Saying dietary protein intake is critical for longevity and quality of life seems a little dramatic. However, protein is considered the most fundamental nutrient for animals and humans.[1]
Even the English word originates from the Greek word “proteios”, meaning prime or primary.[2]
And its deficiency can cause your body to change in a way that can be difficult to reverse.
Imagine the house or apartment you live in slowly losing part of its primary structure brick by brick every year once it turns forty.
I always envision someone watching TV in their living room, minding their own business and different bricks falling out of the wall at specific increments over the night.
Whichever way you look at it, this slow degradation is what happens to our muscle mass between the ages of forty and eighty precisely. Some studies have us losing thirty to fifty per cent of muscle between these ages.[3]
The problem with this is not just that your days posing shirtless for social media are limited but also that you may not have the strength to walk quickly enough across the road under pressure.
This lack of independence is the scarier part.
Muscle strength correlates with muscle mass which rapidly declines after fifty.[4] This accelerated decline in muscle mass and strength makes adequate protein one of the critical nutritional factors in helping you maintain your independence as you age.[5]
That’s huge.
These types of things always make me think of Naval Ravikant, a man famous in the tech and twitter scene and one of his famous quotes.
“We spend our lives chasing enough money to enjoy our lives, but then run out of time to spend it because of our health.”
Now I’ve paraphrased this, but I hope you catch what I mean. Imagine working hard all through your life, then only to lose your independence in the end. Your body not being strong enough to lift your cabin bag from the floor into the overhead locker.
And this is what this article on protein intake is looking to prevent. By helping you assess your dietary protein intake to ensure you get enough and highlighting some of the vital functions of dietary protein in the body.
Finally, I’ll help you to work out your ideal daily protein intake with a rough guide to get you started.
Ok, have I scared you enough yet?
It’s only partially intentional.
Still, the idea here is to present a reality that people commonly face as they age, begin to eat less and only have one serve of protein at dinner.
The good news, of course, is that all of this can be avoidable.
Protein is not just for muscle.
Dietary protein’s most important function is to create proteins.
That could be close to one of the most confusing statements you’ve heard all day. Let me explain by deconstructing what dietary protein is.
What is dietary protein?
Dietary protein is a collection of a variety of twenty different amino acids. These amino acids are linked together by peptide chains.
It’s not until enzymes in your stomach break these chains apart and release the individual amino acids into the body that protein becomes nutritionally valuable.[6]
The amino acids can also remain connected in small ways, for example, in triplets or pairs. The number of amino acids connected will influence their name. For example, a di-peptide has two amino acids bound together.
Some amino acids are essential because the body cannot produce them for itself. The body can produce others by weaving its magic, thus making the amino acid non-essential or conditionally essential.
Some foods can be higher or lower in particular amino acids.
Or, in some cases, the amino acid may not be present at all. For example, plant-based proteins do not naturally contain taurine, carnosine, creatine and hydroxyproline either at all or in high amounts.[7]
This differential in the amino acid composition is one of the primary differences between animal and plant-based proteins. Older versions of classifying protein had animal protein as “first-class protein” and plant-based protein as “second-class protein,” mainly because of the absence of these amino acids. Digestibility and availability of amino acids are also essential in classifying proteins.[8]
In my view, science has shown that the difference between animal and plant-based protein, being good or bad, is a little misleading. It’s just different. For example, a cup of tofu contains the same amount of protein as just under one hundred grams of steak, chicken or fish.[9]
What does vary is the amino acid content of plant-based foods.
This variation means that one might have to eat a more diverse and higher amount of plant-based sources to get an adequate combination of amino acids.[10]
It doesn’t, though, make one protein source better or worse.
Amino acids have different bodily functions; the most important is creating other proteins for the body.
Now that we’ve broken down what proteins are let’s return to the statement I mentioned earlier, dietary protein’s primary function is to create proteins.
It’s going to require us to hit a tiny bit of biochemistry to make this easier to understand.
One way to simplify things is to see proteins as building blocks. These building blocks then form an essential role in molecules such as enzymes. Enzymes can help speed up chemical reactions in the body that generate energy up to one million times.[11]
Enzymes built out of our dietary protein that speeds up these chemical reactions are called catalysts.
And this is the vital part.
Without these enzymes acting as catalysts, about ninety per cent of these reactions would not operate at the appropriate speed required for life. Enzymes, therefore, make reactions easier to occur. If the enzymes weren’t there, approximately eighty per cent of these critical energy-forming reactions wouldn’t occur at all![12]
All this is down to dietary protein.
