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BMR Calculator: What is it and What does it do?

The simple processes of staying alive carry and energy demand. Breathing, digesting, circulation, and cell production all require calories in order to function. These basic processes make up what is called your basal metabolic rate, or BMR. How we arrive at a number that represents our BMR requires a BMR calculator. 

Knowing and understanding your BMR becomes important when you want to, or need to, gain or lose weight. A BMR calculator can give you a baseline number of calories you burn so you can then determine how many calories to consume or not consume. A BMR calculator is important for how you would set fitness and diet goals. 

Put simply, a BMR calculator takes all the basic functions that have a caloric demand and provides a basic figure for how to assess your dietary and exercise needs. If you know what your body uses just to stay alive, you can get the most accurate sense of how many calories you need to manage in the form of a diet. 

BMR calculators are not fads for making the best of a crash diet or gimmick exercise program. A BMR calculator offers you a scientific understanding of how your physiology functions. It gives you an accurate picture of your metabolic rate. With a solid BMR calculator, you can determine a weight management program that is best for your health and overall fitness goals. 

What Is Your Basal Metabolic Rate?

You burn a significant number of calories in a day without being aware of it. Talking on the phone, sitting at your computer-- even just sitting on the couch watching television—all of these things burn calories. Keeping your heart beating, breathing, digesting food all require calories in order to make these physiological processes happen. These are the basic functions that keep you alive, and the rate at which you burn calories in order to sustain these functions is your basal metabolic rate. 

BMR is what we mean when we talk about our metabolism. Metabolic rates vary from one person to another and they are quite different for men and women. The BMR for women must take into account things like reproductive functions. This means a woman’s BMR is necessarily higher than a man. What is more, depending on how we manipulate our caloric intake, we can alter, slow down, or speed up our BMR. Because BMR is not a constant for all people under all conditions, it becomes necessary to calculate your own BMR with a BMR calculator. 

To get an accurate assessment of how many calories you burn in a normal day so you can determine how to lose or gain weight demands that you understand your BMR as a baseline factor. For example, if you feel you need or want to shed about 10 pounds over a period of time, you will want to limit the number of calories you consume relative to your level of activity. You need a net loss of calories. If you are already burning a specific number of calories as a function of your BMR, you need only to add up the additional calories necessary to come up with a net weight loss. 

How Does BMR work?

To lose weight, you need to eat fewer calories than you burn. This is elemental to weight loss. For example, if you want to lose a pound a week, you need to reduce your intake to about 500 calories. To determine your caloric need, you will need to account for things like your activity level, the thermic effect of food, and your BMR. All of these numbers will provide an accurate picture of how many calories you need to remain healthy. 

To get a sense of how many calories you require you will need to calculate your BMR by what is called an activity factor. If you exercise or are otherwise fairly active, you can calculate your activity factor. Activity factors can be determined with charts that plot how much your exercise. If you live a sedentary lifestyle your activity factor is 1.2. An activity factor for someone who exercises one to three days a week is 1.375. This number increases the more you exercise.

How BMR works is as a baseline factor for setting a healthy weight loss goal. If you adjust your diet based solely on caloric intake, you could reduce your calorie intake below the level of your BMR. This would lead to health problems. If you do not properly adjust your diet to include your BMR, you may also achieve nothing since you will not approach the level of calories you already burn. 

What is my BMR?

As we have already pointed out, BMR is not a constant. It will vary widely among individuals. In order to use BMR as a safe metric for weight management, diet, and exercise, you need to calculate a BMR that is specific to you. This calls for some simple math. 

To calculate your own BMR you will use what called the Harris-Benedict formula. This takes into account your body weight, height, age, and sex. Your sex is a crucial piece of information for BMR because women and men require different caloric loads to sustain basic body functions. 

The Harris-Benedict formula is based on total body weight, height, age, and sex and is, therefore, more accurate than the "quick and easy" formula used above.

  • Men: BMR = 66 + (13.7 x wt in kg) + (5 x ht in cm) - (6.8 x age in years) 
  • Women: BMR = 655 + (9.6 x wt in kg) + (1.8 x ht in cm) - (4.7 x age in years) *note: 1 inch = 2.54 cm and 1 kilogram = 2.2 lbs. 

Example: You are a 30 year old female. You are 5'6" tall (167.6 cm) and weigh 120 pounds (54.5 kg). Your BMR = 655 + 523 + 302 - 141 = 1339 calories/day.

The final part of the equation for losing or gaining weight is to determine your Total Daily Energy Expenditure (TDEE). TDEE is the number of calories you burn during the course of your normal daily activities. TDEE can vary widely even among athletes and people with a similar BMR. Our bodies have different caloric requirements based on genetically determined metabolic rates. Some of us are simply born with a higher or lower metabolic rate. 

