Metabolic Damage: Myth or Fact?
When it comes to losing weight, there are a lot of myths out there.
Do you struggle to lose weight even after cutting calories? What about unable to maintain that weight loss? Have you gained some weight back after each diet?
Many may say metabolic damage is the culprit, and that you are doomed to an entire life fighting your weight.
Related - How to Properly Reverse Diet
But before we jump to that conclusion, let's check out some of the facts.
Does Metabolic Damage Really Exist?
To better answer this question, let's take a look at the findings from the Bayesian Bodybuilding Research Team. They spent months digging through research and analyzing studies on weight loss and regain.
Their review was published in December 2016 and they present their key findings and useful tips. The study was titled Metabolic Damage: Do Negative Metabolic Adaptations During Underfeeding Persist After Refeeding in Non-Obese Populations?
Metabolic damage is the permanent slowing of your metabolism after dieting. Basically, when you start eating less, your metabolism will slow down. So your resting metabolic rate decreases because you do not expend as much energy for basal tasks needed to live. For example, your heartbeat.
The research wanted to answer this question:
"Does this metabolic slowing persist after you stop dieting and increase your energy intake?"
If this is the case, our energy expenditure would remain low after dieting, but the increased food intake would make you regain all of the weight you lost.
Here's What They Found
A large part of the study conducted focused on the Minnesota experiment. They took the data from the Minnesota experiment that originally was used in the past as support for the metabolic damage hypothesis.
The experiment took 32 normal-weight, young men and were put on a drastic weight loss diet for 24 weeks. That may not sound like a lot, but that's half of a year.
Their target was to lose 1 kg a week, or 2.2 pounds. Their average body fat level at the end of the diet period was only 5% — which is the body fat level of hard-core bodybuilders when on stage.
The one thing the Minnesota experiment had over hard-core bodybuilders were that none of the men had much muscle mass to start with. The end of the experiment left the men looking like skeletons with skin instead of the genetic freaks we gawk at on stage.
The refeed was under controlled conditions to determine which refeeding strategy was best for their prolonged semi-starvation diet. So they underwent 12 weeks of controlled recovery — receiving a strict prescribed diet.
Afterward, some men decided to stay at the facility for an additional eight weeks and transitioned into eating as much as they wanted to.
During this period, though, the researchers recorded precisely how much each participant ate.
Basal Metabolism Before Starvation and After Refeeding
Studies performed prior to the Minnesota experiment didn't take into account the entire recovery period — only examining the 12-week controlled recovery.
The Bayesian Bodybuilding Research Team analyzed the entire 20 weeks of recovery and found no sign of metabolic damage.
They compared the subjects' basal metabolism, which is their resting metabolic rate in relation to the subject's fat-free mass and fat mass, before and after starvation. They used three different RMR prediction equations to obtain a precise number.
They then compared their predicted RMR to the RMR value measured for each subject.
The results suggest that subjects' metabolism — body composition related RMR — was either the same or even higher after starvation. Again, this was analyzed using three different equations.
Your Energy Intake Influences Metabolic Recovery
There were four groups in this study, and each group received a diet with a different energy content. The lowest energy group had a diet with a slight surplus of a few hundred kilocalories more than they needed to maintain their starved bodies.
The group with the highest calories had a daily energy intake of over 1500 kcal more than they needed to maintain their weight at the end of the starvation period.
They also took a look at lean body mass gain... or building muscle. They found the rate of lean body mass gain were the same between all four groups. It makes sense since none of the participants actually even lift.
Why would the participants with a calorie surplus magically build muscle if they didn't train? The subjects with the highest calories gained significantly more weight — around a 59% weight recovery. This added more fat.
It's pretty basic, but the participants who ate more gained more fat.
They found the groups that ate more had a higher RMR increase, while the lowest energy group surprisingly had the highest metabolism in the recovery period than in the starvation period.
