Why high carb diets don’t make any sense even for athletes

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.


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.


About thegymmonkey

I'm a fitness junkie,interested in injury rehab and get back into competition. View all posts by thegymmonkey

One response to “Why high carb diets don’t make any sense even for athletes

  • JonnyGinese

    Great article.. I did Take Shape For Life awhile ago and lost 60 lbs in about 5 months and they use the “get rid of Glycogen” and keep it out idea… but they don’t starve you off carbs… I used to weigh 265 and I’m now 205 :-). I’m trying to work toward getting down to at least the top edge of my BMI via working out and eating right(and still using the 5 and 1 plan)… Anyways.. I have a few questions that maybe w can chat about when you have some time.

    Please e-mail me if you get a chance and hopefully you can help me out!


    Jonny Ginese

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