One can consume a huge meal and gain no weight, while the other has to carefully count calories to not gain weight. But why this is remains a "black box," said Will Wong, a researcher and professor at the Johns Hopkins Center for Metabolism and Obesity Research.

Researchers have found some predictors of how fast a person's metabolism will be. These include: the amount of lean muscle and fat tissue in the body, age, and genetics though researchers don't know why some families have higher or lower metabolic rates.

Sex also matters, since women with any given body composition and age burn fewer calories than comparable men. You can't easily measure your resting metabolic rate in a precise way there are some commercially available tests, but the best measurements come from research studies that use expensive equipment like a metabolic chamber.

But you can get a rough estimate of your resting metabolic rate by plugging some basic variables into online calculators like this one. It'll tell you how many calories you're expected to burn each day, and if you eat that many and your weight stays the same, it's probably correct.

The effect happens gradually , even if you have the same amount of fat and muscle tissue. So when you're 60, you burn fewer calories at rest than when you're Jensen said this continual decline starts as young as age 18 — and why this happens is also another metabolism question researchers haven't answered.

There's a lot of hype around "speeding up your metabolism" and losing weight by exercising more to build muscle, eating different foods, or taking supplements. But it's a metabolism myth.

While there are certain foods — like coffee, chili, and other spices — that may speed the basal metabolic rate up just a little, the change is so negligible and short-lived, it would never have an impact on your waistline, said Jensen.

Building more muscles, however, can be marginally more helpful. Here's why: One of the variables that affect your resting metabolic rate is the amount of lean muscle you have.

At any given weight, the more muscle on your body, and the less fat, the higher your metabolic rate. That's because muscle uses a lot more energy than fat while at rest see the graphic in section one. So the logic is if you can build up your muscle, and reduce your body fat, you'll have a higher resting metabolism and more quickly burn the fuel in your body.

Jensen also noted that it's difficult for people to sustain the workouts required to keep the muscle mass they gained. Overall, he said, "There's not any part of the resting metabolism that you have a huge amount of control over.

The control tends to be relatively modest, and unfortunately, it also tends to be on the downside. While it's extremely hard to speed the metabolic rate up, researchers have found there are things people do can slow it down — like drastic weight loss programs.

For years, researchers have been documenting a phenomenon called "metabolic adaptation" or "adaptive thermogenesis": As people lose weight, their basal metabolic rate — the energy used for basic functioning when the body is at rest — actually slows down to a greater degree than would be expected from the weight loss.

To be clear: It makes sense that losing weight will slow down the metabolism a bit, since slimming down generally involves muscle loss, and the body is then smaller and doesn't have to work as hard every minute to keep running. But the slowdown after weight loss, researchers have found, often appears to be substantially greater than makes sense for a person's new body size.

In the newest scientific study to document this phenomenon, published in the journal Obesity , researchers at NIH followed up with contestants from season eight of the reality TV show The Biggest Loser.

By the end of the show, all of the participants had lost dozens of pounds, so they were the perfect study subjects to find out what happens when you lose a dramatic amount of weight in a short period of time. The researchers took a number of measurements — bodyweight, fat, metabolism, hormones — at both the end of the week competition in and again, six years later, in Though all the contestants lost dozens of pounds through diet and exercise at the end of the show, six years later, their waistlines had largely rebounded.

Thirteen of the 14 contestants in the study put a significant amount of weight back on, and four contestants are even heavier today compared with before they went on the show. But the participants' metabolisms had vastly slowed down through the study period. Their bodies were essentially burning about calories fewer about a meal's worth on average each day than would be expected given their weight.

And this effect lasted six years later, despite the fact that most participants were slowly regaining the weight they lost. Sandra Aamodt, a neuroscientist and author of the forthcoming book Why Diets Make Us Fat , explained this may be the body's way of vigorously defending a certain weight range, called the set point.

Once you gain weight, and keep that weight on for a period of time, the body can get used to its new, larger size. When that weight drops, a bunch of subtle changes kick in — to the hormone levels, the brain — slowing the resting metabolism, and having the effect of increasing hunger and decreasing satiety from food, all in a seeming conspiracy to get the body back up to that set point weight.

In the Biggest Loser study, for example, the researchers found each participant experienced significant reductions in the hormone leptin in their bloodstreams.

Leptin is one of the key hormones that regulate hunger in the body. By the end of the Biggest Loser competition, the contestants had almost entirely drained their leptin levels, leaving them hungry all the time. At the six-year mark, their leptin levels rebounded — but only to about 60 percent of their original levels before going on the show.

