WeightWatchers dieters can go for a "Friday night curry binge", after the company radically altered the way it calculated how much its customers can eat each week.
The company said it was necessary for any diet to be "realistic" if people were not to "fall off the wagon".
A glass of wine every night, or a spontaneous trip to a curry house after work, will be tolerated in the scheme designed to fit in with the pressures of modern living and an era when will power is in short supply.
The company will no longer use calories, an obsession for many dieters, as the key measure to determine how much food people can eat each day.
WeightWatchers works on a point system with dieters having tot up each item of food or meal. Each product's points is calculated on the amount of calories and saturated fat it contains. Customeres are not allowed to exceed a certain number of points each day – calculated on their size, age and sex – unless they have saved up the points.
However, two major changes are being introduced, starting next week.
First, dieters will be able to eat as much fruit and vegetables as they want under the new Points Plus programme, as these will incur no points at all. The only exception is potatoes and other starchy vegetables. That is because a food's points will be calculated not on calories but on a combination of how much fat, protein, sugar and fibre it contains and how much energy is used chewing and digesting the food.
A spokesman for WeightWatchers said: "Under the old system a banana was 1.5 points and so too was a low-calorie chocolate bar. And if you wanted a treat you would probably always have reached for the chocolate bar. But now you can eat as much fruit as you want. We are trying to encourage people to eat as healthily as possible".
The second innovation is that dieters will be allowed to have a "back pocket" allocation of points which they can use on top of their daily allowance. The minimum amount of daily points that a dieter can have is 29, but they will now have a 49 points "in their back pocket" to use either spread out over the week or in one big splurge.
The spokesman denied WeightWatchers was "going soft" on dieters. The spokesman said: "Not at all. We know that for weight loss to be sustainable it has to be realistic. You cannot lock yourself away in a room and deprive yourself of foods you love. It will not work.
"You have to treat yourself once in a while."