Women who start counting the calories on a Tuesday will give up in under a week (6 days), with over a quarter (28%) actually putting more weight on than when they started.
Those who start their diet on a Saturday have a clear goal in mind and are more likely to see the dieting commitment through to the end to meet their weight-loss targets.
Monday-dieters statistically shed the most weight, losing on average eight pounds over a three week period. Meanwhile, Sunday dieters are less likely to fall prey to the yo-yo dieting cycle, with an impressive 88% keeping the weight they lose off.
The study quizzed 2,000 Brits who have been on a diet within the last year on their attitudes, behaviours and dieting pitfalls. A spokeswoman for Tesco Diets, which commissioned the research, said:
"Changing your eating habits can be a hard challenge whatever day of the week. However, psychologically, dieters are more motivated to begin and continue a diet if they start afresh at the beginning of the week or on the weekend."
"With women struggling with their busy work-life balance, mental and physical preparation has never been more important. Time should be taken to draw up shopping-lists and peruse the supermarket shelves carefully to make sensible, informed choices without grabbing the nearest tin.
The study also revealed the nation’s dieting pitfalls – with lack of will power (39 per cent), boredom (36 per cent) and comfort eating (34 per cent) most likely to 'break' women into going back to their unhealthy ways. An unfortunate quarter admitted to putting on more weight during their diet than actually losing it – on average six pounds.
"There are numerous barriers hindering women from controlling their weight – boredom is something Tesco Diets works hard to combat through convenient eating choices, tailored by experts to support even the most demanding of lifestyles."
The survey found the average female goes on three diets a year with each one lasting three weeks in total.
It also emerged the majority ditch their diet on a Friday after a stressful week at work.