I had a question today from an athlete who wanted to get an RMR (Resting Metabolic Rate) test. The idea behind the test would be to see how many Calories you burn in a day at rest so that you can add on the Calories you burn when exercising and figure out the number you need to take in to either lose weight, gain weight or maintain weight. Having administered these tests before, I have to say that in my opinion, the value of an RMR test is close to nothing, at least for the typical reasons why an athlete might want one.

Let's start with some facts:

- A calorie is a unit of energy. In fact, when you see food labels in most other countries they list "Energy" rather than "Calories". It's interesting that there is such a different connotation in the U.S. I wonder what would happen if Red Bull and Monster called their products "Calorie Drinks"? The other thing that I laugh about is when you see "Zero Calorie Energy Drinks". Maybe I am the only one that gets upset about this but YOU CAN'T HAVE A ZERO CALORIE ENERGY DRINK!!! CALORIES ARE UNITS OF ENERGY!!! And if you are about to say that the energy comes from caffeine, caffeine is a stimulant, not a source of energy.

- One calorie (small c) is the amount of energy required to raise the temperature of 1 cubic centimeter (or milliliter) or water 1 degree Celsius. That's not a whole lot of energy, so normally we talk about kCal (1000 calories) or Calories (with a capital C). This is what you see on food labels.

- There are 3 main sources of energy in our diet: Carbohydrates (CHO for short), Protein and Fat. These are called macro-nutrients. By contrast, micro-nutrients are things like Calcium, Zinc, Sodium and Vitamin A.

- For all of the crazy diets out there, weight loss is very simple. If you burn more energy than you take in, you lose weight. Simple math. Sure, if you actually want to feel good and get the right nutrients, it does get a little more complicated. But if we are just talking about weight, all that matters is energy in vs energy out.

If you take in more energy than you burn, your body will store this extra energy as body fat. Take a second and try to remove the negative connotations you probably have from the words "Calories" and "Fat". Think of your body as a high performance machine, like a race car. (Since I used to work in the automotive industry, I like my car metaphors) If you are designing a race car, it needs to have a gas tank to store fuel (it's energy source). If you make the tank too small, you have to pull into the pits too often. If you make it too big, the extra weight will slow you down. So it's about optimizing the amount of fuel that you carry with you to suit your purposes. It's also about using the most efficient form of fuel. For humans, this is fat. 3500 kCal are stored in 1 pound of fat, so even the leanest people have enough fat to last a while (150 lb cyclist with body fat would have 7.5 lbs of stored fat = 26,250 kCal)

This may be obvious, but the downside of carrying extra fat around, at least from a performance standpoint, is that we have to produce more power to go the same speed do the added gravitational resistance caused by extra weight. Losing 5 lbs could might mean that it takes 10 watts less to get up that climb and that might be the difference between a sustainable power output and completely red-lined. So it's natural that we would want lose all the extra fat that we can lose before it affects our performance, right? Of course, there is no simple way to figure out what our optimal weight is. If you lose too much weight you could feel hungry all the time, compromise your immune system, lose muscle mass, disrupt your menstrual cycle and many other very bad things. It can be dangerous to base your goals off of others because while one athlete may be optimal at 25% body fat another may be optimal at 5%. You have to figure out what works for you. Personally, I figured out my ideal race weight from trial and error. I lost weight slowly until I just didn't feel right (it was pretty obvious). I added a few pounds to that weight and found a weight that was reasonable for me. It's not very scientific but it works. Of course, actually getting to my race weight is another matter...

OK, so let's say now that you have your goal weight and you have your current weight. You don't want to lose that weight too fast because it will screw up your metabolism and deprive you of energy that you will need to do your workouts. And if you are missing workouts because you are trying to lose weight, it's not really helping your performance now, is it? Rule of thumb is to aim for 1/2 to 1 pound of weight loss per week. So if 1 lb fat = 3500 kCal, a discrepancy of 3500 kCal/week = 500 kCal/day (meaning that if you want to lose 1 pound/week you have to burn 500 kCal/day on average more than you take in). If you are shooting for the more moderate 1/2 pound/week goal, that would come out to 250 kCal/day discrepancy. To get to either of those numbers you have 2 basic choices. Burn more or take in less. However, I would assume that most of you already have optimized your training volume to account for your availability, recovery rate, weather and daylight so adding a lot of extra volume probably isn't a good option. Sure, if you could easily add 30 minutes/day to your training without adversely affecting your recovery, being late for work, losing sleep or freezing your ass off, do it. Personally I think it's easier to just have a smaller piece of pie for dessert.

