There are no particular contraindications in consuming mainly plant-based foods It is however important that the diet includes the consumption of a large class of food of plant origin (dried fruit, vegetables, legumes, etc.). In fact, an exclusively vegetarian diet, even if sufficient from the protein point of view, may be deficient in vitamins (B12) and minerals such as iodine, iron and calcium, and essential fatty acids. it is really hard to find the perfect combination in a plant based diet only. The risk is to go through deficiency of vitamins, proteins and nutrients.
It is also important to eat saturated fat which is essential to brain function and cell membrane integrity, and is a great source of energy on a high-fat diet as long as you’re getting it from quality sources.