The GB Pair (Toby Garbett & Rick Dunn) rowing at Henley Royal Regatta 2004.

If you’re an athlete, 50 to 60 percent of your diet should be made up of carbohydrates.

Source:ww.running4women.com

For endurance athletes, the bulk of calories in the diet should be coming from foods that contain complex carbohydrates to fuel workouts.

Source: http://www.running-advice.com

I could go on and on, you’ll find this kind of advice everywhere, even the government and your doctor, but as I wrote in a post the other day none of this makes much sense. I won’t go into the mechanics of this in detail today because you can read the piece here, but the point is that even for trained endurance athletes the most glycogen they can store is around 1,200 calories worth, so why would you want to consume more carbs than you can store as glycogen?

Endurance athletes competing in events that last over 90 mins will often take on extra carbs during the race (to replace partially depleted glycogen stores), but does this even make sense. Surly it would make more sense to increase the body’s ability to conserve glycogen, by metabolizing fat instead. I think the problem for most athletes is that they become sugar junkies. They eat a diet that is 50 – 60% carbs and their metabolism becomes dependent upon them. Then take them away (or use them all up in a long race) and they crash, because their body has lost much of the natural ability to burn fat for fuel.

Look at the way our bodies use the different fuels we store:

1. Very very high output (such as 100 meters sprint) ATP stored in the muscles
2. Very high output (100 meters+) ATP and muscle glycogen
3. High output (such as 800+ meters) glycogen from muscles/glycogen from blood and liver
4. Medium output (5,000+ meters) glycogen stored in blood and liver/fat
5. Low output (walking) fat

OK, so as you can imagine a lot of blurring is going on here, but this gives you a rough idea of what is happening.

If you run 5K it is unlikely you are going to use much muscle glycogen (maybe if there is a hill section, or a sprint at the end) but mostly it’s going to be blood and liver glycogen and fat. If you are a 170 lbs athlete it’s going to be around 300 – 400 calories total for the race. So if you burn 75% glycogen and 25% fat that just 225 – 300 calories worth of carbs (less than 75 grams). During the rest of your day while you are walking about and sitting at your desk your body will happily burn fat in the absence of carbs (except for your brain which will need about 75 grams of carbs). So you can see that as long as you are getting between 150 and 250 grams of carbs between work outs you are easily going to be able to replace the used glycogen within 24 – 48 hours. The only exception to this would be a professional athlete who is undertaking several high intensity training sessions a day, who might want to go to 230 – 300 grams max on their hardest days.

Athletes that are involved in short bursts of intense activity will use even less glycogen. Rugby players, weight lifters/body builders for example use primarily ATP which is then replaced from blood/liver glycogen and fat stores. Of course if you take the intensity down by doing high sets and reps then proportionally more muscle glycogen will be used. This is because it won’t be possible to complete the set using just the stored ATP, this means that ATP will have to be created (on-the-fly) and to do this the intensity will have to drop to give the body time to make new ATP from glycogen.

In a study by Tesch et al. (1986), nine bodybuilders completed five sets each of front squats, back squats, leg presses, and leg extensions to fatigue, comprising 30 minutes of exercise. Biopsies of muscle samples were obtained from the vastus lateralis before and immediately after exercise. Muscle glycogen concentration was 26% lower post-exercise, a rather modest decline considering the demanding exercise protocol completed. This led the authors to conclude that energy sources in addition to muscle glycogen support heavy resistance training. Data from Essen-Gustavsson and Tesch (1990) with nine bodybuilders performing the same exercise regimen (as above) revealed a 28% decrement in muscle glycogen content as well as a 30% decrease in muscle triglyceride content. This suggests that intramuscular lipolysis (breakdown of triglycerides) may also play a role in energy production during repeated high-intensity exercise. Overall, research suggests that intramuscular glycogen is an important fuel supporting weight training exercise, but not the only substrate.
Source: Gycogen and Resistance Training. Todd Astorino, M.S. and Len Kravitz, Ph.D.

So in the above study – 30 mins of squats and leg extensions only depleted muscle glycogen by between 26% and 28%.

So in this context is an ultra high carb diet the best option? What are the long-term health risks of ingesting 2,000 calories a day of carbs? Look at 5 times Olympic Gold medalist Sir Steven Redgrave  -

Being a former rower, for 25 years we’re on a diet of six to seven thousand calories a day…
Sir Steve said in an interview for the BBC.

