TLDR: While the 1st world is renown for having a surplus of calories, most of the USSA is suffering from nutrient deficiency. Even if you’re eating “clean” or “paleo” or “lots of fruits/vegetables” etc; soil depletion means that most of us are not getting enough of the minerals necessary for vibrant health; and lack of sunlight exposure means we are not getting enough vitamin D either.

Iodine, magnesium, calcium, and vit-D are the first ones to look at. It’s location dependent, but our soils have largely been depleted of iodine and Mg for decades. As far as Ca, if you’re drinking a lot of milk or bone broths you might be ok, but if not, you should consider supplementing. Salt is fortified with iodine, but even then it’s just the minimum to prevent people from getting rickets; and the bromine content of many foods causes iodine to be spent on removing this toxic element and its compounds.

For vitamin D, my experience is that it’s better to get sunshine than to supplement, if possible. There is a minimum UV-index threshold before your skin begins to convert cholesterol to vit-D, and the darker your skin, the higher the threshold. Longer exposure time is required to produce the same amount as those with lighter skin, and sunscreen will stop production almost entirely. If you live in a northern latitude, or spend a lot of time indoors during peak sunlight (which is most of us), then you need to supplement 1000-5000 IU of vitamin D3 on a daily basis. If possible, get some direct sunlight on your balls for 5-10 minutes; it can be like a shot of T if you’re deficient (so I have heard).

If you supplement nothing else and just these 4, you’re almost certain to see improvements in mood, sleep, gym results, energy, and clarity of thought; as they are critical for testosterone production, nerve functioning, muscle control, bone density, and a host of other important functions.

Zinc, Potassium, and to a lesser degree – copper, selenium, and iron are also common deficiencies. Zinc is critical for testosterone production, and potassium is integral to muscle and nerve functioning. However, you have to be cautious, as excess iron or selenium can have negative effects. You will want to do your own research and analysis on these to make sure you get the right balance.

I’m going to assume that everyone has heard about A, B and C vitamins and why they’re important. Generally a solid diet will get you sufficient amounts of those. But minerals are a different story, and almost everyone needs to supplement iodine, Mg, Ca, and Vit-D. This is especially true if, like me, you’ve done your fair share of drinking over the years.

Again, do your own research, and 1) take bio-available forms of these minerals, as many supplements package them in ways the body doesn’t absorb, 2) consume with the right foods, as some minerals require certain macro-nutrients for optimal absorption, and 3) be careful not to take a cocktail of everything all at once, as some minerals can compete for absorption. All of these are good reasons to avoid multivitamins - they have not been shown to be all that beneficial.

Conclusion As someone who spent years eating a very clean/healthy diet but neglected minerals and vit-D intake; this is critical if you want to feel good and perform your best. I saw significant improvement not only in myself, but for others who have tried it as well.

EDIT: Here is my personal regimen. Mixed in water: magnesium citrate powder and Lugol's Potassium Iodide/Iodine (5 drops of 2.5%, though you need to work up slowly to that much); along with vit D3 pills for days I don't get any sun. Finally, I eat an eggshell most days (although there are other ways to get Ca). I take all of these together in the morning with my first meal, as they tend to work together for absorption. Later in the day I will take zinc/Cu with lunch or dinner.

This should really help improve your testes and thyroid function. If you're having problems with energy like a couple of the commenters, even after improving your diet; try a similar regimen.