Analysis of your diet and metabolic rate
This page will show you how to easily calculate your metabolic rate, plus teach you what your metabolic rate is, and what affects it. If you are having trouble losing fat while following a sensible fat-loss program, you may need to investigate your diet and understand how much energy your body needs (your metabolic rate).
Warning: I have no qualifications or any expertise in any field related to nutrition, fitness training, biology, medicine or health. The good news is that the information here has been on the web since 2003 and this is a fairly well known page, and I have received no notice of any substantial errors.
How do you lose fat?
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You eat less food energy than your body uses
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You do this over a long period of time
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You do this slowly, without compromising good nutrition
So you need to know
A) How much energy are you eating? See Diet Analysis belowB) How much energy are you burning? See Metabolic rate below
Here is an example spreadsheet (Excel 97)
Diet Analysis: what I did
Firstly, I wrote down most of the food I was eating. Then I filled in the
nutritional information I had from packets.
For the remaining items, I went to a few web sites. The best one I know
of is http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl
I didn't find their figures for red meat very helpful; the fat levels
are too high. I try to eat Australian meat when possible (in general,
it is lower in fat than the grain fed beef more common
in the US), and I used information from the Meat and Livestock Australia
website (nutrition
pages).
1 gram of fat = 9 kCalories
1 gram of carbohydrate or protein = 4 kCalories
1 gram of alchol = 7 kCalories
What is the energy deficit to burn one pound (450g) of body fat?
3500 kcal. Over six days of dieting, you want a deficit of 600kCal, and you'll lose about one pound of fat each week.
Common advice is to aim to lose one to two pounds a week. Weight loss
based on a bigger calorie deficit will starve your body of blood sugar
and the body will respond by burning up muscle as well as fat, and this
is counterproductive and unhealthy. This is also why advice is to combine
some weight training and aerobic training with dieting.
Metabolic rate
I bought a very good book called "Advanced
Fitness Assessment and Exercise Prescription", Dr Vivian Heyward
(now in 4th ed )
This book is a serious text designed for personal trainers, and I've found
it very helpful. It has four methods for calculating your metabolic rate.
Firstly, you need to know your resting metabolic rate. This is theoretically
the same for all people of the same height, sex, age and lean body mass,
and in practice, research has shown there is little variation between
people with the same values for those key variables. I have citations
below.
Then you multiply your resting metabolic rate by a factor depending on
your activity level to give you your metabolic rate.
Three metabolic rate formulas are below ... before you use them, you should
read the information between here and there.
Some FAQs about resting metabolic rate
What are basal and resting metabolic rates (RMR)?
These two terms are used interchangeably, although they are not technically the same. Resting metabolic rate is really what most lay people mean when they say basal metabolic rate, and I talk here only about resting metabolic rate (RMR). Basal metabolic rate is a precise calculation with a precise definition; RMR is close enough for practical purposes.Resting metabolic rate is the energy required by an animal to stay alive with no activity. Therefore, your real metabolic rate is always significantly higher than your RMR. Calculating RMR is a very useful first step in calculating your real metabolic rate.
| Your metabolic rate = your resting metabolic rate (easy to calculate reasonably accurately) + energy consumed by your daily activities (must guestimate). |
What determines Resting Metabolic Rate?
A very small number of people have physical conditions that give them strange resting metabolic rates.However, for the vast majority of people, resting metabolic rate can be calculated knowing a few key variables. They are age, sex, weight, height and fat-free body mass. Fat-free mass is a very important variable. Weight and height are used in one formula to determine body surface area.
When does the body change Resting Metabolic Rate? Does cutting your food intake reduce resting metabolic rate?
The body CAN NOT change resting metabolic rate per unit of fat-free body mass. Studies have shown this.For an article that is on-line in full text by a well-known researchers in the field, see Genetic Influences on the Response of Body Fat and Fat Distribution to Positive and Negative Energy Balances in Human Identical Twins, Claude Bouchard and Angelo Tremblay
Your resting metabolic rate will decrease if you lose muscle, and increase
if you gain muscle. Losing fat alone will not lower your RMR (and note
that you will need to follow a very sensible program probably including
weight training to lose fat without losing muscle). You have probably
heard that people who go on crash diets end up lowering their metabolic
rate, which means when they go off the diet, they put on fat more easily
than before they started. Because they have lost muscle, they have lowered
their metabolic rate. However, the amount of energy burnt per unit of
fat-free weight does not change; poor dieters end up with fewer units
of fat-free weight, and that's where their vicious cycle comes from.
