I probably interact with over a hundred doctors a month, so I have a general idea of what your typical GP has learned in med school.
Family doctors are trained to diagnose and treat common ailments. This is what they do, first and foremost. They know all about common viruses, common chronic illnesses, common infections, common soft tissue injuries…and also common warning signs which say “this is outside my area of expertise, time to refer to a specialist”. All this encompasses an absolute shitload of information. You have to be a pretty bright individual to be a GP.
They also have to earn CME (Continuing Medical Education) credits. These are usually hosted by pharm companies with a specialist as the guest speaker. There is always a fairly specific topic, for example “New advances in glucose monitoring for diabetic patients”. However, the topic always relates to a product the pharmaceutical/med device industry sells. These CMEs are very seldom about “20 rep squats for balls out intensity” or “Ripped abs vs. Freaky ripped abs…crossing the threshold”.
If you do find a GP well-versed in sports nutrition and resistance training, you’re lucky. This is outside the scope of their practice (usually) and they have taken the initiative to learn about these things on their own time. Most GPs in busy clinics simply cannot be bothered. I don’t hold this against them in any way…there are doctor shortages in many areas and they have to focus on learning about the stuff they see everyday.
(People who have graduated med school in the past 15 years have been given at least a basic grounding in nutritional and exercise-related concepts. Some older doctors have told me they used to have to learn about the “food pyramid”.)