Burning Ketones In Your Body While Fasting?

From Excerpt copied from:Exercise Physiology FOR HEALTH, FITNESS, AND PERFORMANCE, Third Edition, Plowman & Smith :

Ketone Bodies and Ketosis
As mentioned earlier, in order for the acetyl CoA produced by beta-oxidation to enter the Krebs cycle, a suffi cient amount of oxaloacetate is necessary. When carbohydrate supplies are suffi cient, this is no problem, and fat is said to burn in the fl ame of carbohydrate. However, when carbohydrates are inadequate (perhaps as a result of fasting, prolonged exercise, or diabetes mellitus), oxaloacetate is converted to glucose. The production of glucose from noncarbohydrate sources under these conditions is necessary because some tissue, such as the brain and nervous system, rely predominantly on glucose for fuel (Marieb, 2007).
When oxaloacetate is converted to glucose and is therefore not available to combine with acetyl CoA to form citrate, the liver converts the acetyl CoA derived from the fatty acids into metabolites called ketones or ketone bodies. Despite the similarity in the names, do not confuse ketones with keto acids (pyruvic acid and the Krebs cycle intermediates) (Figure 2.9). There are three forms of ketones: acetoacetic acid, beta-hydroxybutyric acid, and acetone. All are strong acids. Acetone gives the breath a very characteristic fruity smell.
Ketone bodies themselves can be used as fuel by muscles, nerves, and the brain. If the ketones are not used but instead, accumulate, a condition called ketosis occurs. The high acidity of ketosis can disrupt normal physiological functioning, especially acid-base balance. Ketosis is more likely to result from an inadequate diet (as in anorexia nervosa) or diabetes than from prolonged exercise, since the muscles will use the ketones as fuel. During exercise, aerobically trained individuals can utilize ketones more effectively than untrained individuals.

In general, where you and I are at in our weight loss journeys, I'd say no, fasting is probably not a good idea. You can certainly try it if you want, but fasting, especially IF (Intermittent Fasting), which is what I think you are referring to, is really designed for people trying to go from lean to VERY lean. Like on the order of 10% BF to 7%. It's benefit for overweight and obese folks is less clear and may actually cause some problems. Now, that said, there are some people that do promote fasted exercise, because in theory it may burn more fat. Honestly I think the difference is pretty small and it could also cause you to perform poorly, thus negating any potential gains it might have given you. Also what they generally mean when they talk about fasted exercise is exercise first thing in the morning before breakfast, not necessarily long fasts.

In short, I'll agree with HannahOM. Eat less than you burn, make sure you do both cardio AND strength training, and make sure you're getting sufficient protein. Pretty much everything else is up for debate.

check out low carb/atkins/ketogenic diet.
that's the same thing, minus the fasting.

ketosis is pretty great, i love the way i feel once i'm in it.
the carb detox can be hard for some.

Apparently, while you are fasting, if you work out during the period that you haven't eaten, your body starts using ketones instead of sugar and it burns fat faster and more efficiently....? Is this plausible?

Entirely plausible, that's how the body works to keep the brain going on ketones when there isn't enough glucose around. The brain can't run on fatty acids (unlike muscles) so they are broken down to ketones for brain fuel.

The fat is being used to make the ketones, and to fuel the muscles, so in this situation more of it is being used, yes.

From Excerpt copied from:Exercise Physiology FOR HEALTH, FITNESS, AND PERFORMANCE, Third Edition, Plowman & Smith :

Ketone Bodies and Ketosis
As mentioned earlier, in order for the acetyl CoA produced by beta-oxidation to enter the Krebs cycle, a suffi cient amount of oxaloacetate is necessary. When carbohydrate supplies are suffi cient, this is no problem, and fat is said to burn in the fl ame of carbohydrate. However, when carbohydrates are inadequate (perhaps as a result of fasting, prolonged exercise, or diabetes mellitus), oxaloacetate is converted to glucose. The production of glucose from noncarbohydrate sources under these conditions is necessary because some tissue, such as the brain and nervous system, rely predominantly on glucose for fuel (Marieb, 2007).
When oxaloacetate is converted to glucose and is therefore not available to combine with acetyl CoA to form citrate, the liver converts the acetyl CoA derived from the fatty acids into metabolites called ketones or ketone bodies. Despite the similarity in the names, do not confuse ketones with keto acids (pyruvic acid and the Krebs cycle intermediates) (Figure 2.9). There are three forms of ketones: acetoacetic acid, beta-hydroxybutyric acid, and acetone. All are strong acids. Acetone gives the breath a very characteristic fruity smell.
Ketone bodies themselves can be used as fuel by muscles, nerves, and the brain. If the ketones are not used but instead, accumulate, a condition called ketosis occurs. The high acidity of ketosis can disrupt normal physiological functioning, especially acid-base balance. Ketosis is more likely to result from an inadequate diet (as in anorexia nervosa) or diabetes than from prolonged exercise, since the muscles will use the ketones as fuel. During exercise, aerobically trained individuals can utilize ketones more effectively than untrained individuals.

I love it when you pop into a thread with some exercise science! Thanks for the read.