Answer by Steven Fowkes:

If you mean metabolism in the context of BMR (basal metabolic rate), there are many. Coconut oil, MCT oil, polyunsaturated oils (fish, flax, ext.), mitochondrial nutrients (if deficient), thermogenic agents (caffeine, theobromine, ephedra), exercise, oxygen, superoxide, phototherapy, and more.
If you mean any of the metabolic pathways in the body, then the answer is also yes. But the possibly-effective substances would include all of the essential and conditionally essential nutrients, if they are deficient or competitively inhibited, and many non-essential nutrients that might mitigate a variety of toxic or feedback-loop conditions.
For example, if you have a B6 deficiency, B6 will speed up your metabolism. If your B6 enzymes are fully saturated, pretty much nothing will happen to your metabolism.
That's a short answer.

Is there a supplement to speed up metabolism?