A supermarket chain is warning that people will typically eat 6,000 calories during Christmas Day - a massive increase on the 2,000 per day recommended for women, and 2,500 for men.
The poll for Sainsbury's found people are overeating on December 25, putting themselves at risk of obesity if they carry on indulging after the festive period.
Sainsbury's nutritionist Charlie Parker warned: "It's a relief that Christmas comes just once a year because if we ate like this every day we'd be in trouble."
But she said turkey meat is a good source of low-fat protein, while potatoes and parsnips are full of fibre, adding: "While the festive plate might be heaving, it's still possible to make it well-balanced and highly nutritious - if a little heavy on the calories."
The survey also found that Britons will eat an average of 3.63 roast potatoes and 2.95 chipolatas during Christmas dinner.
Turkey breast is the most popular type of poultry to have with the meal, along with an average 2.54 spoonfuls of sprouts.
One third (35%) of those questioned said they expect to toast their dinner with champagne, while 37% opt for sparkling wine.
The study added that on average, 5.25 people will sit around the table for Christmas dinner.