7 Common Myths About Measuring Metabolism

Metabolism is a cornerstone of human physiology, playing an important role in how we manage energy, body weight, and overall health. Yet, despite its importance, there are numerous myths and misconceptions that cloud our understanding of it. These myths often lead to misguided efforts in diet and exercise, and can even impact long-term health outcomes. Explore some of the most pervasive myths about metabolism and the reality behind it for a more accurate picture of how our metabolism functions.

Myth 1: A Fast Metabolism Is the Key to Losing Weight

Reality: While a higher metabolic rate can aid in burning more calories at rest, it is not the sole driver of weight loss. The primary factor in weight loss is maintaining a calorie deficit—burning more calories than you consume. Effective weight loss and maintenance require a holistic approach that addresses both sides of the energy balance equation—calories consumed and calories expended—through healthy eating habits, regular physical activity, and lifestyle adjustments conducive to sustainable behavior change.

Myth 2: Thin People Have Faster Metabolisms

Reality: Contrary to popular belief, individuals with obesity do not necessarily have a slow metabolism, debunking the idea that one's metabolic rate inevitably leads to being overweight. A pivotal study by Prentice et al. (1986) found that average energy expenditure is significantly higher in individuals with obesity, challenging the expectation of a slow metabolism. When corrected for differences in fat-free mass and total body mass, both basal metabolic rate (BMR) and total energy expenditure (TEE) are comparable between lean and obese individuals.

Myth 3: You Can Boost Your Metabolism with Certain Foods or Supplements

Reality: The notion that specific foods or supplements can dramatically boost metabolism is largely overstated. Substances like caffeine or capsaicin (found in spicy foods) may have a minor, temporary effect on metabolic rate, but these effects are not substantial enough to cause significant weight loss. 

Myth 4: More Exercise = More Calories Burned

Reality: Numerous studies across different populations, including those involving new exercise regimens, reveal that total daily calorie expenditure is often lower than anticipated from activity differences. Sometimes, like with the Hadza, there's no difference between active and sedentary individuals. The body is dynamic and complex, capable of reallocating how it expends energy in unpredictable ways. This complexity is why online calorie counters and smartwatches frequently fall short in accurately predicting daily calorie burn. They operate on the flawed assumption that the body functions like a simple machine, akin to a car engine. In reality, our bodies and metabolisms are far more intricate and adaptive.

Myth 5: You Can’t Change Your Metabolic Rate

Reality: While basal metabolic rate (BMR) is influenced by genetic factors, it is not entirely immutable. You can increase your metabolic rate through lifestyle modifications. Building muscle mass through strength training can elevate your BMR since muscle tissue burns more calories than fat tissue, even at rest.

Myth 6: Metabolic Rate Testing Is Inaccurate and Unreliable

Reality: Certain methods for measuring metabolism, such as the doubly labeled water method, are highly accurate. The doubly labeled water method measures metabolism by using special water labeled with safe forms of hydrogen and oxygen. After the labels have spread throughout the body, urine is collected over time to measure how quickly these labels leave the body. Because the body makes carbon dioxide as it burns energy, the rates at which ^2H and ^18O leave the body show how much carbon dioxide—and thus how many calories—the body is producing. Unlike other methods, DLW gives a precise look at all the energy the body uses, including what's used at rest and during activities, offering a clear picture of a person's metabolism in everyday life.

Myth 7: There Are No Limits to How Many Calories You Can Burn or Absorb

Reality: Emerging science is shedding light on two critical "metabolic ceilings" that define the limits of what the body can sustain. The first ceiling is a hard limit on daily calorie burn. There’s no credible evidence of athletes pushing beyond this limit without experiencing physical breakdown. The second ceiling is the cap on how many calories your body can absorb. This sets the long-term limit on calorie burn since it's impossible to sustain a negative energy balance (burning more calories than consumed) indefinitely. 

By debunking these common myths, we hope to clear up some of the confusion and provide a realistic perspective on understanding and measuring your metabolism. To get a deeper insight into your own metabolism, learn more here.