The Truth About Your Metabolism

It’s a term weight loss companies love to throw into their advertising campaigns without much context or explanation: “metabolism.” From pills and potions that promise to “boost” or “speed up” the metabolism to supposedly “natural” herbal supplements that claim to “rev up” a person’s metabolic rate, the m-word is thrown around with frequency but few disclaimers. So what is metabolism and what does it have to do with weight gain, loss, and maintenance?

To put it simply, your “metabolism” refers to the internal processes that allow your body to convert food and beverages (in the form of calories) to energy. This energy is what enables your body to perform all of its essential functions, like breathing, digestion, and more. Your body needs a minimum number of calories (called your basal metabolic rate or BMR) just to survive. While the widespread belief is that metabolism — and, by extension, weight — comes down to a matter of “calories in, calories out”, this is an inaccurate oversimplification of a process so complicated, even experts aren’t totally clear on all the factors involved. What the pros do know is that your metabolism combines calories and oxygen in order to create and release energy to fuel everything from cell growth to blood circulation and more.

“Metabolism is how our body converts food into energy,” says San Diego-based One Medical provider, David Eisner, MD. “People often think of their metabolism as being ‘fast’ or ‘slow’ and the direct cause of their weight. However, it is much more complex than that.”

How so? Eisner points to some research that has demonstrated that individuals who are considered “overweight” in medical terms can also have a “fast” metabolism. As the Cleveland Clinic explains, this is because people at higher weights need more energy to keep basic body functions going. And as a 2013 paper in the journal Culinary Nutrition explains, “people who are overweight or obese do not necessarily have a slow BMR. In fact, their BMR is usually faster to accommodate for extra fat and for their body to work harder to perform normal body functions.”

“This makes sense because when we hold more mass, we have higher energy requirements,” Eisner says. “Confused yet? Good, then you’re starting to understand.”

Eisner’s right: metabolism is a tricky topic and there are many variables even experts don’t fully comprehend. As researcher and professor at the Johns Hopkins Center for Metabolism and Obesity Research Will Wong told Vox in 2018, the metabolism is a sort of “black box” and "we don't understand the mechanism that controls a person’s metabolism." There are some predictors that can influence a person’s metabolism, but there is no single, surefire method for determining how quickly or slowly a person can convert calories to energy or whether they’ll be predisposed to easily gain weight.

“There are many contributing factors to your metabolic rate: genetics, activity, smoking, age, etc.” Eisner says. “Your metabolism is relatively constant until the age of 60. It is not increased during puberty or decreased in your 40s or after menopause. However, one of the most important modifiable factors of your basal metabolic rate (i.e. the calories you burn when just hanging out) is muscle mass.”

Your BMR is the minimum number of calories your body needs to function while you’re completely at rest. Every person’s BMR is different, and there’s no ​​simple way to measure the rate as the most accurate assessment comes from the use of expensive equipment, like a metabolic chamber). You can get a very vague sense of your BMR by using an online calculator, but, to Eisner’s point, this calculation doesn’t take into account important factors like the amount of lean muscle a person has that can impact BMR. However, even the amount of muscle you have can only go so far as research shows “there is a limit for both men and women as to how much lean muscle mass can be built.” That said, adding lean muscle mass can offer a modest boost to BMR because muscle tissue burns more calories at rest than fat tissue.

“This can be done with strength training (e.g., free weights, body weight, resistance tubing) which also has many other benefits, including strengthening your bones, heart and mental health among other things,” Eisner says.

While calorie intake and certain forms of exercise may have some minor influence on your metabolism, experts do not recommend loading up on any one food, drink, herb, supplement, etc. with the hopes of seeing a significant metabolic shift.

“If there is a product out there that can safely ‘boost your metabolism’ in a meaningful way, I hope someone tells me about it,” Eisner says. “Caffeine, spicy foods, green tea, and some other substances may have some marginal impact on metabolism.” The key word in Eisner’s statement, is of course, “marginal.” While beverages like coffee and foods like chillis have been touted as metabolic boosters, “the change is so negligible and short-lived, it would never have an impact on your waistline,” as Mayo Clinic researcher Michael Jensen told Vox.

And if healthy, sustainable weight loss is a goal for any reason, experts say the fact that few external factors impact metabolism shouldn’t be perceived as bad news. “Metabolism should not be your focus if you’re interested in weight loss,” Eisner says. “The best approach to weight loss, by far, is diet. Exercise is also very important.”

But, as always, moderation is key. Anyone seeking to achieve a weight that is healthy, sustainable, and appropriate for their individualized needs (and not determined by aesthetics or social pressures) should steer clear of crash diets or overexercise. Not only can dramatic weight loss actually slow the metabolism, but it can make weight maintenance more challenging over time for a variety of reasons that experts are still trying to fully understand.

Weight loss in and of itself isn’t necessarily equivalent to “health” for every person, and a “faster” metabolism isn’t a guarantee for improved wellness either. Your best bet for establishing healthy habits that work for you is to partner with a primary care provider who understands your unique needs and who can help you achieve your wellness goals — without becoming overly concerned about the number on the scale or the state of your metabolism.

Have more questions about your metabolism? Book an appointment to discuss your diet, weight, and metabolic health with a provider today.