It's all very well to eat, drink and be merry over Christmas – but you could have a heavy price to pay in the New Year.

It’s estimated that the average person consumes an extra 500 calories per day over the festive period, equating to a possible 5lb weight gain.

The British Dietetic Association (BDA) is keen to help people avoid the unhealthy repercussions of Christmas excess.

Sian Porter, pictured inset, consultant dietician and BDA spokesperson, said: “The aim isn’t to make people feel guilty about indulging at this time of year, it’s merely to outline the amount of calories that can get consumed.

“This time of year, it’s so easy to unwittingly consume a lot more calories than normal, “Make plans to get yourself and the family active – dancing, shopping and post-meal walks will all help to burn off some calories so you can have a very happy and healthy New Year.”

Sensible steps like these are far more achievable – and usually far better for us – than many of the more extreme fad diets doing the rounds.

“The truth is, if something sounds too good to be true, it probably is,” Porter warns.

Permanent, sensible changes are what the experts advise, if you want to lose weight and keep it off.

Here are four trendy diets the BDA says people should avoid: n The Paleo Diet Miley Cyrus and Matthew McConaughey have reportedly tried the paleo plan, also known as the Paleolithic, Caveman and Stone Age Diet. Only foods thought to be available to Neanderthals in the prehistoric era are allowed, and all other foods – like dairy products, grains, sugar, legumes, processed oils, salt, and drinks like coffee and alcohol – are excluded.

However, the BDA says that while eating fewer processed foods and less sugar and salt is a good idea, there’s no need to cut any food group out of your diet entirely, unless advised to do so for medical reasons. In fact, cutting dairy completely without very careful substitution, the experts warn, could compromise bone health.

n The Sugar-free Diet As well as banishing the white stuff from the menu, sugar-free diets – reportedly tried by the likes of Tom Hanks and Alec Baldwin – often ban carbohydrates too, as these are turned into glucose in the body.

But although the BDA encourages reducing added sugar, and sugar-loaded processed foods and desserts, it points out that some versions of this diet demand followers cut out all sugar, which is extremely limiting and unhealthy.

“This is not only almost impossible,” says Porter, “but would mean cutting out foods like vegetables, fruit, dairy products and nuts – not exactly a healthy, balanced diet.”

n The VB6 Diet Beyonce has reportedly tried this diet, so-named because it’s about being vegan before 6pm. But after 6pm, nothing, within reason, is off limits.

The BDA says that while it’s good that VB6 dieters eat less processed food, and more plant-based foods, being vegan doesn’t automatically translate into eating healthily.

Porter says: “The danger is that post-6pm becomes a window of opportunity to hoover up a myriad of foods high in calories, saturated fat and packed with added salt and sugar.”

n The Clay Cleanse Diet This diet claims a spoon of clay a day will remove toxins and negative isotopes from the body, helping you cleanse and stay in shape. Actress Zoe Kravitz has reportedly tried it.

However, stay away from the clay is the advice of the BDA, which points out that the Food Standards Agency issued a warning about the dangers of consuming clay, particularly for pregnant women, after high levels of lead and arsenic were discovered in some products. The whole idea of detox is “nonsense” and the body has its own built-in mechanisms to remove waste and toxins.