BMR and fasting. Help me understand


(Stephanie Hanson) #1

I find myself going around in circular thinking about what happens to BMR during fasting. I listen to 3 podcasts regularly and keep hearing different takes on this. A couple of prominent LCHF peeps still use the term calories and claim that low caloric intake drops BMR. okay. I can sort of buy into low intake can drop BMR. But if that’s true, what happens during extended fasts? Do we drop BMR? If so, does it rise again quickly after resuming eating. Since there’s no direct way to measure BMR easily, how do we know? The more I think about it, the more I’m confusing myself. I suspect I’m missing some data. Pls enlighten me.


Hungry but not hungry
(G. Andrew Duthie) #2

I think this depends, in part, on how much energy the body can get at from your own body fat. @richard wrote about this here:

and created a calculator based on figures from a paper derived from experimental data to help estimate whether or not a given person might need supplemental fat on an extended fast.

My estimate of BF% is around 20%, and current weight is 186, and if we assume that my BMR is just average (around 1700 kCal), that leaves me with a deficit of over 500 kCal per day just in my BMR, without counting any additional exertion (I typically lift 3x per week, though I’m doing less after breaking a bone in my foot last week).

Assuming that the study figures are accurate, and that Richard correctly applied them in his calculator, that would mean that I need an additional 55 or so grams of fat if I’m going to do an extended fast, because I cannot adequately supply my daily energy needs from my own body fat.

That doesn’t completely answer your question, I know, because it doesn’t really answer what happens if we don’t supplement fat. I do know that, in my case, the last time I tried a water-only fast (no additional fat) it was more difficult, and I found that I got cold pretty readily, which is sometimes said to be a sign of the metabolism slowing to preserve energy.

One of my goals in fasting is to go after persistent fat that doesn’t want to go away with just keto, in which case fasting with fat supplementation is a perfectly acceptable answer, since (assuming I don’t go overboard with fat intake) I probably wouldn’t burn more of my own fat without the supplemental fat.

But I also fast for the benefits of autophagy, and on that front I’m just not sure what the impact of fat supplementation is. In theory, since fat should have minimal effect on insulin levels, it should still allow for autophagy, but I may still do occasional water-only fasts for a few days, to ensure that I spend at least a certain amount of time with my body engaged in autophagy.

Hope that helps.


Is a calorie deficit really required on a ketogenic or zero carb diet?
(John) #3

Just read about that in Dr. Fung’s book on fasting.
“To burn fat, two things must happen: you must burn through most of your stored glycogen, and insulin levels must drop low enough to release the fat stores. And neither task is easy. When stored glycogen gets low, your body senses it and starts to get antsy. It triggers hunger signals, so you want to eat more. If you don’t eat enough to fill up the glycogen stores but your insulin remains high, body fat can’t be released. The body’s only remaining option is to decrease your metabolism so that you’re burning less energy…
When we eat, insulin rises and blocks fat-burning, and the body instead burns glucose, which is now freely available from the ingested food. But of the three macronutrients—carbohydrates, fat, and protein—carbohydrates stimulate the production of insulin the most. Refined carbs and sugar in particular have the greatest effect on insulin, so a diet low in these is most certainly a great start for breaking the insulin resistance cycle and losing weight. Yet for some people, this is not enough. Since all foods raise insulin levels, the best answer is to completely abstain from food. The answer we are looking for is, in a word, fasting.”

Fung, Jason. The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended (pp. 114-115). Victory Belt Publishing. Kindle Edition.

So your body will save energy by lowering your metabolism if it has a hard time accessing fat (which is caused by high insulin and insulin resistance) but if you are in ketosis you are already burning fat for fuel, fasting has no reason to cause a lower metabolism, only use of more fat compared to someone eating in ketosis.


(John) #4

I think you and I are on the same page and that’s why my fast ended fairly abruptly. You mentioned in another post your heartrate dropped as well, mine is usually 65 or so, it got down to 52 and blood pressure dropped 20 points. Using the calculator and guessing my LBM and BMR I need to have 42 grams of fat per day supplemental.

I’m not sure at what point you stop getting the effects of fasting. If I have to consume ~400 calories of fat per day during a fast, do I still get into the autophagy zone?
I need to do more research into that piece of it.


(Stephanie Hanson) #5

It does help. I’ve used Richard’s calculator too. It’s brilliant. But I recently had a DEXA scan and indicates I should be able to water fast without the cold symptoms. The report included a calculation of BMR. But it’s just a theoretical calculation. Then I heard Megan Ramos say that the cold feeling is just glucose in the liver burning off.

My goals for fasting are the same. I want my body fat to go down. I also want to fight back any cancer cells.

I have found I can get my GKI down to <= 1 with about 300-400 cals of fat intake a day. I haven’t been consistent enough with it to see what happens for more than 7 days. Then I began to wonder if that intake somehow slows my metabolism setting me up for easy fat gain later. I suspect my thinking is still too much mired in my old CICO training and not quite in alignment with being keto adapted.


