Fasting energy limits and body composition mystery

(BuckRimfire) #1

I’ve been doing IF two days a week, typically Monday and Thursday. On those days I have 150-200 calories of cream + coconut oil in my morning tea, so it’s not a strict fast.

Something confuses me: on a podcast episode some time ago, it was stated (IIRC) that a paper had been published showing that each pound of fat tissue can release only 31 Kcal per day of energy. It makes sense that there would be a limit: a cell only contains so much of the enzymes needed to hydrolyze triglycerides, etc. and one of those steps in the process is going to be rate-limiting.

What is surprising is that the number is low enough that it seems like I should not be able to fast successfully. I weigh 157# and last year (when I also weighed 157#) I had a DEXA scan that said I have 13% bodyfat, so I should have about 20-21 pounds of fat tissue. That suggests I can access only about 650 Kcal/day of energy from fat. So that, plus the ~200 Kcal in my tea in the morning, would be only 850 Kcal per day of available energy. I would expect that to mean that I would feel terrible, but instead I feel fine and as energetic as on a feeding day. Before breakfast the next day (about 36 hours since my last full meal), I actually feel less hungry than I did the previous afternoon.

I really doubt I’m running on <1000 Kcal per day. So, where’s all the “missing” energy coming from? Glycogen and gluconeogenesis?

I should try a three-day fast to see if I run out of glycogen and hit the wall…

(Windmill Tilter) #2

This comes from a back-of-the-napkin, wild ass guess. It was published in a journal, but it was just a researcher who was trying to use a bit of math to work backwards from what was observed during the Minnesota Starvation Experiment where already slim military “volunteers” were placed under severe calorie restriction (not fasting) for months to replicate forced starvation of refugees and POWs during war time.

Nobody has any idea what is possible for fat adapted individuals who frequently fast.

As a side note, you’re not taking into account the calories you are getting from catabolizing your own lean mass. As your BMI decreases, the relative proportion of calories derived from lean mas vs fat increases. Dr. Fung didn’t include this chart in the Obesity Code, but he does provide the caveat “obese people don’t really need to worry about lean mass loss”. If your TDEE (total daily energy expenditure) is 2400kcals, and your BMI is 20, you’re looking at potentially 800kcals of skin, connective tissue, and muscle. Using the (vastly over-simplified) 4kcal/g for protein, that would be about a half-pound of your own non-fat tissue.

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On top of that, you need to take into account that people who fast frequently have metabolic adaptations to fasting. Your metabolism is perfectly capable of downregulating dramatically in response to the exhaustion of exogenous calories when you train it to do that repeatedly. Normal people don’t have that adaptation. Ever feel chilly now on a 3 day fast but don’t remember that happening at the beginning? Ever wonder why? Did you used to feel “hyper” like you were over-caffeinated at some points during multi-day fasts and it used to make it hard to sleep sometimes, but now that doesn’t happen anymore and you sleep perfectly fine?

Get an RMR (resting metabolic rate) test while 48hr fasted and prepare for a surprise. Check it against your Mifflin St Jeor predicted RMR based on Height/Weight/Age and you’ll have a decent estimate of the magnitude of your metabolic adaptation. It’s not a bad thing necessarily. Mine is about 250/kcal per day. I’ve seen them as high as 500kcal/day, validated by a half dozen tests several weeks in a row. It’s not a bad thing necessarily, my metabolism pops right back up on a refeed for me, often higher than even the MSJ would predict. If you’ve got an extra $100, have your RMR tested in the second day of a refeed day too and you’ll be able to measure the magnitude of your current metabolic adaptation to fasting with more precision.

Before you spend any money though, if you’ve only been fasting for a 48hrs at time, and only two days a week, this probably won’t have done very much at all. If you’ve done lots of 3-5 day fasts on a weekly basis though, it will likely be more significant.

(Bob M) #3

Interesting. I used to not get cold or not get that cold, but now I get cold pretty quickly when fasting (though less now that I’m eating higher saturated fat).

I still get wired while fasting, though. Rarely sleep more than 7 hours, usually less, but feel fine and not tired.

(Windmill Tilter) #4

My guess is that this is probably a good thing and feeling colder is probably nothing to worry about. What’s your fasting frequency/duration out of curiosity?

(Chris) #5

The cold feeling, I’ve been told, is a sign of the metabolism slowing. Not sure the validity.

Anecdote: I am currently dieting on 840~ calories and freezing my ## off.