The actual resting metabolic rate value showed a trend towards higher values, even though the subjects' body composition was less favorable during the recovery period than the starvation period. This means their lean body mass was significantly lower.
It's pretty simple — because they ate more.
Take home point: Energy intake will influence your resting metabolic rate.
The previous researchers completely ignored the fact that the subjects were divided into groups receiving diets with a significantly different energy content. They found that "only after you regain all of the fat you lost will the metabolic slowing stop."
But the Bayesian Bodybuilding Research Team suggests their findings completely contradict that statement. They suggest metabolic slowing is a result of an energy deficit, which is reversible by an increase in energy intake.
Fat gain you see after your diet is not a result of a suppressed metabolism... you're just overeating.
Other Studies' Evidence
The Minnesota experiment isn't the only study they looked at. They took a look at studies on malnourished individuals and those diagnosed with anorexia nervosa.
They found even with the drastic, chronically undernourished state, that their basal metabolism of the participant corresponded to their body composition. Their RMR was low, but it was because the subjects' body mass was low.
Another interesting point is some studies suggested during the refeeding of anorectic patients, their RMR increased more than predicted based on their body composition. This means their body essentially wasted the energy instead of saving it as fat.
While these studies took a look at the extreme, what about the normal person trying to lose weight? What about the types of diets bodybuilders use to get extremely lean? The Bayesian Bodybuilding Research Team took a look at studies that are more relevant for real-life strength athletes, or those of us who simply want to get lean.
They found that bodybuilders and other weight class athletes saw an RMR decrease as they were preparing for a competition. After the competition, the athletes refeed and return to their initial body weight with an increased basal metabolism.
Can Months or Years of Dieting Ruin My Metabolism?
The short answer is no. But gaining and losing fat can change the way our body regulates body weight.
You need energy to live. You need more energy to get up and move around. This energy comes from food or retrieved from your fat tissue.
The theory is that if you eat less energy than you expend, you should lose weight. If you eat more energy than you expend, you should gain weight.
If you've ever heard of "energy in" and "energy out," you heard someone quoting the energy balance equation — it's a commonly accepted model for calculating a person's energy balance and how much they will lose or gain over time.
This energy balance determines our body weight, but it doesn't say much about our body composition. That can be influenced by things like your sex hormone levels, the macronutrients you eat (like protein), your exercise style, frequency, and intensity, your age, medications used, genetic predisposition, and more.
This can be frustrating because sometimes the numbers just don't add up, or their results don't match their expectations.
That's fair, because most of the time, the numbers simply don't add up.
There is a mismatch between your expectations versus what really happens... and it's not because the energy balance equation is wrong. It may seem like you are defying the laws of physics, but you aren't.
The equation is more complicated than it sounds.
There are many factors that affect the energy balance equation — and they aren't mutually exclusive. Essentially, what you do for "energy in" will affect what happens for the "energy out."
Eating Less and Moving More is a Good Start
Pretty much everyone I know could go without as many calories and more movement... the couch doesn't burn calories.
The "Energy In" is Trickier Than You Think
It's hard to know precisely how many calories you eat. The calories in a meal don't likely match the number on the label or menu.
Would you believe that companies and even the government can come up with calorie and nutrient estimates that are complex, not very precise, and are centuries old? Studies suggest that food labels could be off by as much as 20 to 25 percent.
What's worse is the energy that a food contains in the form of calories may not necessarily be the same amount of energy that we can absorb, store, and/or use. The food we eat has to be digested and processed by our bodies. Each body is different, so this can all change the energy balance game.
Did you know?
We absorb less energy from minimally processed carbohydrates and fats since they are harder to digest?
We absorb more energy from highly-processed carbohydrates and fats because they are much easier to digest. Basically, the most processed a food is, the easier it will be to digest.
Research suggests that we absorb more fat from peanut butter than whole peanuts.
Researchers found that almost 38 percent of the fat in peanuts were excreted in your stool rather than absorbed by the body.
