Any diet or detox program involving fasting could cause the body to break down, experts have warned.
Some companies have launched aggressive marketing campaigns aimed at young women who want to lose weight.
But doctors insist that such programs are of no benefit.
"There's no medical or scientific evidence that there's any health benefits from fasting," the Daily Telegraph quoted Dr Jane Smith from the Royal College of General Practitioners as saying.
"You could be doing your body harm. There's a lot of money to be made selling magic (solutions) to people," Smith added.
Lemon Detox Diet is one of the most popular programs. Its fans include Beyonce and Tania Zaetta.
The mixture of palm and maple syrup, lemon juice, cayenne pepper and pure water claims to shed weight and cleanse the body.
However, mother-of-two Rylee Page refuses to go near the product after suffering severe side-effects.
"I was so light-headed that I was driving the car and had to pull over. I was walking around like I was in a daze. I would strongly advise anyone who has kids or drives not to use it," she said.
Dieticians suggest that instead of going for such diet programs, people should cut out caffeine, alcohol and high fat foods for a week to achieve the same results.
A Lemon Detox Diet spokesman said that there were some "normal symptoms" including light-headedness, headaches, dizziness and nausea.
"There is no real way of knowing if a person doing the detox will have mild symptoms or no symptoms at all, but if a person has overwhelming symptoms we always advise them to stop the program immediately," he said.