"In simplest terms, RMR is the energy your body uses when you’re doing absolutely nothing—your base energy burn, aka how many calories you need for your body to perform basic functions like breathing," says Ash Wilking, NASM, a Nike trainer and instructor at Rumble.
Why is this important, and is there anything that can be done to improve or optimize one's own resting metabolic rate? Here's what experts say you should know.
Why does resting metabolic rate matter, anyways?
Essentially, the RMR describes the energy your body burns naturally on its own, before any kind of exercise or food gets involved. Your body's natural RMR is crucial to support breathing, blood circulation, and brain function, per the National Academy of Sports Medicine.
Surprisingly, your RMR makes up for 60 to 75 percent of your total daily energy expenditure—so it's actually pretty important in understanding how much energy your body needs to function properly. (Exercise, on the other hand, ranges from 15 to 30 percent.) Wilking says that understanding your personal RMR (kind of like your body's baseline) can help you optimize your body's performance, as well as enable you to meet fitness goals and optimize healthy weight management.
"Don’t set out to 'change' your RMR," Wilking says. "Set out to understand it, so you have an idea of the amount of calories you need on a daily basis. Then, you can use that number to adjust." Think: If you're super active and want to add muscle mass, your RMR can help you inform how much more food you should be eating.
What can impact your RMR?
A couple things. Perhaps unsurprisingly, the younger you are, the better your RMR, says Stephanie Middleberg, MS, RD, CDN, scientific advisor to ASYSTEM, since people's metabolism in general tends to slow down by age 40. Your sex also matters, as men tend to have higher resting metabolic rates than do women.
Female RMRs are not totally fixed, however; they tend to speed up in the week before menstruation due to hormonal fluctuations (hence, an increase in appetite). Similarly, thyroid disorders, which also cause hormonal fluctuations, can likewise cause a person's metabolism to speed up or, on the flip side, slow down, which changes their resting metabolic rate. Pregnancy plays a role, too. "Growth in uterine, placental, and fetal tissues, along with the mother’s increased cardiac workload, contributes to gradual increases in RMR," says Middleberg.
How do you find out your RMR?
RMR is best calculated first thing in the morning. "One of the most accurate ways to calculate resting metabolic rate is by going into a laboratory setting and breathing into a mask that will calculate it for you," says Dana Hunnes, PhD, MPH, RD, a senior dietitian at UCLA Medical Center. There are some gyms and fitness studios that may offer this test for a fee. "However, since that would be cost prohibitive for most people, there are predictive equations such as the Harris-Benedict equation that will give you a rough estimate—based on your height, weight, age, gender—of how many calories you burn in a resting state." (You can just Google "resting metabolic calculator" and find an estimate, suggests Wilking.)
Is there a way to better optimize your RMR?
There's a lot about a person's resting metabolic rate that's fixed and unique to them, and Wilking emphasizes that people shouldn't obsess about changing their number. However, Middleberg and Hunnes say there are a few things people can do to make sure their metabolism is as efficient and effective as possible.
For one thing, reach for some weights. "Lean body mass (LBM) is a primary predictor of RMR," says Middleberg. "Athletes with greater muscular development have higher RMR than nonathletic individuals." Outside of simple strength training, Hunnes says high intensity interval training (HIIT) may have more of a positive impact on RMR than other types of workouts. "It may temporarily increase our resting metabolic rate for 12 to 24 hours after we complete high intensity interval training," she says. But Middleberg cautions that there is such a thing as excess—too much exercise of any kind can trigger an inflammatory response in the body, which will slow RMR. Plus, going too hard too often without enough breaks can put a person at risk of injury. So take your recovery days seriously if you're working in more HIIT into your routine.
Speaking of HIIT, try this awesome HIIT workout with weights from our Trainer of the Month series:
A simpler-to-achieve (read: lazier) RMR boost can be found in your water bottle. "Staying hydrated can increase your metabolism by as much as 30 percent," Middleberg says. "It also helps with the elimination of waste, prevents overeating, and helps the body metabolize food." Fluids aren't the only intake that's of import, either. "We burn calories when we eat, because it requires energy to digest food," says Hunnes. "So foods that are a little bit higher in protein and fiber tend to require more energy for digestion." Fiber-rich chia seeds and flax seeds are just a few examples of foods purported to rev up metabolism.
One action that's not beneficial to your resting metabolic rate? Dieting. "As you lose weight your RMR is decreased, which makes it harder to keep weight off," says Middleberg. "RMR may be depressed even further during starvation [very low calorie intake] or chronic dieting." In other words, fiber-rich foods and strength-training exercises are a better recipe for revving up your metabolism than is any diet.
Feeling the post-40 metabolism slowdown? Celebrity nutritionist Kimberly Snyder has a fix (or 7) for that. And check out this six-minute HIIT workout you can do literally anywhere.
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