What Are Good Sources of Protein? – Micronutrient Content

As I move towards wrapping up this series this week, I need to discuss a couple of other topics of relevance to the question of what are good sources of protein.  A good bit of what’s been discussed in other sections was a bit on the theoretical/sciency end of things and I’m going to keep the next couple of topics a lot more applied.

Today I want to look at an issue that I don’t think is addressed as much as it could be when folks are looking at protein source; that topic is the presence (or absence) of other nutrients.  Outside of a few select groups (that often get a majority of their protein from isolated sources such as protein powders or amino acids), most people get their daily protein from whole food sources and whole foods contain other nutrients.  Some of those nutrients may be beneficial, some of them may be detrimental; all need to be considered when looking at protein sources and deciding which are good, bad, or neutral.

The major ‘extra’ nutrients I want to look at in this article are zinc, iron, B12, calcium. In the next part of this article series, I’ll take a look at the issue of dietary fat content, both in terms of good and bad fats.  This is simply to keep the length a bit more manageable.



Zinc is an essential mineral involved in an amazing number of processes in the body including immune system function, appetite (a lot of early research showed that zinc deficiency did weird things to appetite, zinc has been shown to regulate leptin levels as well) and hormone levels (zinc deficiency can reduce testosterone levels).   Since the body doesn’t store zinc, its intake is required on a daily basis.

Zinc is found to varying degrees in most protein foods with oysters containing the most zinc of any food (this probably explains the idea that oysters are an aphrodisiac, given the role of zinc intake on testosterone levels) Red meat, liver and crab meat contain the highest levels after that, chicken is a fairly close second.  Eggs and milk are not fantastic sources of zinc although cheese has reasonable amounts.

Grains and cereals, along with beans (often a prime source of protein in vegetarian diets) are relatively poor sources of zinc.  As well, compounds in these foods tend to impair zinc absorption in the gut.

Vegetarian diets are often zinc deficient and females (especially female athletes) who have a habit of removing sources of protein such as red meat and chicken also often come up zinc deficient.   I’m a huge believer in lean red meat for most people, especially athletes and ensuring adequate zinc intake is one of those reasons.



Iron is another essential mineral, also involved in a staggering number of processes.  Arguably the most well-known role of iron in the body has to do with keeping red blood cells healthy and working.   A lesser known effect of iron has to do with thyroid conversion in the body; very low levels of iron can cause problems with thyroid production in the liver.   Restoring iron levels to normal reliably improves thyroid conversion, can increase metabolic rate and improves thermoregulation.

In the diet there are two types of iron which are called heme-iron and non-heme iron.  Heme iron is absorbed roughly 10 times more effectively than non-heme.  Like zinc, the best sources of iron (especially heme iron) are meats, especially red meat, liver and organ meats.  Chicken is also a good source of iron; interesting research has found that both red meat and chicken contain a factor that improves non-heme iron absorption by the body.

While many non-meat sources contain reasonable amounts of iron (and many food are iron fortified in the modern world), the iron is typically of the non-heme variety; as well the presence of other compounds in those foods often impairs the iron absorption.  I’d note that vitamin C increases iron absorption and consuming some with iron containing foods is one way to improve iron absorption; cooking with a cast-iron skillet also increases the iron content of foods.

Females, due to the loss of menstrual blood each month are at a higher risk for iron deficiency than men (in this vein it’s interesting to note that women are more likely to have thyroid problems, I have to wonder if these two issues aren’t related) and females (especially athletes) along with vegetarians are likely to be iron deficient.  This is especially true for female athletes who have a habit of removing red meat out of their diet.  That, along with possibly increased requirements from training, along with slight blood losses each month add up to iron deficiency.

I’d note that too much iron can be as bad as too little, iron acts as a pro-oxidant in the body; men should be very careful about going out of their way to take extra iron and many multivitamins for men have no iron in them for this reason.  While women lose some iron each month, excessive iron intake can build up stores in men and cause many problems.

Basically, as with zinc, meat protein, especially red meat is the winner here.  This is yet another reason that I think lean red meat (which has also been shown to lower blood pressure and improve blood lipid levels) should be part of any healthy diet.  Female athletes especially should probably be consuming lean red meat multiple times per week; supplementation may also be necessary.



