There is no best overall nutrition plan, simply because it depends on the type of training they do, their fitness goals (participating in a specific sport, lose weight, increase weight, increase muscle mass, train for a 5k, marathon, all kind of triathlons, etc.), medical conditions, age, budget, location where they reside (each country has different customs and diets) and so many other reasons. This is why we prefer to refer them to a dietitian or a nutritionist, so they can tailor their diet according to their needs.
I hope this helps.
in order to lose fat weight, a negative energy balance has to be achieved between eating less and exercising more. From that perspective, the total number of calories-in is important.
While I do not give specific meal plans as this is not within my scope of practice, I educate my clients on the need to eat nutrient-rich calories, reduce the amount of processed foods and the risk that liquid calories present that come in the form of sodas and even excessive amount of fruit juices. Lots of the famous fruits and veggies. I typically advise against high-protein diets.