Should You Eat Under Your BMR to Lose Weight? What Women Need to Know

The typical woman’s metabolism is slower than the average man’s, so when it comes time to lose weight, eating fewer calories may be one path toward meeting your goals. But, just how many fewer calories do you need to eat? Using your basal metabolic rate (BMR) will help you figure out how many calories you need to burn fat, maintain muscle, and decrease body fat percentage. This method can lead to healthy and sustainable weight loss. However, there are some things you should consider before starting any diet, and we’ll go over what mistakes to avoid. Today, we will discuss the benefits and drawbacks of following a BMR-based weight loss plan, as well as other factors that can affect your success.

Your basal metabolic rate is a calculation of how many calories your body uses to perform essential processes, like breathing, circulation, and energy production.

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How can I lose weight by knowing my BMR?

Do you know how many calories you burn every day? Knowing this can help you if you’re trying to reduce your body weight or maintain it. There are simple ways to estimate your energy balance that will help you learn 3 things:

  1. How many calories your body burns at minimum
  2. The amount of calorie intake you need from food
  3. How exercise impacts calorie burn

This calculation is known as your basal metabolic rate (BMR). It accounts for about 60-70% of your daily energy expenditure, and is a measurement of how many calories your body needs to carry out basic functions (1).  

Once you know this number, you can use it to find out how many calories you should consume each day to reach either a positive or negative energy balance. To lose weight, you’ll need a negative energy balance. To gain weight or increase muscle, you’ll want a slightly positive energy balance.

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How to calculate your basal metabolic rate (BMR) for weight loss

The Harris-Benedict Equation is one equation often used to estimate basal metabolic rate. This accounts for weight, height, age, and gender, but not physical activity level. This equation is accurate within about 200 calories/day for women (2).

Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)

Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)

For example, a 30-year-old woman who weighs 160 lbs and is 5’6″ needs a minimum of about 1500 calories for basic body functions.

Remember, this number is an estimation, and does not take into account activity level or other circumstances that might affect your metabolism. This number alone does not give you the total number of calories you need to sustain every life.

Factoring in exercise

Now, once you’ve completed the step above and calculated your BMR, you can then factor in your activity level to give you a better idea of the calories you burn on an average day.

If you’re:

Sedentary and normally don’t exercise, or only minimally, multiply your BMR by 1.2.

Lightly active and you do things like walking or restorative yoga one to three days a week, multiply your BMR by 1.375.

Moderately active and you exercise vigorously three to five days a week, multiply your BMR by 1.55.

Very active and you engage in strenuous exercise six to seven days a week, multiply your BMR by 1.725.

Extra active and you have a very physical job, or engage in strenuous exercise almost every day of the week, multiply your BMR by 1.9.

The number you get after factoring in exercise is about how many calories you need on a daily basis to maintain your weight. And remember, this equation is accurate within about 200 calories per day.

This formula obviously doesn’t include every factor that affects metabolism. It would be more accurate if it included body composition, previous weight gain or loss, and other hormonal changes (3). 

Read: Stop Overexercising! Find the Best Workouts for Your Body Type

Should you always eat less than your BMR to lose weight?

The amount of calories you burn on a daily basis depends heavily on your basal metabolic rate, but there are a few things that affect this number, besides the amount of food you eat.

  • Exercise and other movements. Non-exercise movement and exercise accounts for about 15%-30% of total calories burned daily (4). The number of calories you burn in a day increases when you add exercise or other movement into the mix. This is because your body has to use more energy to move itself. The more strenuous the activity or the longer you exercise, the more calories you’ll burn. For example, walking burns about twice as many calories as sitting, and running can burn up to five times as many calories.
  • Lean muscle mass. The more muscle you have, the higher your BMR will be. This is because muscle tissue is more metabolically active than fat tissue. So, if you have a lot of muscle and not much fat, you’ll burn more calories at rest than someone with the same weight but less muscle.

Watch: What’s Your Weight Loss Type?

Build muscle to increase your BMR

Building muscle is one of the best ways to increase your metabolic rate and actually keep it high. This will give you the long-term weight loss results you’re looking for, while also providing a strong, toned physique.

Instead of eating fewer calories to reduce body fat, you can add muscle for the best of both worlds—a healthier body composition without reducing caloric intake!

It’s recommended to eat about 15% above your BMR to increase muscle synthesis, which is the building of lean body mass in your body. Fifteen percent might sound like a lot, so let’s look at our example participant mentioned above. For someone whose BMR is about 1500, and who is lightly active (+500 calories), eating 15% above the BMR would only be about 300 extra calories per day. 

Adding extra calories in the form of protein is the best way to achieve this goal. This looks like:

  • Greek yogurt or cottage cheese with crackers and fruit
  • 1 egg and 2 egg whites with cheese and cooked asparagus
  • 1 protein shake with at least 20 grams of protein, and a spoonful of nut butter

Building muscle is the best way to increase your metabolism, burn fat, and lose weight in the long term.

Related: How Much Protein Do Women Really Need?

Other considerations that affect your BMR

If there’s one thing to remember about calculating your metabolic rate, it’s that these numbers don’t take into account you as an individual. Your metabolic function is completely unique, and changes based upon many factors.

  • Thyroid. If you have an underactive thyroid (hypothyroidism), your BMR will be lower than someone with a healthy thyroid. This is because your thyroid gland regulates metabolism. If it’s not functioning properly, your metabolic rate will be slower.
  • Sleep. Getting enough sleep is critical for many body functions, including metabolism. When you don’t get enough sleep, your body doesn’t function as efficiently, and this can lead to a lower BMR and increased body fat percentage.
  • Stress. Chronic or unresolved stress affects adrenal function. The adrenal glands produce hormones like cortisol and adrenaline, which affect how your body uses energy. When adrenal function is impaired, it’s difficult to lose weight and maintain a healthy weight.
  • Hormones. Hormonal imbalances (like PCOS or menopause) can make it difficult to lose weight. This is because hormones play a big role in regulating metabolism and hunger cues.
  • Genetics. Age. A young person’s BMR is going to be higher than an older person’s, because they have more growing and developing to do. Once you reach your adult height and weight, your BMR starts to slowly decline.

Listen: Gain Muscle & Lose Fat After 40 with Stephen Perrine and Heidi Skolnik

Now that you know all this important information about basal metabolic rate, how can you use it to lose weight?

There are a few things to keep in mind. First, remember that your BMR is only an estimate. If you want to be more precise, you can get a BMR or RMR test done by a physician.

Second, don’t forget that other factors like sleep, stress, and hormones also affect your metabolism. And finally, remember that muscle is metabolically active tissue. The more muscle you have, the higher your BMR will be. Eating under your BMR is a great way to lose weight, as long as you do it in a healthy way.