How does metabolism affect body weight?
A human or animal who suddenly eats less reduces energy consumption by being less active. Also, less energy is used from the body’s cells by using a slowed resting metabolism.
As a general rule, a properly functioning metabolism is essential for good weight and health. Calorie restriction leads to slowed metabolism and therefore less burn. Due to various compensatory mechanisms, the metabolism of most people who have lost weight slows down.
In this way, weight loss is somewhat limited. In other words, our body limits the damage we inflict on it if we’re not eating enough.
You also get hungrier, so when the restriction is lifted, you usually eat more than before to quickly compensate (often even overcompensate) for the weight lost.
Read on to understand more about our body’s metabolism and how it can stop you from losing weight.
Table of Contents
- 1 How does metabolism affect body weight? Introduction
- 2 A long-term diet with fewer calories does not work
- 3 Resting metabolism of the human body
- 4 Thermal effect of food
- 5 Activities and sports
- 6 Metabolism may vary
- 7 Resting metabolism is far from constant
- 8 How does metabolism affect body weight? Summary
How does metabolism affect body weight? Introduction
By simply eating less, you will not lose weight permanently.
Data and figures from the United States show that the chance for someone with obesity to lose weight is less than 1%. So this means a little more than a 99% chance of failure.
The traditional way of dieting (experiencing a calorie restriction every day for weeks to months) hardly works, if at all, because the body takes measures to counteract additional weight loss.
For example, through a compensatory hunger response, and because the metabolism adjusts and slows down.
A study showed that metabolism decreased dramatically after malnutrition.
A long-term diet with fewer calories does not work
So a long-term diet with fewer calories usually doesn’t work. Our bodies adapt quickly and just start functioning more economically (in eco-mode, as it were).
Most of us have long since experienced that in practice, too, haven’t we? So how does metabolism affect body weight?
Today, about 50% of adults in the United States are overweight.
A search for answers for these striking figures quickly leads to the subject of metabolism.
But what exactly is metabolism, and why is it so important for our weight?
Resting metabolism of the human body
Our bodies need energy to function.
The brain needs energy to think properly, the heart to pump, and the muscles to contract.
This need for energy is continuous because our bodies are always going.
Even while sleeping, we burn energy, and anyone wearing a smartwatch is pleasantly surprised in the morning to see that they have burned hundreds of kilocalories before breakfast. And this without doing anything.
In other words, the human body is a factory that requires non-stop energy.
When we sleep, our resting metabolism is also in a sort of standby mode. So resting metabolism is all the energy our body uses at rest.
The lion’s share (about 70%) of the energy we burn goes into this.
How does metabolism affect body weight? A properly functioning metabolism is essential for good weight and health.
But we consume even more energy.
Of course, our bodies also need energy for several other things, such as moving around and digesting food. Depending on our age and whether we are still growing, a small or considerable amount of our energy may also be needed for growth.
Thermal effect of food
The human body gets energy from food, consisting of a mixture of food components that occur in large or small amounts.
A macronutrient is a nutrient found in large quantities that also provides energy. Macronutrients are classified into three groups: fats, proteins, and carbohydrates.
The thermal effect of food is the extra energy required to digest and absorb these macronutrients.
The thermal effect of food accounts for about 10% of total energy use and is influenced by the amount and type of macronutrients.
Digesting a meal high in protein or high in fiber from vegetables takes a lot more energy than digesting a fast food meal (which often has fiber taken out of it).
So you burn more not only by exercising more but also by eating old-fashioned high-fiber food.
After all, eating high-fiber foods takes a lot of energy to digest and burn, and this doesn’t even require a fitness center.
In short, you do have an influence on how much energy your body uses through the food you put in your mouth, chew and swallow.
Do you always or very often eat the same thing? Then your body is also fully adjusted to that, and it takes less energy to digest that food.
Therefore, keep surprising your stomach and gut regularly. For example, eat lots and variety of vegetables with lots of fiber.
