Why would my metabolism slow down if I’m getting cals from fat stores?


Funny thing about Hunger Headaches, is I would occasionally get these when I would forego eating for a day or two, but this was before switching over to this WOE/WOL, and while still eating SAD. But since I’ve switched over, became fat adapted, etc., I’ve had none that I can recall? Not even whilst Fasting for days or the entire week? … Only mention this since reading folks speaking about it, so was wondering if this may have ties into how much we might be in Ketosis? … So if one was say closer to maintenance weight, would they experience this more than say someone who still had/has plenty to lose?

Not jumping subjects here, but thought to mention it since it has me thinking on it…

(hottie turned hag) #62

@Digital_Dave this fits my case; other than my gobble-down-entire-bag-of-pork-rinds-w/msg-gorge-induced migraine of a few weeks ago, I’ve had just two (hunger, not migraine) headaches since nigh on to 2 years (since starting keto) ago. Both within past few weeks. Prob ties in to my overall current condition (biochem changes related to low fat reserves) of being so close to maintenance.


There is a 2012 study (www.ncbi.nlm.nih.gov/pubmed/22735432) that compared the effects of low fat and low carb diets on metabolic rates and found that:

Compared with the pre-weight-loss baseline, the decrease in REE was greatest with the low-fat diet (mean [95% CI], -205 [-265 to -144] kcal/d), intermediate with the low-glycemic index diet (-166 [-227 to -106] kcal/d), and least with the very low-carbohydrate diet (-138 [-198 to -77] kcal/d

An earlier 2004 study by Volek (https://www.ncbi.nlm.nih.gov/pubmed/15533250) comparing low-fat and low-carb diets showed:

Absolute REE (kcal/day) was decreased with both diets as expected, but REE expressed relative to body mass (kcal/kg), was better maintained on the VLCK diet for men only [emphasis added].

So, the slow down from keto is not as large as with low-fat diets, but keto is not entirely protective. I’m not sure if either study accounted for the initial increase of metabolic rate on keto diets. In that case, the total delta might be about the same, but you end up in a better position on keto.

Obviously, there are other metabolic advantages from low carb diets, such as the initial increase in metabolic rate (a 2013 study–https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3826507/ – suggests as much as 400-600 calories of increased burn, just from the body’s work to create glucose) or the increased ability to burn fat triggered by lower insulin. All good things that put one in a better overall position regarding ability to lose fat and keep up metabolic rate. But not completely protective of metabolic rate.


The two studies cited are both short term studies. I personally think its probably better than calorie restriction on a carb diet - but I also don’t think there is any good long term scientific evidence to validate it.


Nice studies.

I noticed in the Volek study, the heaviest women lost the fastest on the same calorie restriction. Just taking the mean (red line) doesn’t tell the whole story between different body types studied.
Looking to see if there’s similar individual data for REE, or just the mean…


[Unsuccessful search for individual data sets regarding REE. My main contention is that the more bodyfat you have, the less you need to worry about restriction. This cannot be proven or disproven from the data given.]

(Alec) #66

So, this is the important thing here to answer this question. This data suggests that there IS still a metabolic slow down from cutting calories even on a keto diet. That is what I had as my understanding. This data seems to support this.

The question I now have is whether the people this data is based on are fully fat adapted. Is this what full fat adaption (taking 6-12 months of keto) might give you… no metabolic slowdown from calorie restriction as the body’s fat stores are fully and freely available?

(Alec) #67

@daddyoh, are you trying to look like Colonel Sanders? :joy::joy::joy: :+1:


Yes, but for thin people or fat people? I would expect a slowdown for someone without adequate access to bodyfat, whether through high insulin levels (carbs) or reduced fat mass.

(Karim Wassef) #69

It depends.

You can keto and eat much less, creating a net deficit which loses fat and lowers RMR


You can keto and eat less (not much less), maintaining the same total energy availability (diet deficit, but not total deficit) which doesn’t lower RMR

(Karim Wassef) #70

thin people need to eat more fat to maintain high RMR
fat people can eat less fat and still maintain high RMR

For example, if RMR is 3000 and available energy from body fat is 1000 (fat person), then you only need to eat 2000 and you will lose fat and maintain RMR

If RMR is 3000 and available energy from body fat is 500 (lean person), then you need to eat 2500 to lose fat and maintain RMR


I think all the studies I referenced were under 6 months. I have no idea what the answer is regarding what happens after that, but in the meantime most people have done a lot the “damage” they’re going to do.

