January is the most popular time of the year to start a new diet after the excess of Christmas and New Year parties.

But if you're thinking of trying out a quick-fix fad plan to get instant results, you may change your mind after reading this.

Qualified nutritionists and a GP have exclusively told FEMAIL Food&Drink some of the shocking side effects you can suffer from if you embark on an extreme diet.

And while some can actually cause you to gain weight, others can have potentially terrifying symptoms such as heart problems and complications of the brain and organs.

Many people start a diet in January after over indulging in February, but some quick-fix extreme plans can cause serious side effects

GP Dr Sarah Brewer, Harley Street nutritionist Rhiannon Lambert, nutritionist and co-author of the Cheats and Eats lifestyle programme Rob Hobson, and leading London nutritionist Lily Soutter have all shared the worst diets that they would never recommend to clients, and what t