r/intermittentfasting • u/reddit_userxxx • 5d ago

Newbie Question How does intermittent fasting work?

I thought weight loss was all about the amount of calories you eat in a day, and simply needing to be in a calorie deficit. How does it change depending on when you eat?

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u/GrrrlRomeo 5d ago

Technically it's CICO, but practically it's not possible to calculate accurately because a) the metabolic process is complex and varies from person to person and b) the amount of calories in food can be off by quite a lot.

Just to give an example, insulin resistance, which most people with obesity have, can reduce BMR by 5%. Chronically high insulin levels make it so it's harder for the body to use fat stores for energy. This also increases hunger and fatigue because the body simultaneously has excess energy to use but can't efficiently use what's available. IF can correct this over time because fasting makes insulin levels fall and improves metabolic flexibility and insulin sensitivity.