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.
bicycles.stackexchange.com/users/679/Pēteris Caune
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.
bicycles.stackexchange.com/users/1509/Tom77
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.
bicycles.stackexchange.com/users/5337/James Bradbury
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/
bicycles.stackexchange.com/users/6824/Jonny
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.
bicycles.stackexchange.com/users/1584/Daniel R Hicks
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.
bicycles.stackexchange.com/users/6816/lucaPost
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?
Training fasted: just about weight loss?
bicycles.stackexchange.com
<training><fitness><nutrition>
bicycles.stackexchange.com/questions/15343
bicycles.stackexchange.com/users/5820/kevtufc
Training before breakfast is advocated for training the muscles to use fat stores for energy. This process takes some time to develop, so the practice needs to be maintained for some time.It is a practice essentially used for weight loss and endurance training. There are some disadvantages though as the person may feel fatigued and lose mental alertness due to low blood sugar. mOREOVER, When implementing this type of training, it is important to have a good recovery meal after. The idea is probably to train the body to burn fat rather than carbohydrates, and to store more glycogen. In theory, this should help the body to use fat for energy and have more stamina, while also contributing to weight loss. This can help in a number of ways, but it is a longer term strategy and it is important to eat afterwards. This might also be more effective with low or moderate intensity exercise to avoid fatigue.
The idea is probably to train the body to burn fat rather than carbohydrates, and to store more glycogen. In theory, this should help the body to use fat for energy and have more stamina, while also contributing to weight loss. However, this method could lead to increased tiredness This can help in a number of ways, but it is a longer term strategy and it is important to eat afterwards. This might also be more effective with low or moderate intensity exercise to avoid fatigue.