How To Use BMR To Hack Your Diet

This article originally appeared on the InBody blog and is reposted here with permission. To view the original, click here.

When people decide they want to get into shape, the first thing they typically do is sign up for a gym.  They start off with great excitement, vowing to hit the treadmill or weight room every day.  They keep this up for a couple of weeks, but when the changes don’t come, the enthusiasm wanes.  Every day becomes 3 times a week.  3 times a week becomes “I’ll go when I have time.”  Before they know it, they’ve given up.

Sound familiar?

The reasons for giving up a fitness program are many, and not seeing results fast enough is one of the most common reasons to quit.  However, in many cases, people forget one extremely important foundation for their program: their diet.


Perhaps you’ve heard the expression “six-pack abs are made in the kitchen.”  It’s true.  You can train as hard as you want in the gym, but you cannot out-train a bad diet.  Regardless if your goal is to gain muscle or lose fat, if you’re not optimizing your diet to reach those goals, you’re setting yourself up for failure.

So how do you optimize a diet?  There are many factors that go into planning a diet, such as the type of nutrients consumed, frequency of meals, and the selective use of fasting to name a few.  But a great place to start at the outset of any dietary plan is to determine how many calories your body needs a day.  And it all starts with your Basal Metabolic Rate or BMR.


If you live in the United States (or even if you don’t), you’re probably familiar with the 2000-calorie diet.  This is a calorie range set by the U.S. Food and Drug Administration (FDA) in 1993 for use on nutrition labels for packaged food.


However, even in the 1990s, this was several hundred calories below what the actual average calorie consumption was at the time, and the 2000-calorie figure was chosen in part due to the fact that it was a nice, round number (really) and easy for consumers to remember.  Unfortunately, your caloric needs are probably not equal to 2000.

So what are your actual caloric needs?  A good way to determine that is to start by determining your Basal Metabolic Rate (BMR).  This is the number of calories your body needs each day to perform its basic, life-sustaining functions.  This includes all the involuntary processes in your body such as breathing, digesting food, pumping blood, brain activity, and much more.

To find your BMR, there is no shortage of online resources and apps that will provide your BMR.  Certain medical/fitness devices also provide BMR as an output during body composition analysis. However, there are a few things you should know about how BMR is calculated before diving into the first option you find.

Your caloric needs can be calculated in a couple of different ways and with a few different equations, including the revised Harris-Benedict formula and the Mifflin-St. Jeor equation.  These equations calculate BMR using your body weight, with some adjustments for age and gender.  However, if you fall outside average assumptions for age and gender (if you’re an athlete, for example), these equations may not accurately produce your BMR.

For people who do fall outside the assumed ranges for age/gender, there is a third option. Because BMR is strongly associated with the amount of Lean Body Mass you have, it can be useful to use your Lean Body Mass to determine your BMR.  This is what the J.J. Cunningham equation will do.  Measuring your BMR using this equation has a couple of benefits:

  • It won’t give you results that have been influenced by estimations derived from the typical representative member of your age and gender
  • As you increase LBM by developing your Skeletal Muscle Mass, your caloric needs will increase, and the Cunningham equation will account for this.

Once you have your BMR in hand, you’re ready for the next step.


Remember, your BMR is just the number of calories your body needs at rest and does not account for the calories you need to walk, talk, exercise, etc.  When thinking about your caloric needs for the purposes of planning a diet, you’ll need to convert your BMR to your Total Daily Energy Expenditure (TDEE).   You can do this by multiplying your BMR by a factor that represents your estimated energy level.  Those conversions are:

sedentary lifestyle

So, let’s take the example of a 171.1-pound male with 133.6 pounds of Lean Body Mass and assume he is moderately active.  Using the Cunningham equation, this person would have a BMR of around 1679 Cal/day. Multiply that by the appropriate conversion, and you get 2602.45.  This is how many calories this person needs to maintain his weight.

When trying to improve your body composition and health, instead of thinking about simply gaining weight, you must think about reducing Fat Mass and gaining Lean Body Mass.  It’s very hard, verging on impossible, to do both at the same time.  That’s why in order to change your body composition, you don’t have one goal; you have two.

This also means that your diet must also match what your current goal is – losing Fat Mass or gaining LBM.  This is incredibly important. People who don’t do this often end up sabotaging their fitness goals by setting exercise and diet plans that are at odds with each other.

The most classic example is this: “I want to get in shape, so I am going to go on a diet (eat less) and work out more (increase energy use).”

This isn’t a bad plan – but only if you’re looking to lose fat. If you’re looking to build muscle and get stronger, it’s very unlikely that you will achieve this by eating less than your TDEE while increasing your energy level beyond what your body is accustomed to.

Now we’re getting to the meat of your fitness plan – optimizing your diet using your BMR as a guide.


fat loss

There is a lot that goes into any diet, and it can get complicated pretty quickly. From a dietary standpoint, you can count on one thing: if you want to lose fat, you need to run a caloric deficit.  That means you need to take in fewer calories.  If you’ve found your BMR and converted it to TDEE, you know what your body requires in a day to stay the same.  That’s your starting point.  You need to consistently consume less than your TDEE if you want to lose weight.

How many calories do you need to take out of your diet in order to lose weight? Theoretically, any amount that is less than your normal TDEE can cause you to lose weight; it just depends on how quickly you want to see results.

A lot of resources will tell you that you need to subtract 500 calories out of your diet in order to lose one pound of fat per week. This is based on the premise that one pound of fat represents 3,500 calories, and that by reducing your caloric intake by 500 over 7 days, you’ll reach a weekly loss of 3,500 calories or a pound of fat.  You may have heard this rule mentioned before.