But not every kind of weight loss in every person results in such devastating metabolic slowdown. For example: That great effect on leptin seen in the Biggest Loser study doesn't seem to happen with surgically induced weight loss.

Indeed, all the researchers I spoke to thought the effects in the B iggest Loser study were particularly extreme, and perhaps not generalizable to most people's experiences. That makes sense, since the study involved only 14 people losing vast amounts of weight on what amounts to a crash diet and exercise program.

The Mayo Clinic's Jensen said he hasn't found in his patients as dramatic a slowing of the metabolism in studies where people lose about 20 pounds over four months. With slow, gradual weight loss, the metabolic rate holds out really well.

There are some interesting hypotheses, however. One of the most persistent is an evolutionary explanation. That ability would to some extent increase our ability to survive during periods of undernutrition, and increase our ability to reproduce — genetic survival.

Today, the thinking goes, this inability to keep off weight that's been gained is our body defending against periods of undernutrition, even though those are much rarer now.

But not all researchers agree with this so-called "thrifty gene" hypothesis. As epigeneticist John Speakman wrote in a analysis , one issue with the hypothesis is that not everybody in modern society is fat:.

We would all have the thrifty alleles, and in modern society we would all be obese. Yet clearly we are not. If famine provided a strong selective force for the spread of thrifty alleles, it is pertinent to ask how so many people managed to avoid inheriting these alleles.

And, Rosenbaum added, "The evolution of our genetic predisposition to store fat is quite complex. It involves a frequently changing environment, interactions of specific genes with that environment, and even interactions between genes.

Researchers are also trying to better understand metabolic syndrome — the name given to a set of conditions including increased blood pressure, high blood sugar, a large waistline, and abnormal cholesterol or triglyceride levels.

When people have several of these health issues, they're at an increased risk of chronic health issues, including heart disease, stroke, and diabetes. Again, how this works and why it affects some people more than others remains unclear.

So weight loss is possible. For any would-be weight loser, Rosenbaum said the key is finding lifestyle changes you can stick to over a long period of time, and viewing those as changes needed to keep a disease — obesity — under control. You can read more advice from top weight loss doctors here.

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Perreault L, et al. Obesity: Genetic contribution and pathophysiology. Piaggi P. Metabolic determinants of weight gain in humans.

Department of Health and Human Services and U. Department of Agriculture. Physical Activity Guidelines for Americans. Department of Health and Human Services.

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It's true that two people with the same size and body composition can have different metabolic rates. One can consume a huge meal and gain no weight, while the other has to carefully count calories to not gain weight.

But why this is remains a "black box," said Will Wong, a researcher and professor at the Johns Hopkins Center for Metabolism and Obesity Research. Researchers have found some predictors of how fast a person's metabolism will be. These include: the amount of lean muscle and fat tissue in the body, age, and genetics though researchers don't know why some families have higher or lower metabolic rates.

Sex also matters, since women with any given body composition and age burn fewer calories than comparable men. You can't easily measure your resting metabolic rate in a precise way there are some commercially available tests, but the best measurements come from research studies that use expensive equipment like a metabolic chamber.

But you can get a rough estimate of your resting metabolic rate by plugging some basic variables into online calculators like this one. It'll tell you how many calories you're expected to burn each day, and if you eat that many and your weight stays the same, it's probably correct.

The effect happens gradually , even if you have the same amount of fat and muscle tissue. So when you're 60, you burn fewer calories at rest than when you're Jensen said this continual decline starts as young as age 18 — and why this happens is also another metabolism question researchers haven't answered.

There's a lot of hype around "speeding up your metabolism" and losing weight by exercising more to build muscle, eating different foods, or taking supplements.

But it's a metabolism myth. While there are certain foods — like coffee, chili, and other spices — that may speed the basal metabolic rate up just a little, the change is so negligible and short-lived, it would never have an impact on your waistline, said Jensen.

Building more muscles, however, can be marginally more helpful. Here's why: One of the variables that affect your resting metabolic rate is the amount of lean muscle you have.

At any given weight, the more muscle on your body, and the less fat, the higher your metabolic rate. That's because muscle uses a lot more energy than fat while at rest see the graphic in section one. So the logic is if you can build up your muscle, and reduce your body fat, you'll have a higher resting metabolism and more quickly burn the fuel in your body.

Jensen also noted that it's difficult for people to sustain the workouts required to keep the muscle mass they gained.