But what there’s more.
Dietary protein plays a role in the structural support for muscle growth, the immune system, hormones, and the nervous system, and it also provides a source of nitrogen and sulphur, both of which the body can’t make itself.[13]
Now, it’s fair to say that just finding out how much our biochemistry relies on dietary protein is enough to wonder whether you’re getting enough.
Let’s zoom out and see its influence on the brain, digestion and the rest of the body via amino acids’ non-protein-based functions.
You may remember that earlier in the article, we touched on essential amino acids that the body can’t produce and non-essential amino acids that it can make on its own with a bit of magic and effort.
To keep things simple, and to illustrate their broad-ranging functions, let’s look at one of the most important essential amino acids for the brain and digestion, tryptophan.
L-tryptophan has garnered a reputation for being helpful in mental health and sleep conditions.[14]
Dietary sources of tryptophan include dairy products, whole milk, cheese and whey protein, meat, fish, eggs, bananas, oats, pumpkin and sesame seeds, chocolate, dried dates, soy, tofu, tree nuts and peanuts.[15]
Tryptophan’s role as a building block is undoubtedly just as exciting and also goes some way to explain its popularity in mental health.
If you remember, one of dietary protein’s essential functions is to be a building block for other chemicals to be built. Most notably, tryptophan is one of the main building blocks for serotonin production and the hormone melatonin.
If you are new to serotonin’s action in the body, it regulates mood, anxiety, cognition, impulsiveness, aggressiveness, libido and body temperature.[16]
A recent study in Singapore has connected dietary protein intake and improved sleep duration in middle-aged and older adults mainly to the increased tryptophan levels.[17]
Serotonin is also critical in digestion and regulating motility, which helps your food travel through the GI tract successfully to the toilet.
Tryptophan plays a vital role in the balance between the immune system in the gut and the maintenance of the bacteria in the microbiome.[18] Some consider tryptophan so essential to the gut-brain connection that one article published in 2014 suggested that it’s one of the primary origin stories for developing IBS.[19]
A lesser-known function of tryptophan is its involvement in cardiometabolic illnesses such as diabetes via its role in either increasing or suppressing insulin resistance.[20]
Tryptophan is just one of the twenty amino acids; reviewing them all would be another article.
Hopefully, understanding just how one amino acid can have such a significant effect gives you a further inspiration to evaluate whether your dietary protein levels are high enough.
What should I aim for with my daily dietary protein intake?
This amount largely depends on your physical activity levels, as you may know already. The current baseline dietary protein intake for a person who isn’t exercising is 0.8gms of protein per kilogram of body weight.
This amount then moves up by roughly 0.4gms of protein per kilogram of body weight based on light, moderate and intense levels of exercise.
To make this easier, that’s 1.2gms of protein per kilogram of body weight for light exercise, 1.6gms for moderate and up to 2.0gms for intense training.[21]
This daily amount would need to be personalised based on your height, weight and frequency of exercise.
A small note to consider is balancing animal and plant-based protein intake.
We’ve touched on the absence of some amino acids in plant-based foods earlier. This deficit is why adding some animal protein into your daily intake can be important, primarily from a supply point of view. There are some options regarding supplementation that might fill in the gaps. Still, generally, a predominant amount of plant-based protein with some animal protein mixed in reflects where it seems the consensus is going. Or at least my interpretation of it.
So what do you think?
We’ve seen in this article how dietary protein provides the building blocks for almost ninety per cent of our energy-generating biochemical reactions and nearly all of the other important biochemically active substances in our bodies.
I hope this article serves as a guide to why protein is such an essential part of your dietary intake and how you might be able to align your diet to match how much your body needs.
