Functional Training Zones

Common Dietary Deficiencies

by Dr. Spencer Nadolsky,

It's a testament to our current lifestyle that people forget what supplements are – a supplementation to your diet. Too many people look for a magic pill that will solve all of their dietary needs, which is depressing considering how important diet is to your overall health.

As a practicing physician, I have to find a balance between my patients' ideal diet and the reality of what they eat. It is with that in mind that I have found the following to be the most common deficiencies.

[Please note – like I said, these are supplements. Some people may need all, some people may need a few, and some people may need none! Factor in the diet!]


Being deficient in magnesium has subtle effects on the human body that most people may not notice. The primary two are a potential increase in blood pressure and blood glucose, which can increase your relative risk for cardiovascular disease and type II diabetes. Being deficient can also decrease the quality of your sleep (which can have long-term effects on cognition)!

The problem with magnesium is that there are few food sources which give you 100% of what you need. For example, it's common to find a bunch of fruits that will give you 100% of your daily vitamin C; when it comes to magnesium, the best sources tend to max out around 20%.

The RDI for magnesium is 350mg. Even a supplement containing 200mg should be sufficient (as you should be easily getting the rest through your diet). Choose magnesium citrate as the supplement of choice, since it is well absorbed and carries less risk of laxative side-effects than magnesium oxide.

Vitamin D

Pretty much the most commonly-known deficiency, its RDI was recently upped from 400 IU/day to 800 IU/day (and will be potentially increased more). Vitamin D has a lot of hormone-like effects in the body, and being deficient can impact your testosterone levels, can increase the risk of osteoporosis, and in more severe cases, can increase the risk of mood disorders.

The problem with vitamin D is that people equate "getting sunlight" to "getting enough vitamin D." If you look at your body, your face (and your arms) are a really small part of your body's surface area. To really get enough vitamin D through sunlight, you need to have your legs and torso exposed.  You may also be able to get enough vitamin D if you eat a large amount of fatty fish such as salmon.

A good vitamin D supplement will either come in D2 or D3 form (though D3 is preferred), and will have a dosage between 1000-2000 IU. While 5000 IU pills are common and do not appear to have any harm, dosage that high is not really needed.

Vitamin K

Vitamin K has the potential to become the "next" vitamin D – getting above the current RDI has a host of health benefits. Vitamin K works by activating certain proteins, the most important of which is osteocalcin, which then builds bone tissue. There is not much research on the benefits of vitamin K over the long term beyond bone health, although possible roles in neurology as well as glucose metabolism are both possible.

While the current RDI of vitamin K is set to ~100 mcg (so that you don't have issues with bleeding), a dosage roughly 5x that (500mcg) has the potential to have a very positive impacts on both bone and arterial health.

Vitamin K supplements usually come in two versions – K1 or K2. For K1, roughly 500mcg is a good place to start. For K2 (specifically MK-7), roughly 250mcg (as it stays in your body for a longer time).


Commonly packaged together with magnesium in the form of ZMA, zinc is an important mineral involved in testosterone production. Being deficient can also impair immune function and reduce overall antioxidant potential in the body.

Zinc is only a common deficiency for people who sweat a lot (usually through athletics).

Supplementation only requires enough to replenish what is lost through sweat and exercise, and 10-20mg should cover you. Some gurus recommend 50mg, but they are not proven to be safe, and should be avoided.

The above four are the most common diet deficiencies, and just so happen to be pretty cheap to get too. Factor in your client's diet and see if supplementation can help.

When it comes to supplements, beyond the diet, we always recommend that people look towards targeted supplementation. For example, diabetics struggle with blood sugar levels. For them, berberine can be a great supplement. For those that suffer from high cholesterol levels, garlic (yes as a supplement!) can help decrease it.


Supplementation should be done in an intelligent and targeted manner. To that end, if you want to look up which supplements work (and which don't), the Supplement-Goals Reference Guide is the perfect source to do so. You can look up any supplement (or health goal) and find out what works. And with lifetime access, you can be rest assured that it is always up to date.