PT on the Net Research

Metabolism - Part 1

It is a know fact that up to 95% of health club members join for one single reason: Aesthetics. Translated into "trainer" language- this means losing body fat and gaining muscle tissue. The drive is on to look like a cast member from friends, or the latest Calvin Klein underwear model. We have to face it- vanity is what gets the member in the door of the facility. From there, if you win their trust by designing a program that truly meets their "wants", you may have the chance to work on the client "needs".

Weight Loss is now a $100 billion industry in the United States. Recent statistics from the North American Society for the Study on Obesity (NASSO) convention yielded some staggering statistics:

What does this mean for fitness professionals? Well firstly, that a client "wants" to lose a few pounds may actually be a medical "need", and that given the growth of the obese population (literally) we are presented with an incredible opportunity to be part of a solution to this epidemic.

Trainers are often posed with the question of weight loss, and many have an almost existential philosophy on nutrition and "diet". Counting calories is a common practice among our clients looking to lose weight, but keeping count of calories "in" is only half of the equation. Understanding metabolism is the other half.


Metabolism, put simply, "is the biochemical process of combining nutrients with oxygen to release the ENERGY needed to function." (Alexander, H. 2000) Metabolism (energy expended) is measured in the same format as energy ingested- "calories" (or Kilocalories for you die-hards).

OK- Simply- again- our metabolism represents our bodies caloric "burn-rate".

Again, to keep things simple, we will break caloric expenditure down into two main parts:

  1. Resting Metabolic Rate- The calories the body burns to sustain vital body functions such as brain activity, heart rate and breathing. For the sake of simplicity, we will also categorize the thermogenisis of food into this part. This rate is ultimately determined by a person’s activity level (see below).
  2. Lifestyle Metabolism – The calories expended between bed rest-that includes occupational activity and daily living activities. We could separate out, but this basically includes all other activity above basic life functions, including those calories expended during purposeful exercise.

Many professionals engaged in the practice of metabolic manipulation may even break these parts down even further, however, for our immediate understanding, lets keep metabolism as calories burned consciously, and unconsciously.

Physiology 101

OK- remembering exercise physiology 101, you may even recall the weighting of the metabolic component parts:

RMR = 60- 75% of Total Caloric Expenditure

Lifestyle Metabolism = Up to 25% of Total Caloric Expenditure

The exact percentage breakdown between RMR and Lifestyle Metabolism is determined by the person’s activity level.

Here’s an example of how it works. A highly active individual may have a caloric expenditure of 2500 calories per day. A minimum 60% of these calories will be devoted to RMR (some 1600 plus calories). Your average "couch potato", due to body mass factors, may also have the same caloric output (2500 calories) but upwards of 75% of these calories may be required for RMR (Some 1875 calories). Therefore, in understanding and programming to manipulate Metabolism, we must first learn how to measure and assess caloric needs.

Creating a Metabolic Profile

Creating a metabolic profile for your clients is a critical first step- if their goal is to either gain or lose weight. As the majority of clients are looking to "shed" those extra pounds- our examples will focus on weight loss.

As stated, there are two broad component parts to metabolism. Assessing these is not a simple task

Assessing RMR

76% of Dieticians surveyed at the 2000 American Dietetic Association’s Annual convention stated that they estimate caloric needs based upon a formula. The most common formula is called the Harris- Benedict Equation. The formula, which estimates Resting Metabolic Rate (RMR), does so by measuring an individuals height, weight, age and gender.

Based upon a landmark study performed in 1919 on some 250 adults, mostly men, the Harris Benedict equation has been the most widely used formula to date. Recent studies, however, like the one performed by Gary Foster, PhD at the University of Philadelphia in 2000, show that this formula, while accurate sometimes, can "overestimate" caloric needs by up to 1000 calories.

Foster, in groundbreaking research of his own determined through a study of 80 overweight women, comparing predicted RMR using the Harris Benedict formula, against the process known as indirect calorimetry. Of the trial group, 5 women with almost identical heights and weights showed variance of up to 1000 Calories per day. Dietary prescription using the formula, Foster determined, is flawed.

Several other important studies have shown that the Harris Benedict Equation tends to overestimate RMR by 10-15%, especially among women and individuals with a lower lean body mass. (Nutrition in Clinical Practice 11:99-103, June 1996).

The Harris-Benedict Equation:

Males: 66 + (13.7 x W) + (5 x H) - (6.8 x A)
Females: 655 + (9.6 x W) + (1.7 x H) - (4.7 x A)

where W = actual weight in kg (weight in lb/2.2 lb/ kg)
H = height in cm (height in inches x 2.54 cm/in)
A = age in years

Ex. Joe weighs 150 lbs, stands 5'6", and is 21 years old

150 lbs/2.2 lb/kg = 68 kg
5'6" = 66 inches x 2.54 cm = 168 cm

RMR = 66 + (13.7 x 68) + (5 x 168) - (6.8 x 21)
= 66 + 932 + 840 - 143 = 1695 kcals per day (Estimated)

Why the flaws in the Harris Benedict equation? Well, one of the main reasons is that the study was completed in 1919 at a time when lifestyle was drastically different than it is today. There was a greater prevalence of lean mass associated with overall weight due to the sociological impact of "work". Most work was industrial or agricultural in nature, and very physically active. Today, lifestyle and composition of weight have changed substantially. This "negative evolution" is one of the reasons we have an obesity problem to begin with.

