The FastDay Forum

As above, thanks

[carorees]

What do you need to know Sophie? Do you mean ketosis as in when ketones appear in urine or as in the process of converting fat to ketones so they can be used for energy?

Well I think I know it has something to do with having no carbs on a fast day I think? Would this allow me to get into ketosis mode? Just been reading a few bits and bobs on the forum and wondered if anyone has done it.

If there is inadequate supply of glucose the brain and other organs can use ketones for part or all of their energy supply, the ketones are derived from fat breakdown.

To get into ketosis requires a low carb intake and depletion of available liver glycogen reserves as otherwise glucose from those sources is used preferentially.

Is it something that can be done on a fast day? Sorry for all the random questions!

[carorees]

You can start producing ketones on a fast day yes but to enter ketosis in the sense that you're body is running mainly off them could take some days unless you have been on a low carb/ketogenic diet beforehand. It depends a lot on your diet, your exercise and your glycogen storage capacity. Glycogen stores can amount to 1000-2000 cals so it is unlikely that you could deplete them completely in one fast day, but you can still produce some ketones.

There are some lines of evidence that ketones are good for the brain and cancer protection but no proof.

Is it something that can be done on a fast day? Sorry for all the random questions!

Alternate day (true) fasters certainly achieve fairly high levels of ketones on fast days.

Another paper said..
"In the four subjects fasted for 15-20 hr,
average ketone concentration was 0.94 +- 0.22
pmole/ml and rates of production and urinary
excretion of ketones averaged respectively 880
+ 140 pmole/min and 3.1 + 2.6 pmole/min."

So yes if you were to have dinner and finish by 7pm sometime between 10am and 3pm the next day you should be running fairly high ketone levels.

Couldn't find a nice ketones vs time graph for fasting

[carorees]

I think it's so variable depending on the previous diet, exercise, biological variability, that it's hard to predict. Clearly some people are reporting ketones in the breath, so some people are definitely producing plenty of ketones.

Without wishing to show any disrespect to the OP , my view on the subject of ketosis is that there is too much reference and focus on it with regards to weight loss/dieting.

For me, there an element of vagueness around the term ketosis and how it is used in the online world of weightloss/dieting.

My view on the definition of Ketosis is that it is the state you reach when your brain/CNS stops using glucose as the primary energy source and instead turns to ketones as the primary source, and this state takes roughly 3-4 days to achieve. From a dieting/weight loss perspective who cares what the brain’s primary fuel source is? From a 5:2 perspective I doubt anyone will ever achieve true ketosis either. After 24-36hrs (or less) of fasting we’re back on our high carb diets eating and snacking every few hours.

Surely what’s more relevant to weight loss is the fat metabolism that results in the generation of ATP which in turn goes to fueling the muscles? I don’t buy into the often stated view that ketones are fuelling me, they definitely go some way to providing my fuel for my brain/cns and heart but I’m never totally running on ketones in those organs and it’s fat catabolism to ATP that is fuelling my muscles even if I am in a true state of ketosis.

I appreciate that increased ketone production is an indicator of a greater reliance on fat burning. However we’re always knocking out ketones and we’re always somewhere on the scale of producing a few ketones to being in full on ketosis. Your average Joe (or Jolene) has no accurate way of measuring ketones so again I think why the emphasis on so many websites on this idea of being in ketosis?

Sorry if this sounds like a rant it's just my tuppence worth on the subject

When I did Lighterlife a few years ago they measured ketones in urine each week when you went to the meeting - very low calorie/carbohydrate diets facilitate ketosis, as opposed to ketoacidosis (very dangerous). You can measure the level of ketones in urine with KetoStix (I think that's how it's spelled), available from chemists. I was told not to expect any significant level of ketosis until 3 days into a very low calorie/carbohydrate diet so I'm not sure whether ketones would be detectable via a urine sample during a relatively short 24 hour fast.

[carorees]

Skippy you are right of course. A state of ketosis is not necessary for fat burning or weight loss.

Some of the interest in whether we achieve ketosis while fasting/low carbing comes from the theory that ketones are themselves beneficial in terms of brain derived neurotrophic factor production and that cancer cells often cannot use ketones for energy and so a ketogenic diet may be protective.

But of course this is all theoretical and we have no real proof that fasting produces any other benefits than weight loss. There are some pointers that fasting is different from simple calorie restriction though and we all hope that we are getting some extra benefits!

