The price of food is another factor in poor food choices, with salad ingredients costing much more. Tomatoes yesterday cost $10.99 a kg compared with $3.99 a kg in January.
"People choose to cook winter vegetables in more hearty ways, like roasting. It isn't as healthy as a salad in summer," Dr Boyes said.
The cold weather could interrupt exercise routines and trigger comfort eating, with the temptation to snack on fatty and sugary foods hard to resist.
"It can be very tempting to grab a fast, high-fat takeaway on the way home on a colder winter's night," said nutritionist Bronwen Anderson.
Exercise also suffered as it got colder, with 62 per cent saying if it was below 14C they would not exercise.
Ms Anderson urged people to keep exercising regardless of the weather.
"Keep moving and make sure that there is exercise in every day whether that means parking a little further away from the supermarket door, taking the stairs instead of the lift or joining a local gym or exercise class."
EATING TIPS
* Steam vegetables instead of roasting or frying.
* Make vegetable soups and freeze them for late nights.
* Snack on lower calorie options like carrot sticks or plain popcorn.
* Add fruit to winter breakfasts such as porridge.
* Choose lean meat and fish for casseroles.
* Avoid high-calorie desserts such as puddings.
(Source: Nutritionist Bronwen Anderson)