Most personal trainers - depending on their experience, studies, and credentials - are trained in movement and programming. In general, popular training certifications (like the one I studied for through NASM) provide high-level nutrition education.
We learn about macro nutrients, meal timing, and a LOT of myths. What we don't learn? How to provide personalized nutrition recommendations.
It's FAR outside the code of ethics for a personal trainer to provide customized meal and nutrient prescriptions.
Instead, what you should expect are general recommendations and knowledge that you can take and apply to your own experiences, like:
What's a calorie deficit and why does it matter?
What are the primary macro nutrients and what kind of ratio should I aim for?
What's a healthy amount of water to drink?
Are there certain foods that I should consume more of based on my activities?
But, if you have been struggling on your own for a long time, or you feel like you need extra guidance, who CAN you trust?
Dieticians. In the United States, dietitians are certified to treat clinical conditions - and they're different from nutritionists, who aren't always certified. There are some very fine lines around this work, but the biggest thing your personal trainer should help teach you is how to advocate for yourself.
In my opinion, a huge key takeaway (and something that makes a personal training relationship really effective) is having the support that you need to process your experiences. It's important for my clients to learn to trust their bodies, to listen to them, and to treat them with love. More often than not, we know what we need to do to heal and feel good. We know which foods make us feel like crap, and which make us feel energized. We just don't always like the truth.
And if you DO struggle to get your nutrition under control, your personal trainer should be a resource for you and help guide you to a resource that is credentialed and certified to help you get specific.
In Atlanta, my favorite one-stop-wellness-shop is Stat Wellness, located on the West Side. The healthcare team there (dietitians included) are who I trust with my health, and they understand that everything is connected - movement, nutrition, and lifestyle.
Find you a support team that can do it all!