You're framing a very opinionated (and hotly contested) take "high protein, low fat, low carb" presented as universal truth as just "suggesting to eat well".
Suggesting lifting weights three times a week when all you know is the person has a problem with their joints is not only unhelpful, it can be downright detrimental to their health. It's like recommending someone morbidly obese go for a run. It might be fine, but it might also destroy their joints for the rest of their life, and you can't know which it is without knowing more about their situation and condition.
A wide variety of joint issues are improved by performing a slow and steady progressive overload with lifting weights. Not all of them, of course, and yes there are some issues that preclude lifting, but this seems rather pedantic. There are a trillion things that most humans can do with no detrimental impact that a small subset can't. Trying to couch every suggestion based on edge cases is silly.
The overwhelming majority of people would benefit from doing resistance training 3x a week, cardio 3x a week, and shifting their diet towards more protein and less carbs and fat. People who fall outside of the large majority due to specific medical conditions need to understand their medical conditions and how they impact their daily life, because expecting everyone else to always take into account these issues is unreasonable and unproductive.
> It's like recommending someone morbidly obese go for a run
To be frank, this is a dumb point. The morbidly obese person probably can’t even run for 30 seconds. It won’t destroy their joints for the rest of their life. Suggesting activity over inactivity is good advice for basically every human alive.
Hardly so. I worked as a coach when I was younger and the number of people who hurt themselves this way is considerable, likewise for many completely preventable injuries at the gym. Usually people only turn to professional help once some damage is already done. To exemplify my point, the average BMI in the US is roughly between overweight and obese. If someone in that weight range decides that the treadmill is the way to turn their life around, they will most likely come away with serious injuries if they keep it up.
Suggesting activity is good, yes, but suggesting someone should start with lifting specifically when they have issues with their joints without any further context is moronic.
