juicing is better if:
1) you have trouble digesting fruits and vegetables since your body isn't used to eating raw food
2) you find it difficult to consume the amount of food required to hit your calorie target
more calories than your body needs = weight gain
less calories that your body needs = weight loss
the type of weight loss and gain is determined by your activity. if you're not using your muscles much expect to gain mostly fat, and lose mostly muscle (as they say, if you don't use it, you lose it). if you're looking to gain muscle, then you must perform an activity that regularly challenges those muscles in order for them to grow.
you don't need to eat flesh of animals to build muscle. muscle is built with amino acids - the building blocks of life. the protein you eat is broken down by the body to amino acids which are used to repair tissue and build muscle. you can find amino acids in many leafy green vegetables, think popeye and his spinach. look at the diets of some of the strongest, most muscular animals on earth and you'll find they thrive on a diet of vegetation.
another thing to note, is in order for your cells to live, they need energy. sugar is energy. if you starve the body of sugar, cells die.
the body will break down carb sources into sugar. this does not mean you can go eat candy bars thinking your feeding your cells, this is not the kind of sugar the body thrives on. it thrives on sugar from fruits in their whole food source (sugar processed from fruits is not the same).
this is a very simplistic, big picture explanation, hope it helps.