How Does Metabolism Work?

August 02, 2019

What is metabolism?
Jonathan Thompson

In the health and fitness world, it's impossible to go very far without encountering the concept of metabolism. This somewhat abstract thing is simultaneously blamed for weight loss difficulties and credited with success. And there are tons of myths and misconceptions out there, making the fitness journey even more frustrating. So, what's really going on? What is metabolism? Are there really any safe, reliable ways to boost your metabolism?

What Is Metabolism?

Like so many other things, the key to properly managing your metabolism is to first understand what it does exactly. In simple terms, your metabolism is the system by which your body converts food into energy. More specifically, though, the metabolism can be divided into four different components.

First and foremost, there is the Basal Metabolic Rate (BMR). Accounting for around 70% of your daily energy needs, BMR refers to the energy your body needs just to stay alive and healthy. This energy is devoted to many things that people tend not to think much about in their daily lives — like building and repairing tissue, maintaining heart rhythm, breathing and supporting brain function. In large part, your BMR is tightly regulated and highly personal. Factors like gender, genetics, age, overall health and body composition all impact your BMR.

Activity, of course, is usually what people think about when discussing metabolism. In a scientific setting, this particular component of metabolism is usually divided into one of two categories: exercise activity thermogenesis (EAT) or non-exercise activity thermogenesis (NEAT). As its fairly descriptive name suggests, EAT describes the energy expended while exercising, which typically accounts for 5 to 10% of your metabolism. NEAT, however, refers to all the activities you perform on a daily basis that aren't technically exercise. This would include things like daily chores or work, and usually makes up about 10 to 20% of your metabolism.

Finally, there's the thermic effect of food (TEF). Although it might seem strange, the truth is that even just breaking down and digesting food burns fuel. This process accounts for about 10% of your total metabolism.

Myths and Facts

With a basic understanding of metabolism, it should be easier to understand what is and is not possible. For example, as mentioned above, TEF is a very small part of your metabolism and really only lasts as long as it takes your body to digest the food. This means that the whole idea of metabolism-boosting foods, like coffee and hot peppers, is a deeply flawed and unreliable weight loss approach. This doesn't mean that your diet has no impact on your metabolism. Highly refined foods do not require a lot of energy to digest but give up lots. More complex foods, like those that are rich in protein and fiber, however take more effort to break down. As a result, your body receives fewer excess calories and you are left feeling fuller.

It's also worth revisiting the idea of metabolic regulation. Again, metabolism, very simply, keeps you alive. For this reason, your body is extremely hesitant to let it change. Which can be both a good and bad thing, depending on your situation. One on hand, this means that any fears about your metabolism screeching to a halt because you miss a meal or two can be put to rest. While it is true that your metabolism may slow down after your body gets used to eating less, it will never stop completely or reverse as has been suggested. This has been shown in multiple studies, including the infamous Minnesota Starvation Experiment during which participants were given only half of their daily caloric requirements. The subjects continued to lose weight until they simply had no more fat reserves to burn. Their metabolism never stopped.

The heavy protection surrounding your metabolism, though, also means that it can very difficult to change. In the same way that skipping meals won't slow it down, there is no evidence to support the idea that eating many smaller meals throughout the day will speed up your metabolism.

So, what can you do? Remember, one of the factors controlling your BMR is body composition. This means that the more muscle mass you have, the faster your metabolism will be. Muscle burns fuel all day, even when you're sleeping. For this reason, one of the most powerful things you can do to boost your metabolism is to incorporate strength training into your fitness routine.

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