With the UN warning sugar could be 'the new tobacco' because of its risks to health through obesity, you might think a diet that cuts it out would get the thumbs up from experts.
But a group of scientists has just consigned a trendy sugar-free anti-ageing plan to a list of fad diets it dismisses as a waste of time and money, and potentially dangerous.
While dieters can forgo sugar in yoghurt, ready meals, dessert and biscuits, for example, having none at all is almost impossible.
"Cutting all sugar from your diet would be very difficult to achieve," said biochemist Leah Fitzsimmons, who even warned that such a drastic approach could be fatal.
"Fruits, vegetables, dairy products and dairy replacements, eggs, alcohol and nuts all contain sugar, which would leave you with little other than meat and fats to eat - definitely not very healthy."
The sugar-free diet was one of five assessed by dieticians, biochemists and other experts for the charity Sense About Science.
They also dismissed the caveman diet, said to be favoured by actor Matthew McConaughey, which holds that because we evolved eating a limited number of foods, we should return to our evolutionary roots and eat berries, vegetables and lean meat, while eschewing modern fare such as cereals, lentils, beans and dairy products.
But archaeologist Erika Nitsch said: "While it is true that fluffy white loaves of sandwich bread won't have been known to our hunter-gatherer ancestors, if you are worried about a healthy diet, have lentil soup, but skip the Mars bar."
Also rejected were diets that claim to selectively slim parts of the body by influencing hormones. For instance, it is said love handles are caused by an insulin imbalance and can be shrunk by eating less sugar.
However, biochemist Madeline Burke said: "There is no evidence linking hormone synchronisation and weight loss."
Meal-replacement drinks were also found wanting. Rob Hagan, a biomolecular scientist, said we need variety, not least to avoid 'losing your enjoyment of food' and becoming depressed.
The bizarre clay diet was also considered a health risk. Its followers believe a spoon of clay a day detoxifies the body, boosts the immune system and balances acidity levels.
However, dieticians warn it can cause problems from constipation to poisoning and say 'detoxing' is a marketing myth.
Sense About Science, which has created an online quiz on the issue called Spoof Diets, says: "People actually introduce malnutrition through overly restrictive diets... and they lose heart following unsustainable diets."
Catherine Collins, of the British Dietetic Association, said: "Fad diet promoters never let sound nutrition get in the way of persuasive marketing to promote their myths and generate profit."
- Daily Mail