Why can't I lose weight after 40 even though I eat less and exercise more?

On Ep. 402, Nikkiey explains that at 25, estrogen was quietly doing a lot of work. It protected your muscle during calorie deficits, directed fat away from your midsection, and supported recovery, bone density and insulin sensitivity. Your muscle mass was near its peak, so you could get away with less sleep, more stress, more caffeine and more training volume. That environment isn't the same now. On Ep. 373 she adds that muscle is metabolically active tissue, and every pound you lose means your body needs fewer calories. That's why the food you've always eaten starts producing different results.

The bigger problem is what restriction does on top of that. Nikkiey describes it on Ep. 272 and Ep. 398 as metabolic adaptation. When you underfeed yourself for a long time, your body goes into survival mode. It lowers your metabolic rate, raises cortisol, slows your thyroid, breaks down muscle for fuel and holds on to fat more aggressively. On Ep. 311 she says overtraining sends the same physical-stress signal. On Ep. 138, nutritional therapist Louise Digby explains that under-eating raises cortisol, intense exercise drives it higher, and the body tends to store that energy as fat, particularly around the middle. She adds that cortisol is inflammatory, which can bring water retention and puffiness. Nikkiey notes that the women who struggle most are almost never eating too much. They have been eating too little for years and have nowhere left to cut.

Nikkiey says some women need to build muscle at or near maintenance before any fat loss phase. If you suspect thyroid or hormone issues, work with your doctor. Either way, it's the plan that failed, not you.