Do you have any reputable links?
The list of what the USDA has said is depleted in the food supply is in one of my many bookshelves, and I don't know where it is right off, and I'm tired. I do recall that they said magnesium barely meets the RDA's (but various nutritionists claim the RDA's are ridiculously low in this, in B-6 and in some other nutrients).
FWIW, I do respect the Life Extension people and their obsession with data ( http://www.lef.org/ ). Some people say their research should be discounted since they have products to sell. I say anything funded by government and universities should therefore be doubly-discounted since they have tyranny to sell and tenure to buy. In any case, let the buyer beware, ESPECIALLY when anyone claims to be unbiased.
My apologies. I'm so tired I'm not thinking (not that tiredness has that much to do with it). Nomatter whether the USDA is basing their assumptions on Americans eating 5 servings of fresh fruits and vegetables a day or not, and nomatter whether my recollection of what they had to say is accurate or not, the point really is: MD's SHOULD test each referenced patient for those nutrients from which serotonin is made BEFORE they make THEIR hurried decisions, whether they are to prescribe nutrient supplements, prescription meds or whatever.
As far as which nutrients the body needs to actually synthesize serotonin is concerned, I'm sure a minimal amount of Googling will get you there. Sorry to be so brusk (before my head hits the keyboard!).