Overall, he said, "There's not any part of the resting metabolism that you have a huge amount of control over. The control tends to be relatively modest, and unfortunately, it also tends to be on the downside. While it's extremely hard to speed the metabolic rate up, researchers have found there are things people do can slow it down — like drastic weight loss programs.

For years, researchers have been documenting a phenomenon called "metabolic adaptation" or "adaptive thermogenesis": As people lose weight, their basal metabolic rate — the energy used for basic functioning when the body is at rest — actually slows down to a greater degree than would be expected from the weight loss.

To be clear: It makes sense that losing weight will slow down the metabolism a bit, since slimming down generally involves muscle loss, and the body is then smaller and doesn't have to work as hard every minute to keep running. But the slowdown after weight loss, researchers have found, often appears to be substantially greater than makes sense for a person's new body size.

In the newest scientific study to document this phenomenon, published in the journal Obesity , researchers at NIH followed up with contestants from season eight of the reality TV show The Biggest Loser.

By the end of the show, all of the participants had lost dozens of pounds, so they were the perfect study subjects to find out what happens when you lose a dramatic amount of weight in a short period of time.

The researchers took a number of measurements — bodyweight, fat, metabolism, hormones — at both the end of the week competition in and again, six years later, in Though all the contestants lost dozens of pounds through diet and exercise at the end of the show, six years later, their waistlines had largely rebounded.

Thirteen of the 14 contestants in the study put a significant amount of weight back on, and four contestants are even heavier today compared with before they went on the show.

But the participants' metabolisms had vastly slowed down through the study period. Their bodies were essentially burning about calories fewer about a meal's worth on average each day than would be expected given their weight. And this effect lasted six years later, despite the fact that most participants were slowly regaining the weight they lost.

Sandra Aamodt, a neuroscientist and author of the forthcoming book Why Diets Make Us Fat , explained this may be the body's way of vigorously defending a certain weight range, called the set point. Once you gain weight, and keep that weight on for a period of time, the body can get used to its new, larger size.

When that weight drops, a bunch of subtle changes kick in — to the hormone levels, the brain — slowing the resting metabolism, and having the effect of increasing hunger and decreasing satiety from food, all in a seeming conspiracy to get the body back up to that set point weight.

In the Biggest Loser study, for example, the researchers found each participant experienced significant reductions in the hormone leptin in their bloodstreams. Leptin is one of the key hormones that regulate hunger in the body. By the end of the Biggest Loser competition, the contestants had almost entirely drained their leptin levels, leaving them hungry all the time.

At the six-year mark, their leptin levels rebounded — but only to about 60 percent of their original levels before going on the show. Atkins Diet DASH Diet Golo Diet Green Tea Healthy Recipes Intermittent Fasting Intuitive Eating Jackfruit Ketogenic Diet Low-Carb Diet Mediterranean Diet MIND Diet Paleo Diet Plant-Based Diet See All.

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Aleisha Fetters. Medically Reviewed. Reyna Franco, MS, RDN of American College of Lifestyle Medicine. Editorial Sources and Fact-Checking. Resources Comana F. Resting Metabolic Rate: How to Calculate and Improve Yours. National Academy of Sports Medicine.

Pontzer H. New Human Metabolism Research Upends Conventional Wisdom About How We Burn Calories. Scientific American. January 1, Merritt A. BMR Versus RMR. American Council on Exercise. March 6, Kelly M. Resting Metabolic Rate: Best Ways to Measure It — And Raise It, Too.

LaForgia J et al. Effects of Exercise Intensity and Duration on the Excess Post-Exercise Oxygen Consumption. Fitness Nutrition.

Why You Can Trust CNET. Wellness Fitness. Knowing Your BMR Can Improve Your Chances of Losing Weight and More Finding out your basal metabolic rate can be a stepping stone towards achieving your recomposition goals.

Giselle Castro-Sloboda Fitness and Nutrition Writer. On my spare time I enjoy cooking new recipes, going for a scenic run, hitting the weight room, or binge-watching many TV shows at once. I am a former personal trainer and still enjoy learning and brushing up on my training knowledge from time to time.

I've had my wellness and lifestyle content published in various online publications such as: Women's Health, Shape, Healthline, Popsugar and more. Expertise Fitness and Wellness. See full bio. Giselle Castro-Sloboda.

Burn This Number of Calories in a Day to Lose Weight, According to Experts See at Cnet. Watch this: How Healthy is Your Heart, Really? The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice.

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