The U.S. Food and Drug Administration has warned against using body wraps as a method of weight reduction, in a report published in 1982:
Who can blame the fretfully flabby for being lured by the promise of losing inches without doing anything more strenuous than popping a pill or wrapping up the offending flesh? Who can resist ads for body wraps that promise "to burn away fat even while you sleep," to "lose 4-6 inches the first day?"
They go on:
The Food and Drug Administration has investigated a number of these products and has taken action against several promoters of wrapping devices and latex exercise or sweat suits for making unsubstantiated medical or therapeutic claims.
They continue:
Such treatment will cause a loss of inches and perhaps pounds due to profuse perspiration. But the reductions are temporary. The fluid is soon replaced by drinking or eating. But rapid and excessive fluid loss is potentially dangerous because it can bring on severe dehydration and can upset the balance of important electrolytes in the body. ... Wraps have no effect on fat deposits and will not dissolve fat, even temporarily. Fat is not broken down by perspiration, only when fewer calories are consumed than are needed to meet the body's energy requirements.
Moreover:
A leaflet for the product claims: "Lose up to two inches from those problem areas in just one hour." An advertisement adds, "Its gentle warmth penetrates into your skin and helps melt fatty deposits." But, as with other wraps, any weight or inches that disappear are lost from perspiration. (See "Fat Won't Melt," an Update in the November 1981 FDA Consumer.)
Source: Judith Willis, FDA Consumer November 1982
See more: "Body Wraps Come with Strings Attached," ABC News, July 26, 2009