Detox diets do no more than the body's own natural system to get rid of toxins, US researchers claim.
Detox diets usually advise eating a lot of fruit
People have been "detoxing" for thousands of years, but the scientists say there is no proof that such bodily purges work.
And they say most modern books and detox kits serve up "empty promises".
Writing in Food Technology, experts from the University of Southern California repeat the advice that a balanced diet is best.
In a commentary in the journal, they say detox plans promise all kinds of results; from cell cleansing to skin revitalisation, colon decontaminating and liver purging.
To do this, people are told to have a restricted diet of fruit and vegetables and lots of water.
Caffeine, alcohol and processed foods are banned.
Roger Clemens, professor of molecular pharmacology and toxicology at the University of Southern California and Dr Peter Pressman, an endocrinologist at private medical firm Geller, Rudnick, Bush and Bamberger say many have reported detoxing worked for them.
They write: "There are thousands of testimonials that describe experience of less bloating (actually the result of eating less food), clearer skin (improved hydration) and decreased headaches (reduced alcohol and caffeine)."
But they say the benefits people feel are not due to their body getting rid of excessive toxins.
"The suggestion that elimination of noxious agents is enhanced because of this regimen is categorically unsubstantiated and runs counter to our understanding about human physiology and biochemistry."
They say the improvements detoxers see are instead due to changing from what is likely to have been a "poor" diet.
And they stress the body is designed to "detox" itself.
"Healthy adults, even overweight adults, have been endowed with extraordinary systems for the elimination of waste and regulation of body chemistry.
"Our lungs, kidneys, liver, gastrointestinal tract and immune system are effective in removing or neutralising toxic substances within hours of consumption."
They warn that detoxing can be dangerous for groups such as teenagers or pregnant women, who cannot afford to deprive themselves of food groups.
Ursula Arens, a registered dietician and spokeswoman for the British Dietetic Association said: "'Detox' is a meaningless term that is used all the time.
"And because it hasn't been defined, it's impossible to say if it's worked or if it hasn't."
She added: "All food is made up of chemicals, and all our body does with food is a chemical reaction.
"The body is set up to deal with the chemicals it doesn't want, and excrete them."
Claire Williamson, a nutrition scientist at the British Nutrition Foundation, added: "No single food can provide all the nutrients that the body needs, and therefore it is important to consume a balanced and varied diet in order to obtain adequate amounts of energy, protein, vitamins, minerals and fibre required for good health.
"Cutting out complete food groups in the long term, may have adverse effects on an individual's health."