One of the most disturbing trends I saw at the fitness conference was the implicit sanction of cleansing diets. Two competing companies ran booths at the trade show, giving implied endorsement for fitness professionals to promote detox diets.
Such diets may use a fruit or vegetable drink (and may or may not include a colonic irrigation) to "purify" the body and get rid of toxins. You have probably heard at least one celebrity (usually female) discuss how it keeps her healthy, slim and full of energy. Detox diets have been around centuries, most involve fasting and/or limiting major food groups, and some include a religious aspect. The main commonality is ridding the body of impurities. However, the human body is designed to purify toxins from food naturally: The liver, kidneys, lungs and even the skin do this work. There is no valid clinical research (and please do not confuse cleanse product press releases with research) that such diets work.
You certainly can lose weight (at least temporarily) with a detox diet; they are essentially a starvation plan. But as with all diets, if you do not change your lifestyle and daily eating habits the weight will come back on. As for the claims of “increased energy and better mental focus ”, most experts attribute that to either the placebo effect, or to the fact the body is in a state of ketosis. This happens when you deprive your liver of glycogen and therefore rely on ketones for energy. This causes a change in the brain, which some interpret as a high. It is also the process diabetics go through when their blood sugar is uncontrolled, not something I would want to induce on purpose. The negative effects of a detox diet also include fatigue, irritability and headaches.
If you are in good health and need a psychological boost to jumpstart a diet, then a cleansing diet may help and will probably not hurt. However, children, adolescents, pregnant or nursing women, or those with any type of chronic health issue or compromised immune system are at high risk for serious problems. I am sorry to see anyone in the fitness industry promote these products. There really is no quick fix or easy avenue to a healthy lifestyle. The standard boring advice of regular exercise and a balanced nutritious diet is still the only thing that works.