(Stephanie Hanson) #6

Thank you for refreshing me in this info. Silly me. I should have just gone back to the horse’s mouth. I appreciate all the time you took to type this out for me. Since I am IR, I suspect my fat access is a little slower.


(Stephanie Hanson) #7

I have been using the GKI as a way to measure autophagy by proxy. There’s not enough data on autophagy yet (according to Megan) to really understand what’s happening. I hope someone is doing it somewhere.


#8

There’s a huge difference between having your digestive system in operation (i.e. stomach acids, spleen, pancrease, gall bladder, peristaltic movements, etc), or having them dormant. When you are eating something, all your digestive organs are in operation. And, just like any other organ in your body, you need to fuel the operation of your digestive organs. It’s the “price of doing business” with your digestion. So, as example, when you eat a piece of bacon, you chew, swallow, stomach juices digest, organs (pancreas, gall baldder, etc) secrete enzymes, etc. All this activity doesn’t come “free”. At some point, all your digestion organs need fuel/blood/heat/power/etc.

But…when you are fasting…like…only water/tea/coffee…your organs go into dormant state. Your pancrease, gall blader, stomach juices, etc…are not needed. All the calories/energy/fuel etc they need in normal eating operation is severely dialed down. Your body is smart…recognizes that there is “no need to keep the lights on” in your digestion system, and keeps everything on very low energy expenditure. It’s like if you go on a 2-month vacation, you unplug all your appliances, turn off every light, you turn down the heat/air conditioner, etc, just to avoid wasting energy in your home for nothing.

However, if you “cheat” on your extended fast, and eat a little bit of something, then you start screwing everything up. Because, now your body has to turn on all the organs for digestion, but to process very little calories. It’s like driving your car to go get gas at a station that is 100 miles away, but you only have 60 miles worth of gas left in the tank to get there. So, your body starts to freak out, and turns down your metabolic rate…it looks for other places in your body to “steal” some energy from, to keep your digestion system operating properly…because you cannot half-ass operate digestive organs, or else you die. There is minimal work that your body has to do to clear whatever food you swallow…or else, all hell breaks loose in your digestive system, and it can kill you. So, if you do not properly fuel yourself, you will feel more tired and have less energy to do other stuff (like biking, hiking, staying up late at night, etc)…that’s your body turning the dial down on lower-priority body functions to ensure your survival.

So, the best thing to do is fast properly. Don’t cheat and eat a bit of something when you are fasting…or else, you will turn on your digestive system, without sufficient fuel, and it then forces your body to turn down your metabolic rate.

So, when you fast, your body goes into ketosis and autophagy…breaks down its own tissue for survival. It first scavenges all the bad tissue extra fat inventory…but…when that runs out, it has no choice but to start scavenging good tissue. Usually, this is not a problem (as obese or overweight people, for example, do extended fasting to help get rid of extra body fat). But, for thin people, extended fasting is a challenge. This is why they may supplement with oil or butter, to stay is fasted state, without scavenging good tissue. They can supplement with something that is very digestible (like MCT oil), so again, not activate the entire digestion operation, so as not to provoke the body to lower metabolism.


(G. Andrew Duthie) #9

I had forgotten about the HR…if I recall correctly, I didn’t see a significant drop when fasting with fat supplementation. But I don’t know if I was paying close attention at that point.

I don’t think my BP dropped while doing a water-only fast, but I’m pretty aggressive about supplementing with salt, mag, etc.


(Becky Searls) #10

This is the part I am not totally sure if either…I think @Richard’ s article on why fasting is harder for some people makes total sense and seems to suggest that for someone with less bodyfat like me, having keto coffee and that kind of thing during fasts may be not only helpful but necessary? Yet that seems to fly in the face of “when fasting, fast. When feasting, feast”??

Another question for @carl and @richard following the podcast with Megan Ramos (who I absolutely love)…how is feasting followed by fasting much different than yo-yo dieting? Is it simply more ok bc WHEN fasting and keto, the foods are high in fat and not glucose?? Seems like while feasting and fasting randomly does do a lot to mix it up and confused your body it also could harm your metabolism long term if yo-yo dieting is any indication? Or is this just one more area where conventional wisdom fails us?


#11

Thank you so much for this, @Fiorella. I’m doing regular 24 hour fasts, but I wouldn’t do longer than that, because I don’t have the body fat to support it. I love the fasting calculator on that article - it’s a great help for working out how much to supplement with, but this explanation of resting the digestive tract was a side of fasting I’d not really thought about before. I was aware of the benefits of allowing the body to take a break from processing food, but not to that degree.


(Alex Dipego) #12

Yo-Yo dieting isn’t fasting but underfeeding. Underfeeding is sending a signal of lack of nutrition triggering a slow down, whereas fasting is no nutrition and builds up your metabolism (in the beginning) encouraging to eat food.

