How much protein can you actually absorb from a meal?

Just as you can use Lego bricks to build whatever you want – from a house one day to an aeroplane the next, all using the exact same pieces – proteins work in the same way. Each protein (the Lego model) consists of a sequence of different amino acids (the Lego bricks) that, when consumed, breaks down into independent amino acids that are then used to build cells and muscles and to form enzymes and hormones.

Protein is the only nutrient that provides amino acids. No amino acids, no enzymes. No enzymes, no life. When the stakes are that high, it may come as no surprise that the body prioritises the use of amino acids for its life-sustaining processes. Survival first, six pack later. Once the body has all the amino acids it needs, protein can also be used as an alternative source of energy. In other words, if you have any Lego bricks left after building your house, you can burn the rest for heat.

All the protein you consume is used in some way. Protein beyond what your body needs to fill its amino acid pool or use for building muscle mass is broken down into glucose and used for energy. Whenever your food provides you with more energy than you need, whatever the source – protein, fat or carbohydrates – the excess energy is stored as fat. Nothing is wasted.

There are advantages to having a higher protein intake: the protein takes longer to break down, which affects how long the calories “last”, protein doesn’t cause your blood sugar to spike as much as carbohydrates do and, last but not least, protein can give your metabolism a modest boost. The muscle-building benefits of protein seem to account for a maximum of about 20% of our daily energy intake. And if you want to benefit from the appetite-suppressing and metabolism-boosting power of protein, it’s a good idea to consume as much as 30–35% of your calories from protein – as long as you don’t have any medical issues (such as impaired kidney function).

That brings us to the commonly held belief that we should only consume 30 g of protein per meal. What people tend to do is confuse maximum stimulation for muscle protein synthesis with the actual absorption and total protein balance.

If maximum muscle growth is your aim and you’re looking to stimulate this, it won’t increase further if your body is in “energy balance” and you eat more than around 30 g of protein per meal. If your body is in negative energy balance because you’re trying to lose weight, it’s conceivable that around 40 g of protein would be the upper limit to stimulate maximum muscle growth.

However, maximum stimulation of the muscles at a given intake does not mean that the body can absorb or use protein from a meal containing over 30 g. If it is greater muscle mass that you’re after, this can increase with a higher intake than that, which can thus inhibit muscle breakdown. This is not to say that you should eat more protein with each meal, as you want to spread the protein out across the day to trigger muscle synthesis at more regular intervals and to take advantage of the protein’s appetite-suppressing and metabolism-boosting effects throughout the day while also ensuring adequate intake of carbohydrates and fat within your calorie budget.

Your body can obviously absorb and use just about all the protein you consume during a meal, but just like so much else, it’s “The dose that makes the poison”. And that’s either directly due to the actual intake being too high – researchers have shown this to be around 3.5–4 g per kg of body weight per day – or indirectly through what you miss out on and the health problems that result from not getting enough carbohydrates and fat.

By: Frida Röökas 

Photo iStockphoto

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Campbell, B. et al. (2007) ‘International Society of Sports Nutrition position stand: protein and exercise.’, Journal of the International Society of Sports Nutrition. United States, p. 8. doi: 10.1186/1550-2783-4-8.

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