Of those who quit in the first week, one in ten will have already ditched their new diet by Tuesday. By Thursday, a further three out of ten will have followed suit. By Friday, four out ten say they are so proud of lasting five days that they treat themselves to a reward and fall back into bad habits.
Only one out of ten first-week quitters makes it through to Saturday before giving up the new diet, and the same number makes it to Sunday.
However, some dieters do stand the test of time.
One out of five last a month, and the same number make it to the three-month mark, while the remainder stay dedicated for at least six months. However, only one in 20 is likely to still be following their new healthy eating regime after one year.
The study of 2,000 adults commissioned by Alpro helped to explain why fad diets including the Atkins Diet, the Dukan Diet, The Alkaline Diet, The Baby Food Diet, The French Woman Diet, The Paleo Diet and the new 5:2 Diet are passing trends for the majority of slimmers.
"More and more dieters are realising that the fad diet promises of shedding huge amounts of weight in just a few weeks are either hollow, or that the diets are impossible to follow," said Alpro dietician Kate Arthur.
"The reality is that the majority of these diets are so impractical, and indeed so little fun that we often give up within just a few days.
"There has never been any secret to sustaining a healthy diet. It always has been, and always will be, about eating the right foods as part of a balanced diet, and exercising, while allowing yourself a treat now and again."
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