My son, if left to his own devices, would eat the same meal every single time.

We ensure that his meals are reasonably balanced, with fruit and vegetables at every meal, but it's a challenge to keep the meals varied

Assuming his meals provide adequate nutrition, how important is it that he eat a variety of meals, instead of the same things day after day?

Are there studies that show benefits to diverse diets, or risks from not having a diverse diet?