Australians are expected to gain 15 million kilograms of body fat this winter, according to a study of seasonal eating habits.
The findings are drawn from a national survey of 1250 people commissioned by the NSW Food Authority and the State's health department.
TV's Biggest Loser trainer Michelle Bridges said cold weather led people to fall back into bad habits.
"We exercise less when it's cold and dark, stay indoors more and we seek comfort in fast food, snack food and takeaways," she said.
With one-in-four Australians obese, doctors and nutritionists are stressing the need for healthier meal choices.
"This message is particularly important for younger people so they can develop healthier eating habits before they become overweight or obese," NSW Health chief officer Dr Kerry Chant said.
The study found more than half of the population understood weight gain was caused by exercising less and eating more fast food.
But 90 per cent said they ate more fast food and snack food during the colder months because it made them feel warmer and happier.
The study found men were more likely to accept they would grow heavier over winter.
Fifty-three per cent of males expected to gain between two and five kilograms, compared with just 38 per cent of females.
Nearly half of Australians expect to put on two or three kilograms of hibernation weight.