Although fruits and vegetables are both good for your health, fruits cannot replace vegetables under most circumstances. From a nutrition perspective, the biggest differences between them are sugar content and nutrient ratio. Usually fruits contain a higher level of sugar from 5% to 15%. Also they contain rich nutrients like Vitamin C and potassium. Compared to vegetables, the greatest advantage of fruits is that almost all of them could be eaten raw. Therefore vitamins and minerals could be obtained with little consumption.
And for most vegetables, the sugar level is usually under 5% and they are more accepted after cooking. And vegetables contain various nutrients like carotene, vitamin C, vitamin B family, potassium, magnesium and more, especially those leafy green ones. Everyday your body will need to consume multiple vitamins and nutrients. Totally betting on fruits will not only make you lose parts of the nutrients, but also consume more sugar which will possibly result in obesity.
Besides, the dietary fiber in fruits are mainly pectin existing most in pericarp and seed coats like orange or apple peel. But for vegetables, the dietary fibers can be softened in cooking process, which will improve its absorption significantly compared to fruits.