Four out of five people who started a diet for the new year will have given up by today, according to a report.
The study of 2,000 adults also found that one in five failed within a few days of making a resolution to eat healthier.
The top diet-breaking foods were chocolate, bread, crisps and takeaways.
Kamalesh Subramanian, of V8 juice who carried out the survey, said the results showed Britons were obsessed with extreme crash diets which were impossible to maintain.
Meanwhile, Sky News continues to chart the weight loss progress of four different people on four competing diets.
Safira Ali, 32, weighs 17 stone 2lb, and is doing the 5:2 diet, or fast diet.
“I am finding it quite difficult to be honest although I kind of treat it as if it is Ramadan but I suppose it’s a little bit easier because I can drink so I have things like fruit teas.
“On normal eating days I have noticed a difference because I don’t feel as if I want to snack as much and even though I pour myself the same portions I don’t eat as much as I normally do.”
Philip Wark, 38, weighs 18st 1lb, and is doing the Paleo, or “caveman” diet.
“Crisps and things like that have probably been some of the things I’ve missed a little but I must be honest, on the food side, not really a great deal. There’s enough in here to keep me happy.”
His wife, Quanita Wark, is partly joining him on the diet and says she has noticed a difference in her husband already:
“He’s definitely more positive now. In the beginning it was a bit hard because he was a bit moody. I think it was the withdrawal of all the sugars and stuff but he seems quite motivated.”
Hywel Roberts, 33, weighs 15st 5lb, and is doing a tailored vegetarian diet.
“It’s been hard resisting late at night when you’re tired, and not turning to food on those occasions. It’s early days but I’ve managed to do it so far.”
“I’ve also got a lot more energy. I can also go down to the next buckle on my belt which is good. I guess it gives you a good motivation if you can see a change already.”
Michelle Okpocka, 47, weighs 15st 5lb, and is doing a tailored “diabetic” diet.
“I’m allowed at least one treat a day, I’ve not been having any treats so far. But just knowing I’m allowed one treat a day is helping me to focus. So it’s like an emergency.”
All four are following four different, medically supervised, diets over three weeks.
Professor Tom Sanders, an expert in nutrition and dietetics at King’s College London, says timescale is key to keeping the weight off.
“People lose weight and then the battle always is if they can keep it off. We find that if they keep it off for 2 years they keep it off for life.
“Something happens in the body’s chemistry that is trying to fight you back to the weight that you were before you dieted.”