I speak to people all the time who want me to write them a better training plan because they’re not seeing the results they hoped for. In reality, I often find that there’s nothing particularly wrong with what they’re doing in the gym (sure, I can always optimise their programme), but the real reason they’re not seeing results is because they’re not backing up their efforts with good nutrition.
For weight loss you need to ensure you’re in a sufficient and sustainable calorie deficit.
To build healthy muscle tissue you need to ensure you’re getting enough calories and protein.
For athletic performance you need to ensure you’re getting the right amount and types of carbs at the right times.