More than six out of 10 workers blame colleagues who regularly buy cakes, sweets and treats for their weight gain, according to a new study.
It also emerged desk-based office employees can expect to put on an average of ten pounds during their first year in their new job.
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Additionally most office workers will succumb to their first sweet snack by 10:04am and continue to pig out for the rest of the day.
Janet Taylor, Diet and Health Manager for The Co-operative Food, which commissioned the research into office eating habits, said: "The office appears to be a 'no go area' for people trying to stick to a healthier diet, with boredom levels and the temptation to snack on unhealthy foods from 'diet saboteurs' causing colleagues to pile on the pounds.
"Interestingly, those admitting they need to lose those workplace wobbly bits, say they only manage to stick to a diet or healthy eating plan for six days before caving in to the cakes, chocolates and treats brought in by colleagues."
The report also found 14 per cent of office workers feel under constant peer pressure to join in when goodies are passed round.
And 24 per cent admitted they can't resist the unhealthy snacks brought in to celebrate birthdays and other events.
More than half (60 per cent) of British office workers admit they do need to lose weight. The study also found 74 per cent of office workers admit to consuming far more food at work than they ever would do at home.
And 73 per cent of office workers believe the sedentary nature of their job has led to them put on weight.
A fifth of respondents eat more sweet treats at work in a bid to be more sociable, and four in 10 always go out for a pub lunch if an office colleague suggests it.
And 16 per cent claim that even when they try to stop thinking about food, someone in the office will be talking about it.
As well as finding it hard to say no to colleagues, 21 per cent of people admit that if the snacks are there in front of them, they are impossible to resist.
Chocolate is the biggest temptation for bored office workers, closely following by crisps, biscuits and cake.
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Janet Taylor added: "By following a few simple tips, you can turn your office environment from an unhealthy food den of despair to a fresh and healthy haven.
"Swapping a packet of biscuits for a platter of fresh fruit will help meet your five-a-day target, and having healthy alternatives, such as carrot sticks or rice cakes, close to hand will help you ward off temptation from the office 'feeders', intent on tempting you with unhealthy treats.
"If all else fails, escaping the office at lunchtime for a brisk walk will put you out of harm's way, as well as breaking up your day and burning off calories.
"There's nothing wrong with the occasional treat, but a balanced diet, with plenty of exercise, is the best way to stay in shape and ward off those office-induced pounds."
10 most common reasons for ditching the diet at work:
1. Snack more at the desk
2. To pass away the time when bored
3. Colleagues are constantly bringing in snacks and treats
4. It is always someone's birthday so cakes are brought in
5. Because food is always there and is too tempting
6. Colleagues talk about food all the time
7. Colleagues encourage everyone to eat
8. You actually have more time to eat at work than at home
9. Meetings over lunch
10. Eating and drinking after work with the boss or colleagues
Spare a thought for the Y! Lifestyle team, who not only have very generous colleagues - they also sit next to the biscuit table!