An RMR test is very simple: sit down and breath through a tube for 10-15 minutes

So now we are back to the initial question of how many Calories do I need to take in, and you can see where an RMR test might help you answer that question. Here's the problem: an RMR test tells you how many Calories you burn at rest but you aren't resting all day now are you? You have to factor in training as well as the rest of your daily activities. If you have a good idea of how many Calories you burn at a given heart rate, you can come up with a decent approximation of how many Calories you burned in your workout. The only problem there is that your volume and intensity varies from day to day. And then you have to factor in the Calories you burn the rest of the day, which varies greatly from person to person. If you are a landscaper or a construction worker you obviously burn a lot more than someone that sits in front of a computer all day. But it's not always that simple. You might walk around a lot on certain days, you might take your dog to the park every morning for 30 minutes and you might drink an extra cup of coffee some days (thereby raising your metabolism). Additionally, certain types of workouts (e.g. strength training, climbing, over-gears) will cause your metabolism to be elevated for longer after the workout than others. It gets complicated fast and even if you do manage to come up with a number, it probably has a large margin of error.

The truth is, the actual number of Calories doesn't really matter. All that matters is the balance between input and output. To get that balance you don't need to calculate how many Calories you burn or even how may you take in. All you need is a scale. Measure your body weight every day and after a while you will get a sense of how much weight you are losing or gaining (if either). That said, I do have a couple recommendations:

- Measure your weight at the same time every day, preferably at a time when your hydration levels will be relatively consistent. For most people this is either first thing in the morning or the first thing in the afternoon when they get home from work or school (but before they train). Always urinate before weighing yourself.

- Write down the number you get every day and record in a spreadsheet. Don't even bother trying to interpret anything from the data until you have at least 7 days straight. At that point, use a 7 day rolling average. Body weight often fluctuates as much as 2-3 pounds per day, depending mostly on hydration. Using a 7 day rolling average will help smooth things out. If you see that the 7-day rolling average of your weight today is 1 pound less than the 7-day rolling average for your weight last week, you can be fairly certain that you have actually lost 1 pound.

Tanita body fat monitors won't give you a very accurate number, but they can help make sense of day to day weight fluctuations due to hydration

- Some companies (e.g. Tanita) make relatively low-cost scales that are accurate to 1/10th of a pound and estimate body fat % as well. I wouldn't make too much out of the actual number, but it is a good way to account for hydration fluctuations, since body fat will read lower if you are better hydrated. This is valuable not only to account for weight fluctuations, but to tell you when you really need to make more of an effort to drink more.

If you are morbidly obese you should probably try to lose weight as quickly as possible by any means necessary but for an athlete it's just not smart or safe.

If you start to see that you are losing more than 1 pound/week it can be tempting celebrate. But this should be a warning that you need to increase your intake or decrease your training. Ignore what you see on "The Biggest Loser". You are an athlete and you have to remember that your goal is to perform better. Losing weight too fast will catch up to you and it won't be long before your performance is compromised one way or another.

Lastly, if you really really must know how many Calories you are burning, I think it's easier to count the Calories you take in than to figure out how many you burn. It still can be painstaking, but if you are only doing it for a week it is manageable. (Most nutritionists will want you to do something like this anyway so they can give you the best advice on how to modify your diet). Make sure that you continue to record body weight every day during this time. (Many people find that they consume less when they have to write down everything the eat because there is a sense of accountability). If you know exactly how many Calories you consumed last week and you know exactly how much your weight changed, it's simple addition/subtraction to calculate Calories burned. Boom. Done.