There is a wide gulf between “when you exercise your body saves calories elsewhere in the day…when you eat less your metabolism slows down” and “some people can’t lose weight on 50% calorie restriction.”

The former is very well supported in the literature. The latter is only supported in low quality studies like where people self report their diet.

The CICO hypothesis accounts for metabolism. Your weight is a function of CICO and time. You can track calories in, weight, and time. From there you derive calories out.

The problem isn’t that CICO is wrong, the problem is that it turns out actual caloric restriction over time is really really hard.

The current best advice for weight loss is to avoid highly palatable and/or calorie dense foods, prefer foods that are highly satiating and low in calories, and strength training helps. Do whatever cardio you need for heart health; more cardio is at best unnecessary and at worst demotivating because extra effort will not net extra results. Slow and steady is easier to stick to.

One problem is that even though small deficits lead to more long term success, small deficits are very hard to track, and very hard to stick to.

When the size of your calorie deficit is two tablespoons of ranch dressing and a cookie per day, it’s easy to blow past it without even realizing.

CICO isn’t a diet strategy. By itself it won’t help you lose weight any more than kinematic equations help you to throw a ball.

But it’s not wrong.