I’m a little skeptical of the 32kcal per lbs of fat figure. I don’t doubt the science is real, but I’m not sure how it generalizes. The amount of fat that can be mobilized depends on hormones, so high levels of insulin will inhibit lipolysis (as we know), but high levels of glucagon will increase it, as will growth hormone which increases to above baseline during fasting. This blog post by Jason Fung links to several studies that show protein sparing during fasting, which has to mean the subjects derived more than the 32kcal/lbs figure amount of energy from their fat stores. I’m not entirely convinced either way, there certainly seems to be more to it than we currently know.
Anyway, that was a bit of a digression from the topic at hand. Now it’s time for me to become long-winded.
To me set-point theory seems pretty solid. I think of it this way: On some level Calories in = Calories out, that has to be true because of thermodynamics. I should note that I’m putting calories stored as part of the “calories out” bin, and calories released from storage in the “calories in” bin. Now, if calories in becomes larger then calories out has to become larger as well.
There are a lot of things for the body to spend energy on. Some things are top priority, the brain, heart, lungs etc. all need energy for the whole body to survive, but once the minimal requirements are met we start doling out energy to secondary concerns. This could be more energy to the brain to make us smarter, more to the muscles to increase exploration and wanderlust, more to wound healing etc. or we could store it for later.
Exactly how to prioritize energy expenditure depends a lot on the state the body is in. Storing fat is considered an important energy investment, and the less fat you have the more important it becomes. At some point, when you have low body fat, it becomes important enough that energy is skimmed off of other vital processes so it can be stored and you become weak, dumb and lethargic. If you have a lot of body fat, storing it becomes very low priority to the point where the body thinks running in place is a much better investment. Likewise, how much body fat you have affects the calories in side as well, with high body fat giving the body a much larger budget even facing a modest food intake.
Other things also affect the energy prioritization, for example if you’re eating a lot of carbohydrates then the body focuses more on eating and storing energy and less on movement and thinking. I’m just speculating here, but I think this is because evolution figured out carbohydrates are plants. Edible plants spoil pretty quick so you need to square them away fast but they don’t usually try to run away or outsmart you so it’s okay to be dumb and lethargic. This is why keto works for weight loss in overweight people, because it shifts the body’s energy management priorities and under the new regime they have an overabundance of body fat.
This is where the obvious conclusion that is set-point theory comes. As your body fat drops you eventually reach a point of homeostasis where your food intake and energy expenditure is in balance. If you body fat increases your body simultaneously gets a larger energy budget and lowers fat storage causing you to quickly lose that extra fat, but conversely if you lose fat the body will decrease its energy expenditure to regain that fat pretty soon. An obvious corollary to this is that decreasing your body fat below this set point is not a trivial task.
I should preface the next part by saying I’m not at all sure how true it is. It’s something I’m looking forward to experimenting with once I get close to my own set-point.
I think this is the point where exercise has to come in. Exercise alone is not going to help you lose weight because any calories spent exercising is going to come out of the rest of your energy expenditure. Remember, calories in = calories out, you can’t spend more energy than you’re consuming. What exercise does allow you to do is eat more without putting on weight; it gives your body an energy sink other than fat storage. My hypothesis is that the increased food intake will signal energy abundance and make up for the energy deficiency signals from low body fat and the body concluding that fat storage is not a high priority. I think that if I combine this with (extended) fasting which also deprioritizes fat storage it should be possible to lower body fat below the set point. If this will eventually cause the set point itself to lower or if it will be like pulling a rubber band remains to be seen.
This is similar to the leangains protocol, so there’s some anecdotal backing there. It is also somewhat similar to what I did 5 years ago the first time I was on a keto diet, but back then I didn’t have a set protocol in mind, and extended fasting wasn’t really a thing so I only did a few 48 hour fasts. Still, my weight decreased from 95kg to 90kg over a few months even though I didn’t watch my eating at all. When I first reached 95kg I noticed my appetite skyrocket compared to before and my weight loss stalled. For a couple months I tried to cut back on my eating but I was constantly hungry and felt a decrease in energy so eventually I just gave in. I started eating as much as I wanted again and just enjoyed the extra energy I had to move around and lift heavy. A few times I didn’t feel hungry at all when it was time to eat, so that’s when I did my 48 hour fasts, kind of as a challenge to myself more than to lose weight, but that’s also when the scale moved. The whole time I was doing this I was also getting more in shape, and while I didn’t measure myself my shirts were all getting tighter around my chest and looser around my waist.