Fueling for Endurance Training

March 05, 2021 6 min read

Fueling for Endurance Training

We know that many of you out there are big lifters, like us, but we also want to cater to our readers who may love endurance sports more!  Although nutrition does not vary that much between those who lift and those who run, swim, or bike, if you are training for longer races, then there are certain things we must know about fueling and recovering our bodies.  Things can look very different compared to your normal weight-training session!  

We’re going to break this down into the main focuses we find serves our endurance athletes best when looking at how to eat, hydrate, and recover for those long training days!  

Carbohydrates vs. Fats 

Which is better for endurance athletes?  Although the research is pretty clear for resistance training, or higher-intensity sprint athletes that carbohydrates are the best fuel source, the research around endurance athletes is actually quite inconclusive (SOURCE).  When comparing a high-carb, low-fat diet to a high-fat, low-carb diet, the endurance athlete’s performance remained largely unchanged.  

With that being said, we always recommend experimenting with your own diet to find how you feel and perform best!  When we coach endurance athletes, including triathletes, marathon runners, IRONMAN athletes, and cyclists, we typically err on the side of fueling with carbohydrates, as they are often tolerated a bit better than high fats by most individuals.  They’re a bit easier and more appetizing to consume in high amounts, and most intra-race or intra-workout sources are pretty carb-based.  We also like keeping our options open!  When you go to a low-carb, high-fat approach, your body loses its ability to utilize carbohydrates as an energy source.  So when we maintain a higher carb, moderate fat diet, the body can utilize both energy sources for training! 

Carbohydrates are the fuel to our body’s tank and they get stored in our liver and our muscles.  These stores are what our body uses to stabilize blood sugars which allows for muscles to avoid major fatigue and the body to not drop too low on blood sugar and result in dizziness.  

The general rule of thumb is that we are able to store about 2g of carbohydrates for every pound of lean muscle mass, plus an additional 100-125g of carbohydrates in our liver at any one point (SOURCE).  We will discuss later on how you can fuel for a specific long run or race day! 

The Role of Protein in Endurance Training 

We’ve talked many times here around protein and its importance to maintaining muscle mass, improving blood sugar responses, and helping to reduce cravings.  As for endurance athletes, protein can be really helpful when it comes to longer efforts or training days.  Research has shown that including small amounts of protein during longer training can work to spare muscle glycogen as well as aiding fluid uptake - meaning we don’t burn through our muscle when training, and we actually absorb and utilize fluids better (SOURCE). 

Protein needs to be balanced properly though because protein also has the highest thermic effect of food, meaning it takes the most energy and the longest amount of time for the body to break it down.  When consuming too much protein within or around your training, it can slow digestion and cause stomach upset, bloating, cramping, or overall muscular fatigue.  

We typically recommend that our endurance athletes consume a minimum of 0.6-0.7g of protein per pound of body-weight.  For example, a 160lb individual would be consuming 96-112g of protein each day.  This is adequate to help support body muscle maintenance as well as optimal body-functions which require protein!  We will discuss later how we recommend taking in protein on race day. 

Electrolytes and Hydration 

Unlike strength athletes, endurance athletes have a special need for additional water and electrolyte intake because of the fluid loss that can happen during long periods of endurance training.  The problem with only taking in water is that it dilutes the electrolyte supply and can actually make things get worse for those trying to avoid major dehydration.  Believe it or not, studies have shown that electrolyte depletion is actually a bigger problem in long-races like IRONMANs than straight dehydration (SOURCE).  So we want to cover the main electrolytes and what their purpose is for not only endurance athletes, but all of the population in general! 

