How to lose weight, by me, someone who has lost 30 pounds and kept it off:
Step 1: Count every calorie you consume. If you don't know the exact amount of a dish, do your best. Apps like MyFitnessPal make this easier.
Step 2: Limit that amount to 1500 calories per day.
Step 3: Weigh yourself everyday first thing in the morning, and only look at 7 day averages at least. Daily fluctuations don't matter.
Step 4: After 2 weeks, see how much you've lost (if any). If you've lost more than 1% of your body weight per week, raise that 1500 number. If you've lost less than 1% per week, lower that 1500 number.
Repeat until satisfied!
How can you make this easier?
1. Eat things that are filling with fewer calories. Think vegetables and protein. Stay away from things that aren't filling and have a lot of calories. Think candy bars. Water helps too.
2. Walk/run. This will burn calories efficiently and if you attach a fit bit to it, you can incorporate the calories burned into your 1500 number above. Weight lifting doesn't burn many calories, though it's nice for your overall health of course.
You're stuck on how fat cells are stored or insulin levels? How is that at all approachable.
In technical terms, CICO is a very leaky abstraction.
I'd call everything else an abstraction. Intermittent fasting and Keto all conform to CICO as an abstraction.
Which is fine and you're right. Calorie counting is the most direct diet but is not for everyone.
They can only do so acutely until the blood sugar drops. It will not matter in the long run if there is a calorie deficit. I like to summarize it like 24 hour calorie balance is far more important than short term acute effects.
I eat low-carb foods and intermittently fast to compensate, but if I ate a "mainstream heatlhy" diet (3 meals a day, grain bowls, etc), my blood sugar would be moderately elevated for most of the time.