Can Dieting Damage Your Metabolism?

Can months or years of dieting do long-term harm to the way our bodies process food? Not entirely. However, there is evidence that gaining and losing fat can change the way our brain regulates body weight. As a Personal Trainer and Nutrition Coach, I’ve been asked this question many times, which is why I’m tackling this complicated topic in this month’s blog.

If you’re amongst those curious to understand if dieting has damaged your metabolism (or is preventing you from reaching your fitness & nutrition goals), read on. I’ll outline the differences between “Energy In” vs. “Energy Out”, provide some tips on how you can set better body expectations, and offer strategies to losing fat and keeping it off!

The Energy Balance Game (Energy In vs. Energy Out)

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Our bodies need a certain amount of energy - in the form of calories - to stay alive, as well as to move around. Energy comes from food or fat tissue (aka stored energy). Weight loss or weight gain is calculated by the Energy Balance Equation, which is a fancy name for the relationship between “energy in” and “energy out.”

Energy In

The idea: If you eat more energy than you expend, you should gain weight.

There’s plenty of margin for error for energy input (i.e., did you know that food labels can be off by as much as 20-25%?), which is why I encourage clients to use a hand-based measuring model for portions. This type of energy is tricky, even for the conscientious calorie counter. In fact, if you want accurate calculation, you’ll probably have to live in an elaborate metabolic lab.

Energy Out

The idea: If you eat less energy than you expend, you should lose weight.

“Energy out” is energy burned through daily metabolism and movement and varies from person to person. In truth, this side of the equation is just as hard to pin down as “Energy In.” There are also four parts to this complex system (click on the links to learn more): Resting Metabolic Rate (RMR), Thermic Effect of Eating (TEE), Physical Activity (PA), Non-Exercise Activity Thermogenesis (NEAT)

In theory, the Energy Balance Equation should help us navigate our weight loss or gain, but it isn’t always dependable. In addition to the reasons above, the Energy Balance Equation doesn’t tell us much about body composition, which is influenced by things like:

  • Sex Hormone Levels
  • Macronutrient Intake
  • Exercise Style / Frequency / Intensity
  • Age
  • Medication Use
  • Genetic Predisposition (and more…)
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In fact, many factors of this equation aren’t mutually exclusive. While it might seem simple to “Eat less, Move More,” there are too many complex, intersecting factors that debunk this concept. As you can imagine, this can be very confusing and frustrating for those who are working out consistently and intensely, in addition to eating carefully, and not seeing the results they want (and deserve!).

Real Life Weight Loss in Real People

Scientists at the National Institutes of Health have studied the data from people who have lost weight and created a mathematical model that represents how weight and fat loss happens in the real world. Let me introduce you to “Frank” – a fictional character I’ve created – who will portray a “real life” person to illustrate how weight and fat loss should work…

Meet Frank

Frank is a 40-year-old male who works a desk job, he’s 5’10” in height, and has a starting weight of 235 lbs. He’s looking to lose weight but doesn’t plan on changing his physical activity (which is fairly limited already).

You may or may not know, but 1 lb. is equivalent to 3,500 calories. To maintain Frank’s current weight, he’ll need 2,976 calories of energy per day. If we take away 500 calories from his daily diet, Frank should lose 1 lb. per week (500 x 7 + 3500). So, after some quick calculations, Frank’s daily intake would drop to 2,496 calories, which means that after a year of consistently eating 500 calories less each day, Frank will be 183 lbs. Wow! Way to go, Frank!

But, wait…something is off…

If this math were to be accurate, this would mean that Frank would weigh 0 lbs. within 5 years. That’s simply not possible.

Do you see where I’m going with this? Living, breathing human beings don’t operate on these equations, which is why so many people hit a wall of defeat when the numbers don’t add up! We might even tend to think our bodies are broken, but I’m here to tell you, nobody is broken. Like Frank, we just need to understand how weight loss works and set some appropriate behavior goals and realistic expectations.   

Dieting Changes Our Brain, Not Our Metabolism

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How your metabolism reacts to changes in energy balance will be unique to you. In fact, how much you lose, or gain, will depend on your age, genetic makeup, biological sex, if you have had relatively more or less body fat and for how long, medications, and several other factors that we don’t even know about yet.

It’s also important to know that losing weight won’t damage your metabolism. Gaining and losing fat can alter the way our brain regulates our body weight. Think about the adaptations your body undergoes in response to fat loss (metabolic, neuroendocrine, autonomic, etc.). Because of these adaptations, “Energy Out” will always be lower for people who have lost significant weight in comparison to those who were always lean, but their metabolism isn’t damaged.


Someone who was never overweight might need 2,500 calories to maintain their weight, while someone who had to “diet down” to that weight may only need 2,125 - 2,375 calories to hold steady. In other words, someone who has dieted down will often require 5 – 15% few calories a day to maintain their weight. It might not seem fair, but this is the way the energy balance game is played.

If you’d like to win at this physiological game, I’ve got a number of strategies that will help you lose weight and keep it off.

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Knowledge Will Help You Set Better Expectations

If you’re feeling “stuck” or can’t seem to get lean, despite working out harder than ever before, knowing how your metabolism works, paying attention to “energy in” and “energy out,” and following strategies to keep weight off can be helpful. If its simply too much to think about (I get it!), I can create a custom nutrition program for your unique body type. The thing is, while dieting can be complex, you can win at this game. And, no, your metabolism is not damaged.

Connect with me HERE to learn more or set up an appointment.


Karen Berenson