jimDr Michael Colgan is a world renown nutritionist … Head of a consulting, educational and research facility concerned with the effects of nutrition on physical performance and on inhibiting the degeneration of aging.  Best know for his work with world class athletes at the Olympic level.  He is a great influence!  His article will make you re-think carb loading on pasta the night before a competition!

Carb Loading  Dr Michael Colgan 1 February 2015

In 1967, Scandinavian researchers Bergstrom and Hultman rocked the athletic world with a brilliant study showing how endurance athletes can load their muscles with glycogen and run farther and faster (1). I was training marathon runners at the time and adopted their procedure right away. Done correctly it works like a charm.

But today, after more than 200 studies, commercial greed to sell gels, modified starch drinks, high-fat gunk, and other tomfoolery, have distorted carbohydrate loading into a complete mess. Most of the protocols on the internet are next to useless. Some of them likely REDUCE performance. So much so, that the best coaches have long since stopped giving public advice on loading except to warn folk it’s complicated and uncertain.

In this article I try to sort out the mess, and give you a clear and concise method that can DOUBLE your usual glycogen store, and raise your available calories from fat as well. To do so makes running a marathon, or completing an Ironman, not only easy and fun all the way, but also a source of personal pride that’s difficult to beat.

The Race Distance The distance you are trying to race is critical. Some trainers get people to carb load for a half-marathon. Waste of time. Here’s why. In my 28 Jan article, Fuel for an Ironman, I pointed out that the average trained, amateur runner, of 154 lbs (70 kg), normally stores about 400 grams (4 calories/gram) glycogen. (It varies quite a bit but I can only talk averages in this short article) That’s 1,600 calories of fuel without carb loading.

LoriAs an endurance runner you should always run at a speed below your lactic acid threshold, that is, at the top of the non-panting, “fat-burning zone”. (Run any faster and your body will stop burning fat, and burn up all your glycogen within a few miles.)

At the right speed, the fit body will pull about 400 calories from its fat store during a marathon. So, running right, you have about 1,600 calories from stored glycogen + 400 calories from fat. That’s 2,000 calories available without carb loading.

Even with poor running technique, (about 70% of amateur runners I see), and carrying up to 20lbs excess fat (about 60% of amateur runners I see) , running at the right speed will use only 100-120 calories for each mile. So, the most calories you need to run a half-marathon is 13.1 miles x 120 calories. That’s 1672 calories.  You likely have about 2,000 calories available without carb loading – plenty for the half marathon.  Carb loading will not help you at all. If you are having trouble with the last couple miles of the half, you need to improve your running training not fiddle with your nutrition.

The Marathon The marathon is a different story. At the worst case scenario of 120 calories a mile, total energy cost is 26.2 miles x 120 = about 3,350 calories, way above the average storage reserve of 2,000 calories.

As I pointed out in the previous article, you can absorb only about 300 calories per hour from food and drink on the run. And nothing works in the last 30 minutes because you can’t absorb it in time before the finish. If your marathon time is 3:30, you have just 3 hours to fuel – that’s 900 calories at the most.

So, without carb loading, you have 2,000 calories in store + 900 absorbed on the run = 2,900 calories – well short of the 3,350 calories you need to finish without dropping to a walk, or crawl. This is where carb loading becomes the miracle you need.

How to Carb Load First, a few don’t’s. DON’T use high fat nutrition, (except when I tell you to). During exercise, carbs always yield more than twice the energy of fats. “Wait a bit,” some coaches say, who have been gulled into feeding their athletes high fat foods and supplements. “Fat is 9 calories a gram, carbs only 4 calories”.

Sorry guys, basic physiology – all the fuel has to be oxidized first. You forgot that fat needs more than double the oxygen of carbs to get the energy out. And fat can’t burn at all without carbs. Add oxygen into the equation and the energy from carbs during intense exercise jumps to nearly five times what you can get from fat (2,3). Carbs are always your limiting fuel.

DON’T use modified starches or sugars. It’s easy chemistry to modify a mix of carbs, change the molecular weight and digestibility, or alter the glycemic index, etc, etc. I’ve done it a few times for sports companies, who then give the mix a fancy name, and claim it’s the latest miracle for athletes. Bottom line – they have some medical uses in diabetes and insulin resistance, but they don’t improve performance for fit folk any more than natural carbs that cost pennies (4).

