Welcome to Part Two of my three part series on the nutritional value and health benefits that animal foods provide. In Part One we explored the nutritional abundance provided by animal foods, and addressed some of the concerns with consuming animal foods. In this article we will explore why animal foods may be the optimal protein source for human beings.
What is Protein?
Proteins are one of the three basic components of food, alongside carbohydrates and lipids. They are a combination of 22 different amino acids (chemical building blocks). Proteins are digested down into amino acids for various uses in the body.
There are nine Essential Amino Acids (EAA’s), meaning the body cannot produce them - these must be obtained from your food. Essential Amino Acids include: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, thronine, tryptophan, and valine.
There are also eleven Non-Essential Amino Acids (NEAA’S) - these can be produced by the body. Non-Essential Amino Acids (NEAA’s) include: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.
Foods containing the EEA’s are called “complete proteins” and provide all of the essential amino acids in appreciable amounts. Foods that provide “incomplete proteins'' are generally lacking at least one of the EEA’s, or do not contain them in appreciable amounts. All animal foods are complete proteins. Plant proteins are generally incomplete, and the ones touted as complete proteins do not contain all the EEA’s in significant amounts.
Proteins and amino acids (that make up proteins) have a plethora of functions in the body:
They are the primary component of muscles, hair, skin, nails, eyes and internal organs.
They are needed for protective structural strength, growth, and maintenance of the body's tissues.
They help establish communication between the body’s cells and organ systems.
They form all the enzymes that drive our metabolism.
They impact the expression of certain genes.
They form several hormones that regulate our body chemistry.
They form antibodies that neutralize bacteria and pathogens.
Muscle contraction is dependent on them.
They are important for fluid and salt balance in the body.
They are important for maintaining an acid alkaline balance in the body.
They act as neurotransmitters, and are important for brain function.
The protein content and amino acid ratios of a food are very important to consider when it comes to providing your body the materials for building, repairing, and maintaining a healthy body. This is why consuming an abundance of complete sources is important.
When you read food labels, it will tell you a full breakdown of the various fats, carbohydrates, sugar and fibre, and then the protein will just say protein. It tells you nothing about the quality of protein or the amino acids contained in them. It doesn’t provide the full story on the spectrum of amino acids or how digestible the protein is by a human. Because of that, you could be eating what seems like enough grams of protein but still not be getting adequate amounts of amino acids. It’s not the protein per se that’s the most important, it’s the essential amino acids protein provides.
Are Conventional Protein Recommendations Too Low?
The Dietary Reference Intakes (RDI) by the Institute of Medicine provides a reference range for minimum protein requirements for an average man or woman:
0.8g per kg of bodyweight
For men (154Lbs/70kg) it’s 56g of protein per day
For women (125 Lbs/57kg) it’s 46g of protein per day
However, the reference range doesn’t apply to most people (as you can see from the female and male weights above). This also doesn’t tell you the optimal protein range, just a minimum to avoid disease.
RDI are based on nitrogen balance studies (intake of nitrogen vs excreted nitrogen, which is difficult to measure and varies greatly between people). In adults, it is generally presumed that protein requirements are achieved when an individual is in zero nitrogen balance. This assumption poses problems that may lead to underestimates of the true protein requirement.
This also doesn’t account for the satiating qualities or nutrient density of different protein sources. Remember, humans need the amino acids that make up proteins, and it just so happens that meat and animal foods have a perfect balance of these essential amino acids, alongside an abundance of micronutrients that plants cannot provide.
An alternative set of numbers for protein consumption needs is the Acceptable Macronutrients Distribution Range (AMDR). AMDR is defined as a range of intakes for a particular energy source that is associated with a reduced risk of chronic diseases while providing adequate intake of essential nutrients. In the AMDR, the protein consumption range is 10-35% of caloric intake.
One study in the US found that most people are getting about 16% of their calories from protein, and those over the age of 50 were not even hitting the RDI targets.
Those not meeting protein recommendations were more likely to have intakes of other nutrients below recommended levels, and those below the recommendations had significantly more functional limitations across all age groups.
Compared to the RDI, the AMDR range for a 125 lbs female would be 50-175 g of protein per day and for men 65-228 g of protein per day.
That’s a pretty wide range, and as you can see the 45 g and 54 g RDI recommendations don’t even meet the lowest AMDR ranges. This is especially concerning if you take into account the associated reduced risk of chronic disease and the adequate intake of essential nutrients aspect of the AMDR
If you take a 2000 calorie a day diet, and 1 gram of protein is 4 calories, then 20% (between 10-35%) protein intake would be 400 calories or 100 grams of protein.
So for an average woman (125 Lbs/57kg) eating 20% of calories from protein on a 2000 calorie a day diet she would need 100 grams of protein. That’s over double the RDI. Whatever your diet, the RDI is likely far too low for almost everyone on earth to thrive.
