Animal vs. Plant Protein – Which is better for health?

To meat or not to meat? 🤔 That is the question.

Look, I get it. There’s so much information out there about the benefits of plant-based diets, how vegetarianism/veganism leads to a longer life, lower risk of heart disease, etc. Then, on the other hand, we have the proponents of the Paleo lifestyle, Carnivore dieters, and fitness enthusiasts who tout the animal protein as being the top choice for optimal health.

So, which is better: animal or plant?

While animal protein has traditionally been regarded as superior to plant-based sources, plant protein has been getting a big reputation boost recently (have you seen the “broccoli has more protein than beef” infographic that’s made its way around Instagram?). This has led a lot of people to believe that plants are just as good (or better) than animals as a source of protein.

Plants are an incredibly important part of a healthy diet; they are a great source of plenty of nutrients, but protein is not one of them. In terms of quality, digestibility, and density, they take a back seat to animal sources.

What is protein?

Protein is made up of long chains of amino acids; they are the building blocks of all tissues in our bodies. Our body uses and assembles about 50,000 different proteins to form our organs, nerves, muscles, and flesh. Besides building tissues, the key roles that amino acids plays in our body include: hormone production, DNA regulation, and neurotransmitter production. Proteins also help fight infections (antibodies) deliver oxygen in the body (haemoglobin), manage biochemical processes (enzymes) and regulate metabolism (hormones).

Insufficient protein intake can lead to muscle atrophy and weakness, decreased immune function, lethargy from a lack of oxygen being carried to tissues, hair loss, brittle nails, and cold hands and feet. 

The RDA for protein is only 0.8g per kg of bodyweight, which actually is the minimum amount of protein needed to avoid loss of lean muscle mass. Note the difference between “minimum” and “optimal” amount for health. I would argue that 20-30% of your daily calorie intake is a good starting point for a balanced diet. Of course, this number also depends on your age, body size, activity level, and hormone status – some people may need more.

Though over 500 amino acids have been identified, we only use 20 of them for our metabolic processes. Ten of these amino acids are considered essential: we can’t synthesise them ourselves, so we need to get them from our food. The essential amino acids are:

  • Tryptophan
  • Threonine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Valine
  • Histidine
  • Arginine

“Complete proteins” are foods that contain all ten essential amino acids in adequate proportions. In general, animal products are complete proteins, whereas most plant proteins are missing one or more essential amino acids. This is why vegetarians/vegans are often advised to pair certain foods together (whether in the same meal or eaten throughout the day) to fill in the gaps; for example, rice and beans: beans are low in methionine, but high in lysine and rice is low in lysine, but high in methionine.

A small portion of plant foods have complete protein: quinoa, soybeans, chia, hempseeds, buckwheat, potatoes, pumpkin seeds, and cashews, for example, but the proportions of essential amino acids may not be optimal as that of animal products.

We should note that completeness is not the be-all end-all of determining how good a protein source is. Non-essential amino acids are also important to consume in our diet because having to continually synthesise them is inefficient if we could just eat them, and many of them serve functions outside of protein synthesis.

Completeness also does not take into account bioavailability: how well our bodies digest and absorb the amino acids. This is why protein quality is important!

Protein Quality

The Protein Digestibility Corrected Amino Acid Score (PDCAAS) was traditionally adopted as the preferred method of measuring how well different proteins met human nutritional needs. This method shows beef, eggs, milk, and soy as the top ranking protein sources. However, the PDCAAS score does not take into account the ‘anti-nutrients’ often found in plant-based sources like lectins and tannins, which can reduce amino-acid absorption. Age and the state of our gut also affects how well we digest and absorb proteins.

