People lose a lot of weight when they begin juice diets because the lack of carbs causes the body to lose a lot of water. This makes them think that juice diets are a magic way to lose weight, but when they start eating carbs again, their bodies start retaining water once again. Juice diets are also not conducive to long term weight loss, because after the diet people go right back to their old habits and gain back the weight they lost. A better strategy to lose weight would be to cut down sugar and junk food intake on a long term basis.