BMR, BMI, TDEE and Other TLAs

Huh? What? What’s with all the TLAs (Three Letter Acronyms)? Ok, TDEE is technically a four letter acronym, but whatever.

One of the questions we all wonder when we are thinking about losing weight is “How much should I be eating each day?”. The only proven way to lose weight (more properly lose fat) is to reduce the amount of calories consumed in proportion to the amount of calories burned. The FDA’s report “Calories Count: Report of the Working Group on Obesity” (http://www.cfsan.fda.gov/~dms/owg-toc.html) states:

Fundamentally, obesity represents an imbalance between energy intake (e.g., calorie intake) and energy output (expended both as physical activity and metabolic activity; see text box on Calorie (Energy) Balance at Appendix B). Although there is much discussion about (1) the appropriate makeup of the diet in terms of relative proportions of macronutrients (fats [lipids], carbohydrates, and protein) that provide calories and (2) the foods that provide these macronutrients, for maintenance of a healthy body weight it is the consumption and expenditure of calories that is most important. In other words, “calories count.”

No matter what we might see on a late night infomercial or read on the Internet, this fundamental truth is the foundation of healthy eating and fat loss. There is no magic diet or device that can breach this scientific bulwark. When a diet claims that you will lose weight by eating this or that, or taking this supplement, I’ll bet that if you research the eating plan carefully, you will see that in fact, there is a significant reduction in calorie intake. It is the reduction in calorie intake (vs. calorie expenditure) that causes the fat loss. As the report states, the most important factor in realizing weight loss is calorie control, not the manipulation of macronutrients (e.g. a high protein, low carb diet). Low carb diets work because overall calorie consumption is reduced, not primarily because carbs are restricted.

That said, how can we determine what amount of calories to eat to meet our goals? Actually, the concept is quite simple and just takes a little calculation. To determine how much to eat each day we need to determine how many calories we are burning. We do that by calculating 2 numbers: our BMR and our TDEE. Don’t worry, it isn’t hard.

BMR stands for Basal Metabolic Rate and it represents the number of calories burned in a day if we were asleep or in a coma as it were. It is the amount of energy used by the body to sustain life. This number is the basis for finding out how many calories we burn each day and it accounts for 60 – 70% of total calories burned. It also represents another important concept: the least amount of calories we should consume in a day. If we consistently consume much lower calories than our current BMR, we run the risk of triggering a “starvation response” in our body and effectively lowering our metabolic rate. This makes it more difficult to lose weight and keep it off in the long run.

The next important acronym is TDEE: Total Daily Energy Expenditure. This is your BMR plus the amount of calories burned through activity such as work, chores and exercise. You determine TDEE by applying a factor to your BMR dependent on your activity level. TDEE also represents that amount of calories you should consume to maintain your current body weight. Your BMR will change as you lose weight – it will reduce along with your weight. For example, a 30 year old male who is 6 feet tall and 200 pounds has a BMR of about 2022 calories. If that man loses 40 pounds for a new weight of about 160 pounds, his BMR will be about 1773. That’s almost 250 calories difference per day.

OK, I am going to share the formula for calculating BMR and TDEE but first I’ll share an easier way to do all the number crunching. You can visit my website where I have an easy to use calculator that will handle all of the heavy lifting for you! Here are the links:

BMR Calculator (Harris-Benedict)

So, how many calories should you eat in a day to lose fat? A pound of fat is equal to about 3500 calories. Therefore to lose a pound of fat in one week, a caloric deficit of 500 calories per day would be about right. Well, if 500 calories per day equals 1 pound per week, then consuming 1500 calories less per day is better because that equals 3 pounds, right? NO! NO! NO! To lose fat AND keep it off, it is important to make sure we don’t trigger a starvation response in our body (and cause our metabolism to slow down). In addition, unless you have a large amount of fat weight to lose, if you are losing 3 pounds per week, some of that weight is likely coming from lean body mass (muscle). This is not good. Muscle loss results in a metabolism slowdown. Each pound of muscle burns about 30 – 50 calories per day.  You want to lose fat and keep your lean body mass intact.

So here are some guidelines:

• Never eat less than your current BMR
• Eat 500 – 750 calories less than your TDEE or
• Eat 15% – 20% less than your TDEE (a moderate reduction in calories)

Another good rule of thumb may be to eat what you will eat when you are at your target weight. Simply enter your target weight into the calculator and view the calories for your target activity level. If you eat this amount now, eventually you will level off at your target weight. And here’s the best part – you will never be on a diet! You will simply change your lifestyle to that of someone at your target weight. If you do that, you will not only lose the fat, but you will KEEP it off. Of course, to lose the last few pounds it is likely that you will want to dip below your TDEE at your target weight for a while, but you’ll ease back up to your maintenance level after you meet your goal.

Alright, here is the formula for men:
BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) – (6.8 X age in years)

And for women:
BMR = 655 + (9.6 X wt in kg) + (1.8 X ht in cm) – (4.7 X age in years)

Keep in mind that these calculations are approximations. If you are eating with a 500 calorie deficit (and you are correctly logging your calorie count and correctly estimating your activity level), but are not losing weight after 2 or 3 weeks, try reducing the calories or better, increasing your activity level. If you still can’t seem to lose the pounds, check back with your doctor (you did check with your doctor before starting a weight loss program, right? If not, stop everything and do so now…). You may have a medical condition that may need attention in order to reach your goals.

I know this post is longer than usual, but hopefully you found it useful. I will be posting recipes in the near future and will be talking about ways to jump start your metabolisim by changing when you eat and perhaps even by eating more than usual!

Have a great day!