6,000 calories a day – 60% from carbs (900 grams of carbs). Is the human pancreas designed to take that? Possibly not. No wonder Sir Steve became type 2 diabetic at 35.

The important thing I want to get across here is not ultra low carb or no carb diets for sports. It’s just is the ultra high carb diet the best for all athletes all the time? Are their advantages to eating just enough carbs to replace used glycogen and trying to force the body to use fat stores where it can?

If as an athlete you consistently flood your system with carbs, your body gets lazy at metabolizing fat stores. Also, you tend use energy roughly in the proportion it’s ingested. So if your diet is high in carbs, then that’s what you’ll burn, but if it’s low in carbs and high in fat, then guess what? That’s right more fat gets burnt. Remember I’m not saying you don’t need glycogen, I’m just saying most people don’t realise how little is needed. Remember, as long as your not working near your lactic thresh-hold the primary energy source to replace ATP is your fat stores – not blood and liver glycogen.

Perhaps the most intense use of glycogen is in sports that last between 30 seconds and 6 minutes. But think of it this way, how many calories can you burn in a race this short? The coxless pair that Redgrave competed in is a race over 2,000 meters and lasts around 6 minutes 15 seconds. Most rowers are over six-foot so lets say a maximum of 150 calories during the race (even if three-quarters are burnt from glycogen that’s only 112 calories worth). If Sir Steve is burning through 7,000 calories a day (approx 4,000 over maintenance levels) then he’s going to be training for 5 or 6 hours a day. In other words the majority of the training volume will be low-level aerobic conditioning (somewhere between level 4 and 5 above). Which means he could get at least two-thirds of his calories by converting fat to ATP instead of carbs. In other words even with this kind of massive volume from a 100 kg athlete, I would imagine that 300 – 400 grams of carbs a day would be sufficient. The rest of the energy could come from fat. Now I know some people will say that 400 grams of carbs is a high carb diet, but not in the context of an athlete eating (and using) 7,000 calories a day.

What would the advantages of a higher fat diet be?

A paper by Craig S. Atwood, and Richard L. Bowen that I looked at in another post recently suggests that part of the success of top cyclist Lance Armstrong may be due to the more efficient way his body metabolises fat due to the operations he had as a result of his being diagnosed with testicular cancer. In summary:

Although a champion cyclist in 1-day events prior to his diagnosis of testicular cancer at age 25, he was not a contender in multi-day endurance cycle races such as the 3-week Tour de France. His genetic makeup and physiology (high , long femur, strong heavy build) coupled with his ambition and motivation enabled him at an early age to become one of the best 1-day cyclists in the world. Following his cancer diagnosis, he underwent a unilateral orchiectomy, brain surgery and four cycles of chemotherapy. After recovering, he returned to cycling and surprisingly excelled in the Tour de France, winning this hardest of endurance events 7 years running. This dramatic transformation from a 1-day to a 3-week endurance champion has led many to query how this is possible, and under the current climate, has led to suggestions of doping as to the answer to this metamorphosis. Physiological tests following his recovery indicated that physiological parameters such as  were not affected by the unilateral orchiectomy and chemotherapy. We propose that his dramatic improvement in recovery between stages, the most important factor in winning multi-day stage races, is due to his unilateral orchiectomy, a procedure that results in permanent changes in serum hormones. These hormonal changes, specifically an increase in gonadotropins (and prolactin) required to maintain serum testosterone levels, alter fuel metabolism; increasing hormone sensitive lipase expression and activity, promoting increased free fatty acid (FFA) mobilization to, and utilisation by, muscles, thereby decreasing the requirement to expend limiting glycogen stores before, during and after exercise. Such hormonal changes also have been associated with ketone body production, improvements in muscle repair and haematocrit levels and may facilitate the loss of body weight, thereby increasing power to weight ratio. Taken together, these hormonal changes act to limit glycogen utilization, delay fatigue and enhance recovery thereby allowing for optimal performances on a day-to-day basis. These insights provide the foundation for future studies on the endocrinology of exercise metabolism, and suggest that Lance Armstrong’s athletic advantage was not due to drug use.

Many studies have shown that the less carbs we eat, the better the body becomes at living without them. Sure if you take an athlete who’s getting 60% of their calories from carbs and you suddenly restrict them to 200 grams of carbs a day they are going to crash. But give them time to acclimatise and become efficient fat burners then providing they are eating enough carbs to replace their glycogen stores then the increase in the efficiency of their fat burning will mean their glycogen stores will last longer and that’s got to be an advantage. And in a world where the difference between winning and losing is becoming ever finer, any advantage is worth looking at.

