Jan. 30. 2015
Nutrition Articles
McKel Hill, MS, RDN, LDN

McKel Hill, MS, RDN, LDN

Dietitian, Founder

Learn the answer to what is protein, where it comes from, and the best protein sources for a healthy diet.

As a dietitian nutritionist, I get questions all the time about the basics of macronutrients, especially protien. I love that you all are hungry for knowledge when it comes to nutrition and learning the basics of micro and macronutrients amongst others. Protein is an all too popular topic, especially when you’re living a plant-based lifestyle which many of my recipes and what I promote here is about. Today, I’m not talking about vegan, nor paleo. Instead, I’m strictly educating you on what protein is, where it comes from, and the best sources of protein. I’ve wrapped it all up for you into an easy-to-read guide to keep bookmarked for future use.

What is protein? It all starts with amino acids.

Protein actually isn’t protein unless we first learn what amino acids are, the literal building blocks of protein. You may hear about amino acids or hear the term aminos in relation to their type or how “essential” they are. There are technically three groups of amino acids, non-essential meaning that our bodies have a supply of them or we have the ability to make them on our own (pretty cool), essential amino acids meaning we must gather these from the foods we eat, or conditional meaning these amino acids are not essential unless during times of severe stress or trauma (think of a surgery, medical illness, etc.).

Why does it matter to know about essential amino acids?

Well, if you’re vegan or vegetarian, you should know and sorry I’m singling ya’ll out, but you’re in the group who should be the most mindful. Given that we now know amino acids are the building blocks of protein and that all life forms need protein in order to live, build, grow, etc.; we know that having enough variety of all amino acids is important. Before we get into the sources of protein, here’s a list of all the amino acids:

Non-essential amino acids

1) alanine, 2) asparagine, 3) aspartic acid, 4) glutamic acid

Essential amino acids

1) histidine, 2) isoleucine, 3) leucine, 4) lysine, 5) methionine, 6) phenylalanine, 7) threonine, 8) tryptophan, 9) valine

Conditional amino acids

1) arginine, 2) cysteine, 3) glutamine, 4) glycine, 5) ornithine, 6) proline, 7) serine, 8)tyrosine

True or false…

You need to consume all amino acids at each meal to make a complete protein?

False. This has got to be one of the biggest myths I read time and time again, even by nutrition professionals! You do not, I repeat, you do not need to consume all amino acids at each meal to make up a “complete” protein. Remember to give our bodies some props here- our bodies are incredibly resourceful and we naturally have a “pool” of amino acids in supply to use for when a meal might be a little low in one amino acid or the other. The key is to consume a wide variety of amino acids every single day! This will make sure your body has enough to make up for those times where you might be lacking- definitely something to share.

Here’s a little bit more science if you’re interested. Just like we talked about in Carbohydrates, part I and part II, proteins have different molecular structures. Proteins can be found as primary, secondary, tertiary, or quaternary structures all of which have different bonds, groupings, and ultimately structures, and remember amino acids are what build these! Primary structures are simply a linear amino acid sequence, secondary is a regular substructure containing alpha-helix and beta-strand, tertiary structure is a 3 dimensional structure, and quaternary is the largest and most complex structure. Okay mini science lesson is over, but here’s a little picture depicting proteins!

…but what does protein do?

Protein plays a HUGE role in the body, as do carbohydrates and good fats, but protein is probably one of my favorites to talk about. It’s involved in digestive health, rebuilding tissue and muscle, energy, hormonal production (ex. growth hormone), immune health as antibodies, enzymes (ex. phenylalanine hydroxylase), structure, and storage/transportation of other molecules (ex. ferritin). Protein is part of every single cell in our body. Let’s just soak that in for a minute…

If protein is involved in every cell in our body, now you can understand the importance of eating enough, but also eating the best quality and most bioavailable forms if possible. Let’s put this into perspective, every cell in your body including the cells that make up your gorgeous skin, thick hair, strong nails, lean muscle and tone, healthy digestive tract, and so much more. Now you can see not only the structural importance, but also how it may manifest physically (since that’s the easiest for most of us to notice).

Protein comes from many food sources all of which have different levels of bioavailability- simply put our bodies digest and absorb some proteins a little better or worse than others. The higher bioavailability and absorption, the better (an egg is often used as the golden standard of the “perfect” protein). There are many ways to measure how protein is digested and utilized in our bodies such as Biological Value (BV), Protein Efficiency Value (PEV), Protein Digestibility Corrected Amino Acid Score (PDCCA), and Bioavailability Score. For most of us, I don’t think these need to be on your radar, but know they’re out there. The main point is that different food sources of protein result in different absorption. As you can guess, animal proteins such as eggs, beef, chicken, fish contain high amounts of protein and are also more bioavailable; but this doesn’t mean you can only achieve high protein bioavailability with these foods.

Food sources of protein

Animal Protein

  • Those coming from animals: wild caught fish, grass-fed beef, wild game, fresh eggs, etc.

Plant-Based Protein

How is protein digested?

Knowing how protein is digested is important as well, you can see that the structure of animal proteins and vegetable/plant-based proteins are very different. Some digest animal proteins with ease and their bodies “do” very well on them whereas others may suffer from constipation, bloating, or sluggish digestion which most likely means their body doesn’t have the digestive capacity or strength to break that food down. It could also result from lower than normal HCL levels in the stomach, HCL (hydrochloric acid) is a natural part of digestion in the stomach and is the first enzyme to break down food in the gut.

Of course we know the first place digestion takes place is the mouth, but when we’re talking about protein it’s mainly focused in the stomach and gut. The stomach releases gastric juice which helps breakdown the food/protein for our example, into chyme which is just a word for food + gastric juices. Our gastric juice has important components for protein breakdown including pepsinogen which is converted to pepsin, which digests protein. HCL converts pepsinogen into pepsin, which breaks down the proteins into peptides and also keeps our stomach pH in the normal range of 2- dissolving food and killing harmful microorganisms, hence the importance of HCL. I could talk at length about HCL and digestion, but for the sake of knowing it’s role in protein, we’re set. Little note, if you think you have low HCL, it’s nothing to self-diagnose- go see your physician. Cris Kessler loves talking about digestion and HCL, read up on some of his resources if you’re interested.

There are a couple foods that help digest and break down protein by their enzymes: pineapple, papaya, apple cider vinegar. Both pineapple and papaya contain bromelain which is an enzyme that helps our digestion when breaking down protein, the apple cider vinegar is great to add acidity to breakdown proteins as well. I’ll be sharing much more detail about this in entire post on digestion soon!

Part II will cover more detail on food sources, portion sizes, how much protein do you need, optimal times to eat protein, and more of your questions answered. What other questions do you all have around protein? Are there topics you’d like to see covered or mentioned about protein in part II. Comment below and share.

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