• Question: If we don't get enough of the required Amino Acids in our diet does our body prioritize a particular group of proteins to give it to? Or does it distribute them evenly to all the proteins that require them? If so, how? - Thanks :)

    Asked by izzabop to Rachael, Penny, Jennifer, Jean-Paul, Dave on 8 Jan 2014.
    • Photo: David Christensen

      David Christensen answered on 8 Jan 2014:


      That’s a really good question izzabop, thanks.

      I don’t actually know for certain how this works and my guess is that nobody knows completely how this is controlled, but I think it is likely that their would be prioritization.

      What I do know is that there is a protein called mTOR that is an important sensor of available nutrients, including as a sensor for amino acid levels. mTOR is also a regulator of cell growth, cell proliferation, and protein synthesis. This means that mTOR, and other sensors, detect the levels of amino acids and then, if there aren’t enough, they will stop the cell dividing and growing and also start to inhibit protein synthesis. This would then lead to production of proteins in general being stopped, but by stopping production of proteins necessary for cell growth and cell division, then hopefully more amino acids will become available for synthesis of other important proteins. How this is all regulated in the cell would involve a large network of proteins interacting with each other and turning other genes on or off, so it would all be massively complicated and my guess is that nobody has worked out how this all works yet.

      I’ll also just point out something that you might or might not already know. We can make many of the amino acids in our bodies, so in many cases detecting low levels of these amino acids will just stimulate more of them to be made. However there are also a group of amino acids that we have to get from our diet, so there are greater problems when our cells run out of these. If you’re really running out of these I think your muscles start to be broken down so that your cells can still get the amino acids they need for building other proteins, but the cells are initially hoping that if they slow certain processes they can get more amino acids for other functions.

    • Photo: Penelope Mason

      Penelope Mason answered on 8 Jan 2014:


      Hey, I think Dave covered it, but I wanted to add some points! We do have about twenty ‘essential’ amino acids, but it would be pretty rare to be deficient in just a sub-set. Most foods contain all the essential amino acids, even if in low quantities and it’s pretty easy for people to get the necessary amounts of all of them by eating a variety of things, even if they are on a restricted diet e.g.vegan. Further, although all twenty are essential, some can be converted into each other so we can usually make up a deficiency to adequate (if not perhaps optimal) levels. It’s possible to set up an experimental diet to look at specific deficiencies, but it’s often hard to see the effects because getting rid of one essential amino acid looks very much like getting rid of them all.

      Therefore I think the only way a normal diet would truly lack essential protein was if a person was basically not eating enough of anything. In this case, the body would break down a little muscle to liberate proteins, as losing a bit of skeletal muscle isn’t immediately a problem but a small amount of essential amino acids circulating is essential for every normal cell to keep working. This is why starving people eventually often die of heart failure as eventually the heart muscle is used up to where it becomes too weak to pump adequately.

      Also, as Dave said, the nutrient sensing equipment of each cell would basically put a big slow-down order on everything, with obviously the absolutely essential pathways in the cell/tissue/organ/body being prioritised over non-essential pathways. If you were actively growing, e.g. a child, this would be noticeable because you would then stop and if it persisted, you would never recover and even if you survived, and started ingesting enough nutrients, you’d be stunted and have other body issues.

      Its interesting that warm-blooded animals that eat less than the required amount often have a drop in body temperature. This has lots of effects. Firstly, they are saving the energy to keep to the higher temperature, as this is very energy-costly. Also, though, in cells, proteins tend to work more slowly and last longer as they get a bit colder (but only to a certain temperature) so the colder temperature might be both saving the energy from the proteins working quickly, and preserving them for longer so less new ones have to be made. It all works interconnectedly!

      But as I said, if you are eating a fairly normal, varied diet, it’s not hard to get all the amino acids you require, and meat usually contains all of the essential ones, as does a mix of grains and legumes for non-meat eaters. Interestingly, though, the real issue for optimum intake might be the balance of amino acids – the amounts relative to each other. One study on fruit flies showed that flies that were restricted in (although had some) methionine (which is essential in every protein as it forms the ‘start’ codon that begins every protein being made) actually lived longer. Different amounts of the various amino acids gave different effects on lifespan and fertility (a measure of health) in the flies. Is this relevant to us? Work is ongoing…

Comments