Oh boy, what a huge topic this is. And a confusing one.
There are so many things a person can take to influence their health; proteins, greens, fats, ketones, vitamins, the list goes on and on. The challenge is knowing what to take, when to take it, how do you know if its working.
My golden rule is if you can get it through your diet that is best. But I'm not about to stand over a stove for 2 days making bone broth soup for its collagen, or eat pounds of spinach for my greens, or massive amounts of fish for its clean protein just to meet the bare minimums. Fasting is a great way to get yourself into ketosis though this seems to work better intermittently. So this is where supplements come into play. If you can't get it through your diet, if your body needs more than you can consume, you need to support your body's needs with supplementation.
Quality, get the best you can afford. Good quality supplements are more bio-compatable with your body, have less by-product for your system to filter out and are typically more potent and reliable. If you're not sure, ask a reputable professional like your naturopath, doctor, etc. In this day of online shopping we are no longer restricted to just what is available at our local shops.
Pay attention to your body, if your instincts say you feel better taking something, then you're probably right. Stick with something, it takes time to replenish a body's stores of nutrients before most external symptoms are seen. Notice the small changes, while the pain may be marginally better maybe the knee that used to click all the time doesn't. Maybe your daytime energy isn't quite there yet but you can fall asleep better. Don't give up right away, it took time to deplete your body, it won't refuel immediately.
Sometimes talking to a nutritionist or naturopath is the best first step. Having a live blood cell analysis done is one way to see how healthy your body is and where it needs help. Doing this in conjunction with your medical tests can paint a much clearer picture of your overall health. Our goals as health professionals is always to help you become the healthiest you possibly could be.