Drinking more than three large glasses of wine can push people over a "tipping point", meaning they consume about 6,300 extra calories in the following 24 hours, a report has said.
The extra calories could lead to gaining 2lb a week (900g), the survey of 2,042 people suggested.
About half (51%) of those who drank alcohol said crossing the threshold had made them binge on fast food.
But experts warned the study showed trends and not "hard science".
Slimming World, which commissioned the research from YouGov, said 50% of the people who said drinking impacted their food choices had also cancelled physical activities the day after drinking more than 9.3 units, equivalent to slightly less than four pints of beer.
They had opted for bed, TV and using social media to stave off the hangover - along with another extra 2,051 calories, on top of their usual diet, the next day.
On the night, they had consumed about 2,829 calories extra in food and 1,476 extra calories in drink, the survey said.
And the following day, the drinkers ate on average 2,051 extra calories.
Dr Jacquie Lavin, head of nutrition and research at Slimming World, said alcohol loosened self-control.
She said people who had consumed more alcohol tended to eat at a greater rate and for longer.
"Alcohol makes the food even more rewarding. It tastes good and feels even better than it would do normally," said Dr Lavin.
She called for the government to launch a communications campaign to inform people of the impact of drinking on weight gain, and for calories to be included on alcohol labels.
Call for action
Bridget Benelam, nutritionist at the British Nutrition Foundation, said: "The survey is very interesting. But it is a survey and not a scientific study.
"It is useful as well as the hard science, to be aware of what people are thinking in the real world, to get messages out there."
She said the survey confirmed a link between alcohol and obesity.
Dr Alison Tedstone, chief nutritionist at Public Health England (PHE), said: "The report raises awareness of the high calorie content in alcoholic drinks.
"Excess calorie intake can lead to being overweight and obese which increases your risk of heart disease, type 2 diabetes and some cancers."
She said PHE's campaign, Change4Life, encouraged people to "eat well, move more, live longer" and to manage their alcohol and food intake.
Luciana Berger, shadow health minister, said the survey showed more needed to be done to raise awareness about the "ways excessive alcohol impacted on weight".
She added: "With health problems associated with being overweight or obese costing the NHS more than £5bn every year, it is time the government took the bold action that the scale of this threat to our public health demands."