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BMR Calculator: How to Calculate Your Basal Metabolic Rate to Lose Weight

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Anyone who’s dieted before knows the truth: losing weight and keeping it off can often be hard. A recent study published in the journal Obesity found that changes in a person’s basal metabolic rate (BMR) — essentially, the number of calories they burn at rest each day — has quite a bit to do with both how well people lose weight and how easily it is to keep the pounds from returning.

If you’re hoping to change your body composition for the better, whether that means dropping body fat or adding muscle mass, it’s very helpful to understand how many calories you’ll require everyday while at rest, and also once you factor in physical activity.

Utilizing an online BMR calculator allows you to plug in your data and get customized nutrition and diet recommendations based on your goals, making it easier to increase or decrease your calorie intake as needed.

What Is BMR?

BMR stands for basal metabolic rate, which is the defined as “the rate at which the body uses energy while at rest to keep vital functions going, such as breathing and keeping warm.”

You can think of this number as the amount of calories you’d burn everyday while simply sitting or lying down, doing basically nothing active at all. Even though you might not be doing any exercise or even moving much, this doesn’t mean that you’re not using up calories.

In most people, about 70 percent of all energy expended is actually attributed to their basal metabolic rate. Yes, that means even if you exercise for hours a day, working out accounts for just 10–30 percent of the calories your body burns on a daily basis. So the higher your BMR, the more calories your body burns even when it’s not being active.

The most accurate BMR measurements assume that your digestive system is inactive, which requires about 12 hours of fasting, since eating affects how many calories your body uses.

What is a normal BMR rate? This really depends on a number of factors, including your gender, weight, age and body composition. All of these affect your metabolism, which is the process your body undertakes to convert food and drink into energy.

The calories in what you eat and drink are combined with oxygen to allow your body to perform the functions it needs to keep you alive and well — because even if you’re lying in bed doing nothing, your body requires energy for things like many things like digestion and blood circulation.

BMR vs. Resting Metabolic Rate:

Basal metabolic rate and resting metabolic rate (RMR) are two terms that are often used interchangeably. Both account for the energy your body requires mostly at rest, but don’t factor in exercise and other types of activity.

Technically, however, there is a slight difference between the two. The National Academy of Sports Medicine has explained that “BMR measures energy expenditure in a darkened room (reclining position) after eight hours of sleep and following a 12-hour fast whereas RMR measurements are less restrictive and reflect the body’s resting energy expenditure after an overnight fast.”

Chances are, whether you use a BMR calculator or a MRM calculator to determine your needs, the amount of calories will be similar.

How to Calculate Your BMR

Now that you know what your basal metabolic rate tells you about your overall metabolic function, you’re probably wondering, “How can I calculate my BMR?”

When you use the online BMR calculator one above, most will utilize either the Mifflin-St. Jeor equation or Harris-Benedict equation to determine your calorie needs.

These equations take into account your gender, age, height and weight, but not other specific factors such as the amount of muscle mass you have. While they are useful for determine your BMR/RMR, certain other equations may be more accurate if you’re an athlete with lots of lean muscle.

Here are the main four formulas that are most often used to estimate your energy needs — and which the above online calculator allows for.

1. Mifflin-St. Jeor Calculator

This formula is generally considered the most accurate for calculating BMR, but it doesn’t take into account an individual’s lean body mass or their physical activity level.

2. Harris-Benedict Calculator

This was one of the earliest calorie equations to be used, first introduced in 1984. Since then it’s been updated to be more accurate, and it’s still used by organizations such as the World Health Organization, but some feel that the other calculators are still more accurate since they take into account information such as muscle mass.

3. Katch-Macardle Calculator

This equation calculates your resting daily energy expenditure (RDEE), which takes your metabolic rate and lean body mass into account. This makes it unique compared to both the Mifflin-St Jeor and Harris-Benedict equations. Katch-McArdle is recommended most for people who are generally lean and know their body fat percentage.

4. Cunningham Calculator

This equation is used to calculate resting metabolic rate and has been found to yield acceptable estimates in muscular physique athletes. It’s recommended most for athletic and active adults.

If you want to calculate your BMR by yourself, do the following:

A standard BMR Formula for men is:

  • 66 + (6.23 x weight in pounds) + (12.7 x height in inches) – (6.8 x age in years)
  • Example: If you’re 170 pounds, 5’11” and 43, your BMR is 66 + (6.23 x 170) + (12.7 x 71) – (6.8 x 43) = 1,734.4 calories.

A standard BMR Formula for women is:

  • 655 + (4.35 x weight in pounds) + (4.7 x height in inches) – (4.7 x age in years)

Related: Calorie Calculator — What Are Your Daily Caloric Needs?

How to Use BMR to Lose Weight

Should you eat your BMR in calories to lose weight?

If weight/fat loss is your main goal, you’ll want to eat no less than your BMR number of calories. Any less than this can cause your body to go into “starvation mode,” which actually slows down your metabolism.

It’s long been known that a person’s metabolism slows when they diet as the body tries to keep the person at his or her old weight. When someone tries to deviate from that weight — by restricting calories, for instance — the body fights back to keep them within their genetic ideal weight range. In cases of weight loss, this happens by slowing the BMR down, effectively reducing the amount of calories the body burns when at rest.

Ultimately, you want to keep your BMR up in order to maintain a healthy weight, since BMR accounts for 70 percent of all calories burned most days. This means you should avoid a variety of factors that can cause your metabolism to slow down.

