Does the diet have any impact on how fast your metabolism is working or does it not at all change or interfere with the total calories in and total calories out science of burning fat and losing weight?
Is intermittent fasting only based on psychological management of your eating habits?
In: 90
The simplest explanation I can offer hinges on appetite and insulin. No carb intake means little to no insulin production which means less appetite. Only eating carbs once per day helps alleviate appetite the rest of the time, and we can only eat so much once a day, anyway.
The slightly more complex explanation follows:
Carbs raise our blood sugar and accordingly stimulate insulin. Insulin stimulates appetite and lowers blood sugar (which we also perceive as hunger by way of tremors, chills, etc). You’ll notice when fasting that the first and second regular meal times are the hardest: your body is beginning to produce insulin in anticipation of a meal that never comes, then quickly halts rather than risk hypoglycemia.
The US military did some neat studies decades ago and found that you absolutely could lose weight on a calorie restricted diet. Those soldiers who ate regularly timed but smaller meals were voraciously hungry and many were kicked out of the study bc they were cheating food on the side. Those assigned to eat once per day did not have this problem, even though they were eating the same number of calories as the first group. Additionally, the first group lost more muscle mass then the second group. Which leads us to the last important part of fasting: ketosis.
You’ll find all manner of information (and disinformation) on ketosis online, but fundamentally it’s when our body transitions from burning carbs to burning fat. This happens when we fast, or when we very specifically eat essentially no carbs (less than 20g per day). It is well documented that being in ketosis is associated with reduced hunger and reduced muscle loss.
From an evolutionary perspective, it all makes sense. We evolved in an environment that most of the time was hostile and hard to find food. If we found food, our bodies would demand (by way of hunger) that we eat everything in sight to store as fat. When times got hard again, rather than get progressively weak and tired (which makes it tough to Hunter/gather) we convert to ketosis for extended periods of fasting, until we can find food again. While in ketosis, energy and strength are relatively preserved as we burn fat stores, enabling us more opportunity to chase down and eventually tire out that antelope (or whatever).
This is a gross oversimplification, but hopefully ok for eli5 audience.
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