead to greater dietary variety and better health," Mr Feren said.

Nearly half - 40 per cent - of Australians over 65 years are either malnourished or at high risk of malnutrition.

Being undernourished can lead to a number of serious complications, including an increased risk of osteoporosis, an impaired immune system and poor wound healing.

Speaking from experience, 87-year-old Julia O'Brien - who lives alone in rural Victoria - says sharing a meal with her seven children and 15 grandchildren is the best gift for her.

"We each bring our favourite dish and enjoy a delicious meal together," Ms O'Brien said.