Nutrition for the Athlete, Part 1

“Nutrition makes me puke” – Jimmy Piersall

“What should I eat?”- Such a simple, innocuous question that leads to so much complication.  Nutrition for the athlete, or for the active person in general, is a topic that has generated incredible controversy over the years. Low fat diets, low carb diets, ketogenic diets, Paleo diets, South Beach diets, raw food diets- you name your dietary preference, there’s a school of thought out there that purports it to be the best way to stay lean, keep your energy levels high, maximize performance, etc.

So what sort of rules should you be following when it comes to eating for maximum performance?  First, to clarify what that means- “eating for maximum performance” is defined here as “A diet that is sufficient to fuel the desired volume and intensity of workouts, maximize recovery, and maintain an optimal body composition”, in other words eating enough that you won’t suffer in your workouts, but not so much that you put on unwanted weight.

A basic digestion primer
The first, most important thing to understand about nutrition is HOW what you consume is getting into your body, which is the purpose of this first installment.  First, the digestive process:

When you eat anything, the process of digestion starts in the mouth.  Amylase, an enzyme contained in saliva (also produced by the pancreas, but not relevant at the moment), begins to break starches down into individual sugar molecules.  Food then makes its way to your stomach, where a number of things happen, but more importantly, a number of things do NOT happen.


The stomach is NOT an absorptive organ- it can absorb some water and lipid soluble compounds, as well as small amounts of amino acids, but for the most part, it is really just a large blender filled with acid and a few enzymes.  This is important, as food remains in the stomach for hours- one to two hours for small, easily digested foods (say, whey protein), up to five or six hours for large, hard to digest meals (rare beef, thick fibrous starches).  Bear in mind that this process is a continuum- there is no timer controlling food’s exit rate, just a small aperture that doesn’t let large objects through. The speed of gastric emptying is also controlled by various hormones and feedback mechanisms, including the “ileal brake”.  The ileal brake refers to the ileum- a portion of the small intestine.  When nutrients are present in the ileum, the stomach empties more slowly.

Once food is mixed and broken down in the stomach, the bolus makes its way to the small intestine, where buffers neutralize the acid and other enzymes get to work, including all the various proteases that break down protein and the lipases that break down fats.  For the next four to five hours, food is pushed through and the majority of nutrients are absorbed, before the remainder is pushed into the large intestine, where it remains for upwards of 20 hours.  In that time, bacteria process the remaining nutrients (and fermentation of certain carbohydrates occurs), and water and electrolytes are removed.

This is certainly a much more complex process overall than explained above, but this information is necessary to understand a few basic facts.  First of all, look at the overall transit time- nutrients are being actively absorbed from any meal for well over ten hours.  Most nutrients, with the exception of pure glucose and free amino acids (or very short chain polypeptides) do not even begin processing until several hours after ingestion.  On top of this, the presence of food in the small intestine slows emptying of the stomach, which means that nutrients from a meal eaten eight hours ago are still being absorbed and slowing digestion of anything eaten more recently.

Also note that digestion is a 98-99% efficient process- there are MINIMAL nutrients left in human waste matter, and what is left are primarily fibrous starches that we cannot digest (like cellulose), a few undigested food particles, small amounts of fat, and water.  Though perhaps not a wonderful subject, this nevertheless illustrates an important point- no matter the macronutrient, your body WILL absorb it.  There is no upper limit to the amount of, say, amino acids your body can break down and pull into the bloodstream.

A final note on the fate of amino acids- once absorbed, amino acids can be used directly by cells for the synthesis of new enzymes or new cell structures,  for the building of structural proteins (such as actin and myosin in the muscles), for the synthesis of OTHER amino acids (via transamination), or used for energy.  The latter is important to understand, as deamination (the process by which the amino group is removed) creates two products: Ammonia and a carbon skeleton (Acetyl CoA/acetoacetate or pyruvate).  The ammonia is combined with carbon dioxide in the urea cycle, and excreted in urine, and the carbon skeleton can be either used for energy directly or converted into other compounds, such as glucose or fatty acids.  This last point is particularly important, as it is critical to understand that once this amino acid is broken up, your body only sees the carbon skeleton, and doesn’t care if this carbon skeleton came originally from a glucose molecule or from a protein.

Why this is relevant
The first question that people often ask is “How often should I be eating?”  In light of the above information, the logical response seems to be “It doesn’t really matter all that much”.  For a normal individual, this is quite true- a large meal can take more than 24 hours to pass through the system, and your body is making use of nutrients for over half that time.  To ensure a constant supply of nutrients, your system could easily do very well off of two large meals a day.

The second question is often “How much protein can my body actually use or absorb?”  The answer is: A nearly unlimited amount.  It may not NEED all that protein for basic function, but what isn’t used is simply converted to other forms of energy and can be stored if need be (this includes stored as fat).  The only limiting factor here becomes the amount of ammonia produced by deamination.  For a healthy individual, this is not a problem, as the kidneys can easily process the ammonia and excrete it as urea.  However, for individuals with kidney problems, or individuals who are chronically severely dehydrated, this may be a problem, as in both these cases urea production and excretion may be compromised.

The third question could very well be “Great, but I’m not the average individual, I’m an active athlete, what should I do differently?”  This is the crux of this article.

Eating for performance
What is adequate and what is ideal are often two different things entirely, and this is where the details come in.  The ideal, incidentally, does not often involve a dramatic switch in eating patterns, or adopting any sort of radical new diet- it is simply a bit of juggling to maximize energy levels at certain times of the day.  There is a tremendous amount of information and misinformation being spread in the fitness community regarding meal timing, ghrelin and leptin manipulation, the benefits of ketones or ketogenic processes… all this can be safely ignored for the time being. The place to start- calories.

Many consider “calorie” a dirty word, which is rather backwards- counting calories is nothing more than calculating how much energy you are consuming and attempting to match that to your desired output.  There is nothing wrong with that, and at the end of the day, this is the single biggest factor in determining weight loss or gain, performance improvements versus performance deterioration, etc.  And, again, contrary to belief, there are no magic solutions that allow any body to circumvent the basic calories in versus calories out- even the most severe genetic or metabolic conditions do not significantly alter the math. This is why gastric bypass surgeries (even the non-malabsorptive types) have success rates over 95%- simple portion control.

However, for the athlete, calorie counting is not about restriction, it is about calibration. The goal is simple- get a basic idea of what you need to maintain (I.e., what you are currently eating), then adjust this intake up or down depending on expenditure and training cycle.  Easy enough.  No need to calculate the calories in your maintenance, then simply calculate your approximate additional energy expenditure through activity and take in more food to compensate- in a ratio of roughly 9:1 carbohydrates to protein.  (Note- there is absolutely zero research to back up this ratio.  As with many “rules” in sports nutrition, it is an educated guess.)  But what should this food be, and when?

Food types and timing
Much of what was said above in the segment on digestion still holds true- it’s clear from the fundamentals of human digestion that meal timing is vastly overrated when it comes to overall nutrient uptake and body mass loss or gain.  There is one major factor that needs to be taken into account for the athlete, however, is WHEN glucose levels and energy levels are peaking, and when they are dropping. This is far more critical than attempting to eat to minimize catabolism or maximize muscle gain, as insulin and glucose levels (and therefore energy levels) can peak and trough within minutes, whereas skeletal muscle synthesis and degradation is a slow, ongoing process.

The next installment will discuss how to manage insulin and glucose levels, as well as how to adjust your food intake around your workouts to maximize energy levels.  In the meantime, take a moment to digest (groan) the information above, and consider if you are spending too much time focusing on aspects of your diet that do not matter.


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