@SofiaSoFar
The things you have said are common misunderstandings about metabolism and biology (I have a biology degree and a physio degree, so I have a lot of contextual knowledge and the ability to critique a source. I only peruse modern, reputable, peer-reviews sources by medical professionals. It’s not snake oil. It’s science. You are free to disagree, but I ask for your sources)
Of course metabolism can slow down (and speed up) in response to hormonal cues. Like every other biological system. We can reproduce it with drugs. And of course it can stop and you die of starvation. But its not one or the other. It’s very, very dynamic. You don’t just carry on using the same amount of calories until you drop dead. You starve slowly, conserving what you can for as long as you can. People on diets feel cold and show a measurable change in body temperature. That’s a metabolic slowdown, but it doesn’t kill you instantly. And your body makes other changes. It’s changes your physiology to motivate you to seek food. Initially, it’s thought to increase metabolism while you still have reserves to enable you to seek food. If you continue to not eat, or eat with a moderate calorie reduction (like most diets), then it will slow down to try and wait for better times.
Your body is not an engine. It doesn’t have a fixed output, and its output is not only (or even mostly) exercise. If you eat 2000 calories a day and use a few hundred moving around, what happens to all the others? How does your body choose whether to repair a cut, maintain your body temperature or go for a hike? How does it set body temperature anyway? Every time you eat anything, your body ‘decides’ what to do with that energy. How do you suppose it does that? If you drink a lot of water, you don’t just carry around with you until you need it, do you? No, you have a delicate balance of hormones that detect how hydrated you are and increase urine output to maintain your water balance. But if you eat too much salt, your body will drive you to drink more, because it needs water to excrete the salt. So you can choose whether or not drink, but thirst is driven by hormones. And so is appetite and body weight. It’s just a lot more complex, because there are multiple substances is involved, and harder to study because metabolism is technically complex to measure.
Your specific points:
16:8 (I didn’t actually mention this, but anyway) does not work by calorie restriction. One of the hormones in your body drives fat storage. Insulin is well known for it, and supplementing people with it makes them fat. However, you cannot burn fat, and store fat at the same time. You just can’t. They are controlled by hormones that inhibit each other. Insulin is triggered by eating food. Sugar most of all, but all foods increase it. So if you spend more time in the ‘eating than not eating it wont fall. Crucially, when it does fall, it doesn’t have time to fall to zero between your tv snacks and your breakfast, whatever they are. Each day, it creeps higher and higher. Something like 16:8 will lower the baseline and allow you to spend more time in a fat burning metabolism than a fat storing one. Longer fasts even more so. That’s why they are now using fasts to reverse diabetes. For the record, I dont think 16:8 I a great weight loss method, although I suspect it can help. I also suspect when you eat influences what you eat. People eat crap in the evening, so reducing evening snacking changes what you eat, as well as when.
Dr Kevin Hall’s experiment matched the nutritional content of the processed/minimally processed diets, including fibre. However, it seems you are under the impression that feeling ‘full’ is a physical response to volume in your stomach. It’s not. Both hunger and fullness are manufactured by hormones, they aren’t feelings generated by pressure. Processed foods do not produce these feelings of fullness with the same calorie intake as minimally processed foods AND those extra calories translate directly into weight gain, even when nutritionally identical. The current theory seems to be that digestion starts as soon as you anticipate a nutrient and continues until you receive it. If your brain is expecting a whole lot of protein from the beef-extract in the crisps you are eating, it doesn’t cue you to stop eating until figures out it not getting it. That takes time, so you keep eating them.
Professor Rachel Batterham’s work showing how hormones are acting in people living with obesity is fascinating. There are genes which pre-dispose people to eat more, enabling UCL to predict who gastric surgery will work for. There are some gastric surgeries which affect hormonal control of appetite and some which do not. Guess which one works best? They test levels of gut hormones post surgery and it correlates with the success of the patients weight loss. Not their mental strength, their gut hormones (I’m still getting my head around, its pretty new. They have tried supplementing people with satiety hormones, but it didn’t work. It seems that, like every other biological system, its the dynamic relationship between a number of different hormones that matters, so just pumping in one is very crude and doesn’t work. There’s a new one on the market that has better results, apparently though. I haven’t had a good look at it yet). Just as your water balance is controlled by hormones, even though its up to you whether you drink or not, your weight and appetite are tightly controlled by gut hormones, regardless of how disciplined you are. But modern living is disrupting them massively. Because of what food we eat, what not-food we eat, when we eat, how often we eat, and what else is going on in our bodies.
For every problem there is a solution that easy, simple and wrong - I’m sure you’ve come across this in your field - CICO is the weight one. It’s so, so, so much more complex. We are unforgivably failing obese and overweight people by giving them poor, and very unscientific, information and very little help and blaming them when they don’t lose weight. I think we will look back at the ‘eat less, move more’ advice with horror in twenty years, the way we look back at tobacco companies telling people with colds to smoke.