Activities and sports
We don’t necessarily have to exercise to burn energy through activity.
We constantly make small movements such as using our hands, wiggling in our chair, tapping our fingers, walking, waving our hands when speaking, fidgeting or shuffling our feet, opening our mouths while talking, twisting our toes, blinking our eyes, etc.
If you start paying attention, you will see that many people make peculiar fidgeting movements. Good to know: If you make many of these small movements during the day, you will increase your metabolism. So you start burning more energy again.
A study published in 2016 in the British Medical Journal showed that sitting in a so-called rocking chair, a chair where you keep moving and wiggling your feet under the table a lot, causes you to burn 20% more energy.
Everyday movements like walking to the car, running errands, mowing the lawn and gardening also burn energy. And, of course, we burn energy during and after exercise. This is called the afterburn (the so-called afterglow).
So even though you’ve been sitting at home relaxing for a long time, you can still feel your muscles burning.
People who are well trained have a higher energy expenditure (energy consumption) during exercise at a certain intensity than people who are not well trained. This is due in part to increased muscle mass.
Exertion increases energy use. Exactly how much depends on person to person:
- Physical activity accounts for about 15 to 30% of total energy use in moderately active people.
- In athletes, on the other hand, physical activity can account for as much as 50% of total energy use.
- And in professional cyclists riding challenging mountain stages, physical activity can account for as much as 70 to 80% of total energy use. The total energy consumption in such riders can reach just under 10,000 kcal during tough mountain stages.
- And people who do little walking or exercise sometimes consume just 10% of their total energy for exercise.
Metabolism may vary
The total amount of calories we burn in a day is a sum of:
- Resting metabolism (around 70% of the energy used goes here).
- The thermal effect of food (around 10% of the energy used goes here).
- Physical activity (variable and depends on person to person, but around 15% of energy goes to this).
- Growth and recovery (around 5% of the energy goes to this).
We can already see that the lion’s share of our daily energy burn goes into our resting metabolism (and not our sports or exercise activities).
But what exactly about our resting metabolism?
Resting metabolism is far from constant
We often think that only physical activity impacts our energy consumption.
On the one hand, this is true because when we move more, we consume more energy, and when we move less, we consume less energy.
Yet most energy (between 60 and 70%) goes to our resting metabolism.
It turns out that our resting metabolism also varies!
We may have a fast resting metabolism or a relatively slow one. So resting metabolism is precisely far from constant.
What about extreme hunger and calorie restriction?
During and shortly after World War II, the American scientist Dr. Keys researched what happens in the body during starvation, i.e., during famine or war, for example.
So a situation where one has little to eat for an extended period. His book The Biology of Human Starvation discusses metabolism during extreme hunger or calorie restriction.
The participants had a remarkably slowed metabolism, which was logical because nothing or almost nothing came in. So, the engine goes into economy mode, the body temperature goes down, and one is constantly cold.
Resting metabolism is very sensitive to scarcity
Over millions of years, our combustion has been fine-tuned. This was useful in prehistoric times to deal well with periods of scarcity or abundance of food.
In the past, of course, scarcity was more common than abundance. Prehistoric man was much more vulnerable, and there were no supermarkets full of spare food.
Our modern bodies have changed very little since prehistoric times. Only in the last few hundred years (that is, only a few generations ago) has abundance rather than scarcity become more prevalent for more people in the Western world.
However, our resting metabolism still responds the same as in prehistoric times and is very sensitive to scarcity.
If we eat less for an extended period, our metabolism simply adjusts. The body then thinks there is less to eat, and it believes it has to be frugal and not just burn all the energy.
In other words, the body enters a kind of hibernation mode. Logical, of course, because it would be foolish not to. After all, who guarantees that there will be enough food tomorrow or the day after?
Using energy sparingly means, for example, relaxing on the sofa, watching television, and burning as little energy as possible.
Anyone who has been on a diet for more than a few weeks probably knows what that feels like. You are a little tired, quite listless, and maybe even a tad grumpy.
