Liquid diets are most effective for weight reduction

False. Whether a diet is liquid or not has no bearing on how it will help weight reduction. It so happens that a new generation of low-energy diets was heralded by the appearance of high-protein liquid diets. There were initially some deaths with their use, possibly because of the poor quality of the protein and the electrolyte (mineral) composition. They were also probably used for too long, and in people who may have been prone to side effects like abnormal heart rhythm.

Liquid diets are sometimes used in treating very obese people. There are now nutritionally complete (as far as we understand) formula feeds of about 2100 kilojoules (500 kilocalories) per day which in selected obese patients may be suitable for use for up to eight weeks, under medical supervision. For long-term weight loss, however, behavioural changes must take place.