In the gym, on medical and wellness websites and on social media, the phrase “boost your metabolism” gets thrown around a lot. Supplement marketers promise pills to make it happen, health mavens pinky swear their diet routine will rev the rate, and probably most of us, starting around our 30s, think that aging has reduced the efficiency of our metabolic engine.
And almost none of that is true.
There isn’t a method to boost metabolism “in a way that’s durable or real,” says Herman Pontzer, an evolutionary anthropologist at the Global Health Institute at Duke University. He says most things people promise will boost metabolism fall into two categories. “There are things that are dangerous and illegal and things that are BS, and you should probably avoid both of them,” Pontzer says.
Basal, or resting, metabolic rate refers to work performed by cells when we are doing nothing. It’s the baseline hum of being alive as cells keep blood circulating and lungs functioning. Formally, it’s the calories per minute used for these housekeeping duties. That adds up to about 50 to 70 percent of the total you burn through each day, depending on age, says Samuel Urlacher, an anthropologist and human evolutionary biologist at Baylor University in Waco, Tex.
Most popular interest in basal metabolism centers around ways to kick it up a notch and increase our energy use while doing absolutely nothing, with the prospect of losing weight in the process.
A common perception is that having a higher metabolism means you can get away with eating more while doing less, without gaining weight. The relationship between basal metabolism and weight is complicated, however, Pontzer says. “The larger you are, the more cells you’re made of and the more energy you burn because your metabolism is all your cells at work, all day,” he adds. But each individual cell is not more active or burning more calories per minute just because there are more cells, Pontzer says.
How much energy each of these cells uses depends on its role in the body. Cells forming muscle, nerves or liver tissue use more energy than those forming fat. Although some factors can cause temporary changes in energy use, cells generally hum along at a rate that is sufficient for their role. One way to nudge the metabolism needle is to change the amount of some cell types by building more lean mass or muscle. More muscle means more metabolically demanding muscle cells, which translates into a higher resting metabolism. Individual differences in this mass underlie most of the variation in metabolism from person to person, according to Urlacher. Two people with the same body weight but different proportions of lean mass to fat can eat the same number of calories and still have different weight-gain outcomes. That’s because metabolically hungry cells will use up more of those calories than less-hungry cells.
“If we go to the gym, and we successfully lose some fat and gain some muscle, we will have a very small result on increasing metabolic rate,” says Susan Roberts, a nutrition researcher and leader of the Energy Metabolism Team at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. “Changing body composition can make a little difference but not a lot.”
In terms of weight loss, the timing of a gym visit also might make a tiny difference, Urlacher says. “Those who exercise early in the day have better success with weight loss because it helps control appetite throughout the course of the day.”
Intuition might whisper that a brisk resting heart rate would also correlate with an increased basal metabolism, but that isn’t the case. A resting heart rate of 50 beats per minute for one person versus 70 for another just means the heart with the slower resting rate might be more efficient at getting oxygen to tissues, Pontzer says.
“I think of resting heart rate as more related to fitness levels,” says Jennifer Rood, an exercise testing researcher and associate executive director for Cores and Resources at Louisiana State University’s Pennington Biomedical Research Center. “Maybe indirectly, [if] you’re more fit and you have more muscle mass, you have a higher metabolic rate.”
Bumping up an exercise regimen to burn through more calories may also seem like a sure way to boost metabolism and lose weight. “One of the big myths is probably people think it’s easy to make long-term changes in how many calories we spend each day,” Urlacher says. Evidence suggests instead that daily energy expenditure has a boundary. If you try to push past this boundary, the body adjusts metabolic expenditure in other activities to get back inside the lines.
“Each metabolic activity or system in the body is interconnected, and [if] you start exercising more, over weeks and months, your body adjusts and starts spending fewer calories on overall tasks and resets back to where it was,” Urlacher says. This energy compensation may explain why simply adding more miles a week can yield fitness and other gains but has little effect on weight. People who exercise also tend to increase caloric intake to compensate for the additional energy expenditure.
But how might metabolism change if you exercise and restrict caloric intake? Some fitness gurus have suggested that too little intake will “slow metabolism.” Roberts says that some of this perception may trace to a study of a few participants in NBC’s reality TV show The Biggest Loser, which began in 2004 and ran for 12 years. Researchers at the National Institutes of Health followed 14 contestants during their time on the series and for six years afterward and found that most participants gained back much of what they’d lost. In addition, their basal metabolic rate, which had declined by the end of the competition, was still below baseline six years later. Since then, however, “we have not had that [finding] repeated in nutrition science,” Roberts says, “and I would personally want to see that replicated. Science needs to be deliberate about these major health issues.” Some experts have hypothesized that because the participants ramped up physical activity for a long period of time, their body dialed down energy needs for other activities to keep energy usage in a consistent range, much as Urlacher describes.
Intermittent fasting and other timed eating regimens ultimately reduce caloric intake, raising similar concerns of slowing basal metabolism. This idea has also not been verified by any conclusive science, Roberts says.
Fundamentally, “weight gain is about eating too many calories, and weight loss is about finding a way to eat fewer without being miserable,” Pontzer says.
There is one way that calories going in may affect the calories going out. “One of the big black box elements in all of this is the thermic effect of food,” Urlacher says, referring to how much energy a person burns in digesting food. “That’s another contributor to your overall energy expenditure, in addition to basal metabolism and active energy expenditure.” Scientists think this thermal effect accounts for about 10 percent of what a person burns through each day. But protein requires more energy than carbohydrates to break down, “so what you eat is directly impacting your energy expenditure, too,” Urlacher adds.
Protein and fiber can also indirectly help a person reduce caloric intake. “If you’re eating 100 calories of sugar versus 100 calories of primarily protein and fiber, you’re going to feel fuller longer” with the high-protein and high-fiber diet, Roberts says.
That doesn’t mean bumping up protein is a metabolic panacea. “Assuming that a high-protein diet will fix everything is a common belief, which isn’t really borne out by data on diets within a healthy range,” Roberts says about increasing protein intake as a metabolism booster or weight-loss tactic.
Another common belief is that our metabolic rate starts to drag during our 30s or 40s. Most people who have accumulated a few decades of life can attest to the other accumulations that come with age, and often a “slower metabolism” gets the blame. But research suggests that your basal metabolic rate does not really begin waning until you near retirement age. “There’s not that middle-aged dip or that late 30s dip,” Urlacher says. Instead a metabolic rate decline of about 0.7 percent per year, on average, kicks in around age 60. What some of us experience before then might relate more to a reduced proportion of muscle mass with aging, he says.
As people age, the basic advice for maintaining a healthy metabolism seems to be consistent, including “get good sleep.” Rood says that some studies suggest an association between disordered sleep and slower metabolism, and she notes that the body needs water to process calories, so avoiding dehydration is important.
Focusing on maintaining lean mass, managing the types of calories you take in and paying attention to basics such as getting good sleep might be the best way to stay at optimal cruising metabolism. Just don’t expect a miracle. It’s possible that these influences could add up, Roberts says, but even in sum, “we are not talking about huge effects.”