The researchers noted that seemingly all of the peanut butter's fat was absorbed.
The number of calories we absorb can depend on if they are cooked or not. Foods that are cooked, chopped, soaked, or blended helps break down the plant and animal cells — increasing their bioavailability.
This means if we eat raw starchy foods like a sweet potato, we won't absorb many calories.
After cooking, though, the starches are more available to our bodies and triple the amount of calories we will absorb.
Another cool fact is if you allow your starchy foods to cool before you eat them, this decreases the number of calories that we can absorb. This has to do mostly with the formation of resistant starches.
Lastly, we may absorb more or less energy depending on the type of bacteria in our gut.
Here's how the whole process works. The USDA researchers had test subjects consume 45 grams — or about 1.5 servings — of walnuts daily for three weeks. They found on average, people only absorbed 146 out of the 185 calories in the nuts. That's 79 percent of the calorie content listed on the label.
Another similar study found that people only absorbed about 80 percent of the calories in almonds and 95 percent of calories in pistachios.
Even more interesting, they noticed individuals were all different. Some people absorbed more energy in the nuts, while some absorbed less. Researchers feel it is likely due to the different populations of bacteria in their large intestines.
Energy Out Also Varies Per Person
If the energy in phase wasn't confusing, the energy out phase is different for each individual.
There are actually four parts to this complex system.
#1 - Resting Metabolic Rate
Your resting metabolic rate is the number of calories you burn every day at rest. Simply breathing, thinking and living. This is about 60 percent of the energy you burn and depends on your weight, body composition, age, sex, genetic predisposition, and possibly the bacteria in your gut.
Generally, a bigger body will have a higher resting metabolic rate.
- A man who weighs 150 pounds may have a resting metabolic rate of 1600 calories per day.
- A man who weighs 200 pounds may have a resting metabolic rate of 1900 calories per day.
- A man who weighs 250 pounds may have a resting metabolic rate of 2200 calories per day.
Your resting metabolic rate can vary up to around 15 percent from person to person. That means if two 200-pound men were on the treadmill, one may burn 286 more or fewer calories than you did.
#2 - Thermic Effect of Eating
It may be a surprise to you, but we do burn calories digesting food. Digesting food is an active metabolic process, and is the reason you may experience the "meat sweats" or a little warm after eating a big meal with protein.
The thermic effect of eating is the number of calories you burn by eating, digesting, and processing the food you eat. This is roughly five to ten percent of your calories burned per day.
As a general rule of thumb, you'll most likely burn more calories digesting proteins than you would carbohydrates or fats. Protein takes about 20 to 30 percent of its calories to digest, five to six percent for carbs, and three percent for fats.
#3 - Non-Exercise Activity Thermogenesis
Any activity that isn't purposeful exercise like fidgeting, and staying upright all burn calories. This also varies from person to person.
#4 - Physical Activity
Like it sounds, physical activity is the calories you burn from purposeful exercise. This could include walking, running, gardening, riding a bike, going to the gym, or any other physical activity.
In order to burn more calories, you'll need to move more.
The energy balance equation sounds simple, but all of these variables make it tough to understand what's going on. It's hard to control exactly how much energy you are taking in, absorbing, burning, and storing.
Your Body Tries to Keep Your Weight Steady
If all of the variables in this equation isn't enough, it can get even crazier when you start changing variables because this also can change other seemingly unrelated variables.
Our metabolism has evolved to keep us alive and functioning when there was no food. This means when if the amount of energy in goes down, the amount of energy out also goes down to match it.
You're basically burning fewer calories in response to eating fewer calories. While this isn't set in stone, that's how our bodies are supposed to work. Our bodies attempt to avoid unwanted weight loss and starvation. This is why we've been able to survive for 2 million years as our body fights to maintain homeostasis.
On the other hand, when your energy in goes up, the energy out tends to go up, too. This means you can burn more calories in response to eating more.
