It is important for a fruitarian to take a vitamin-supplement containing vitamin B12. Women who are pregnant or nursing especially need vitamin B12.
By eating only the fruit of a plant, the plant does not have to be killed (when you eat a carrot, which is the root of a plant, the whole carrot plant dies). Fructarians note that, in many cases, eating fruit does the parent plant a favor. All fleshy fruit is designed to be eaten by animals and either travel through the animal's digestive tract before it sprouts in a pile of ready-made fertilizer; or, in the case of fruits with cores or pits, to be carried away from the parent plant, eaten, and the core or pit which contains the seeds or is the seed, tossed aside to sprout. Without animals eating fruit, the fruit would not travel far enough away from the parent plant to grow successfully. Many plants depend on animals for seed dispersal.
However, a fruitarian diet is very difficult to follow, and on a long-term basis fruitarians often suffer health problems caused by nutrient deficiency. The high sugar content of their diet can cause diabetic or hypoglycemic-type symptoms, while it is lacking in protein, minerals, and fat-soluble vitamins. Long-term fruitarians are prone to food cravings and consequent binge-eating, either of 'allowed' foods or 'illegal' ones, and they often become addicted to dates (for their high sugar content) and avocados (which are extremely high in fat). Some fruitarians develop a type of eating disorder called orthorexia.