Human Nutrition: Protein Functions and Needs

If you’re new to the series, you can start here.

We have a problem in the US: we eat way more protein than is necessary, and much of it is animal protein. It’s understandable. We’ve been told that protein helps us bulk up, gives us energy, and it’s okay if we overeat protein because the body will just get rid of it. I wish all of those things were true, but they’re not, or not entirely.

Plant-based proteins are not inferior sources of nutrients. I’m not advocating dropping that steak entirely, and becoming vegetarian. I am an omnivore, enjoy my animal-rich diet, and know vegetarians with worse eating habits than mine. In this post, we’ll explore why we need protein, what our minimum protein intake is, and how often we should eat it. And just so you know, it is highly likely that if you live in a developed nation, you eat way more protein than your body could possibly use.

So, how much protein is the right amount to eat? It’s complex, so read on.

There are ~4 kcals/gram of protein. That’s an average measurement, and what we use to determine how many calories come from protein sources. However, the quality of the protein can vary widely, so that number can shift slightly. For the purposes of this series, we’ll stick with 4 kcals/gram.


The acceptable macronutrient distribution range (AMDR) for protein is 10-35% of your daily intake. There’s math involved here: you need to eat 0.8g of protein per kilogram of healthy body weight. My numbers look like this:

healthy body weight ÷ 2.2 = kg body weight


kg healthy body weight × 0.8 grams of protein = how many grams of protein I need each day (minimum)


120 ÷ 2.2 =54.4 kg

54.5 × 0.8 = 43.6 g protein per day (minimum)

Proteins contribute to the pH balance in your body. They are the building blocks of your body components, hormones, and enzymes, and help with maintaining fluid balance. They assist with immunity and provide the highest feeling of satiety after you eat.

Your body cannot absorb protein, and it must be changed into amino acids so that it can be changed into glucose in your liver. This is called gluconeogenesis. Proteins are made of amino acids, and there are 20 of them. Nine of them are essential, because your body can’t make them. You must eat them to have them. The other 11 can be made in the body, and they are called nonessential. The order of amino acids in a protein determines its shape, and its shape determines its use in the body.

The digestion of protein begins when you cook it, and then the acid in your stomach begins the process of uncoiling the peptide strands, ultimately breaking down the poly-peptide chain. Then, its on to the small intestine, where the hormone that makes you feel full (CCK- Cholecystokinin) triggers enzymes in the pancreas (trypsin and others) to break down the protein the rest of the way, into singular amino acids. The small intestine is where proteins, as singular amino acids, are absorbed and sent to the liver to be changed into glucose, used for energy when your diet is deficient, or converted to fatty acids and stored as triglycerides in your fat tissue (also for use when your calorie intake is insufficient). You lose very little protein in your excrement, so it is a myth that you’ll just get rid of the extra. The extra actually gets stored for possible later use. 

Complete vs. Incomplete

There are two types of proteins: complete and Incomplete. Complete proteins are considered high quality, because they provide all 9 essential amino acids. Complete proteins are foods like dairy, meat and fish, and soy. Animal proteins contribute about 70% of our protein intake. 

Incomplete proteins are missing one or more amino acids, and require another protein source to complement (or complete) the essential amino acid intake. All plant proteins are incomplete proteins, with only a few exceptions (soy). So, red beans and rice are complimentary proteins. Some others are green beans and almonds and pasta with tomatoes.

A 2,000 kcal/day diet requires 50-175 grams of protein per day. So, I’m slightly under 50 grams in my minimum requirements, because we already know my calorie intake is 1,967 per day. I eat quite a bit more protein than 43.6 g every day, and much of it is animal protein. That is pretty common in this country, and not particularly healthy.

The top contributors to protein intake in the US are beef, poultry, milk, bread, and cheese. This explains the generally-high levels of triglycerides, cholesterol, and saturated fats in our systems. 

The research says that, compared to non-vegetarians, vegetarians have decreased risks for diabetes, hypertension, obesity, cardiovascular disease, and some types of cancer. They also have increased longevity because they often exercise more, meditate, and avoid alcohol and tobacco. As you probably guessed, these may contribute to their overall wellbeing. 

Again, I’m not advocating for dropping meat altogether. Meat is a complete protein, and I quite enjoy a steak once in a while. I am saying to limit it. There’s a reason the Mediterranean diet is widely regarded as the healthiest on the planet. We’ll go over it in-depth a little later, but animal proteins are at the top of their pyramid, which means they limit their animal protein intake and instead choose to eat complimentary proteins.

Why Choose Plant Proteins

We know that plant proteins are incomplete, lower quality, and require other plants to complete our daily needs for all 9 essential amino acids. Why on earth would we choose plant proteins over animal proteins? Because they also supply phytochemicals, vitamin E, Iron, Zinc, Magnesium fiber, and folate. Plant proteins have no cholesterol, limited saturated fats, and a higher proportion of those triglyceride-fighting mono- and poly-unsaturated fats.

Some plant sources of protein:

  • carrots ~3 g/serving
  • corn ~3 g/serving
  • broccoli ~3 g/serving
  • apples <1 g/serving
  • oranges <1 g/serving
  • bananas <1 g/serving
  • grains (varies)
  • seeds (varies)
  • nuts ~7 g/serving
  • legumes ~7 g/serving

Health Risks of a High-Protein Diet

The amount of protein you eat is not as important as the quality. There is little evidence that links high protein intake to chronic disease. However, excessive intake of red meat (including processed red meat) is linked to colon cancer,  heart disease, stroke, diabetes, and weight gain. Protein puts a huge burden on your kidneys, and can increase calcium loss – increasing the risk of osteoporosis later. It also increases your urine output, which increases your risk of dehydration.

There are plenty of delicious ways to meet your daily protein requirements. Decreasing your red meat intake, replacing it with poultry, fish, and plant-based proteins may reduce your risk of the disease above. Plus, really, how wants to only eat red meat all the time? There’s only so much you can do with it. 

As always, if you have any questions, drop them in the box below, or email them to me.

Protein function and needs - PIN NOW, READ LATER!

About Terra Walker

Terra loves creating recipes, imparting wisdom, searching for an amazing cider, owning this website, and traveling the globe. You can catch up with Terra on the channels above, where she never uses third person, because she hates writing about herself that way.

What do you think?