(Bob M) #6

Right now, only between meals of OMAD or 2MAD. I was fasting a ton 3.5+ years ago when I started fasting, many 4.5+, 3+ day fasts. Then backed off that and did many fewer but longer fasts of 4.5 days. Then tried to do 36 hour fasts 1-2 times a week, only ever made one. Now that I’m eating a high saturated fat diet, I can’t go one 36 hour fasts. I can eat OMAD, though, as long as I eat the meal during the day (say, noon) and skip dinner. I can’t eat OMAD at dinner, as I eat too late.

There’s something about high saturated fat that causes me to burn up. I have a hard time having covers on me, for instance, if I eat a high saturated fat meal at dinner, and we keep our rooms in the low 60s at night.

(Bob M) #7

Eat cocoa/cacoa butter and real butter for some or a lot of those calories. Let me know if you get warmer in a few days (might take 2-3).

(Chris) #8

Can’t. Have to hang onto as much mass as possible - it’s not for long. I can deal :slight_smile:

(Katie) #9

Are you cutting for a show/competition?

Dread's Carnivore Muscle Thread
(Bob M) #10

If it’s short-term, it won’t be that bad. (Just read a study where the participants ate about 800 calories for three months! Yikes.)

When I get cold fasting, I sometimes have multiple covers on at night. Now, with my high sat fat diet, if I do that, I sweat. When fasting, I’ve even worn an extra long-sleeve shirt and socks to bed. Socks! I never wear socks in bed unless I’m fasting or sick, and I haven’t been that sick in years.

(Chris) #11

It ain’t that bad lol. I still sleep in my undies. But going from the house to the (warm) car is absolute frozen hell…

(Chris) #12
(Utility Muffin Research Kitchen) #13

Depends. In this study here discussed on hyperlipid people lost 3,5kg of lean mass plus 11kg fat in 6 months. For obese people that’s quite a lot of lean mass. They had to eat carbs though, 800-1000kcal a day, so it might be different if you go keto. 3,5kg doesn’t sound too bad for half a year of starvation, but I would have expected that the ratio of lean muscle to fat is better.

Interestingly enough they regained 4,5kg in the next 6 months, but regained only 1kg lean mass and 3,5kg fat. So during the rebound the fat:muscle ratio was even worse.

6 months, if it’s the study mentioned above :slight_smile: 800kcal for 3 months and then 1000 kcal for another 3 months. They didn’t check adherence though, ITT study, so I’d bet those people cheated a lot. No way anyone can go this long on a high-carb starvation diet.

(Utility Muffin Research Kitchen) #14

Keto? How long? Please share. In the light of the study mentioned here it would be very interesting to see how a 800-kcal keto diet compares to a 800-kcal high carb diet.

(I’m taking a different approach. I had a lowered bmr recently so I’m currently doing two 48h fasts a week, feast for the remaining time.)

(Chris) #15

Nope not keto at the moment. I’ll elaborate in my thread linked above. :blush:

(Bunny) #16

Wow you bring up some fascinating points to me and I think it parallels with this:

[1] “…It has been shown that some mice fasted on alternate days can eat twice as much on the feeding day, such that their net weekly calorie intake remains similar to mice fed ad libitum; despite the lack of overall calorie restriction, the former still display beneficial metabolic effects compared to the latter, including improved glucose levels and insulin activity, as well as enhanced neuron resistance to a neurotoxin, kainic acid [54] …” …More

[2] ”…During the fasted state, the switch is “on,” theoretically upregulating autophagy and survival pathways in neurons, whereas during the fed state, the switch is “off,” emphasizing remodeling and growth pathways. Thus, unlike calorie restriction, fasting capitalizes on each sequential bioenergetic challenge by “setting the stage” for a relatively stress-free cell recovery phase; in other words, it is the switching—the intermittency—that may provide the advantage for neuron metabolism. Indeed, chronicity can be harmful, regardless of a fed or fasted metabolic state—for example, acute mTOR activation promotes muscle hypertrophy, whereas chronic activation produces atrophy [58–60], and intermittent AMPK activation enhances neuroplasticity, but sustained AMPK activation impairs it [61]. …” …More

[3] …see also: Metabolic switching and different forms of fasting. - Dr. Peter Attia

(Jenna Ericson) #17

This is an interesting thought. I think I get what you are saying, but I don’t understand enough about the mechanics of enzyme use to know if it can somehow be up-regulated depending on how fat adapted a person is. I suspect that it can be up-regulated, or at least that our ability to burn fat at a higher rate can be up-regulated, again, depending on how fat adapted you are. I think this has something to do with an increase in LDL which helps transport the body fat faster for energy production. It would be interesting to know if you are a hyper-responder. I think there’s a good chance you are.