Is my metabolism broken from years of dieting?

On Ep. 354, Nikkiey says metabolic damage is real, but the words damaged and broken do a lot of misleading work. If your metabolism had stopped functioning, you'd be dead. A significant calorie deficit held for a long time reads to your body as a threat. It doesn't know you're trying to lose fat, only that energy is scarce. So it lowers your resting burn, cuts your everyday movement (fewer steps, less fidgeting), reduces the thermic effect of food, ramps up hunger hormones and preferentially burns muscle because muscle is expensive to keep. That's why the intake that worked in month one stops working by month four.

Yo-yo dieting makes it worse. On Ep. 179, Nikkiey explains that dropping to around 1,000 to 1,100 calories slows your metabolism, and when you go back to normal eating your body stores more fat in preparation for the next deficit because it doesn't trust you yet. She also says repeated cycles can disrupt hormonal balance, including the thyroid. On Ep. 311 she adds that slower digestion, poor sleep, night-time cortisol spikes and afternoon cravings are adaptations, not malfunctions. If you suspect a thyroid or hormone issue, that's a conversation to have with your doctor.

As she puts it, you can't force a depleted system to burn fat. You rebuild trust with your body first. She recommends doing it with a coach so you don't second-guess every step.