Indirect Calorimetry

Indirect calorimetry, performed through the use of a Metabolic Cart or one of the new hand-held calorimeters on the market present the best option for getting accurate RMR measurements. These products are becoming readily available in the fitness industry and will play a vital part in the weight management equation to overcome equation-based predictions.

Indirect Calorimetry is a science that has been valid for some 100 years. In this method of determining RMR, subjects breath into a device (like those mentioned above) to gain a steady state measurement of total oxygen consumption. Once this number is known, we can determine the amount of energy being used in the body. Remember, energy is measured in calories, so "Indirect Calorimetry" provides a valuable piece of the weight management equation.

Assessing Lifestyle

Once you have a clients RMR, through accurate indirect calorimetry, or by an equation based "guesstimate", you have a good piece of the "Caloric Expenditure" puzzle. Estimating Lifestyle behaviors provides the remaining link in the chain to understanding a total metabolic "burn-rate"

The chart below represents lifestyle categories that you can use with your client. Developed by Camille Richardson M.S. (2000), it provides a valuable tool in diagnosing total metabolic rate.

RMR x (Lifestyle multiplier) = Total Metabolism (or) Metabolic profile

Sedentary…you lead a very quiet life, spending most of your time sitting or reclining. You walk only occasionally, and not very far. You may work at a desk sometimes, but don’t have to move around a lot. Somebody else does most of the cooking and cleaning where you live.

Very Light…Your activities at home or at work requires little physical effort. You may cook and perform light housekeeping chores, but nothing very demanding. You do not walk much at all, and do not exercise or play sports except, perhaps, on rare occasions.

Light…You spend most of your work time at a desk or in a vehicle. You do no heavy lifting in your occupation. You may walk a fair amount to get from place to place, but usually less than 20-25 minutes in a typical day. You exercise or play sports occasionally, but averaging no more than 90 minutes a week.

Moderate… Your work involves some heavy lifting, heavy equipment operation, delivery, cleaning, or is otherwise physically demanding much of the time. Or, if you are more of a desk jockey, you work out, exercise, or play vigorous sports as least 3 times a week for at least an hour or so, and you try to work up a good sweat in doing so.

Moderately Heavy…You have a somewhat physically demanding occupation (on the order of a road construction worker) and play a sport or exercise at least once a week. Or, perhaps your occupation is a little less demanding, but you exercise or work out 3-5 times a week for an hour or more, with vigor.

Heavy…You are an avid sportsman or dedicated to your fitness routine, working out 5-7times per week for an hour or more. Or, you are a little more moderate in your exercise, on the order of 3-5 times a week, but you have a very demanding occupation with lots of heavy lifting (like a furniture mover), or near constant motion (perhaps a bicycle messenger).

Very Heavy…Get real! We are talking Olympic decathlete in training here, or, an occupation that is extremely demanding, on the order of a lumberjack working major overtime. Or both.

O.K. Now you have an indication of the type of lifestyle the client leads by the selection of one of these categories. This will provide a multiplier that will yield total caloric expenditure. The multiplication factors are as follows:

Activity Level



Very Light
Moderately Heavy
Very Heavy

Now for the Math…

RMR x (Lifestyle multiplier) = Total Metabolism (or) Metabolic profile


For example. Say you equate or measure an individual RMR as 1600 calories. You have determined from the chart, and in consultation with you client that they are "sedentary". The equation is simple

RMR (1600) x Sedentary Lifestyle (1.28) yields a total caloric output of 2048.

This is the total calories expended throughout the day for this individual, and therefore the Metabolic Profile of that client.

Sounds simple enough- right? Well, programming for weight loss takes on a whole new meaning once you have the starting numbers to deal with.

Manipulating Metabolism

You can immediately affect the lifestyle side of the metabolic profile through – you guessed it- diet and exercise. Increasing caloric expenditure and restricting caloric intake is a sure bet to alter the metabolic profile.


By creating a negative caloric balance for a client, he or she will lose weight. Guidelines and recommendations from the American Dietetic Association suggest this be limited to no more than 2 pounds per week. A simple 500 calories per day restriction for our client above that would mean ingesting 1548 calories- would yield about 1lb per week of weight loss. Remember, no diet should consist of less than 1200 calories a day.


Another way to create the caloric imbalance is through increasing energy expenditure on the lifestyle side of the equation- obviously through programmed exercise. Our sample client above could eat 2048 calories a day and exercise to burn 500 additional calories a day and still lose one pound per week,

When it comes to weight loss (or even gain for that matter) it is simply a numbers game.

Quality of diet is certainly important to health and performance, but if your focus is truly weight loss or gain- play by the numbers.

RMR is Dynamic

If you have access to an indirect calorimeter, try to take RMR readings about once per week. It is natural for a client’s RMR to change (decrease) when caloric restriction is introduced. The body, ever seeking homeostasis, lowers its immediate caloric needs for life support to a bare minimum. Ever wonder why your clients on a diet feel lethargic and tired?

Exercise CAN affect RMR and will be the subject of a later research summary based article.


Knowing a client metabolic profile can mean the difference in success or failure as you navigate a path to reach a weight management outcome. If you don’t know – or can only guess- as to what their bodies are expending in terms of calories, it will be a long road of trial and error to reach a positive result. Studies show that (on average) most clients fall out of a weight management and fitness program in about eight weeks. Quite often this is due to poor professional direction or "failure" to achieve a short-term goal.

Place emphasis on your client’s metabolic profile. You will then have the beginnings of a longer and more successful relationship.