To further illustrate the point, let's take a look at how our body tries to keep our weight steady.
- Our thermic effect of eating will go down because we eat less.
- Our resting metabolic rate will go down due to weighing less.
- Since you weigh less, your physical activity will not burn as many calories.
- Your non-exercise activity thermogenesis will go down as you eat less.
- Your calories not absorbed will go down and you will absorb more of what you eat.
This response may seem modest, but the adaptation will really ramp up as you start losing more weight or trying to get super lean.
What's more, once you start reducing the number of calories you eat, your hunger signals will start to increase and could cause us to crave food or overeat. This net effect is what slows our rate of weight loss. It could also lead to weight gain.
Since we are dieting, the stress of dieting could raise our cortisol levels which could cause us to feel bloated and hold onto more water weight.
But this is just one example of how robust the body's response is to manipulating these variables.
You Need to Set Better Expectations About Body Change
It's important to note that if you have a lot of body fat to burn, many of these metabolic adaptations won't happen right away. As you become leaner, though, the adaptive thermogenesis will start to kick in.
How your metabolism reacts to these changes in energy balance is unique to you.
The amount you can lose or gain depends a lot on your age, genetic makeup, your biological sex, and if you've had relatively more or less body fat and for how long, medications, and your microbiome in your gut.
There are probably more factors out there that we don't know about yet, either.
The scientists at the National Institutes of Health studied data from people who have lost weight, and created a mathematical model that represents how weight and fat loss actually happens in the real world.
Say you're a 40-year-old male that weighs 235 pounds and you are 5'10" tall. You work at a desk job and only slightly active outside of work. This means he needs 2,976 calories of energy per day to maintain his current body weight.
If he knocks off 500 calories per day, his intake would drop to 2,476 calories.
You've probably heard somewhere that roughly 3500 calories equal a pound, so he should lose around 1 pound per week. Going off of this math, he should end up at 183 pounds after one year of consistently eating 500 fewer calories per day.
But then again, according to this math, he would weigh 0 pounds after 5 years... and that should raise some red flags.
But we know this isn't how real life works... maybe you should try that juice cleanse?
But Does Dieting Damage Your Metabolism?
Despite all of the myths you may have heard, you cannot "damage" your metabolism by losing weight.
The adaptations your body will undergo in response to fat loss, on the other hand, will. The energy out for individuals who have lost a significant amount of weight will always be lower than those who have always been lean.
Losing weight and keeping it off is accompanied by adaptive metabolic, neuroendocrine, autonomic, and other changes. That means as we lose weight, we expend less energy.
This adaptive response that happens after someone has dieted down will often require five to 15 percent fewer calories to maintain that weight and physical activity than someone who has always been at that weight.
This means if someone needs 2,500 calories to maintain their weight, someone who dieted down to that weight may only need 2,125 to 2,375 calories to maintain that weight.
Studies suggest this adaptation can last for up to seven years after you lose weight. This indicates that it may be permanent or at least persistent... but nothing has been "damaged."
Wrapping It Up
When it comes to maintaining a healthy metabolism, your body composition is the most important factor. This is going to determine how much energy you expend.
Small changes in your energy intake — such as eating less or eating more — could decrease or increase your resting metabolic rate. But they found after one to three days after you stop dieting and return to your regular maintenance intake, your basal metabolic rate also increases.
The human metabolism is flexible and can adapt to changing conditions quickly.
Based on the evidence from the Bayesian Bodybuilding Research Team, metabolic damage doesn't exist.
Start making better food choices. Fill your diet full of whole, minimally processed foods. The calories you absorb may be significantly less than what you expect.
Eating highly-processed foods increases the number of calories you absorb, and you will burn fewer calories in the digestion process.
Remember, the number of calories you think you are consuming could be off by 25 percent or more. Your carefully curated diet of 1,600 calories could actually be 1,200 or 2,000.