We hear time and time again, “you need lots of carbs to fuel sports activity”. On the face of it this seems like reasonable advice, particularly for high intensity activity, but the amount of carbs that is often quoted doesn’t seem to make any sense to me. Personally I know my body does not deal with carbs very well. So I’m interested in training on a low carb diet.
What piece of the jigsaw puzzle am I missing. Why does nearly every expert recommend a very high carb diet for athletes.
Anyway, here’s the way I see it.
The body can’t store carbohydrate, so any carbs you eat (if not used ) get converted to glycogen stored in both muscles and the liver and then once these stores are full the remaining carbs are stored as fat. The liver can hold between 250 calories worth of glycogen and muscle holds between 800 – 2000 calories worth (depending on how big and how well-trained an athlete you are).
They key thing to remember is that:
a) If your glycogen stores have been completely depleted then maybe it’s going to take a lot of carbs to get back to a full state but unless you’re running marathons or playing 80 minutes of rugby every day that’s not happening.
b) These upper limits of 2,000 calories worth of glycogen stored in muscles is for very highly trained world-class runners. Most people are much closer to being in the 800 calorie range.
c) Lots of sports don’t actually use that much glycogen. An hours intense weight training only uses about 60 grams of carbohydrate and sprinters like Usain Bolt use hardly any. This is because this type of activity relies heavily on the ATP already stored in the muscle for fuel, which can be replaced from fat stores as well as from glycogen.
When you start to exercise the majority of calories come from your glycogen stores, but as the duration continues the percentage of energy from fat increases. What this means in practice is that even if you work moderately hard (say 600 – 800 calories) it’s going to be difficult to burn more than 300 – 400 calories worth of glycogen during normal 60 – 90 minutes of training. With 4 calories per 1 gram of carbohydrate that means that to refill the glycogen stores you only need 100 grams of carbohydrate!
There has been a bit of research around ketogenic diets (for a detailed explanation and a complete overview of all the research I would suggest you get hold of a copy of Lyle MacDonald’s book – The Ketogenic Diet). I’m not recommending a ketogenic diet for athletes, but what I am saying is that the research around ketegenic diets shows that a few headline facts to keep in mind:
a) A carbohydrate intake of 50 grams per day is enough to limit the need for the body to use amino acids for gluoconeogenesis. In other words stop muscle mass breakdown.
b) Assuming that we are ingesting enough carbohydrate to stay just outside ketosis, the brain (the only organ in the body that can’t bun fat for fuel) needs 250 – 300 calories per day (60 – 75 grams of carbohydrate)
This means that a base level of carbohydrate (assuming we not trying to be in ketosis or lose weight) is around 110 – 120 grams per day. Now if you factor in another 100 grams of carbohydrate to replace the used muscle glycogen from exercise, then we get to a level somewhere in the region of 200 grams a day.
Now I know that top marathon runners can store large amounts of glycogen and that after a race their stores are fully depleted. But 99% of the sprinters and middle distance runners, footballers, weightlifters, judoka, MMA fighters, boxers, rugby players etc etc, out there could easily get by on the 200 – 250 grams per day. By this I mean during day in day out training. For sure if you play a hard football/soccer or rugby game, then yes you might need an extra 100 grams or so on top, but that’s only once a week, not every day.
It’s worth noting I think that with regard to long distance runners one of the biggest problems they have is “hitting the wall”. This is basically the reaction their body has to depleting their glycogen stores. However, (and this is just my theory) part of the reason they get such a drastic reaction is because they have trained for so long on such high carb diets that their bodies don’t like running without it. Here’s an interesting study done on endurance athletes on ketogenic diets (i.e. no carbohydrates at all) which interestingly shows no difference in performance compared to a high carbohydrate diet. And there are a lot of studies that show that the longer someone is on a low carb diet the better the body becomes at using fat for fuel.
Anyway, I don’t have any trouble at all maintaining training intensity or putting on muscle mass on around 150 grams of carbs per day.
Just for fun here are some recommendations on carbohydrate intake I Googled today:
About.com, Sports Medicine, Nutrition Tips for Strength Training
Experts recommend at least 500 to 600 grams of carbohydrate per day to keep your muscle glycogen stores high. You can base your personal requirement on the following formula:
3.6gr carb x body wt(lbs)= grams carb/day. For a 140 pound person this is about 504 grams per day
Irish Rugby, Nutrition
As a guide, approximately 60% of the total calories consumed should come from carbohydrates.
Training and conditioning.com, Fueling for Football
An ideal diet for football players requires 55 to 60 percent of their daily caloric intake to come from carbohydrates, 15 percent from protein, and 30 percent from fat. The way I translate these numbers to football players is that each meal should be two-thirds carbohydrate and one-third protein…
55 to 60 percent from carbs. Assuming moderate to high training per day of 800 – 1,500 calories. For a 160 lb male that’s 500 grams of carbs every day. If their base metabolic system needs just 60 grams and they are only need to replace 100 grams through exercise, what are the remaining 350 grams for?
Answers on a postcard please, or in the space below.