What is BMR?
Whether you’re biking on a park trail or reading calmly at a desk, you need fuel to get through your days. The minimum amount of energy your body needs - i.e., while you’re doing absolutely nothing - is known as your basal metabolic rate (BMR). “That’s the energy it takes to be alive,” says Dr. Douglas White, PhD, an associate professor in the department of nutrition, dietetics, and hospitality management at Auburn University. BMR, usually expressed as calories per day, covers the vital functions of the heart, lungs, digestive system, and more, he explains.
In general, BMR likely accounts for 60% to 80% of all calories you metabolize. Figuring out your exact BMR, however, would require some fairly involved measurement. The process generally requires an overnight stay in a lab setting under strict conditions - no eating for 12 hours beforehand, with a full night of sound sleep required. First thing in the morning, a lab specialist would have to measure your internal heat production by analyzing the gases you breathe in and out (a technique known as indirect calorimetry), then use those findings to arrive at the baseline number of calories your body needs per day. Most people do not know their actual BMR - nor do they need to in the absence of a metabolic issue or related health concern, Dr. White says.
You may have also heard of a similar measurement called resting metabolic rate (RMR), or resting energy expenditure. In clinical settings, specialists calculate RMR using the same calorimetry technique used for BMR but under less restrictive conditions - no fasting required, for example. An RMR value is generally a bit higher than a BMR value because it may include heat generated from, say, digesting the blueberry waffles you had for breakfast that day. Among metabolic specialists, BMR is considered the preferred standard over RMR, Dr. White says.
How to calculate my BMR
There are formulas aimed at calculating your BMR or RMR based on factors such as your age, weight, height, and sex. One of these is the Harris Benedict Equation:
Women:
BMR = 655 + (9.6 × weight in kg) + (1.8 × height in cm) – (4.7 × age in years)
Men:
BMR = 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age in years)
Just note that equations like these, while seemingly convenient for estimating baseline calorie needs, vary in the results they produce and may not align with what a lab test would tell you.
How to change my BMR
Metabolism is essentially the body’s engine, Zelman says, and some people’s engines just run faster than others. Apart from weight - which is modifiable - much of a person’s metabolic rate is hardwired by the following factors.
- Genetic factors: “There’s a huge genetic component to how [our bodies utilize] the food we eat,” Dr. Summers says. Genes determine up to 80% of metabolism, he adds.
- Sex-based factors: The hormone testosterone supports muscle growth, and muscle mass is one factor that stokes BMR, White says. That may be one of several reasons cisgender men have been shown to have higher energy requirements than cisgender women.
- Age: Somewhere around age 30, our bodies naturally start to lose 3% to 8% of their muscle mass per decade, a loss that can ultimately ding our metabolic rate, Dr. White says. Strength training may be helpful for maintaining muscle mass and minimizing age-related declines in BMR, he says.
- Height: Similar to the way a higher weight increases the body’s daily energy needs, tall people tend to have higher BMRs than folks of smaller stature.
To date, research hasn’t turned up any quick “hacks” that can noticeably turn up the dial on your body’s rate of calorie burn. While a few small studies suggest that lifestyle measures such as eating more protein, getting better sleep, turning down the thermostat, or drinking more water may boost metabolism, the findings aren’t consistent and most effects observed are marginal. (Adequate sleep and hydration are good for other reasons, though!) Experts say metabolism is largely determined by heredity, as well as sex-based factors, body size, age, and physical activity.
Regular physical activity that includes strength training could boost your daily energy expenditure beyond the calories you burn during the activity itself. Some of the credit goes to lean muscle mass. “Adding muscle can increase metabolism and help you burn calories at a higher rate,” Zelman says. That's not to say you need to be pumping iron every day. Several studies report that people who regularly engage in almost any form of exercise - whether swimming, running, or tennis - may burn more calories independent of those activities than people whose lifestyles are sedentary.
How to lose weight with WW
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