No such thing as a healthy variation of a single-category food diet. When you restrict the diet to all fruits or all vegetables, you will not be getting very much protein and no fat. Protein is required to maintain tissues, and certain fats are required for normal functioning of tissues. You risk essential fatty acid deficiency and breakdown of muscle and bone. Not the best way to lose weight.
If you want an effective way to lose weight, start walking 30 minutes a day. More effective at lowering your risk of chronic and life-threatening diseases than changing your diet.