How Does Your Body Decide Which Proteins To Make?
Will eating protein make your muscles grow? Will eating keratin make your hair and nails grow?
While this may seem intuitive, the biological reality is much more complex than this.
This article sheds light on how your body regulates protein synthesis, and what happens “from bite to bicep”. Through this lens, it become clear that many protein-based supplements are not the magic bullets we’d like them to be. Buyer beware!
Before, we get into the journey, let’s start with some protein basics:
- A protein is a chain of amino acids. Imagine a necklace made of alphabet beads, drawn from a 20-letter alphabet. Each letter represents one of the commonly used amino acids.
- Proteins each have a unique sequence of amino acids (beads).
- All life uses the same “alphabet”.
For more protein primer, read: What is a Protein? What Do Proteins Do in My Body?
The Journey From Bite to Bicep
- Your food contains a mix of proteins, in varying amounts.
- Protein digestion — breaking down the long chains of amino acids — starts in the mouth (with chewing), continues in the stomach (enzymes) [Box 2] and finishes in the small intestines [Box 3].
- The “free” amino acids (small chains of 1,2, or 3 amino acids) pass through the intestine wall and travel first to the liver [Box 4], your metabolic powerhouse, which gets ‘first dibs’ on the amino acids.
- The “free” amino acids then enter the general circulation. Your veins are the highway through which the amino acids travel around your body to wherever they are needed[Box 5].
- Cells that need more fuel open their gates to let the free amino acids enter [Box 6].
Key Message: By the end of digestion, the original intact proteins have been broken down into basic building blocks, ready to be used to build new proteins.
Inside Your Cells: How Proteins Are Built
- Inside your cells, free amino acids are strung together into new proteins. This process is called “translation”. Once assembled, proteins either stay inside the cells or are pumped out.
- Each cell writes its own poetry by layering many bead necklaces (or mixing its own unique cocktail of proteins).
- Our DNA provides the ‘recipe book’ that cells use to assemble proteins — i.e. which amino acids (letters) to string together, and in what sequence. The ‘central dogma’ of biology is that information in DNA is translated into proteins through a genetic code. The genetic code is considered universal — virtually all life on earth uses the same code.
Key Message: The new proteins in your cells at the end of the journey are not the same as the ones that came into your mouth at the beginning of the journey.
What Happens to the Excess?
Excess fuel — whether ingested as fat, sugar, or protein, can ultimately be converted to fat and stored. These molecules all share the same atoms at their core (though proteins uniquely contain nitrogen and sometimes sulfur). Your body has a lot of tricks up its sleeve to reduce, reuse, and recycle!
How Your Body Regulates Protein Synthesis: Which Proteins, When, How Much?
Each of your cells is deciding from moment to moment which proteins to make. Biologists use the term “regulation of gene expression” to talk about this dynamic, complex decision, which incorporates many inputs:
- Genetic factors (DNA sequence-based). Only a small fraction of our DNA codes directly for proteins. A much larger portion plays a regulatory role. The regulatory parts of our DNA influence how much we make of a given protein, in what cells, and when we make it. For example, adults can vary in how much they make of the (protein) enzyme for digesting lactose based on their genetics.
- Epigenetic factors (DNA modifications). Different cells in your body have the same DNA sequence but have different modifications to the DNA. These epigenetic factors allow different cell types to be specialized — they differ in which proteins they make, how much, and when.
- Signals. Your cells are constantly sensing the environment inside and outside the cell. Signals can be physical molecules (such as hormones or nutrients) or more abstract stimuli (such as physical activity or temperature).
Two Roles For Your Amino Acids
The amino acids from your dietary proteins play two roles:
Building Blocks: Amino acids impact a cell’s ability to make a given protein. When a cell is missing a critical ingredient for building a certain protein, production grinds to a halt. This latter role is only relevant in nutrient deprived conditions.
Key Message: When you eat, you are giving your cells building blocks to play with. Our ability to shape how our body uses these blocks is limited.
Signals: Amino acids act as signals that inform the cell about the body’s nutritional status. Thus, they impact a cell’s drive (or desire) to “turn on” protein synthesis. Different amino acids play different signaling roles.
Leucine love: The branched-chain amino acid leucine appears to help stimulating muscle protein synthesis (growth of new proteins). Yet, this doesn’t mean it’s a bodybuilding panacea. According to a review of leucine’s effectiveness by Examine.com “Whether this results in more lean mass over a period of time is somewhat less reliable though, and leucine appears to be more effective at promoting gains in muscle in people with lower dietary protein intake and in the elderly (who tend to have impaired muscle protein synthesis in response to the diet).”
Speaking Your Body’s Language
We can shape which proteins our bodies make using these two levers:
- Provide enough fuel / building blocks.
While failing to get enough can cause muscle wasting, eating more protein than you need will not, itself, cause muscles to grow. In most cases, it’s easy to meet our protein needs without protein supplements.
2. Provide the best possible signals to nudge your cells into action.
Physical activity, such as lifting weights, sends a signal to your muscles to grow or remodel. Male hormones are another powerful signal to your muscles (not one I recommend messing with!).
You can’t treat baldness by eating hair! Getting your body to make more of a specific protein is not as simple as eating more of it — you also need the right signals.
Examples of effective signals include resistance training to promote muscle mass, hormone-blocking drugs to treat baldness, and lasers to rejuvenate skin. These examples are more of the exception than the rule. In most cases, the biology is so complex that we don’t yet know how to control it (like how strong and thick our hair is).
Please think twice before you buy the latest protein-based wonder-product (from keratin to collagen to powdered muscle protein). There is no guarantee that your body will use it the way you want it to. If it sounds too good to be true, it probably is!