Your resting energy, often called resting metabolic rate (RMR), is the number of calories your body burns just to stay alive: breathing, circulating blood, maintaining body temperature, and keeping organs running. It accounts for roughly 60 to 70% of all the calories you burn in a day. If that number seems low, the cause is usually some combination of body composition, dieting history, sleep habits, hormonal shifts, or even the tool you used to estimate it in the first place.
Your Estimate Might Be Off
Before assuming something is wrong with your metabolism, consider whether the number you’re looking at is accurate. Most people get their resting energy from an online calculator or a fitness tracker, both of which use predictive formulas based on your age, height, weight, and sex. These formulas have surprisingly poor accuracy. Compared to indirect calorimetry, which measures the gases you breathe in and out and is considered the gold standard, predictive equations are only accurate 40 to 75% of the time. That means the number on your screen could be meaningfully higher or lower than your actual metabolic rate.
If a wearable device is telling you your resting energy is unusually low, treat that as a rough estimate, not a diagnosis. The only way to get a precise measurement is through indirect calorimetry, which some sports medicine clinics and dietitian offices offer.
Body Composition Matters More Than Body Weight
Muscle tissue is far more metabolically active than fat. At rest, a pound of muscle burns about 4.5 to 7 calories per day, while fat burns considerably less. That gap adds up across your whole body: muscle contributes roughly 20% of your total daily energy expenditure, while fat tissue contributes only about 5% (in someone with around 20% body fat).
This is why two people who weigh the same can have very different resting metabolic rates. If you carry less muscle mass, whether from inactivity, aging, illness, or simply your build, your resting energy will be lower. It also explains why strength training is one of the most effective long-term strategies for raising your baseline calorie burn. Adding muscle doesn’t transform you into a calorie furnace overnight, but over months and years, the cumulative effect is real.
Dieting Can Slow Your Metabolism Down
If you’ve been eating in a calorie deficit, your body has likely turned down its metabolic thermostat. This is called metabolic adaptation, and it’s one of the most well-documented reasons for a lower-than-expected resting energy. When you restrict calories, your metabolism drops by more than the loss of body mass alone can explain. Your body becomes more efficient at running on less fuel.
The CALERIE trials, some of the most rigorous human studies on calorie restriction, measured this effect precisely. Participants who cut calories by 25% saw their sleeping metabolic rate drop by about 8% after three months and still remain 5% below predicted levels after two full years. In free-living conditions (not just during sleep), the adaptation was even larger, hovering around 8 to 13% below what their new body size would predict.
What makes this particularly frustrating is that the adaptation persists even after you stop losing weight. Most participants in these studies stopped losing weight after 6 to 12 months, yet their metabolism stayed suppressed. Follow-up research has found that metabolic adaptation can linger for one to nine years after the initial weight loss. This is a major reason why maintaining weight loss feels harder than losing it, and why your resting energy might read low even if you’re no longer dieting.
Sleep Loss Lowers Your Burn Rate
Poor sleep directly reduces resting metabolic rate. A controlled study found that sleep restriction lowered morning RMR by about 2.6%, and the effect reversed once participants got adequate recovery sleep. That may sound small, but over weeks or months of consistently short sleep, the calorie deficit your body creates by slowing down adds up. The mechanism appears to be an energy-conservation response: when your body senses it isn’t getting enough rest, it dials back non-essential energy expenditure to protect vital functions.
If you’re sleeping fewer than seven hours most nights and wondering why your resting energy seems low, that’s a likely contributor and one of the most fixable ones.
Age-Related Changes Are Real, but Later Than You Think
A large-scale study published through Harvard Health found something that contradicts the common belief that metabolism crashes in your 30s or 40s. Resting metabolic rate actually stays remarkably stable from age 20 to 60, regardless of sex. The meaningful decline begins around age 60, when both metabolic rate and lean body mass start to drop. After that point, resting energy falls by about 0.7% per year, and that decline is larger than the loss of muscle mass alone would predict.
So if you’re in your 30s or 40s blaming age for a sluggish metabolism, the more likely culprits are changes in activity level, muscle mass, sleep quality, or diet. After 60, though, the age-related decline is genuine and compounds over time.
Certain Medications Can Suppress It
Some prescription drugs reduce resting metabolic rate as a side effect. Beta-blockers, commonly prescribed for high blood pressure, anxiety, and heart conditions, are among the best-studied examples. Research on healthy men taking beta-blockers found that resting metabolic rate dropped by 7 to 9% within one to two weeks of starting the medication. The effect comes from blocking the part of the nervous system that helps regulate energy expenditure at rest.
Other drug classes with similar effects include certain antipsychotics, antidepressants, and anti-seizure medications. If your resting energy dropped noticeably after starting a new medication, the timing probably isn’t coincidental. Talking with your prescriber about the metabolic effects of your specific medication is worth doing, especially if unexplained weight gain has accompanied the change.
Your Environment Plays a Small Role
Your body burns more calories when it has to work to maintain its core temperature. Researchers measuring resting energy at different room temperatures found that people burned about 96 extra calories per day at 64°F (18°C) compared to a warm 82°F (28°C) room. Even at a mild 72°F (22°C), the increase was about 73 calories over the warm baseline.
This means if you spend most of your time in climate-controlled environments at comfortable temperatures, your body isn’t expending much energy on thermoregulation. It’s not a major factor on its own, but it does contribute to the overall picture, and it partly explains seasonal fluctuations in resting energy that some people notice on their devices.
What Actually Raises Resting Energy
The levers you can pull are straightforward, even if they take time. Building and maintaining muscle through resistance training is the most impactful long-term strategy, since it directly increases the amount of metabolically active tissue in your body. Getting consistent, adequate sleep (seven to nine hours for most adults) prevents the energy-conservation response that drags your metabolic rate down. And if you’ve been in a prolonged calorie deficit, gradually increasing your intake toward maintenance levels can help reverse some degree of metabolic adaptation, though the timeline varies.
Staying physically active throughout the day also matters, not because it changes your resting rate directly, but because regular movement helps preserve lean mass and supports the hormonal signals that keep your metabolism functioning normally. The combination of these habits won’t produce dramatic overnight changes in your resting energy number, but over months they address the most common and correctable causes of a low reading.