I do not know Mark Hyman Personally. I have had no academic discussions with him and was not under his care.

From looking at some of his you-tube videos, His list of publications, and trying to learn a bit more about "functional medicine" and the functional university ( I read some of what they have on their site, and also asked them to send me some of their teaching cases).

I have reached the following conclusions:

1. This is a very well-spoken charizmatic physician.

2. There are very few original thoughts or ideas in what he says or in his publications. He mostly writes very good reviews about what is known.

3. the vast majority of his publications are in a journal in which he is on the editorial board.

3. He is making an excellent academic (and I believe also well-paying) career out of this.

4. There is nothing novel in the "functional medicine" approach. It is based on studies published in the medical literature (some out-dated) and scientific journals. They do put more emphasis on nutrition and environmental exposure, but again they do not have any novel data or their own original research. Much of what they suggest is based on reasonable and intelligent assumptions. Yet, they sell it as the "medicine of the future".

5. the kind of medical practice they encourage is very time consuming (so unfortunately not practical without major and required changes in the health care system), and expensive to the patient ( much of it will probably not be covered by most health care plans). They do suggest health care reforms, but not in the position to do much about it. (and in that they are not different from many physicians around the world).

6. They do not advocate abandoning medications, but do advocate carefully reading the medical literature and using them wisely (and in that they are no different from many good physicians around the world).
Although, some of the you-tube videos may be interpreted in that way.

If I summarize what he says in plain language (without the spins and hypes) it would be:

The combination of being overworked, having significant emotional stress (due to a hard divorce), poor nutrition (like most american physicians I was grabbing junk food which I quickly ate, not to waste precious time) and an infection made me collapse.
instead of understanding this, I went to numerous physicians, who looked at me like pieces of a puzzle. They gave me names that meant nothing and symptomatic treatments without trying to seriously understand what is wrong with. Even the psychiatrist just gave me antidepressants.
None of them bothered to look at me as a person. None of them realized that what I need is some rest, proper nutrition and emotional support. None of them realized that I was not ill or depressed just overworked and under enormous stress. I too (being an over-ambitious person failed to understand that).
Trying to understand what is wrong with me, I went back to what I learned in medical school (well, I know I said what I learned there didn't help, but where the heck do you think is my knowledge in biochemistry and metabolic cycles from?). I realized how important it is to have proper nutrition and letting my body rest.

It also made me realize that the american medical system is treating so many people in my condition as suffering from diseases which require medications, instead of advising life-style changes and proper nutrition.
Going back to basic biology (which I failed to realize its importance in medical school) also made me read some more. I found out that while I was busy working as a GP, there has been enormous amount of research going on.
I learned about systems biology, epigenetics and numerous other biological research. I was fascinated by it (even though I never got a very deep understanding so failed to understand the current limitations of applying this kind of research to medical practice). I also realized (like many other physicians, among which are the former editor of the prestigious journal NEJM) that many of the medications I was giving my patients on a regular basis are based on poor evidence. And that there is too much influence of large pharma companies. (what a revelation!)

As I gradually recovered (with better nutrition, rest and emotional support), I started to realize that this is a true gold-mine. I can treat (basically healthy) people or people with relatively mild chronic diseases (in which the harm of pharmacological treatment clearly outweighs potential benefit) and make their life better, I can teach other health care professionals and share my "insights" with them, and I can join the editorial board of a journal which advocates what I have learned and publish numerous papers that way.

There is nothing wrong in any of that, as long as it doesn't lead to people reaching wrong conclusions and as long as he is aware that he too is selling a product and has a lot to gain from it.