However, hard-and-fast “rules” like these are tricky because although they’re usually based in fact (caloric reduction does lead to fat loss), this doesn’t mean they are advisable, recommended, or safe for everyone.  Someone with a TDEE of around 2,600 calories might not have any problems dropping to 2,100, but someone whose TDEE is 1,400 will probably have significant difficulties living a normal life and exercising while consuming 900 calories a day for any length of time.

The safest way to handle a caloric reduction is to reduce your intake by something marginal – 200 or 300 calories a day, for example – and be consistent with this for a week or two.  After a week, weigh yourself, or better yet, have your body composition analyzed to ensure you aren’t losing Lean Body Mass.  If you see your Fat Mass numbers begin to drop, you can see by how much and adjust your caloric needs accordingly.

How can you cut calories safely?  The first thing to do would be to cut any unnecessary high-calorie snacks and treats in your diet – soda, chips, chocolate, alcohol, etc.  Depending on how much of these existed in your diet before, this simple step might be enough to cause you to lose weight without making any other changes!

But what if you were already eating clean before?  Where do you cut calories on a clean diet?  If you’re in this situation, you need to make sure that you are cutting calories from nutrient sources that you can afford to cut from.  This is why a properly balanced nutritional plan, in conjunction with the right amount of calories, is so important.  One nutrient group you should be careful to not cut too much from (if at all) is protein.

Why would protein be an important nutrient to consider when losing fat?  Because as you lose weight, if you are not meeting your protein needs, you may actually be losing Lean Body Mass in addition to your Fat Mass, and you want to retain as much Lean Body Mass as you can at all costs.

One way to do this from a dietary standpoint is to consume foods that are low in calories but high in protein content.  Here are a couple of foods to consider:

With proper caloric restriction, nutrition, and exercise, you’ll start to shed off the fat while hopefully retaining as much muscle as possible.


obesity analysis

If your goal is to build Lean Body Mass, then your caloric needs and dietary goals are going to be different than if your goal is to reduce Fat Mass.  While some aspects of your diet, such as eating cleanly and avoiding unnecessary calories will be consistent with the Fat Mass diet described above, the major difference between the two diets is instead of consuming fewer calories than you need, you need to exceed your daily caloric needs.  Additionally, strength training is going to be much more important – it’s not like you can just eat your way to Lean Body Mass gains!

As before, start with your BMR and convert it to TDEE by multiplying it with the factor that best reflects your current exercise level.  For the sake of consistency, we will use the same BMR in the previous example (1679 Cal/day) and exercise factor (x1.55) to produce a TDEE of 2602.45. This is the number that must be exceeded in order to have enough energy to produce the desired results.

How much should you increase your energy intake by in order to gain Lean Body Mass? According to research, you need to consume approximately 15% more calories per day than what is required to maintain your body weight (that’s the TDEE).  So in this example, this individual should look to increase their caloric intake to about 2992.3 calories which, for convenience’s sake, could be safely rounded off to an even 3000 Calories/day.

How should you be adding these extra calories in your diet?  The study cited above suggests that to maximize Lean Body Mass gain while minimizing Fat Mass gain, the increase in calories should be made up of both protein-rich foods and carbohydrates.

However, a word of caution about protein.  Before you conclude that you’ll just increase your diet with nothing but protein, consider this: there is a point which adding more protein to your diet won’t have any measurable increase in Lean Body Mass gain.  In a 2006 study of collegiate level athletes, no benefit in muscle or strength gain came from protein consumption that exceeded .09 g of protein per pound of body weight.

While protein is important, calorie intake is arguably more so.  In the article cited above, the athletes consumed their required protein amount but failed to consume the total amount of calories appropriate for their fitness level, which led the authors to comment (emphasis added):

The low energy intakes observed in this study confirm previous reports that have shown that collegiate athletes generally do not meet their nutritional needs, specifically as it relates to energy intake. Caloric intakes of strength/power athletes should exceed 44 – 50 kcal·kgBM·day-1, however, the caloric intakes reported in this study (33.0 ± 5.5 kcal·kgBM·day-1) were below these recommended levels and likely impacted the ability of these subjects to make significant gains in lean tissue accruement.

Bottom line: you need to exceed the number of calories you require each day if you are designing a diet to gain Lean Body Mass.


healthy eating

As with any dietary plan, you will expect to see changes over time.  All this hard work has to produce results, right?  So, how long will it take to see results?  Unfortunately, that is going to vary for each individual.  A good rule of thumb is to weigh yourself every 1 – 2 weeks.  If you are looking for a more precise analysis, you should get your body composition measured as well.

There is another important factor to consider: because your BMR is closely linked with your amount of Lean Body Mass, any increase/decrease in Lean Body Mass will affect your total energy needs and diet.

For example, if your plan is to gain Lean Body Mass, and over a period of time you are successful in doing so, your energy needs are going to increase.  This is why it is so important to be measuring body composition.

Conversely, if you lose some Lean Body Mass as a result of going on a strict caloric deficit, your BMR will lower – resulting in less energy needed per day.  If you end up losing too much Lean Body Mass but don’t take that change into account when designing your diet, you might be taking in more calories than you actually need, which could sabotage your goals.

Finally, it bears mentioning again that there is much more to planning a diet than just counting calories, which is what your BMR will help you to do.

That being said, knowing your BMR will help you significantly with planning any diet.  You must know how much energy your body needs because, without this information, you won’t be able to know how much you need to add or remove from your diet in order to achieve your goals.  With this information, you’ll be able to see results quicker and reach your goals faster.

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