We all know protein is essential for building muscle and recovering from training. Many people might be aware or have at least heard about muscle protein synthesis and optimal feeding strategies to maximise protein synthesis and optimise muscle growth. Research has established that even protein feedings every 4-6 hours with 20-30g of protein are getting towards optimal for muscle growth, however little research has been performed into the digestion and absorption of different proteins. Why would this be important? Well, it is likely that the rate at which amino acids appear in the blood stream after eating is going to affect our levels of protein synthesis.
If we stick closely to the ‘every four hours’ rule and we assume we have a normal protein synthesis response, then it might seem logical that we want to get the fastest digesting and absorbing proteins into the body at these times to elevate blood amino acid levels and let protein synthesis do its thing. However, things aren’t quite that simple. The problem with this idea is that if we have rapid increases in blood amino acid levels then there is an increased chance that these will be oxidised and used for energy as opposed to being driven towards generating new proteins. A slower digesting protein source such as casein will elevate blood amino acid levels slower but this steady supply of amino acids is more likely to be directed to maintenance of protein balance than be oxidised for energy.
So does that mean we should only use slow digesting protein sources? Well, not exactly. The danger of having too slow a digesting protein is that although it will prevent muscle breakdown and support a positive net protein balance, it may not elevate leucine levels sufficiently to maximally stimulate muscle protein synthesis. It appears that there is a trade of between digestion and absorption rates, stimulation of protein synthesis, prevention of excessive oxidation of amino acids and prevention of protein breakdown.
So where does this leave us? Well at certain times we could use the benefits of a faster digesting protein such as whey or amino acids in periods where we want to stimulate protein synthesis rapidly. This is in keeping with the use of essential amino acids and whey proteins around resistance training as demand for protein will be amplified by the act of resistance training. The elevated levels of insulin associated with fast digesting proteins will also offer other muscle protective effects and contribute to a more positive net protein balance, especially if combined with carbohydrates. This might also be an advantage for those training early in the mornings that haven’t got time for a proper breakfast to keep the body in a more anabolic state. Upon waking, our muscles are actually in a state where they are losing amino acids. When we cannot provide a steady supply (like when we are asleep), it releases them from muscles to fulfil the other roles in the body that we require amino acids for.
The longer digestion times and more steady and sustained release of casein might not be optimal for stimulating protein synthesis, but its popularity as a pre-bedtime supplement is founded on the fact that for up to seven hours (compared to around three hours for whey) blood amino acid levels will be elevated and this is likely to help prevent a large release of amino acids from muscle tissue overnight.
There are many other factors that are likely to affect the rate of digestion and absorption of protein, including the amount of protein in the meal. In essence we want the ‘goldilocks’ amount; Enough to stimulate protein synthesis for sufficient time but without so much that it slows digestion, impairs protein synthesis and leads to protein wasting as excessive amounts will still be oxidised. Again this leads us back to an often touted amount of protein consumption of around 20-30g every 4-6 hours for most people to maximise protein synthesis. Obviously those with more muscle require more protein, so these amounts may need to increase slightly to meet overall daily protein requirements.
But what about regular protein sources such as meat or eggs? Well this is likely to depend on a number of things including cooking method, the amount of cooking and the surface area of the food. For example, minced beef is likely to be digested and absorbed a bit quicker than an overcooked piece of steak. However, determining the exact rates of digestion and absorption of different protein sources and their impact on protein retention and muscle protein synthesis is to some extent, guesswork, as only a small amount of research in this area exists. Digestion and absorption rates of most meat is likely to fall somewhere between whey and casein (but probably closer to the casein end of the spectrum if I had to make an educated guess at around 4-5 hours).
Another spanner in the works in determining protein feedings are the effects of mixed meals including carbohydrate and fats (which again have different types and digestion rates) and the effects that any undigested food from a previous meal might have on the digestion, absorption and measures of protein synthesis/breakdown. This area is largely under researched and is something to consider especially in the periods around training where we might eat protein in quick succession in pre, intra and post workout periods.
But all is not lost… What do we know? Well, we know that more regular feedings of protein have a better impact on muscle protein synthesis than less frequent. Three 30g feedings 6 -8 hours apart is going to be better than two 45g servings 12 hours apart, so we can start to determine that there is some benefit in smaller more frequent protein feeding. Looking at the data available it appears the safe bet at present is to eat as suggested around every 4-6 hours as this should allow time for digestion and absorption for even mixed meals, as long as they are not excessively large. Assuming you care about maximising protein synthesis in any case, it might be worth considering that saving all your macros for one meal might not be the best idea if it’s going to affect your digestive system adversely and potentially impact on the absorption rate of amino acids and other nutrients.
***Obviously you should eat how you enjoy eating, and eat what best helps you adhere to a diet if that’s more important!***
In summary, protein sources have different digestion and absorption rates and these are likely to be impacted by a number of different factors including processing, cooking methods, the amounts and types of fats and carbohydrates in a mixed meal and the remanence of any previous meals. Regular, consistent protein feedings show evidence for improved protein synthesis compared to smaller feeding frequencies or when protein distribution is uneven, but few studies have factored in the above limitations. Current guidelines suggest 20-30g of protein every 4-6 hours to maintain protein synthesis near to maximal rates, however protein supplementation in and around training will likely be dependent on your pre and post workout eating patterns and training demand.