Post Workout Shake – Whey vs Casein – Shaking up the Truth

Post Workout Shake – Whey vs Casein – Shaking up the Truth

What makes up your post-workout shake? Whey or casein protein?

Chances are, it’s whey, followed up by a casein protein shake later on before bed. But is casein in a post workout shake really that bad? Should we question the Gym Bible that says whey after training, casein before sleep? Well yes, we think we should.

Brand new, hot off the press research suggests that the type of protein makes no difference to the ultimate outcome – increased lean muscle mass and strength.

Whey and casein protein

Both whey and casein are milk proteins, naturally found in cow’s milk. How they’re absorbed and used, however, are quite different [1].

Whey protein is known as ‘fast’ protein. It’s anabolic, meaning that it builds up muscle. It’s so often used in post workout shakes because it’s so quick to be digested. Within around half an hour, the whey protein will be fully absorbed by the digestive system, filling your bloodstream with amino acids.

From there, your body will use these amino acids for growth and energy. Your muscles will use what’s available to repair all the little tears in them caused by working out. It’s these repairs that lead to the eventual bulking up of muscle.

Casein, on the other hand, is known as ‘slow’ protein. It’s anti-catabolic, which means that it reduces the level of protein breakdown.

It clots in the stomach, slowing down the breakdown and absorption of other proteins into the stomach and liver. This leaves more for protein synthesis in the muscles. It takes around four hours for casein to raise the level of amino acids in the blood, and even then, not to the level that whey protein does.

Post Workout Shakes - Whey vs Casein | Fitness Savvy

Post Workout Shake – Whey vs Casein

Protein-based post-workout shakes and their impact on training

Protein shakes are synonymous with resistance training. It’s already known that protein shakes help to build muscle mass and strength and increase performance. A study in 2015[2] confirmed this and also found that in the initial weeks (if you’re new to exercise) protein supplementation is unlikely to have an impact.

However, as the duration, frequency, and volume of resistance training increases, protein supplementation can support gains in muscle strength and aerobic capacity in both exercise newbies and trained individuals.

Protein, whether from food or from supplement powders, helps to form more muscle mass via protein synthesis. The body also uses protein to perform bodily functions, breaking it down as it does so. In order to build muscle, there must be more protein being synthesised than being broken down.

Protein, regardless of type, equals muscle, then?

Yes. Whey protein acts quickly and dramatically on the level of amino acids in the blood. It then increases the level of protein synthesis. And casein has a slower, less dramatic effect on blood amino acids levels. It reduces the number of proteins that are broken down, making more available for the muscles.

It’s easy to see then, why whey protein has always been used directly after a workout. And why casein is a slow-acting top-up working its magic whilst we sleep.

So, about this new study…

Researchers in France [3] have carried out what they believe to be the first-ever study into the consumption of whey and casein workout shakes immediately after exercise.

Studies in the past have looked at both before and after exercise, but not only after, or taken together.

Researchers in this double-blind study gave subjects 20 g protein mixed with 250 ml water immediately after resistance training, four times a week over nine weeks. Some subjects were given 20 g of pure whey protein, some were given a 50:50 mix of 10 g whey and 10 g casein and the rest were given a 20:80 mix of 4 g whey, 16 g casein (which is similar to their natural ratio in milk). The researchers specifically wanted to look at the impact of these protein-based post-workout shakes on lean muscle mass development.

Interestingly, they found that “post-exercise drinks varying in fast-to-slow protein ratios did not affect the responses of fat mass, fat-free mass and muscle strength after nine weeks of resistance training”…

Hold on, no difference between whey and casein after training?

Nope. All subjects, regardless of the ratio of fast (whey) to slow (casein) protein experienced the same responses. They all had their body composition (weight, fat mass and lean body mass) measured before, during and after the study using a DEXA scan. All subjects experienced fat loss and an increase in lean muscle mass, and there was no reportable difference between them. Whey and casein as post-workout shakes did the same job.

The study did find that those taking the 100% and 50% whey shakes did have an increased blood level of amino acids, in particular, leucine. Leucine is a branched-chain amino acid crucial for muscle growth [4]. It’s a potent activator of protein synthesis and inhibitor of protein breakdown.

Add whey or casein to your post workout shake | Fitness Savvy

Add whey or casein to your post-workout shake

Despite this, the higher levels of amino acids “did not have a more measurable and positive impact on the long-term adaptations to resistance training”. In other words, those taking whey as a post-workout shake increased their blood leucine levels more than those taking a higher concentration of casein straight after training. But this had no impact on the amount of increased muscle mass at the end of the study.

So it seems, from this study at least, that a post-workout shake containing protein, regardless of whether it’s whey or casein, result in the same longer-term gains in muscle strength and levels of lean muscle mass.

The study concluded that what really matters, is making sure you consume a sufficient amount of protein post-exercise. The ratio of slow to fast protein in it making little difference.

Obviously, one small study isn’t enough to change the general consensus on whey vs casein. But it certainly is (protein-laden) food for thought…



Hannah de Gruchy
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