Calories in vs calories out.....is it that simple?

I had someone ask isn’t it all about calories in vs calories out and this comes up a lot so I thought I would address on here. While it is true if you eat less than your body burns, you will lose weight, people often forget that the only thing constant about our bodies is they are constantly changing. Our bodies are very good at adapting, at surviving. When you create a caloric deficit either through diet or exercise or a combination of the two, your body starts making adjustments to offset the lack of energy. These adjustments to prevent starvation occur through hormones. When dieting, the hormones leptin, thyroid, and testosterone all go down and the hormone cortisol goes up. These hormones drive/effect metabolism and the importance of these hormones for retaining muscle and losing fat, cannot be overstated. These hormone adjustments are usually referred to as starvation mode.

The advice that I give when trying to help someone lose weight if they are stuck typically revolves not around calories in vs calories out, but hormones. Some of this advice includes spike/refeed days, carb depletion/carb loading, sprinting or other intense cardio instead of long duration, two week diet breaks and one week break from exercise, All of these things center around preventing, slowing down, or helping to rebound the negative effects that occur to your hormones with prolonged caloric deficits.

So in a perfect world we could do the math and everyone would lose 1-2 pounds a week and reach their goals right on time, but our bodies are far too complex for that. Calories in / calories out is a good starting point but only a starting point.