DON’T believe anyone (or product hype) that tells you that you can load glycogen on you run. You can decorate your shorts with gels like a Christmas tree, but it’s not going to help. As I wrote in the previous article, you can’t absorb more than 300 calories an hour while running. Think, most of your usual digestive blood is being diverted to the muscles.

Even after absorption, carbs are nowhere near as good as stored glycogen. Basic physiology again. Your body can use stored glycogen directly for energy. But not carbs absorbed on the run. They have to go through complex chemistry first. It’s called phosphorylation, and uses an enzyme called hexokinase. Hexokinase unfortunately happens to be sparse in human muscle, so conversion to usable energy is slow (2).

Used sparingly, bars and gels help a little while running a marathon. But they are nothing compared to the miracle of a proper carb load beforehand.

Day 7. The basic system we use is a glycogen depletion run seven days out from the marathon. Do not load with fuel before this run, and take as little fuel as possible during it. Do not restrict water. The run should not be an all-out effort, but it should be a long one, at least 3 hours. The more you deplete on this run, the more you will load (6).

Glycogen is depleted only in the muscles used (5). So, do not jog on a treadmill, or elliptical, or stair thingummy. They do not simulate road running, and will not deplete glycogen properly.

In elite runners that I and others have trained, muscle glycogen levels typically fall to 20% of normal levels (1-3). Do not eat carbs afterwards. If you must eat, take a protein drink. Do not restrict water.

Days 6, 5, and 4. Drop your carb intake to 30% of daily calories. During these days jog lightly for no more than 60 minutes. You will feel uncomfortable because your body is now burning more fat than usual, and increasing the ketones from it into your blood.

Day 3. Increase your carbs to 80% of daily calories. You need 11 grams per kg bodyweight per day. For a 154 lbs (70kg) athlete that’s 770 grams, a bit over 3,000 calories of carbs. And increase your water intake by 50%.

Use small frequent meals, 5-6 a day. Taper jogging to no more than 30 minutes. If you do it all right, you will feel great by the evening of Day 3.

Days 2 and 1. Maintain 80% carb intake and 150% normal water. Jog 15-30 minutes. For every gram of carbs you load, you automatically load 2.7 grams of water. Big bonus for hydration during the marathon, because the water is released gradually as the glycogen is used.

Some athletes more than double their normal glycogen levels in this way, from 400 to over 800 grams. Together with the water the extra glycogen stores, by Day 1, a 154 lbs athlete (70 kg), will be 3-4 lbs heavier than on Day 6 (7).

Race Day. 2-3 hours before the race have a high-fat meal. The meal should be at least 1,000 calories and about 60% fats. And sip a 12% carbohydrate drink up to 30 minutes before the race. The reasons are way complex but I will report the science shortly on drmichaelcolgan.com Members of the Colgan Team can also get detailed information on the foods and schedule there.

Finally, practice all this beforehand. Use the last long run of your marathon training, which should be 3-4 weeks out from your race. I advise athletes to work up to a 24-miler for the last training run. Start the practice carb load seven day before the last training run, exactly as set out for the race. You will be glad you did.

  1. Bergström J, et al. Diet, muscle glycogen and physical performance. Acta Physiol Scand. 1967 Oct-Nov;71(2):140-50. 2. Colgan M. Optimum Sports Nutrition. New York: Advanced Research Press, 1993. 3. Ivy JL, et al. Skeletal muscle determinants of maximum aerobic power in man. Eur J Appl Physiol, 1980;44:1-8. 4. Ormsbee MJ et al. Pre-exercise nutrition: The role of macronutrients, modified starches and supplements on metabolism and endurance performance. Nutrients 2014, 6(5), 1782-1808; doi:10.3390/nu6051782 5. Richter EA, et al. Enhanced muscle glycogen after exercise: modulation by local factors. Amer J Physiol, 1984;246:E746-752. 6. Zachweija JA, et a. Influence of muscle glycogen depletion on the rate of re-synthesis. Med Sci Sports Exer, 1991;23:44-48. 7. Burke LM Nutrition strategies for the marathon : fuel for training and racing. Sports Med. 2007;37(4-5):344-7. 8. Murakami I, et al. Significant effect of a pre-exercise high-fat meal after a 3-day high-carbohydrate diet on endurance performance. Nutrients. 2012 Jul;4(7):625-37. doi: 10.3390/nu4070625.