  • SodiumThis is the most abundant and, for endurance athletes, could also be argued to be the most important electrolyte.  All cells depend on sodium, and potassium, to bring nutrients into cells and remove waste.  Our muscles, in particular, are pretty dependent on it, as it helps with muscle activation and preventing spasms or cramps. 
  • Potassium - This is sodium’s best friend and the primary electrolyte found in cells.  It helps maintain fluid balance and cellular health.  We lose this electrolyte when we sweat, pee, and when our muscles contract to utilize stored glycogen during exercise. 
  • Calcium - Bones are the largest storage site for calcium, but soluble calcium in body fluid is what we’re talking about here - which assists in muscular contraction, intracellular messaging, and glycogen metabolism.  Calcium is lost rapidly in sweat, and some studies even have linked loss of calcium in sweat and lower mineral density to correlate with stress fractures over time! 
  • Magnesium - We love magnesium, and we believe it is perhaps the most under-appreciated electrolyte.  Many endurance athletes know sodium and potassium are important, but low magnesium is often the culprit behind poor performance because it is themain driver behind energy production.  Magnesium can also have direct effects on sodium, potassium, and calcium.  

This is why we developed our HYDRATE with the essential electrolytes we need to help our bodies thrive, and it is not just for endurance athletes!  If you live a high stress lifestyle, or you are weight training, electrolyte balance is just as important to keep an eye on.  

Race Day Preparation

So what about Race Day or leading up to it?  How do we prepare given all of this information?  If your race is longer than 2-3 hours worth of work, it is definitely something to prepare ahead of time for.  We will caveat all of this with the fact that these things should be something you experiment with!  This is not stuff that you just throw into your routine on race day and hope for the best.  Use some of these methods on your longer training days leading up to the race to find what works best for you! 

Week prior to the Race 

Don’t change much the week leading up to the race besides your carbohydrate intake, which will also help your electrolyte balance.  We usually recommend to avoid too many vegetables and fruits the 2-3 days leading up to your race to reduce fiber in the system.  This can help with digestion and avoiding digestive woes the morning of or during your race!  If your race is longer than 3-4 hours, we recommend taking the 1-2 days prior to the race and increasing your carbohydrate intake utilizing low-fiber foods like pretzels, cereal, pasta, white rice, potatoes, sports drinks, etc.  

We will usually take a client’s estimated lean body-mass and multiply that by 3-4g to get their carbohydrate intake to shoot for the 1-2 days leading into the race.  

Morning of Race 

This always depends on the individual, their size, their fitness level, and their digestive abilities, but these are some general recommendations we have for our athletes for the pre-race meal and timeframe: 

  • Carbohydrates - About 100-150g of low-fiber carbohydrates at least 2.5-3 hours prior to the race.  This could be a bagel with nut butter, or cereal with bananas on top.
  • Protein - 15-20g of protein in your morning meal with the carbohydrates could include eggs, yogurt, or a protein shake.  
  • Electrolytes and Hydration - Since we lose water overnight, we need to get in some hydration the morning of before the race.  You can get electrolytes from your food sources in the morning, but we advise sipping on about 20-24 oz. of water leading into the race. 


Again, this will always depend, but the general recommendations we make around intra-workout fueling are the following: 

  • Carbohydrates - For every hour beyond the initial hour of a race, we advise adding 30-50g of carbohydrates per hour and this is dependent on the weight and intensity of the athlete.  You can get this through gels, chews, energy drinks, bars, etc. 
  • Protein - If the race is under 3-4 hours, you probably won’t need much protein.  Although if the race is longer than 4 hours, we recommend a small amount (about 5g/hour) to help with muscle sparing.  Things like a peanut butter sandwich, energy bars, or sports drinks can help. 
  • Electrolytes and water - We recommend no more than 20-24 oz. per hour unless it is extremely hot out, so we do not risk over-hydrating the body.  With each of the 20-24 oz. bottles, we advise about 200-500mg TOTAL sodium, and small amounts of the other electrolytes.  Keep in mind that sodium will also be coming from other sources of energy like your gels, food, and sports drinks.  Too much sodium can cause bloating, so we need to make sure we aren’t taking in more than our body needs. 

Fueling for endurance training is very different compared to fueling for weight training or any other general fitness approaches, so make sure if you are gearing up to increase your miles, or take on a new distance you’ve never conquered before, to ensure you are fueling your body with the right nutrients and food!

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