Vitamin B12 is, as its name suggests, one of the B vitamins.  It plays critical roles in the body not the least of which is brain function.  While B12 requirements are staggeringly tiny, and the body can actually build up a fairly long store of B12 (in the liver), deficiencies are not unheard of.

B12 is ONLY found in animal source products and vegetarians are often at risk for deficiency for this reason.  Females who remove animal source proteins from their diet are, as with zinc and iron, at risk for deficiency.

I’d note that there is an oddity with B12 in that a specific factor is required in the stomach for B12 absorption; some people lack this.  Even with plenty of B12 in the diet, they don’t absorb it and can end up with deficient.  This can cause something called megoblastic anemia (this is a bit of weirdness to do with red blood cells) along with mental fuzziness.  People who lack the absorption factor can’t simply supplement normal B12, they have to get a specific form called Methylcobalamin and this will have to be taken forever to avoid deficiency.

For everyone else, simply ensuring sufficient protein intake from animal source proteins will provide plenty of B12.



Finally, I want to talk about calcium.  Known primarily for its effects on bone health, calcium is turning out to play a number of other major roles.  Early research found an effect on blood pressure of high dairy intakes and more recently some work has found an impact of calcium (and dairy foods seem to work better in this regards) on fat loss; the mechanism is still unclear although calcium may be affecting fat absorption from the gut, fat oxidation in the body, or some other aspect.

As well, the exact reason that dairy calcium seems to work better is an issue of some question; it may be due to greater absorption of dairy calcium compared to non-dairy calcium or it may have something to do with another factor inherent to dairy products.

The most well-known source of calcium in the human diet is, of course, dairy products.  While there is calcium in many vegetable source proteins (vegetarians often claim that broccoli has more calcium than milk), the presence of other compounds in vegetables impairs absorption of the calcium that is present.  Meats, grains and nuts are a poor source of dietary calcium.

I’d note, tangentially, that while there has been a long-standing belief that high-protein intakes are bad for bone health but this isn’t supported by current research.  As detailed in Protein Controversies, a high protein intake is only a problem when calcium intake is insufficient; a high protein intake along with plenty of calcium actually improves bone health.

As discussed The Protein Book, I am a big believer that low-fat dairy products should be part of any healthy diet.  Not only do dairy foods provide an excellent combination of slow and fast proteins, they provide the most available source of dietary calcium and seem to improve body composition and calorie partitioning.

As well, as I discuss in Contest Dieting Part 1, I also think that the weird bodybuilder ideas about dairy on a contest prep are not only invalid but actually do more to harm fat loss than anything else.

Of course, not everyone can consume dairy, either due to a true allergy (which is rare) or a lactose intolerance (which is more common).  Of course, lactose free dairy products do exist (for example, Lactaid Milk) and there are pills of varying sorts which help with lactose digestion (either by providing the necessary enzyme or helping the gut to start producing more naturally).  Failing that, calcium supplements would be indicated for someone who can’t consume dairy (for whatever reason).


Summing Up

There are a number of important micro-nutrients that can go into the decision of What are good sources of protein.  Zinc, Iron and B12 are all critical nutrients which are found in the largest and most well-absorbed amounts in animal sources foods.  Lean red meat (to avoid excessive fat intake), chicken, seafish can all be good sources of those foods; vegetarians and others who try to limit their intake of those foods (for either good or bad reasons) can be at risk for deficiency.

Dietary calcium plays an enormous number of roles in the body; while the most well-known is bone health, current research indicates that sufficient calcium (and dairy calcium appears to be superior to non-dairy calcium) can lower blood pressure and decrease body fat levels through a variety of mechanisms.  I strongly believe that no- or low-fat dairy products should be part of any healthy or athletic diet for those and other reasons.  Individuals with lactose intolerance have a number of potential solutions but if dairy simply can’t be consumed, supplements are at least adequate.

In the next part of this sub-series, I’ll look at the issue of dietary fat and its presence or absence in various dietary protein sources.  This will include a quick look at both the contentious issue of saturated fat as well as the importance of the omega-3 fish oils.

Go to What Are Good Sources of Protein – Dietary Fat Content

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The Protein Book

What is the Best Source of Protein?

While many continue to argue that a single source of protein is the best source, this can not possibly be the case. Among all of the other factors that go into deciding which protein source might be best, the presence or absence of nutrients such as iron, zinc, B12, etc. all play a role. The Protein Book examines all of these aspects and more to help athletes optimize all aspects of their protein nutrition.