A more comprehensive method is the Digestible Indispensable Amino Acid Score (DIAAS), which analyses faecal matter at the end of the small intestine for how well amino acids were digested [1]. The higher the score, the higher the quality of the protein. Some common food sources include [2]:

Whole milk: 1.32
Whey protein isolate: 1.25
Whole egg: 1.18
Whey protein concentrate: 1.1
Beef: 1.1
Soy protein isolate: 1.0
Garbanzo beans: 0.66
Peas: 0.64
Cooked rice: 0.59
Rolled oats: 0.54
Red kidney beans: 0.51
Barley: 0.51
Black beans: 0.49
Rye: 0.47
Wheat: 0.43
Roasted peanuts: 0.43

As we can see, meat and animal products have the most bioavailable sources of protein, while plant-based sources trail behind. Along with bioavailability, we should also consider protein density when choosing between animal and plant sources.

Protein Density

Protein density refers to how much protein we’re getting per bite of that food. Not only can plant sources contain antinutrients that inhibit absorption (thereby lowering quality scores), but even the highest quality plant proteins come packaged with carbohydrates (and fibre), which dilute the amount of protein we consume per bite (note: we are referring to whole food sources, not plant sources that have been processed and isolated into protein powders).

On the other hand, animal products are extremely protein dense with the majority of calories being made up from protein – chicken breast is 80% protein and tuna is over 90% protein. You’d need to eat A LOT more of the plant food to get the same amount of protein as a serving of meat. In essence, animal protein gives you more bang for your buck in terms of calories.

Let’s go back to the broccoli vs. beef argument: yes, broccoli may contain more protein per 100 calories compared to beef, but do you know how much broccoli you would have to eat for 100 calories worth?? 3 1/2 CUPS or just under 250g. And that only gives you about 7g of protein.

Meanwhile, beef gives you an easy 13g per 100 calories, or 21g of protein per 100g of meat. So even though calorie for calorie broccoli may win, pound for pound beef takes the prize for protein density and therefore efficiency.

The table below shows how much of each food you would need to eat (in calories) to get 30g of protein: 

So, basically, to get 30g of protein you’d need to eat 10 potatoes or a piece of fish.

Now that’s a bit far-fetched as no one claims potatoes to be a source of protein. But let’s have a look at lentils: you’d need to eat about 1.5 cups of lentils (or 337 calories worth) to hit the 30g mark versus 100g of fish at about 1/3 of the calories.

Now, I’m not a huge believer in the whole calories in vs. calories out argument, but I won’t dismiss the fact that calories do matter to an extent. Also, food quantity matters! You’d have to eat a MUCH larger volume of food to get your protein – if you can stomach it all, great! But, I also find a lot of people have issues digesting this much plant matter, because of the amount of fibre in there, as well as the sheer volume.

Beyond the protein

We can’t overlook the fact that animal protein provides additional benefits over just being an efficient protein source. Meat is a rich source of heme iron, which is better absorbed by the body than non-heme iron found in plants. Vitamin B12 can also only be found in animal meat, which is why we often see a deficiency in this nutrient in the plant-based population. Symptoms of B12 deficiency [3] include:

  • Weakness, tiredness, or lightheadedness
  • Heart palpitations and shortness of breath
  • Pale skin
  • Constipation, diarrhea, loss of appetite, or gas 
  • Nerve problems like numbness or tingling, muscle weakness, and problems walking
  • Mental problems like depression, memory loss, or behavioral changes 

Animal proteins are also richer sources of vitamins A and D, calcium, iron, zinc, iodine, choline, selenium, creatine, taurine, methionine, glycine, and EPA and DHA.

While it is possible to supplement all of these nutrients, nothing beats getting them straight from the food you eat because you can be certain of their bioavailability and it’s way cheaper then spending your money on pills!

Don’t stop eating plants!

Let’s be clear here: I’m NOT saying that you should stop eating plants. I’m merely pointing out the fact that they are not an optimal source of protein. BUT they are a great source of other nutrients and a very important part of a healthy diet.

Plants provide us with fermentable fibres to optimise our gut health, a myriad of phytochemicals—such as flavonoids, lignans, polyphenols, carotenoids, and chlorophyll, as well as other healthful micronutrients that animal products only have a small amount of. We shouldn’t rely on plants for protein, but we should definitely be eating them for all the other awesome things they contain!

There is no single optimal diet that works for every human being, but a natural human diet contains a healthy balance of both plant and animal foods.

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