A widely adopted way to measure how proteins best meet human nutrition needs is called the Protein Digestibility-Corrected Amino Acid Score (PDCAAS). Beef, casein, eggs, whey, milk, and soy have the highest scores in nutritional value.
The PDCAAS however, does not account for anti-nutrients such as trypsin inhibitors, lectins, and tannins, which can hinder protein digestion and amino acid absorption from plant based proteins. These anti-nutrients can inhibit and interfere with the function of digestive enzymes and contribute to digestion issues.
With legumes for example, your ability to digest their protein content and utilize the amino acids could be hindered due to their anti-nutrient content. However, these plant compounds can be reduced with proper cooking and preparation methods such as soaking, sprouting, fermenting, and pressure cooking.
Digestibility of plant proteins is also affected by age and the health of a person's gut. Although the same could be said for animal foods, the protein source without the anti-nutrients will obviously be ideal.
Animal protein is widely agreed to be the most bioavailable protein source, and has no limiting amino acids (meaning they are “complete proteins”). Soy for example is low in the amino acid methionine and is considered a “incomplete protein”, and needs to be paired with other plant foods to make it complete. Although soy is the closest to animal protein, there are also issues relying on a giant monocrop grain as a protein source, and the inability for soybean cultivation to improve soil health (which is what we desperately need from our farming practices).
Could A High Protein, Animal Inclusive Diet Be Optimal?
The protein leverage hypothesis suggests that people will continue to eat food until they have satisfied their protein needs. Higher protein intake can be very effective for weight loss, improving body composition, reducing cravings, and improving overall health; in my personal experience I have found this to be true.
Protein is the most satiating of all the macronutrients and when protein intake is increased, your overall calorie intake will likely go down. If fat loss is your goal, then upping protein is an excellent strategy to create a comfortable caloric deficit to do so. If too much of your food is calorie dense, nutrient poor, ultra processed foods, that are low in protein and high in refined carbohydrates and fats, then avoiding cravings and overeating, and feeling satiated will be incredibly challenging.
A high protein diet is completely safe and arguably optimal. The Dietary Reference Intake by the Institute of Medicine sets no upper level for protein on the basis of chronic disease risk because higher protein has not been found to have detrimental effects.
Some concern over a diet high in animal protein stems from the ‘acid-alkaline hypothesis’ that says a more acidic diet from meat and animal products will affect bone health negatively. However, animal foods are rich in alkalizing minerals and our food intake has no significant effect on our blood pH, which our body tightly controls at all times. The research does not support this hypothesis.
Some also have concerns about high protein damaging the kidneys. If you are a healthy person there has been no danger found with high intake, even above 3g per kg of bodyweight (much higher than the RDI). If you have kidney issues then limiting protein may be a wise choice, but there is no proof that increasing protein causes kidney disease.
A protein intake of 15-30% of your total calories can help regulate appetite by increasing your sensitivity to the satiety hormone leptin, as well as improving your blood sugar control.
A meta-analysis of randomized control trials (high quality nutrition research) showed high protein diets of 25-32% calories compared to the control groups of 15-20% (still higher than RDI) to have beneficial effects on weight loss, HbA1C levels, and blood pressure in type 2 diabetics.
When it comes to fat loss, protein may be the most important macronutrient to emphasize. In research where protein is equated, comparing low-fat-high-carb diets and high-fat-low-carb diets (which have both been shown to help people lose weight), there isn’t much difference in the weight loss results.
If you have increased protein needs, like when pregnant, are under high stress, have an illness, are recovering from trauma, are trying to lose fat, or put on size and muscle, you will likely need a higher protein intake, and an abundance of bioavailable-nutrients that are easily utilized (like with meat and animal foods).
There are a lot of potential issues with a diet too low in protein. Your immune function can decrease since proteins make up the antibodies in your immune system. Protein is used to make your body’s enzymes and to carry oxygen to the tissues, and inadequate protein intake could contribute to feelings of lethargy. A diet low in protein is also associated with hair loss, brittle nails, and cold hands and feet. Low protein consumption can even lead to weight gain. A low protein diet, especially one excluding animal foods, can also very easily result in B12 deficiency, which has been shown to be an independent risk factor for heart disease, and serious neurological disorders in infants of vegan mothers. Muscle wasting and weakness can also occur as the body begins to break down the muscle it has in order to meet its amino acid requirements (more on this in Part 3).
So, if you’re looking to lose excess fat and maintain or build muscle, meet your nutritional needs efficiently with whole foods, and avoid overconsuming calories, then higher protein intake and emphasizing high quality, complete proteins from animal sources is paramount.
But how much protein should we be eating? Buckle up for Part 3 on protein intake to optimize your muscle (whether you lift weights or not) and why muscle is the key to healthy aging for everyone.