According to research, 60-70% of overweight Americans will successfully be able to lose the weight.

However, 95% of diets fail. How is that possible? Well, 95% of people who lose weight will gain it all back and then some.

Why? And how? And again why? Is Mother Nature against our best efforts to get healthy?

I sympathize greatly with this plight. I am the epitome of a yo-yo dieter in both the macro and the micro sense. On the macro level, I’ve successfully lost a significant amount of weight twice, only to gain it all back again and then some in company with those other 95% of people. On the micro level, I’m always trying some new approach to dieting to get back to where I used to be.

So, what have I been doing wrong?

Simply put, our bodies are not adapted to our modern life of plenty. They’re equipped to survive times of extreme famine. Most of this information in this article came from the nutrition expert Layne Norton. I highly recommend that you check him out online.

Our starvation defense system

One of the main threats of survival to our ancestors was starvation. So, our bodies adapted in very clever ways to defend against that danger. These defenses unfortunately are extremely ill-suited to our modern lifestyle.

1. A more “efficient” metabolism

Our metabolism refers to the energy we burn every day. The total amount of calories we burn a day is our Total Daily Energy Expenditure (TDEE). It’s comprised of our Basal Metabolic Rate (BMR) or the amount of calories we burn from existing, the Thermic Effect of Food or the calories it requires to digest our food, Non Exercise Activity Thermogensis (NEAT) or all of our daily movement that isn’t exercise, and exercise.

While in a diet, the aim is to take in fewer calories than you burn, so now you’re decreasing the amount you eat and upping your exercise activity to make this happen. This calorie deficit should force the body to burn stored energy, a.k.a. fat, to fuel us through our day to make up for this deficit. Essentially, to our bodies, a diet is controlled starvation, and our really bodies don’t like starvation. If you’ve ever been in a calorie deficit, you can attest that the pangs of hunger are seriously hard to withstand!

The first way the body defends against this perceived famine is called metabolic adaptation. Our metabolism adapts to get more efficient. Efficiency is a good thing, except in this case. Fat is like fuel in a car. If we have a lot of excess fat, we want to burn through that fuel as quickly as possible. We want a gas guzzling engine in a big truck. However, our body reacts to a calorie deficit by becoming more efficient. It’s akin to pouring all of our excess fat into a Toyota Prius, not good for those of us looking to shed extra fat. Some of the ways our body slows down our metabolism are by making us feel more lethargic and decreasing our NEAT by having us fidget less and even blink more slowly! Layne Norton attested that on a large calorie deficit he would even speak more slowly. The body sure is crafty.

This phenomenon is why many people plateau on a diet. Initially, they experience great success with consistent weight loss for weeks. Then, despite eating at the same calorie deficit and adhering to a rigorous exercise schedule, fat is no longer shed. Your body has adapted to this new, lower intake of calories in order to help you survive. The only options at that point to continue fat loss are to increase the deficit through a larger decrease in calories and an increase in movement or to begin what’s called a reverse diet. I’ll talk more about reverse diets and how to avoid the pitfalls of yo-yo dieting in a future article.

2. Energy capture and storage

The body’s second defense against starvation is an increased ability to capture and store energy a.k.a. fat post-diet. Being in a diet turns on genes that prime you for fat storage. Your body gets ready to store food with its greatest efficiency when you finally come across lots of food.

If you took two genetically identical people (both have the same TDEE, the same fat mass, the same genes, etc.) and the only difference was that one had been dieting and one hadn’t, they would respond very differently to the same high-calorie meal. If both ate a high-calorie meal, the the dieter would capture and store that surplus energy at a much greater level than the person who hadn’t been dieting who would probably get rid of some of that surplus energy as heat rather than capturing and storing it. Again, being on the diet alone primes your body to prioritize capturing and storing as much energy as possible when it comes across a big meal.

This makes sense from a survival perspective because the body’s goal is to restore depleted reserves in order to protect itself from future famine, but again, it’s sucky news for dieters. We like to believe that we can’t gain fat from one bad meal. However, in this post-diet situation, we absolutely can when our bodies are in this energy-capture mode.

Studies on rats have also shown that if you overfeed calories rapidly enough after a diet, the body will make new fat cells. New fat cells are only created when a person becomes so obese that existing fat cells have no more space for fat and during the third trimester of pregnancy. It’s an extremely rare situation. Of course, more fat cells = greater success at storing fat. Again, your body is primed and ready to capture and store as much energy as possible at the end of a diet if you suddenly begin eating a surplus of calories.

Think about it for a second: how do you respond at the end of a diet when you finally reach your goal weight?

I delete my food tracking app, hide my gym clothes, and spend a week eating like I’ve been stranded on a desert island. Now I’m on dessert island. It’s natural. We want to celebrate and relax the strict restrictions we’ve placed on ourselves for the past several months. But, our body’s starvation-defense system makes this the worst possible action we can take if we want to maintain our success. In this crucial time post-diet, it’s easier than it’s ever been for us to put the fat right back on.

3. Your body’s diet memory

The body’s final defense system against starvation is a diet memory.

If we tell our bodies that food is scarce over and over again through multiple calorie deficits follow by a surplus followed by a deficit (yo-yo dieting), our bodies have a diet memory to defend against the impact of these future famines a.k.a. diets.

If a person regains weight post-diet as 95% of Americans do, this diet memory has a nasty defense mechanism in store for us. A study done on rats revealed that once the rats had been on a diet and then regained the weight, it was TWO TIMES harder to lose the weight the second time around. The rats regained the weight again, and this time it was THREE TIMES harder to lose the weight the third time around. Their bodies remembered the diet or starvation from the first and second times and wanted to ensure it would be able to more keep its energy reserves intact should another famine occur again. Their bodies purposefully made it harder for them to shed this reserve energy. Great news for our ancestors. Bad news for us.

The main takeaways

Binging post-diet and yo-yo dieting are extremely detrimental to our long-term weight loss goals and it’s why most people fail to keep off weight after a diet. Post-diet, our body is primed and ready to pack on fat if we so much as look at a doughnut or pizza or indulge in a gigantic cheat meal.

However, it isn’t hopeless. After a diet, if you stop eating in a deficit and eat at your maintenance calories, meaning consuming an amount of food = to your TDEE, your body won’t have the surplus of calories to capture and save. An issue arises, however, if your TDEE calories isn’t sustainable. Since our metabolisms get more efficient during a diet, your new TDEE might be pretty low and unrealistic.

In future articles, I’m going to outline the behaviors of those 5% of people who successfully keep weight off and the process of a reverse diet that helps you increase your daily calorie intake (make your metabolism more like that gas guzzling truck) without gaining back the weight you lost.

Are you a yo-yo dieter? Did you know about the body’s starvation defense system?