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.

Lance Armstrong finishing 3rd in Sète, taking over the Yellow Jersey at Grand Prix. Midi Libre 2002.

Here is some extracts from a paper by Craig S. Atwood, Richard L. Bowen that examined the metabolic performance of an élite cyclist, Lance Armstrong, before and after his treatment for testicular cancer. What the authors are saying is that the improvements in Armstrong’s performance were caused largely because the treatment allowed his body to use fat as a fuel more efficiently.

There are two primary sources of energy available to athletes: fat and carbohydrate. Muscle and liver store most of the body’s carbohydrate, enough fuel (400–600 g) for about 90– 120 min of high-intensity exercise. Fat stores on the other hand could supply energy needs for 60–100 h due to its higher energy content and abundance throughout the body compared with carbohydrates. Endurance athletes use a mixture of both fuels and when the carbohydrate becomes fatigued they ‘hit the wall’, which is characterised by a drop in speed as a direct result of decreased carbohydrate use which in turn is as a result of a fall in blood glucose levels due to depletion of muscle and liver glycogen stores and blood glucose stores.

Atwood and Bowen state:

Fatty acid utilization is unchanged during fatigue, indicating that lipid is the preferred fuel of muscles, but is rate limiting, and that carbohydrate utilization is required for optimal performance. Therefore, those athletes that can use a higher FFA/glucose ratio at any given speed (i.e. _V O2 ) for their overall energy needs will endure longer than those with a lower FFA/glucose ratio. Furthermore, athletes that do not utilize all their carbohydrate stores during an exercise period will have a greater chance of replenishing their carbohydrate stores to maximal levels compared to those that start with lower carbohydrate stores. This means exercise of a similar or greater intensity and duration can be achieved on subsequent days, and is perhaps the key to understanding the remarkable day-to-day endurance of Lance Armstrong compared with other cyclists1.

So whilst carbohydrate is necessary for high output, one way to improve performance is to make the racers use of fat for fuel more efficient and so slow down the rate that the precious carbohydrate is consumed during the race. In this way the time/distance a racer can keep up optimum performance is increase and at the same time because the carbohydrate stores in the muscles are less depleted at the end of a race, the recovery post race is quicker.

So how do you improve your body’s ability to metabolize fat? Certainly exercise has a big role to play:

Atwood and Bowen go on to say:

These changes indicate an adaptive response to endurance training that decreases glycogenolysis in muscles and spares glycogen reserves. Conversely, detraining leads to an increased reliance on carbohydrate metabolism during exercise, as shown by a higher exercise respiratory exchange ratio, and lowered lipase activity, GLUT-4 content, glycogen level and lactate threshold [48]. Hence, well-trained individuals using a higher proportion of FFA for energy will spare more muscle and liver glycogen, and together with their higher basal glycogen reserves, can therefore maintain a similar level of intensity for a longer period of time compared with untrained individuals1.

But it’s not the only way. As part of their research they conducted the following experiment:

The advantages of increased fat utilization on performance are highlighted by the results of a chronic (4 week) eucaloric ketogenic diet (high fat) on submaximal exercise performance in trained cyclists. The mean ergometer endurance time for continuous exercise to exhaustion at 62–64% _V O2 max on this diet was 151 min compared to 147 min prior to the ketogenic diet [79]. Despite a drop in RQ (from 0.83 to 0.72), a 3-fold drop in glycogen oxidation and a 4-fold reduction in muscle glycogen, the endurance of these well-trained cyclists was slightly better. These results indicate that aerobic endurance exercise by well-trained cyclists is not compromised by 4 weeks of ketosis. Thus, physiological adaptations to a high fat diet conserve limited carbohydrate stores (glucose and muscle glycogen) and make fat the predominant muscle substrate at submaximal exercise.

Now I’m not suggesting that élite endurance athletes adopt a ketogenic diet, but very high carbohydrate diets reduce the body’s ability to utilise fat for fuel so perhaps there are benefits to a low carbohydrate diet for endurance athletes.

1. Metabolic clues regarding the enhanced performance of elite endurance athletes from orchiectomy-induced hormonal changes. Craig S. Atwood, Richard L. Bowen