When it comes to nutrition there are thousands of different diets, and methodologies. But in the world of coaching there are two major methods for giving clients their nutrition coaching; Meal Plans & Macro nutrient Calculations.
Meal plans involve outlining specific types of food and the quantity to eat on any given day. This gives simplicity to the client because everything is outlined for them. While macro nutrient calculation plans just specify the amount of calories, fat, protein, and carbohydrates necessary on any given day. Both are valuable to different clients but in my opinion one is vastly superior for athletes.
Meal plans suffer from 3 major flaws; inflexibility, a lack of empowering the client to make informed choices for themselves, and lack of trainer knowledge.
Let's start by tackling the inflexibility. During a meal plan you will be given daily meal plans that will hopefully encompass your macro nutrient requirements; as a side note, many don't, they give a cookie cutter program to many clients in order to save time rather than making one individualized to each client. These plans will outline exactly how much meat source, vegetable source, fat source, and carbohydrate source you will intake and maybe 1-2 variations of those sources in case you don't like the taste of those foods. The issue becomes if you don't have access to these foods you won't be able to effectively adjust your diet. Many of the people I know who have followed these diets will just stop following them if they cannot be perfectly executed which becomes a huge issue if you cannot plan perfectly.
Next we have the empowerment issue, part of our job as a coach is empowering and teaching our clients how to effectively train without us needing to watch over everything they do. We are there to direct, guide, and maximize performance. With nutrition coaching we do this by providing them with the necessary relevant information for them to achieve their goals then giving them a framework to operate within (generally a macro nutrient calculation). With meal plans this gets removed completely, you are given a food with a weight of how much you need then you are left alone. No knowledge of why this is healthy, why you need to each that much, or even why that variety of food. You are stuck dependent on your coach and left in the dark. Some tracking softwares wont even show the macro nutrients present in the foods which means people get completely lost if they need to switch up their intake for different foods.
Finally is a systemic issue we see with under qualified coaches and personal trainers. Because they aren't confident in the knowledge they have accrued, they are unwilling to create set content to show it off and potentially be called out. To get around this they will utilize meal plans for their clients under the guise it is for the client convenience. Not all will do this but it is a common trope among poor quality trainers. At the very least be cautious when getting meal plans from any personal trainer or coach and have at least a working knowledge of nutrition to ask them test questions if you are unsure of their quality.
Realistically both Macro and Meal Plans can be valuable tools used to better your health. But a lot of the value is derived from what the client is looking. Does the client want something prescribed and just follow along with or do they want to learn and have more flexibility in their diet. The choice is up to the individual but when comparing the positives and negatives to both the plain and simple winner for any serious athlete is the macro nutrient calculation.