To arrive at a formula by which you can set diet goals, you multiply your BMR by your TDEE. This gives you the number of calories you need to maintain your health and your lifestyle. 

Once you have your BMR using the Harris-Benedict formula, you can then estimate the number of calories you burn on an average day by multiplying BMR by TDEE. This will depend on your lifestyle:

  • Sedentary: If you do not exercise and get little activity you multiply by 1.2.
  • Slightly Active:  Exercise 1-3 days a week, multiply by 1.375. 
  • Moderately Active: You exercise 3-5 days a week, multiply by 1.55. 
  • Very Active: Serious exercise 6-7 days a week multiply by 1.725.
  • Extremely Active: Intense exercise 6-7 days a week and have a physically demanding job, multiply by 1.9

The number you get from this scale will be the number of calories you require in a day to simply maintain your current weight. To lose weight, subtract calories from your diet. 

This number is an estimate. Studies have shown that we get a more accurate picture if we include things like weight history, body composition, and other factors. 

BMR Versus RMR: What’s The Difference?

Basal Metabolic Rate (BMR) is sometimes mistaken for Resting Metabolic Rate (RMR). Resting metabolic rate is the rate at which you burn calories while your body is completely at rest. BMR is the minimum number of calories required to sustain basic bodily functions like breathing and blood flow. While these two numbers are close, they are not quite the same. You can estimate your BMR using your RMR, but to get an accurate estimate of your BMR, you will need to use the Harris-Benedict formula. 

Why BMR and TDEE Matter?

When formulating a plan to lose or gain weight, it is essential that you get a sensible estimate of your BMR. You need to make certain you are getting enough calories to sustain the basic functions of your body. Crash diets and other dangerous weight loss methods can cause serious physical damage if they drive you below your BMR. 

TDEE adds the number of calories you need to get through your day. Even if you live a sedentary lifestyle, you still require calories in order to keep live. If you are an active person, you will not be able to support the level of activity you are accustomed to if you do not pay attention to your TDEE. 

Taken together, BMR and TDEE make up the fundamental caloric intake you need to survive. Barring something severe, failing to properly account for BMR and TDEE and be counterproductive. 

If you do not properly sustain your caloric intake for a healthy BMR and TDEE, your metabolism may slow down. Several studies have shown that failing to eat the minimum number of calories can cause your metabolism to slow down by as much as 23 percent. This means that even as you cut calories, you may not lose weight because your body is no longer burning calories. It is essentially in survival mode and holding onto calories. 

Slowing down your metabolism can also result in muscle loss. A diet that cuts calories and is also low in protein will force your body to begin breaking down muscle to make up for the shortfall from fats. Any progress you make toward weight loss and building lean muscle will be negated if you do not properly account for BMR and TDEE in your diet and exercise schedules. 

Failing to properly account for BMR and TDEE can also result in fatigue and mineral loss. The caloric deficit will inevitably lead to vitamin and mineral deficiencies. This can lead to fatigue and anemia. A diet that is too low in carbs can also cause fatigue.  

What effectively happens when you do not take BMR and TDEE into account is your body thinks it is starving. You will not burn calories the way you should because your body holds onto them. Any calories you need to maintain BMR will come from somewhere, and if you have not properly fed yourself, those calories may come from muscle tissue. Finally, if you do not have enough calories to maintain a healthy BMR, you will get tired and unable to go through your normal day. Weight loss and fitness are important, but not at the expense of your health. 

Wrapping things up

As we can see, BMR is not just any number in a weight loss and diet plan. BMR constitutes the fundamental level of nutrients we need in order to stay healthy and alive. We are never aware of it, but the most basic functions like breathing, heartbeat, digestion, and organ functions require calories. We must provide a baseline level of calories just to stay alive. 

BMR is different that RMR because RMR is only a measure of the calories we need to go through a day while at rest. BMR is more precise. While it is possible to get a rough estimate of your BMR from your RMR, to get an accurate picture of your BMR you will need to use the formulas detailed above. 

Once you determine your BMR with a BMR calculator, you will then need to figure out how many calories you burn in support of your lifestyle. Even a sedentary lifestyle requires calories. Being a couch potato does in fact demand calories. But if you are an active person, your daily caloric needs will increase. This amounts to your total daily energy expenditure or TDEE. 

 By taking account of your BMR and TDEE, you will be able to set weight management and healthy fitness goals. You will be able to make allowance for your own specific metabolism and daily activity. This will make it possible to lose or gain weight while maintaining optimum health. 

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