Here are some of the reasons you’re BMR can drop:

  • You’re getting older — Unfortunately there’s nothing you can do to stop yourself from aging. However, it’s useful to know that your metabolism naturally slows as you age. After the age of about 25, it’s estimated that your metabolism drops around 2–3 percent each decade.
  • You’re sedentary/not active.
  • You’ve recently dieted, which slows your metabolism.
  • You’re sleep deprived and chronically stressed, which affects your hormone output, appetite, energy and more.

So what can you do to increase your BMR in hopes of losing weight? If your goal is to lose body fat and improve your body composition, here are some ways you can go about this using this information, including your basal metabolic rate:

1. Increase Daily Calorie Expenditure

  • In simplest terms, if your calorie consumption is equal to your TDEE (the total amount of calories you burn each day through daily living plus activity), you will maintain your current weight. For help calculating this number, see below.
  • If your calorie consumption is less than your TDEE, then you will lose weight. This means that to drop weight, you need to eat less calories and move more.
  • One common recommendation for weight loss is to figure out your TDEE then subtract about 500 calories so you’re in a deficit. This is a general recommendation, so keep in mind that between 300 and 600 may be better for you, depending on your reaction and progress.

One study found that BMRs were about the same between older and younger men who had similar exercise volume and food intake. Making sure you get some physical activity in each day will go a long way toward keeping your metabolism running.

Not only should you add intentional exercise to your day, but also try increasing your NEAT (non-exercise activity thermogenesis), which is all the activity you do throughout the day just living your life, such as walking around, cleaning, showering, etc.

2. Build More Muscle Mass with Strength Training

Even if you’re at a normal weight, if you lack muscle, your RMR could be lower than you’d like. It’s harder for your body to maintain muscle mass than fat, so the more muscle you have, the more calories are being burned, even while at rest.

Start adding strength training to your workout sessions to ensure your metabolism is working hard long after you are. Too many dieters think that lifting weights will put on unwanted bulk, but in my experience, as long as you keep your repetition range above 10 (well outside of the powerlifting zone), you’ll only get fitter … not bigger.

Also, keep in mind that strength training gives your metabolism a bump for 48–72 hours (!) compared to just two hours for a cardio workout.

3. Try High Intensity Exercise/Interval Training

The more intense an exercise is, the longer it takes the body to recover, which means your metabolism is working harder than when you exercise at a moderate level.

Start adding high-intensity interval training or HIIT workouts to your rotation. Not only do these burst workouts kickstart your metabolism and keep it going after you’ve finished working out, but because you give ‘em all you’ve got, they’re shorter in length, perfect for busy people.

4. Get Enough Sleep

If you consistently find yourself skimping on sleep, you might be setting yourself up for failure when it comes to raising your BMR. When your body doesn’t get enough rest, your metabolism will actually slow down to conserve energy.

Aim for 7–9 hours of sleep each night, including weekends. Catching enough zz’s will also help keep your hormones that can contribute to weight gain, at healthy levels. Having trouble sleeping? Try one — or all — of these 20 strategies to fall asleep fast.

5. Eat Foods That Boost Your Metabolism

Although our bodies are designed to lower RMR when we try to lose pounds, we can take natural, healthy steps to counteract biology and speed up our metabolism by eating a nourishing diet.

Choose quality protein like grass-fed beef, raw dairy, cage-free eggs and wild-caught fish to give that basal metabolic rate an extra boost. Try stashing some of these 50 high-protein snacks to boost your metabolism in your bag for a nibble on the go.

6. Avoid Highly Processed Foods and Empty Calories

Foods like fruit juice, refined vegetable oils, trans-fats, sugary snacks and artificial sweeteners are basically metabolism death foods because your body classifies them as toxins. They can cause other unintended weight-gain consequences like gut problems, thyroid dysfunction, bloating and more.

How to Use BMR to Build Muscle

If your goal is to add lean body mass to your body frame, you’ll need to eat enough calories to support your body’s ability to repair and build muscle tissue.

Eating enough combined with consistent strength training is the key to building muscle.

  • To estimate your calorie needs while in a “bulking” or building phase, first use your BMR to determine your “Total Daily Energy Expenditure” (TDEE). This is an estimation of how many calories you burn per day when exercise is taken into account.
  • To determine your TDEE, multiply your BMR by the factor that best reflects the amount of physical activity you do most days.
  • Activity level factors range from 1.2 – 1.9. A factor 1.2 applies to someone who is pretty inactive, while 1.9 is very active. If you typically exercise 3–5 days per week, multiply your BMR by 1.55. If you work out somewhat intensely most days of the week, multiply your BMR by about 1.7, or 1.8 if you also have an active job.

Once you know your TDEE, you can add between 3oo and 500 calories per day if you want to gain muscle. Alternatively, some experts suggest increasing calorie intake by about 15–20 percent. This should be done while doing strength training, which stimulates your muscles to grow back stronger.

Final Thoughts

  • A BMR calculator is one that estimates your basal metabolic rate, which is the amount of energy expended while at rest.
  • This number (which is very smiler to your RMR) doesn’t account for exercise or physical activity, but it’s useful because it gives you a rough idea of your calorie needs so you can add or subtract some based on your goals.
  • How do you use BMR to lose weight? First use your BMR to determine your TDEE, which accounts for activity. Then either subtract or add calories depending on your goals.
  • To help keep your BMR up and to support a healthy metabolism, focus on: being more active, adding in strength training, sleeping enough, eating a nutrient-dense diet, cutting out processed foods.
Josh Axe

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