Actually, I will follow up further on the obesity issue - if someone is truly obese, they will not burn carbs very efficiently at all. If you put them on a high carb diet, chances are pretty good that they will see quickly elevated blood sugar, with no way to burn the carbs immediately for energy (since the machinery is all switched over to burning lipids for energy instead of carbs for energy) and so they will just convert those carbs over to fat in order to get them out of the blood stream and they will be stored to burn later. This, of course, would explain why carbs make these people gain weight through the reversed math. You're eating a 4 gram carbohydrate and
Thanks for diving deeper into this. Its very complex overall. I again probably haven't done the deep dive into this that you have. There are some aspects I do not really agree with from a physiology stand point but I agree that calories in vs calories out is complex, but I believe the concept is still true. Most of enzyme and cellular related stuff when it comes to carb burning vs fat burning likely has a very minimal impact on one's results over a cutting phase of 8-16 weeks, I agree with you here, as these are not static phases and more so just differing levels of activity at differing time points. Since most of us are not obese and highly insulin resistant I just don't see the benefit going down this path as these metabolic abnormalities do alter physiology as some of your information clearly points out. If you want to have a further discussion about this I will happily do it, I always enjoy learning and discussing complex topics, I just don't know how much it would help this thread lol.
A side note, the concepts you discuss seem to be the most interesting to me when it comes to cheat meals/refeeds on a cut/maintenance anyways. In acute over feeding studies based on a carb or fat based overfeeding, they have shown that it can take some time for the body to upregulate the enzymatic processes related to converting carbs into fats for storage. Thus in an very acute setting it can take up 2-3 days of constant overfeeding high amounts of carbs to result in substantial fat storage so while your glycogen levels will likely tap out and you will hold some water, the net fat gain is less when the same amount of cals are consumed in fats as they do not require much in the way of conversion to be stored. So I like these concepts when it comes acute overfeeding as it points to carbs being the better choice as you are less likely to net the same fat gains from equal amounts of consumed cals. This will not apply to someone who eats a lot of carbs daily, such as during massing over course as these enzymatic processes are already upregulated. I went on this point as it does related to your discussion and gives some potential guidance on how to structure planned cheat meals/refeeds as most are likely to benefit from carbs over fats in this case.
So, yeah, I was hesitant to get into this because your initial response was more than suitable for answering this thread and this is more for just going down the rabbit hole...
As far as the enzyme stuff - what I am actually saying is that the caloric adjustment that is actually needed during a diet is minimal, or almost non-existent. The actual perception of reduced weight loss can easily be explained by the enzymatic changes (Pyruvate Dehydrogenase Kinase) that switches on fat burning for substrate vs. carb burning. Ultimately, you aren't slowing your metabolism, you are just getting the same calories from less mass - which is more efficient. And this makes a lot more sense then believing your body can slow down it's caloric burn and achieve the same work output. If it could do this, it would always operate at that level - and store the excess calories for the future.
And this ability to switch between fat/carb as a fuel source is really the basic component of metabolic flexibility and this is one of the biggest determining factors in "metabolic syndrome" and of course metabolic syndrome leads to things like diabetes - and following the logic you can see why and how it really isn't "sugar" that causes diabetes - but caloric overload. As a side tangent, one of my other pet peeves is how often people claim high fat, low carb diets are good for improving insulin sensitivity, and while there are some components of this that are true, there is no more reliable way to induce diabetes than with a high fat diet. Just ask any researcher who is trying to make a mouse diabetic. 99% of the time it involves high fat or high fat and high carbs - almost never just high carbs.
So you are right, in a healthy individual, you will be in a constant flux where your body's demands dictate whether you are burning 80% carbs and 20% fats or 80% fats and 20% carbs or some other mix of those two to meet your energy needs. But, as you become overweight, you start shifting toward more and more fat burning - you have to, because you always have fat to burn. So you elevate your PDK levels, fat burning ramps up, carb burning ramps down. And this constant elevation in PDK really hinders your ability to switch back to carb burning fully.
And then you go on a diet and calories drop and fat burning ramps up more - which ramps up PDK more and makes carb burning even harder. And then my math comes into play - a pound of carbohydrate will provide almost 1820 calories, but you only need 0.45 pounds of fat to provide this same energy. So if you think of it in that extreme, instead of losing a pound in an 1820 calorie deficit, you only lose less than a half pound. Think about how often we say that weight loss happens half as fast as we expect? Now, this is vastly oversimplified (because I don't have the mental capacity to quite pull it altogether anyway). It leaves out factors like, human bodyfat usually is estimated to have 3500 calories/pound and not 4,200 calories because it's not pure substrate.
But more to your path of thinking - you're right. Think about the supposed benefits of refeeds, including the more recent data that suggests a single refeed will not have the intended effect we need, it may take a few days. Why? Because it isn't "ramping up the metabolism" that we are trying to achieve. We are trying to achieve a reduction in PDK and switch carb burning back "On" - and this switch back to burning carbohydrates would start us getting more of those 1820 calories from carbs, which are have a lower density. In other words, it is making us a little less efficient at burning mass.
And the mass gain is less than you'd imagine in that case because you top out your glucose stores, and whatever is left over can't be burned, so it gets stored as fat. Energy cannot be created, nor destroyed - so your 4 calories/gram carb cannot become a 9 calorie/gram fat on its own - it takes other resources and this probably means you body has to metabolize 454 grams of carbs into something like 202 grams of usable fat and get rid of the rest of the unusable material. This would be a direct calorie-calorie conversion and I do suspect it is a little more efficient then this, maybe you get 300 grams of fat, I don't know. But at the end of the day, you think you're going to gain 3 pounds and you only gain 1.5-2 pounds.
No need at all to increase metabolic rate or slow it down. It's just the conversion of mass that changes and this explains the slow down of weight loss as well as the slow down of weight gain as we eat more (along with increased bodymass/work, and NEAT and some minor input from up regulation of unconscious processes.)
This entire thing hit me one day while working out, and it seemed so obvious I don't know why I've never heard it anywhere before. I had been studying the Kreb's Cycle and some of the enzymes involved, particularly PDK - and I've found it hard to believe that evolution would lead to an adjustable metabolism for some time - and then it just came to me. SO maybe I'm really crazy.