So you’re having difficulty finding the energy to do anything, but it has little to do with your character. Our bodies simply send us the message to move less.
Calorie restriction leads to slowed metabolism
So with a calorie restrictive diet, you first lose weight for a while. Then you usually just enter the infamous plateau phase… Nothing happens at all.
And then when you go back to your old way of eating, you gain some pounds too!
This is partly why calorie restriction often doesn’t work in the long run. If you start eating less for an extended period ( as opposed to intermittent fasting ), your body is just going to burn less in response.
Your resting metabolism slows down and goes from consuming about 70% to, say, 60%. Our bodies automatically go into economy mode to hold out until food is available in abundance again.
And because of the slowed metabolism, with less energy consumption, you will gain weight again despite the fewer calories you eat. So you have achieved the opposite of what you wanted and attribute the failure of the diet to yourself because you couldn’t stick with it.
But of course, you couldn’t keep it up! Your whole body is screaming inside for you to get back to eating normally. At the same time, you appear to be getting heavier than ever.
Tip: So if a calorie-restrictive diet is not helping you to lose weight, how should you be eating? Find out in our other article What Are Healthy Eating Guidelines? Tips and Eating Rules from a Nutritionist
Example: The Biggest Loser
An example of a famous calorie restriction diet with very disappointing results was shown on television a few years ago, The Biggest Loser.
This drastic American diet and lifestyle intervention program put 16 participants on a strict diet with a calorie intake of about 1200 to 1500 calories per day. Daily exercise was also a minimum of 2 hours.
The analysis showed that the participants lost significant weight over 6 months. However, a follow-up sometime later revealed that the weight had returned to almost all participants.
During an interview, one of the contestants revealed that a reunion of the contestants was never seen on TV because they had all regained their weight.
Slowed metabolism as a cause of diet failure
Measurements showed that the participants’ metabolism was lowered by an average of just under 800 calories per day.
The researchers stated that they did expect resting metabolism to decrease. This makes sense because you also start to burn less when you lose weight.
They had initially calculated that the participants would burn something like 300 kcal/day less. But this turned out in practice to be almost 800 kcal/day, an incredible 500 kcal more than calculated.
They had hoped that the metabolism would remain active due to the amount of exercise, but unfortunately, this proved not to be the case.
Thus, it became increasingly difficult to lose weight with the slowing of metabolism, and one entered the infamous plateau phase.
Again, the body went into a kind of winter mode and cut back on energy consumption. Even 6 years later, most participants were still found to have slowed metabolism!
So you can see that heavily calorie-restrictive diets encourage yo-yo dieting and have less to do with perseverance than we might think. Because there is nothing to be done against a metabolism that has decreased by almost 800 calories a day.
Thus, the amount of energy consumed by our resting metabolism is a variable. For example, it depends on how many heavy diets you have followed.
Frequent dieting slows down your metabolism (as many an experience expert probably knows), and as the participants of The Biggest Loser unfortunately also had to experience.
Resting metabolism also varies from person to person. For example, a man often burns more than a woman. It also depends on how big you are and how much muscle tissue you have.
It even depends on your age (the older, the slower the metabolism), your hormonal status (postmenopausal women burn slower than before), and how much brown fat you have.
How does metabolism affect body weight? Summary
Due to various compensatory mechanisms, the metabolism of most people who have lost weight slows down.
A low amount of brown fat, less production of leptin, and a less satiated feeling all contribute to the fact that, after a diet, our bodies do everything they can to regain the weight they have lost as quickly as possible.
It is almost impossible for most people to fight this. Obesity is gaining ground in the United States and around the world.
Fortunately, if you understand how metabolism affects body weight, then you can beat the trend.
Related: The ability to lead a healthy lifestyle also depends on what goes on in our heads and how we deal with stress in particular, check out our other article for more on that: Ignoring Stress Is Bad for Our Health: Managing It Is Important