The only way to shed the post-festival extra pounds is the good old way - eat less and exercise more.

Now that you're discovering all the extra flab from the Christmas and New Year food and booze binge, you're casting around for the latest diet to lose it all in time for summer.

But take care before you choose.

The British Dietetic Association (BDA) says that there are many varied "fad" diets offering miracle weight loss, but warns consumers that losing the pounds while on one of them is simply due to eating fewer calories.

"It may not sound the most exciting way to lose weight but healthy eating, activity and long-term behavior change not only works but helps you maintain weight loss too," says Rachel Cooke, registered dietitian at St Martins' Hospital in Bath and BDA spokeswoman.

The BDA has produced a list of the "worst fad diets to avoid this New Year" including such regimes as the maple syrup, blood group, warrior, peanut butter and banana or the cabbage/fat-burning soup diets.

It says some regimes, such as the cabbage soup diet were based on "pseudo science" and that adhering to them over the long term could result in nutritional deficiencies.

"Firstly, no food can burn fat; only physical activity can do that," the BDA says of the cabbage soup diet in which the adherent exists largely on home-made cabbage soup.

The BDA also blasted the myth of the detox diet, saying that the human body is a complex organism that is more than capable of detoxing itself.

"The liver works to rid the body of everyday toxins so a 'special diet' is not necessary," the BDA says.

It says detox diets - often popular with celebrities -recommend cutting out entire food groups and living on fruit/vegetables and water and that they can also lead to nutritional deficiencies as whole food groups are omitted.

"After 'the Christmas feast,' simply reducing food intake as well as eating more fruit and vegetables will lead to a reduction of calories and weight loss," the BDA says.

The professional body for British dietitians also took aim at two famous diet plans.

It says the Atkins diet, sold around the world, contravenes "evidence-based healthy eating messages" and that the Zone diet goes against Britain's Food Standard Agency recommendations.

The BDA says the rigid version of the Atkins diet means no bread, potatoes, pasta, rice or cereals and only a minimal allowance of fruit and vegetables.

"This diet goes against evidenced-based healthy eating messages, can lead to high intakes of saturated fat and virtually none of the five-a-day fruit and vegetables that help reduce heart disease, stroke and some of the UK's most prevalent cancers," it adds.

Atkins (www.atkins.com) said in a statement that it strongly refuted the BDA's comments and objected to its inclusion on the list of the "worst fad diets to avoid this New Year".

"It is clear from the report that the author is not familiar with the new 'Atkins Nutritional Approach'," the vice president of education and research for Atkins Health and Medical Information Services Colette Heimowitz said in an e-mailed statement.

"This diet is not a fad but offers a long term healthy eating plan with reduced levels of refined carbohydrates and sugars, and encourages the consumption of lean protein, high fiber, fruit and vegetables."

The Zone Diet (www.ZoneDiet.com) also objected to its inclusion on the BDA list as an eating plan that was "probably more complicated than making small changes to intake that will result in long-term healthy weight loss".

"The Zone Diet has in fact the same guidelines as the newest dietary guidelines for treating obesity, Type 2 diabetes, and pre-diabetes from the Joslin Diabetes Research Center affiliated with Harvard Medical School," Zone Diet marketing manager Kari Haering said in an e-mailed statement.

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