Why Dieting Sucks for Your Metabolism

Take a moment to think back on your diet history.

What was the first diet you went on? How old were you? Why did you go on it in the first place? What results did you get? Did they last? How has your diet history progressed from there?

Diets promise to make you healthier and happier by virtue of making you thinner, but the research shows that they fail time and time again. In fact, we know that most dieters will go on to regain more weight than they initially lost. [source]

Weight– loss, gain, or maintenance– is not just a simple math equation. It’s more than calories in versus calories out.

Body weight is regulated by a complex neuro-hormonal system that is impacted by genetics, environment, behavior, and more. And when you lose weight quickly through a diet, that system has checks in place to reverse that loss, returning to the original weight or higher. [source]

And it’s not because your body doesn’t want to feel good in a bikini.

It’s because it wants to survive.

How many times have you lost and gained the same weight? Maybe you’ve noticed that the longer you diet, the more your weight creeps up? And it just keeps getting harder. The quick weight loss tricks that got you into your sorority formal dress feel so much more difficult today, and they don’t even breed the same results. What gives?

While the diet industry will chalk it up to your lack of self-control or insufficient willpower, that’s simply not the case. You’re not failing the diets, they’re failing you. Here’s how it happens:

Your metabolic rate

As previously mentioned, you’ll commonly hear weight management boiled down to the very simple balancing act of calories in vs. calories out. And while it’s not total BS– within reason and without underlying issues or imbalances, weighted is gained in a caloric surplus and it’s lost in a caloric deficit– it is a drastic oversimplification.

Let’s take a moment to dig into this idea of energy balance:

Calories in = calories out, which really means…

Energy from food = total daily energy expenditure (TDEE), which really means…

Energy from food = RMR + TEF + EEE + NEAT

RMR = resting metabolic rate, or the energy required by your body at rest over a 24 hour period. This makes up the majority of your TDEE.
TEF = thermic effect of feeding, or the energy it takes to digest, metabolize, and absorb the food you eat. This contributes the least to your TDEE.
EEE = exercise energy expenditure. You know what this means.
NEAT= non-exercise activity thermogenesis, or the energy burn associated with non-exercise activities like fidgeting, brushing your teeth, walking to your car, etc.

So what happens when that “calories in” side decreases when you’re on a diet? Well, our bodies haven’t evolved in the 150 years since the advent of dieting. Your body doesn’t know you’re cutting back to fit into a bridesmaid’s dress. Your body thinks you’re in a famine and will seek energy balance above all else.

So when “calories in” dips, over time, “calories out” will too. In other words, your metabolism will slows. And thanks to a phenomenon called adaptive thermogenesis, it will actually fall more than you’d expect based on body composition or decreased TEF. [source]

And that’s not all…

Hormonal changes

Again, weight is more complicated than the simple energy balance equation makes out. There are other factors at play and hormones are a big one. There are many hormones involved in your consumption and utilization of food– ghrelin, gastric inhibitory peptide, leptin, PYY, CCK, and insulin, to name a few.

For now, let’s just focus on what happens with leptin and ghrelin in light of that drop in “calories in.”

Leptin is a hormone that’s released by your fat cells. When leptin is released, you feel satisfied. In light of caloric restriction, leptin levels decrease. So the harder you diet, the less satisfied you feel.

Then there’s ghrelin, which is commonly referred to as the hunger hormone. When you restrict calories, your ghrelin levels increase, which increases your hunger levels.

So let’s put it all together:

You’re dieting, AKA restricting calories. The “calories in” side of the equation is down. So your body kicks in to restore energy balance:

Your resting metabolic rate will slow. [source] Your thermic effect of food dips because you’re consuming less food. And, you probably won’t consciously realize it, but your non-exercise activity thermogenesis will also decrease as you subconsciously begin to become more sedentary.

In terms of hormones, your leptin levels are down, so you feel less satisfied. And your ghrelin levels are up, so you’re feeling more hungry. Plus dieting, a stress on the body, will cause an increase in cortisol which will increase carbohydrate cravings. [source]

And while all of this is happening in your body, your mind is also at work to restore energy balance as the quantity and intensity of food-related thoughts start to spike.

As frustrating as it feels to live this out, it’s truly a recipe for survival. If you were in a famine and not just trying to lose 7 pounds as quickly as possible, you’d be grateful for the cascade effect that kicks in during caloric restriction.

The thing is, you deserve to feel comfortable and confident in your body. You deserve vibrant health that fuels the life you desire. And while diets position themselves as the quick fix to get you there, your body knows better.