What's the best source of protein?

Protein is now mainstream, before it was reserved for weirdos like us, gym rats and meatheads. Now it’s everywhere and from all different sources. Everything seems to be labeled “source of protein” now a days, but not all protein is made equal. Animal vs Plant sources, whey vs pea protein. You get the picture.

Did you know there is actually a protein quality index, a score if you will. This is called the Digestible Indispensable Amino Acid Score (DIAAS). This score rates the amino acid profile of the protein source and its digestibility in the human body.

What you'll find out ⤵️

Why protein quality matters
Muscle Protein Synthesis - the low down.
What the DIAAS scoring system looks at.
How your favorite protein source stacks up
Casein Protein Intake before bed

Why it matters 🤔

Protein is an essential macronutrient, it is made up of amino acids which are the building blocks of your body.

An easy rule of thumb for someone starting out on their fitness journey is to consume 1.4-1.8g of protein per kg of bodyweight, spread evenly throughout your daily meals. We will get into the finer details of how to set up your protein intake in another article.

If you want to get technical, preferably more than 3 meals per day. This is because consuming protein triggers Muscle Protein Synthesis, this is the metabolic process which helps you recover, build and maintain muscle.

You want to trigger this frequently as a study by (Atherton et al., 2010) [1] showed MPS returning to normal levels by the 2 hour mark. Muscle protein synthesis (MPS) requires all nine essential amino acids (EAA’s), specifically leucine, as this amino acid is accredited with the stimulation and signaling to start MPS in the body. Therefore, you want to consume complete protein sources to ensure you getting all nine EAA’s.

The scoring system 🤓

The Food and Agriculture Organization (FAO) and World Health Organisation (WHO) originally recommended the PDCAAS scoring system in 1993, which looks at the content of all 9 EAA’s and the protein’s digestibility by the human body. Since then the FAO & WHO have recommended using the DIAAS score, which scores based off the ileal amino acid digestibility.

In Short, the DIAAS score basically measures the protein sources amino acid profile and its bioavailability.

Most animal protein sources (Milk, Whey, Eggs and Beef) have a complete amino acid profile with a digestibility rating of 95-98%, however plant sources usually lack one or more amino acid and have a lower digestibility rating between 70-85% (Tomé, 2023) [2]. Alternatively, Soy has a similar score to milk and whey! You can get more information on the chart below.

Plus the ridiculous volume of broccoli you would need to consume to get the same amount of protein a chicken breast would provide would just be a sad state of affairs to get yourself in! Not to mention your not even digesting and getting use out of the all that tasty broccoli protein!

Your reference. Your Welcome ✌️

Anything with a DIAAS score of over 100% is considered excellent and anything with a score of between 75-99% is considered good.

It is also worth mentioning that foods with low DIAAS scores, although might be a poor choice for your protein source, could fit well into a healthy balanced diet with its other nutrition qualities - vitamins, minerals and other micronutrients.

DIAAS Score in % for Various Sources

Pea Protein Isolate - A recent study by (Guillin et al., 2021) [3] found that pea protein isolate had a DIAAS score of 100% making pea protein isolate a brilliant plant protein source up there with Tofu and Soy.

What about Casein Protein? 💤

Casein Protein is an animal protein source derived from milk, in fact milk protein is 80% casein and is a complete protein source. It’s also digests slower than whey and other protein sources, hence why it is typically consumed before bed as it feeds your muscles with amino acids at lower levels over a more prolonged period of time.

According to the findings of this study (Guillin et al., 2021) [3] Casein Protein has a DIAAS score of 145%! One of the highest scores I’ve came across for any protein source.

A study by (RES et al., 2012,) [4] looked at 16 males who performed resistance training and 30 minutes before bed consumed casein protein. The results showed that it was effectively digested resulting in a rise in amino acids in their system which remained throughout the night, increasing full body protein synthesis rates. Showing the idea that it digests slower and provides more sustained at longer supply to the muscles during the night.

The main form you will probably buy to supplement is Micellar Casein.

For your consideration ✍️

As you can see from the graph above animal protein sources tend to be a more complete protein, however on the plant side, there are plenty of good options with Tofu, Soy and Pea Protein all above the 75% mark.

It could be worthwhile for some vegans to supplement with EAA’s or BCAA’s to bring their daily consumption of Amino Acids up.

Based on your current diet goals, protein sources should also be considered. Most tubs of Peanut Butter claim to be a “Source of Protein”. However Peanut Butter should be considered a source of fat, due to its low protein content, high fat content and of that peanuts have a low DIAAS score of 43%.

Fun Fact - A study by (Derbyshire et al., 2023,) [5] found that pistachios are the nut with the highest DIAAS score. Raw at 86 and Roasted at 83.