Ketones are produced in small amounts in most people every night while asleep. This is normal and isn't considered ketosis, since ketosis is defined as elevated levels of ketones. How elevated? There's no set answer to this, but the usual indicator is that the level of ketones is high enough to spill out into the urine, sweat, and breath.

Ketones are produced when fat is burned in the absence of carbohydrate. This happens during sleep because even though you have plenty of carbohydrate stored in the liver as glycogen, the liver doesn't release much of it during sleep. This stored glycogen is reserve fuel for active time, so it mostly stays in the tank and you burn fat instead and produce ketones.

Acetoacetate is a ketone that can be used for energy, or broken down into two other ketones. One of them, acetone, can't be used for energy--in fact, it's toxic--so it's entirely excreted. Since acetone is the main ingredient in nail polish remover, this accounts for the distinctive "ketone breath" smell.

According to Wikipedia, excess acetone has been offered as an explanation for spontaneous human combustion! So who says we can't burn acetone?

Most tissues that can use glucose for fuel can also use ketones (the other two ketones) instead, but they don't normally do so until glucose is scarce. As skippyscuffleton said, this can take 3-4 days of very low carb consumption. When this happens, ketosis levels will appear to fall because more ketones are being used for energy and less are spilling out into urine to turn Ketostix purple. People who do zero carb diets often show only trace levels of ketosis after they've adapted to using ketones for fuel. This transition from using mainly glucose to using ketones is sometimes called "keto-adaptation." It shouldn't happen on a 5:2 unless your feast days are very low-carb.

Some cells can't use ketones; they're completely glucose-dependent. Red blood cells need glucose, and the brain can only get about half of its energy from ketones.

For weight-loss purposes, I agree with skippyscuffleton again that the whole ketosis thing is overblown. Yes, if you're in ketosis you're certainly burning fat. It doesn't follow that you're burning stored fat, however, and it also doesn't follow that if you're not in ketosis you're not burning fat.

Ketones are produced in small amounts in most people every night while asleep. This is normal and isn't considered ketosis, since ketosis is defined as elevated levels of ketones. How elevated? There's no set answer to this, but the usual indicator is that the level of ketones is high enough to spill out into the urine, sweat, and breath.

Ketones are produced when fat is burned in the absence of carbohydrate. This happens during sleep because even though you have plenty of carbohydrate stored in the liver as glycogen, the liver doesn't release much of it during sleep. This stored glycogen is reserve fuel for active time, so it mostly stays in the tank and you burn fat instead and produce ketones.

Acetoacetate is a ketone that can be used for energy, or broken down into two other ketones. One of them, acetone, can't be used for energy--in fact, it's toxic--so it's entirely excreted. Since acetone is the main ingredient in nail polish remover, this accounts for the distinctive "ketone breath" smell.

According to Wikipedia, excess acetone has been offered as an explanation for spontaneous human combustion! So who says we can't burn acetone?

Most tissues that can use glucose for fuel can also use ketones (the other two ketones) instead, but they don't normally do so until glucose is scarce. As skippyscuffleton said, this can take 3-4 days of very low carb consumption. When this happens, ketosis levels will appear to fall because more ketones are being used for energy and less are spilling out into urine to turn Ketostix purple. People who do zero carb diets often show only trace levels of ketosis after they've adapted to using ketones for fuel. This transition from using mainly glucose to using ketones is sometimes called "keto-adaptation." It shouldn't happen on a 5:2 unless your feast days are very low-carb.

Some cells can't use ketones; they're completely glucose-dependent. Red blood cells need glucose, and the brain can only get about half of its energy from ketones.

For weight-loss purposes, I agree with skippyscuffleton again that the whole ketosis thing is overblown. Yes, if you're in ketosis you're certainly burning fat. It doesn't follow that you're burning stored fat, however, and it also doesn't follow that if you're not in ketosis you're not burning fat.

Excellent, comprehensive response, Ubizmo - informative but not too technical. Thanks for posting.

According to Wikipedia, excess acetone has been offered as an explanation for spontaneous human combustion! So who says we can't burn acetone?

Ubizmo - you've got me worried now. Two predecessors of mine (username only) allegedly met this fate.. I'm not sure sure they were 5:2ing though?

Thank you all for your delightful informative responses, I think that has answered my question. I tend to try and have very little carbohydrates on my fast days as I did today but I am a carb lover, I doubt I could keep it up for 3-4 days. If it isn't essential to 5:2 then that is ok, I shall continue doing what I am doing. Completed my 5th fast today, 482 calories knowing that there is cheesecake in the fridge - pretty chuffed at my willpower today even though the evening is not over.