Hope this helps xx
References
[1] Reeds PJ, Burrin DG, Stoll B, van Goudoever JB. Role of the gut in the amino acid economy of the host. Nestle Nutr Workshop Ser Clin Perform Programme. 2000;3:25-46. doi:10.1159/000061799
[2] Wu G. Dietary protein intake and human health. Food Funct. 2016;7(3):1251-1265. doi:10.1039/c5fo01530h
[3] Faulkner JA, Larkin LM, Claflin DR, Brooks SV. Age-related changes in the structure and function of skeletal muscles. Clin Exp Pharmacol Physiol. 2007;34(11):1091-1096. doi:10.1111/j.1440-1681.2007.04752.x
[4] Larsson L, Grimby G, Karlsson J. Muscle strength and speed of movement in relation to age and muscle morphology. J Appl Physiol Respir Environ Exerc Physiol. 1979;46(3):451-456. doi:10.1152/jappl.1979.46.3.451
[5] Lonnie M, Hooker E, Brunstrom JM, et al. Protein for Life: Review of Optimal Protein Intake, Sustainable Dietary Sources and the Effect on Appetite in Ageing Adults. Nutrients. 2018;10(3):360. Published 2018 Mar 16. doi:10.3390/nu10030360
[6] Tomé D. Digestibility issues of vegetable versus animal proteins: protein and amino acid requirements–functional aspects. Food Nutr Bull. 2013;34(2):272-274. doi:10.1177/156482651303400225
[7] Wu G. Important roles of dietary taurine, creatine, carnosine, anserine and 4-hydroxyproline in human nutrition and health. Amino Acids. 2020;52(3):329-360. doi:10.1007/s00726-020-02823-6
[8] Adhikari S, Schop M, de Boer IJM, Huppertz T. Protein Quality in Perspective: A Review of Protein Quality Metrics and Their Applications. Nutrients. 2022;14(5):947. Published 2022 Feb 23. doi:10.3390/nu14050947
[9] LaPelusa A, Kaushik R. Physiology, Proteins. [Updated 2021 Nov 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555990/
[10] O’Neil CE, Keast DR, Fulgoni VL, Nicklas TA. Food sources of energy and nutrients among adults in the US: NHANES 2003–2006. Nutrients. 2012;4(12):2097-2120. Published 2012 Dec 19. doi:10.3390/nu4122097
[11] LaPelusa A, Kaushik R. Physiology, Proteins. [Updated 2021 Nov 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555990/
[12] LaPelusa A, Kaushik R. Physiology, Proteins. [Updated 2021 Nov 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK555990/
[13] Wu G. Dietary protein intake and human health. Food Funct. 2016;7(3):1251-1265. doi:10.1039/c5fo01530h
[14] Richard DM, Dawes MA, Mathias CW, Acheson A, Hill-Kapturczak N, Dougherty DM. L-Tryptophan: Basic Metabolic Functions, Behavioral Research and Therapeutic Indications. Int J Tryptophan Res. 2009;2:45-60. doi:10.4137/ijtr.s2129
[15] Bichitra N. Nayak, Ram B. Singh, Harpal S. Buttar, Chapter 51 – Biochemical and dietary functions of tryptophan and its metabolites in human health, Editor(s): Ram B. Singh, Shaw Watanabe, Adrian A. Isaza, Functional Foods and Nutraceuticals in Metabolic and Non-Communicable Diseases, Academic Press, 2022, Pages 783-798, ISBN 9780128198155, https://doi.org/10.1016/B978-0-12-819815-5.00003-3.
[16] Palego L, Betti L, Rossi A, Giannaccini G. Tryptophan Biochemistry: Structural, Nutritional, Metabolic, and Medical Aspects in Humans. J Amino Acids. 2016;2016:8952520. doi:10.1155/2016/8952520
[17] Sutanto CN, Loh WW, Toh DWK, Lee DPS, Kim JE. Association Between Dietary Protein Intake and Sleep Quality in Middle-Aged and Older Adults in Singapore. Front Nutr. 2022;9:832341. Published 2022 Mar 9. doi:10.3389/fnut.2022.832341
[18] Gao J, Xu K, Liu H, et al. Impact of the Gut Microbiota on Intestinal Immunity Mediated by Tryptophan Metabolism. Front Cell Infect Microbiol. 2018;8:13. Published 2018 Feb 6. doi:10.3389/fcimb.2018.00013
[19] Berstad A, Raa J, Valeur J. Tryptophan: ‘essential’ for the pathogenesis of irritable bowel syndrome?. Scand J Gastroenterol. 2014;49(12):1493-1498. doi:10.3109/00365521.2014.936034
[20] Oxenkrug G. Insulin resistance and dysregulation of tryptophan-kynurenine and kynurenine-nicotinamide adenine dinucleotide metabolic pathways. Mol Neurobiol. 2013;48(2):294-301. doi:10.1007/s12035-013-8497-4
[21] Wu G. Dietary protein intake and human health. Food Funct. 2016;7(3):1251-1265. doi:10.1039/c5fo01530h
