How does IF work?

I don't understand how/why IF works. Let's consider 16/8, for the sake of concreteness. I thought that the idea behind IF was this: After 16 hours of not eating, your body has run out of calories from the food that you ate previously. Let's say that takes 12 hours. So, you run a caloric deficit for 4 hours. So, you lose weight. But now I don't see how that works. Suppose that your eating window is 12 PM to 8 PM. Over that time, you eat 2500 calories. The average man burns ~2500 calories per day. So, let's say that, when noon rolls around the next day, you have burned 2500 calories. Since you consumed 2500 calories within that same period, when do you ever run a caloric deficit? If the solution is to eat fewer than 2500 calories, then you are doing CICO in conjunction with IF. So, why not just do CICO? Does IF help support CICO?

Answer

Its more about insulin, and keeping it down, to a lesser degree calories.

Jason Fung explains all this in the obesity code if you want the science.

But I found his analogy apt: think of insulin like batman, calories like robin, Its the reduced insulin release thats the big deal behind IF, calories not so much.

Answer

IF forces you to not overeat, simple as.

There’s things going on that has big words, but thats where it becomes unnecessarily complicated.

IF goes hand in hand with caloric restriction. Also those who get into these diet styles are extra aware of what to eat, so it’s unlikely you throw in 1500 calories of peanut butter next to your 1800~2400 actual calories.

Answer

Because IF:

May be an effective indirect way of keeping energy intake in check.
May benefit compliance, on the one hand by helping regulate physical hunger (Ghrelin), on the other psychological hunger, by establishing a solid binary / black-n’-white boundary around food.
May encourage eating to satiety, albeit less frequently – for some a major bonus point.
May help keep circulating insulin levels lower on average, in turn over time favoring body fat mobilization (lipolysis) over synthesis and storage (lipogenesis). The effect is by no means profound enough to be proclaimed a “free pass”, just a nudge mildly “biasing” the energy balance scale in favor of catabolism. For metabolically healthy individuals this may not mean a lot, but for individuals struggling with insulin resistance and metabolic syndrome, as is all too commonly the case in the developed world, it might mean the difference between effortlessly losing and struggling to even maintain on comparable intake. For instance this study found that healthy weight subjects on OMAD exhibited an increase of ~200 kcal/day in expenditure, but maintained when fed the same intake (calories and macros) partitioned over 3 daily meals.
May promote the making of healthier food choices.

Answer

It’s all about insulin and what your body uses for fuel. In a typical fed state, it feeds on glucose for energy. At 12 hours, however, as long as you didn’t trigger insulin (sticking with strictly black coffee, herbal tea with nothing fruity, and water), insulin reaches its baseline. When it does, the body releases hormones that switch to burning fat for fuel rather than glucose. It’s also better than calorie-restriction alone, because just reducing calories can cause your body to break down muscle for fuel. The hormones from fasting protect the muscles, making them more resistant to getting broken down. People love doing 16:8 because it gives them four solid hours of fat burning. At 18 hours, the fat-burning amps up even more. For those doing OMAD, it gives them a solid 11 hours of fat burning a day. Things to watch out for that could trip up insulin and send you back to the starting line: Tasting something sweet: Even certain sugar-free gums can cause the body to think it needs to release insulin; vitamins and supplements, especially soft gels which have oil as the base.

Answer

When you consume calories, your body begins its digestive processes. The type of energy it uses (and how) changes as time progresses after that point. You go through metabolic stages.

If you eat in a shortened time span, your body has many hours to progress through these stages. A later stage being ketosis.

If you eat several times a day, your body “restarts” this process each time. So you never give your body a chance to reach later stages–those that burn fat as energy more than earlier stages.