Is it True That You Are What You Eat?

A Protein’s Journey From Bite to Bicep

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They say that you are what you eat. Is this true?

Is Andrew ‘Spud Fit’ Taylor, who dined exclusively on potatoes for a year, doomed to morph into Mr. Potato Head?

You may laugh, but the reality is I often see people behave in a way that suggests they take this saying too literally. Bodybuilders cram as much protein into themselves as they can, hoping to build more muscle. Many dieters stay away from fat, fearing will go straight from ‘lips to hips’.

The biological reality is much more complex than this.

This article tackles one piece of the puzzle, focusing solely on proteins. We will follow the proteins in your food or supplement and see how they end up woven into the fabric of your body.

This journey will prime you to understand what your protein needs are, how to meet them, and how to navigate the sea of protein-boasting products.

Protein Primer

Before, we get into the journey, let’s start with some protein basics:

You can think of a protein as a chunky, messy, alphabet necklace. Photo from Etsy.
  • 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

Photo credit: My Sports Science (I’m a big fan!)
  • 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 it’s sleeve to reduce, reuse, and recycle!

How Your Body Decides Which Proteins to Make

Your cells are integrating many inputs at all times. Photo from Pixabay

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).

Building on this, amino acids play a twofold role in regulating gene expression.

  1. They can impact a cell’s drive (or desire) to make a given protein. They do this by acting as signals that inform the cell about the body’s nutritional status. Some amino acids play a more prominent role than others as signals.
  2. They can 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 essentially giving your cells building blocks to play with. Our ability to shape how our body uses these blocks is limited.

Be a Smarter Consumer

Getting your body to make more of a specific protein is not as simple as eating more of it. You can’t treat baldness by eating hair! However, you can treat it using drugs that block signals (from a type of testosterone) at the hair follicle. The concept that the signal is as important as the fuel applies broadly.

Speaking Your Body’s Language

We can shape which proteins our bodies make using these two levers:

  1. Provide enough fuel / building blocks.

In the case of proteins, a mixed diet is a safe way to ensure you cover all your amino acid needs. However, be aware that more is not always better.

2. Provide the best possible signals to nudge your cells into action.

In the case of bodybuilding, 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!).

Closing Thought

Before you buy the latest protein-based wonderproduct, think carefully about whether it makes sense to expect benefits beyond those provided by a healthy, varied, whole-foods diet.

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