Carbo Loading, Should We or Shouldn’t We?

The Boston Marathon is quickly approaching. Every year this is an exciting time for runners, and most certainly the city of Boston. This year will be especially special for athletes and Americans alike. Because of last year’s terror attacks at the marathon, both our nation and the running community suffered loss. But, in true American and athlete style, we’ve picked ourselves up and this years race will be better than ever. No terrorist will stop runners from running, or make Americans live in fear. So, what better to talk about today than carbo loading. Carbo loading has always been a hot topic, especially with marathon runners. Spaghetti dinner anyone? As a coach and an athlete, I always say “never try anything new on race day.” The same thing applies with what I’ll talk about below.

After watching the finish of the 1924 Boston Marathon, scientists wondered if the “state of shock” (this is referring to what the runners looked like) could have been prevented, or at least ameliorated, if a larger supply of carbohydrate had been taken the night before, or the morning of the race, Levine SA et al (1924) JAMA. It’s funny they didn’t even think about taking in carbs during the marathon at this time. That would come many more years down the road.

So, what they did next was to start to perform many different research studies, to either prove or disprove that ingesting carbs pre race helped. I’m sure you can guess the outcome of those studies, that yes, carb loading did work. But lets now talk specifics. What is carbo loading and should we do it…..?

Traditional Carbo Loading:

  • Started in 1969 with marathon runner Ron Hill. Side note: Ron Hill won the European Championships in Athens in 1969 with a 2:19, then again in Edinburgh in 1970 with a 2:09. A 10 min drop!
  • First step is to do an exercise workout to exhaustion.
  • Second step, 3 days of low carbohydrate, very little if any exercise
  • Third step, 3 days of high carbohydrate intake, very little exercise
  • Fourth step, race!
  • Ron’s most telling anecdote is that at mile 20 of every one of his marathons, when everyone else started fading, he was able to pick up the pace and win decisively. Yes, he was a great athlete and might have won anyway, but he was the first to start thinking outside of the box with carbohydrates.

Later studies in the 70’s showed that following this protocol did not allow the athletes to run faster in the early stages of the race, but they slowed down less. Karlssan & Saltin (JAP 1971). This shows the exact thing that Ron’s racing showed.

There are many studies that show this traditional carbo loading protocol works. These are from the 70’s-90’s. There are more recent ones as well:

  1. Maughan, RJ, Poole DC 1981 Eur J Appl Phys
  2. Saltin et al 1973
  3. Goforth el al, 1980
  4. Bangsbo et al 1992
  5. Nicholas et al 1997

So, then with all of this good data, we should all be following this carbo loading strategy right?

Potential Problems with Carbo Loading:

  • Adverse symptoms during the low carb phase Fatigue, muscle weakness, hunger, cravings, GI discomfort
  • Bloating and GI problems once you’ve started loading back up with carbohydrates
  • Psychological issues during your training taper
  • Uncertainty over food choices can make you nervous, stressed or cause you to over or under eat

But, going back to all the data from the 60’s-90’s. All of those studies showed with doing a traditional carbo load, the athletes could increase their glycogen stores by almost double their beginning stores. Wow! So, then the researchers thought, if doing a traditional carbo load can work this well, I wonder what a modified carbo load would do.

Results of a modified carbo load:

The modified carbo load was this: the athlete took in a high carbohydrate diet (10g/kg/day), and rested/tapered for 7 days.

  • From day 1-4, the athlete’s glycogen stores went up twofold. From days 4-7, the athlete’s glycogen stores stayed elevated at their high levels.
  • When looking at the traditional carbo load, from day 1-4, the athlete had much lower amounts of glycogen stored in their muscles. From days 4-7, the athlete was able to replenish the amount of glycogen, plus gain a little bit more
  • So, when comparing the modified diet to the traditional carbo load, the traditional carbo load gave just slightly higher glycogen stores. Is this enough to do a traditional carbo load vs just a higher carb diet in the week preceding your race, not in my opinion. Especially with how eating low carb makes you feel in the 3 days.
  • The other thing to think about is you don’t want to be overloading your body with a lot more carbs than you are used to. If you normally eat 5g/kg/day, then the week before you eat 10g/kg/day, you will also feel bloated and sluggish. So, eat a high amount of carbs, but practice to see what your body can handle.
  • Also, unlike traditional carbo loading, prior glycogen depleting exercise in not necessary to achieve high muscle glycogen levels. Just eating a high carb diet, plus resting is enough to super-compensate your muscle glycogen levels.

Another way to Enhance Glycogen Storage: Creatine

In the late 90’s till today, there has been several good studies done on creatine supplementation and increased glycogen storage.

  1.  Robinson et al, 1997
  2. Van Loon et al, 2004

These studies showed the highest glycogen stores ever recorded to date. I’ll reference the first study. Robinson, looked at glycogen, glycogen placebo, creatine placebo and glycogen/creatine . Over 6 days, the athletes took 1 of the 4 fuels. The group that took the creatine plus glycogen showed the highest amounts of stored glycogen, and the longest amount of time to exhaustion. The study used 5g doses of creatine, 4x per day. So, 20g of creatine, plus a high carb diet. There are more studies needed to show further effects of creatine and glycogen storage though.¬† Additionally, there are studies being done with caffeine and glycogen storage as well.


To Sum up, traditional carbo loading does work, especially for endurance athletes and team sport athletes like soccer players. It does have some downfalls though. These are mainly GI distress, fatigue and bloating due to the low carb diet. However, if you can do the traditional carbo load successfully, it will help your performance. If you aren’t wanting to do something this drastic the week before your race, feel free to follow a modified carbo load. You’ll want to make sure you are getting in a lot of good carbohydrates in, while resting. With these two things, you’ll be primed for your race. And lastly, it shows us once again that low carb diets just don’t work. Your performance will be impaired with a low carb diet, at least with the sports mentioned above.




Leave A Comment