I’ve had a fire in me ever since I saw someone on Twitter making a statement that losing weight is as simple as moving more and eating less. When many commenters we’re pointing out the flaws in this thinking, the poster doubled down.

His message couldn’t be more clear: if you’re overweight, it’s because you’re lazy and eat too much. This is actually a very lazy view that prevents people from attempting to understand the complexity of the human body, and the even more complex ways our modern world is messing it up.

I’m not a doctor. Please don’t just take medical advise from me. I went to school with an education in physical education and I’ve been an athlete for most of my life. Additionally I’ve spent a lot of time researching science behind exercise and nutrition, as well as modern lifestyle. I want to help share what I’ve learned with others because I think we desperately need it.

Our bodies are amazing. It’s one of the reasons I absolutely loved studying them. A modern machine would be lucky to have been built the way our bodies are, and there are STILL systems we don’t fully understand. These systems have allowed humans to remain at the top of the food chain, despite the fact that we are not the fastest or the strongest predators.

The problem is that our modern lifestyle is so out of touch with the way humans have lived for centuries and we are paying a hefty price. Our bodies were made to survive in times of starvation and stress. An understanding of human metabolism is not simply a formula of calories in equal’s calories out to maintain weight.

Let’s start simple and talk about basil metabolic rate (BMR). This is the amount of energy (measured in kcals or just calories for short) that it would take to sustain your life if all you did was lay in bed without moving and eating food from a tube. But no one really does that. So how do we measure something like that? So we estimate, and these estimates can be completely in accurate. To figure out how much energy you require daily, you need your BMR, which is estimated based on your height and weight and also your typical activity level, plus the energy you burn doing additional activities (mostly this is any exercise you do).

So then the simplistic view is that to lose weight, you must get your energy needs to be higher than the energy (or calories) you’re taking in each day.

The problem is, once you start going in the negative TOO MUCH, your body thinks it’s starving, and as I said before, we’ve got a solution for that! So your BMR, basically lowers and now the amount of energy you require to rest all day is even lower! So basically, the formula you were using before is no longer a calorie deficit. I’ll show an example.

Say a woman’s BMR is 1,500 calories a day and let’s say she wants to lose 50 pounds. She’s going to do this by exercising to burn 300 calories a day and reduce her calories by 200 per day, for a total of 500 calories per day deficit.

So if her BMR IS 1,500 + 300 from exercise, she requires 1,800 calories per day to maintain her current weight. But she’s trying to deduct 500 calories a day, so she’s going to eat only 1,300 calories a day.

She probably will lose some of this weight in the beginning but then her BMR gets the message that less food is available, so it reduces down from 1,500 per day to 1,300 a day. So then her formula is 1,300 + 300 = 1,600 calories a day to maintain her current weight, and if she’s still eating only 1,300 calories a day, her deficit went from 500 per day to only 300 per day. Her weight loss slows down and to top it off she’s always tired and hungry.

To make matters worse, since her body thinks it’s starving, she’s holding onto more body fat and starts breaking down muscle mass. This isn’t going to be obvious on the scale, which is how most people measure weight loss. The loss of muscle mass lowers the BMR even further until eventually she has a new set point that’s lower than the original. And her weight loss stalls which makes her even more discouraged because she’s working so hard and hungry and tired ALL THE TIME!

So the old advice to just eat less and move more doesn’t work.

What does work? It’s actually very complicated but I’ll write about it in another post. Just know that it’s not so simple and when you consider women’s hormones and the consequences of them on every system of the body, it’s very very complicated.