In regards to low access to bf it means you have to supplement with fat. If you think about it when heavier you have more fat to use for energy so you can cut it out. The less fat you can metabolize in the long run the more you will add to run. So someone who is 5%bf vs 15% the 5% will need much more fat to operate.


#13

Feasting and fasting allows the body’s hormones to conserve and cleanup during the fasting phase where insulin falls and glucagon rises as well as growth hormone. Feasting signals that there’s plenty of material to rebuild and repair after the cleanup.

Dr. Valter Longo (Fasting Mimicking Diet) says that fasting reduces white blood cells (WBC) by about 40% during the fast and that would be bad if the story stopped there, but after refeeding, the WBC counts return to normal, so what’s happening is that old WBC are being scavenged during autophagy and rebuilt with newer ones after refeeding.

I’ve done a lot of yo-yo dieting, and this is usually chronic undereating to lose weight, followed by returning to normal eating habits that regain weight and then the cycle repeats itself. There’s never really an opportunity for insulin to drop to normal levels and no clear signals for repair and rebuild.

Unfortunately I learned about the dangers of yo-yo dieting the hard way and gained/lost about 500+ lbs since my early teens and resulted in sarcopenia (muscle loss) and osteopenia (bone loss). It was only after going keto that I stopped the yo-yo dieting and since adding feasting/fasting I’m beginning to feel better and perform better, although I have a lot of damage to undo.


(John) #14

He says specifically in that post that if he were not to supplement his metabolism would drop. Sounds like we are asking for trouble if we often go into a fasted state without extra fat. This is even more reliant on the amount of body fat we have, so I need a much better read on my body fat % than a guess.


(Alex Dipego) #15

Isn’t he saying more that you need to supplement __ protein to save protein on your body not so much your metabolism?

Studies show metabolism speeds up to near the 60hr mark in fasting. Not eating is better than eating small amounts.


(G. Andrew Duthie) #16

I think that advice is most applicable for those with a good deal of weight to lose, and hence, sufficient body fat to sustain daily energy requirements. But as with many such things, the advice has become somewhat generalized, but may not serve everyone equally well.


#17

Not really, @beckyjoy. There is good reason why fast and feast is not like yo-yo dieting.

Let’s first be clear what is yo-yo dieting. To me, it’s like someone who turns down calories, because of CICO mentality. So, the body, searches for what mechanisms it can turn off, to save on calorie expenditure. For example, let’s say you wanted to save money on your monthly utilities bill. So, you turn off all lights you don’t need, unplug appliances, turn down heat or air conditioning, wash clothes in cold water, etc. this is why people with lowered metabolisms feel cold all the time. I’ve screwed up my metabolisms after years and years of following bad advice (low calorie dieting). So, for someone who is yo-yo dieting, when the food comes back in at higher calories, the body still maintains lowered metabolism and starts storing fat (“just in case the low calorie yo-yo happens again”).

When fasting, something else is happening. The digestive system is “mothballed”. Everything is shut down and put on a care and maintenance program. Just like someone going on a very long vacation, shutting every process down in the home (no one turns on lights, or use dishwasher, or use vacuum, or use clothes washer. The heat and air conditioning is shut down, and no water being used). The amount of energy to run a moth balled house is almost nothing, so the body does not go in a panic state…there is plenty of energy on board to do care and maintenance of a digestive system that takes almost no effort to keep alive. So, the body does not turn down your metabolism. In fact, it patiently awaits when food comes back,…and when it does, it’s “all hands of deck”… Or maybe the pun “all glands on deck” :joy: to rev up the digestive system.

Our bodies have evolved from a feast or famine (fasting) way of eating. The body recognizes this as a normal way of survival. Today, we have freezers and refrigerators to store food. In ancient past, you killed an animal, you ate it, and then you don’t eat until you kill the next one. There is no refrigerator. Same with fruits…when the strawberries are out, great, eat strawberries for two weeks, and then they are gone until next year (for only two weeks in season).

This is why yo-yo is completely different from feast-fast.


(Becky Searls) #18

This all makes sense…but then if you are adding fat due to low bf…the fast isn’t “pure” anymore (not that I care in theory…but where is the line between a fat fast that’s benefitting your metabolism and calorie reduction that’s slowing it down?)


(John) #19

I wonder how long the effects last, this makes it sound like just from having high blood sugar you have lower metabolism.


(Todd Allen) #20

Another consideration is your BMR dropping due to deficiencies leading to impaired functioning or is it due to improving metabolic efficiency? During an extended low calorie spell of typical low calorie dieting, without a lot of care one is likely to become deficient in a wide range of vitamins and minerals. Fasting, at least in moderation, promotes recycling and deficiencies are less of an issue.

But regardless of how it is achieved reducing fat mass lowers the amount of metabolically active tissue which all else being equal lowers the amount of calories needed to sustain BMR. One can counter this by increasing lean tissue mass. And some believe reducing BMR by enhancing metabolic efficiency is a good thing that reduces oxidative stress and slows aging.


Why Am I Getting Cold When I Have So Much Body Fat?