Preparing for a 100mile ride in August I was thinking of following a training plan which came in a "Sportive Guide" given away with Cycling Plus magazine this month.

Some of the days on the plan mention training for an hour before breakfast in order to burn fat.

Is this just about losing weight? (If so, I'm pretty sure I don't need to since I'm 6ft tall and weigh about 67kg) Or is there some reason that training before breakfast is somehow better?

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    A bit of not-so-scientific knowledge, but if you eat just after moderate exercise, there is a peak of nutrient absorption. This means not necessarily fat buildup, but glycogen restoration and other muscular nutrients restoration, such as proteins. Commented Apr 17, 2013 at 13:30
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    I read recently that training before breakfast increased your body's ability to burn fat in endurance sports. Useful for a century, I suppose, I'm struggling to find the reference though.
    – alex
    Commented Apr 17, 2013 at 14:12
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    At that weight, you might want to consider eating before and after the morning ride :)
    – Kibbee
    Commented Apr 17, 2013 at 16:21

6 Answers 6


Advice in book Racing Weight by Matt Fitzgerald goes something like this, paraphrased:

Yes, training without carbohydrates will train your body to use stored fat better. But your capacity to train will go down (not enough fuel!), and net result will be less improvement.

It references this study, which compares two groups of athletes on hi-carb and low-carb diet during a hard training block.

One of the general themes of the book is, you want to improve your performance and body composition, not your weight per se.


Exercise is fuelled by a combination of carbohydrate and fat. In theory, if you exercise while your body is deprived of carbohydrate it will become better at utilising fat for energy.

I know some running coaches advocate this approach for marathon training:

Any carbohydrates ingested will be used by the body for fuel, and we don't want this. We want to deny the body carbohydrates in these runs so that the muscles will become better at sparing the carbohydrate stores, more efficient at burning fat and used to running with lowered blood glucose levels. Now, many people think I'm crazy when I say this, but it works.

Personally, I wouldn't do it. It's a lot of pain for what is probably a very small gain. If you're looking to wring every last bit of performance out of your body it's worth trying though.

  • I wonder if this has been scientifically tested. The body would most likely use up all (or just about all) carbohydrate stores before starting to use the fat stores. I'm not sure if you can train your body to use fat before all the carbohydrates are gone, or if that's even something you would want to do, since I'm not sure that the body can burn fat fast enough to supply the energy you need while cycling. Anybody who's "hit the wall" knows that not ingesting enough carbs means the body does not have enough capacity to fuel your during exercise on fat alone.
    – Kibbee
    Commented Apr 17, 2013 at 16:18
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    If you run out of Glycogen and the closer to aerobic threshold you are exercising, the more protein and less fat is burned. If your 1 hour morning ride is intense, it's likely you will be cannibalizing your muscles in the last 15 minutes..
    – mattnz
    Commented Apr 17, 2013 at 22:03
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    @mattnz That is exactly the problem I recently saw a nutritionist explain on another site regarding this question. In short, your body needs some readily available energy to begin breaking down and using fat. Lacking that available energy, you will lose muscle rather than fat. So you need a small, high-carb snack prior to exercise. An energy bar, a banana, a glass of milk -- anything with some readily digestible carbs will do. With that you really will burn more fat. Without it, you'll burn muscle. Commented Apr 18, 2013 at 0:55
  • Endro athletes do burn fat sooner (when they still have glycogen stores) than non-enduro - provided they are operating well below VO2 Max. I don't know if its training, genetics or both that improves it. Fat takes a lot of O2 to metabolize - as you approach VO2 Max, and glycogen runs out, your body transitions to burning Protein unless there is excess oxygen for metabolizing fat. Eventually a balance is stuck based on how hard you are going. If you ever get a "sweat" smell in your urine after exercise - that is by-product of metabolized protein.
    – mattnz
    Commented Apr 18, 2013 at 3:00

The short answer is "No". Intermittent fasting is not all about weight loss, although it can help with that, apparently without compromising performance.

There's research showing that this approach can increase the effect of training, in particular VO2 Max, which is often of interest to cyclists.

For example Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state.

The FAST group showed a significantly greater training-induced increase in VO(2max) and resting muscle glycogen concentration than FED (P=0.014 and P=0.047 respectively), but there was no gender interaction.

This blog post is a few years old, but discussed the detail of a study comparing fasting or fed regimes in training.

There are also claims of long-term health improvements, I think these are less well-studied, but there is some relevant research.

It does also help to lose weight, or improve power-to-weight ratio, although that may not be of interest to the OP.

If you're actually thinking of doing it, one of the essential points is to have a good recovery meal after training.


I ride mornings in a fasted state and i believe it has helped, not just in terms of weight but also endurance. This type of exercise should not be high intensity just moderate. There is a scientific study that looked into this it was referenced in this NY Times blog article: http://well.blogs.nytimes.com/2010/12/15/phys-ed-the-benefits-of-exercising-before-breakfast/


It's not just fat utilization but also glycogen, a chemical resembling starch that is stored in the liver and also directly in the muscles. I don't know the ideal conditions for doing so, but the muscles can be "trained" to store more glycogen. (In part this is what causes muscles to "bulk up".)

Presumably training in conditions where the blood glucose level is low would help to "train" the muscles to store glycogen, though this would be a long-term thing, over months, not something to work on a few days before a big ride. And glycogen is important not only because it can help to fuel muscles several hours into a long ride, after blood glucose is exhausted, but also because it can help provide "peak energy" even when one is well-fed.

(Note that burning fat directly in the muscles is quite inefficient and can lead to "ketosis", causing a sense of fatigue and loss of mental acuity. Fat is more efficiently "burned" in the liver, but the rate of fat processing by the liver is insufficient to support a sustained high-energy effort.)

It needs to be remembered that there is a lot of really crappy advice out there, often from "experts", re nutrition. Probably 80% is bogus. In particular, many "experts" who talk about "burning fat" have probably never even heard of glycogen. My "expert" opinion is informed by having a genetic disorder (myoadenylate deaminase deficiency) that affects how muscles use energy, so I've taken interest in these topics for decades.

  • I have a problem with the word "presumably." Can you cite evidence your presumption is correct? Commented Apr 18, 2013 at 0:59
  • @CareyGregory - I don't think anyone can cite clear evidence for any of this stuff. It is known that athletic training (football camp, et al) causes an increase in stored glycogen in the muscles, but I've never head of any controlled studies that attempted to isolate the factors involved. Commented Apr 18, 2013 at 1:25
  • (The thing is, the body responds to "challenges" by increasing it's ability to handle similar future challenges. Glycogen is accumulated by the body because "experience" has shown it necessary. The trick is to give the body that "experience" without giving it counter-productive experiences at the same time.) Commented Apr 18, 2013 at 1:29

I believe the intensity level of training should be further considered; it's ok to take a walk first thing in the morning on an empty stomach, but an interval training session would probably be counter-productive.

  • Welcome to Bicycles.SE. Would you consider expanding this into a more complete answer?
    – amcnabb
    Commented May 3, 2013 at 16:51

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