Both studies I referenced were done with overweight and obese people–people who needed to lose weight and therefore had fat stores they needed to use up.


Just had a thought to look in the population that has had the most study on a ketogenic diet - eplieptics.

Here’s a 15 month study of children that concluded…"The longer-term ketogenic diet treatment resulted in a decline in linear growth status in children with intractable epilepsy, with no associated alteration in weight status or REE over time. The linear growth deceleration in the settings of stable weight and REE supports the hypothesis that ketogenic diet may decrease IGF-I without caloric deprivation. "

There’s probably more to this literature - but this was the first longer study i found


Looking at the chart I posted above, the women varied in weight from ~65 to 100 kg at the start. The heavier ones lost weight significantly faster than the lighter ones. 35 kg of weight difference at ~32 kcal/lb/day is a potential difference of over 2000 kcal per day.

(Give me bacon, or give me death.) #74

Let’s define the question: Is this strict ketonian setting a caloric limit for his or her body to subsist on, or eating to satiety? How much excess fat does this ketonian have?

Now, remember that the following cases are all in the context of a low carbohydrate intake. The rules are different when glucose and consequently insulin are chronically elevated.

The problem with setting a caloric limit is that any arbitrary limit is by definition going to be too high or too low.

  1. If intake is too high, the body will try to cope by raising the metabolic rate, wasting heat, and excreting excess nutrients, but there are limits, and the person is likely to feel uncomfortable eating so much.

  2. If the caloric limit is by some miracle exactly what the body needs that day, then the metabolic rate remains normal, and the body is happy.

  3. If the caloric limit is too low, the body slows the metabolic rate to compensate and, if necessary shuts down such non-essential processes as hair and nail growth, the reproductive system, etc. This limited caloric intake is the signal that this is all the food there is, so the body had bettter hang onto its resources to get through the hard times.

  4. If the ketonian does not set a caloric limit, but instead eats to satiety (in other words, waiting to eat until hungry, stopping eating when hunger goes away, and not eating again until hunger comes back) then the body is automatically given the right amount of food to fuel its activities. The amount of calories consumed will be the total energy needed minus a percentage of excess stored fat, IF ANY. In other words, if there is no excess stored fat to use, caloric intake from eating to satiety will match caloric expenditure. If there is some excess stored fat to use, the body will set the appetite to make the ketonian eat a bit less, so that some of that excess stored fat can then be used. Total energy consumed still matches total energy used, but some of it comes from storage and some from intake.

  5. If the ketonian embarks on a fast, the body responds by supplying its energy needs from stores—this is the whole point of having body fat, after all. Men have 10-12% body fat, because that’s what they need for successful hunting; women have 20-24% in order to provide a cushion during gestation and lactation, which are metabolically demanding processes.

The evolutionary reason that fasting does not slow the metabolism is that we evolved on a feasting/fasting cycle, eating the meat from the most recent hunt until it’s gone, then going out and hunting for more. If fasting slowed our metabolism, we’d never have survived going out to hunt, right? And the women can use their more abundant fat reserve to make sure that the baby in the womb or at the breast is not stunted while the hunters are out getting more food.

(Karim Wassef) #75

Keto and IF did not slow my metabolism but EF did. Fasting does reduce metabolism to align with the maximum available energy accessible from body fat.

(Eric - NSV count!) #76


what lengths of extended fast lower your BMR? I’m careful to eat to satiety the day or two after a EF. Mine are typically 2 to 3 days only.

(Karim Wassef) #77

I had fasted for 19 days when I had mine measured

(Eric - NSV count!) #78

Okay I don’t think I’m going that long. Thanks for the info.

(Give me bacon, or give me death.) #79

Again, context is all-important. Is the calorie-cutting arbitrary, or determined by the body? Is the metabolic slowdown from needing to match an arbitrarily lowered intake, or the result of not needing to expend as much energy to stay alive and healthy?

After all, fat people do lose some muscle mass as they lose fat, simply because they no longer need that extra muscle to heave all that fat around. This is healthy adaptation, not muscle wasting. It makes the body healthier and more efficient, and it means that TEE goes down, because there is less need for it to be expended.

(Alec) #80

Fair point: so if the calorie deficit is body driven ie on keto and eating to satiety (but that results in a calorie deficit), then there should be minimal to no metabolic slowdown. But if the calorie deficit is forced ie by targeting a number on an app and the person is NOT eating to satiety (say eating some way short of satiety and is hungry some of the time) then there would be a metabolic slowdown.