Are some people's digestive systems more efficient than others?
No (except perhaps some people with disorders). And your system does not become more or less efficient in response to changing food intake. See the above study, or this interview with another researcher http://www.loop.com/~bkrentzman/obesity/liebel.html.Even obese people rarely have more efficient bodies. Researchers inspect the energy value of faeces to determine this.
Given the same values for the variables, how much does resting metabolic rate vary between people?
In other words, what is the error in the formulas used to calculate RMR?The latest research indicates there is a low variance in RESTING metabolic rate between individuals who have the same values for the key variables. That is, given someone's age, their fat free mass, their height and their sex, the formulas are accurate.
"Recent evidence thus supports the conclusion that within-subject variations in BMR [more or less the same as RMR] are small and insignificant, even when energy intake and physical activity are uncontrolled, (Shetty & Soares, 1988). This effectively refutes the Sukhatme-Margen hypothesis." (See link at the end of this page).
Formulas for calculating metabolic rate
Apart from the formulas here, you can also use what is the best calculator on the web (that I've seen) ... the Healthy Body Calculator.You don't need to fill in all the information to get your metabolic rate. This is your total estimated daily metabolic rate, not your resting metabolic rate.Formulas from "Advanced Fitness Assessment and Exercise Prescription", (4th ed) , Dr V. H. Heyward. pub Human Kinetics and available at Amazon (I own the third edition).
There formulas only calculate Resting Metabolic Rate! There is a second step after this: calculating your energy use due to your daily activities.
Output is in kcal (1000 calories; nutritional information is nearly always given in kcal even when it says calories. It is often also shown in joules or kilojoules, which is different).
Harris-Benedict equations
Fat Free Mass formula
Quick estimate formula
Note that only one formula uses fat free mass, even though this is a
key determinant (so the other formulas are tuned. Calculate your RMR with
all three methods, and take an average, unless you are obese. Then you
should pay more attention to the Fat Free Mass equation. Work out a plus
and minus amount using the three formulas. If the first method tells you
1720 kcal, the second 1750 kcal and the third 1760 kcal, then you would
say that your RMR is about 1743 +- 20
Calculating your total metabolic rate
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I am a professional (or office worker). Doing the BFL program means I do exercise each day, so I use a percentage of 45%.
If my RMR is 1743 (from above) then my total metabolic rate estimate is 1743 + 1743*0.45 = 2528.
Now, what about the error? My percentage figure could by +- 5%.
This means my lowest figure is (1743 - 20) + (1743 - 20)*0.40 = 2412
My highest figure is (1743 + 20) + (1743 + 20)*0.50 = 2644.
So I'm confident that my metabolic rate is about 2500 +- 150.
Now go back to my FAQ to see what you do with your newfound knowledge.
Links about calculating metabolic rate
http://www.unu.edu/unupress/food2/uid01e/uid01e00.htm#ContentsA university report backing up important points I made above.
In progress: adding the Schofield equations taken from http://www.med.monash.edu.au/medicine/mmc/courses/2042/2042work.htm
Note that this formula as presented here is 100% metric: the output is
MJ (mega Joules) not kcal (kilo calories) unlike the other formulas on this
page.
The activity factors are almost the same, of course.
To convert to kcal, multiply the result by 238.846.
ACTIVITY FACTORS |
MALES |
FEMALES |
| Bed-rest, chair or bed bound | 1.2 | 1.2 |
| Very sedentary, mostly seated with no option of moving around and little or no strenuous leisure activity | 1.4-1.5 | 1.4-1.5 |
| Seated work with requirement to move around but little strenuous exercise | 1.6-1.7 | 1.6 |
| Standing work/light exercise (e.g housework, billiards,lawn bowls golf, shop assistant) | 1.8-1.9 | 1.7-1.8 |
| Strenuous work or highly active leisure | 2.0-2.4 | 1.9-2.0 |
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STRESS/INJURY FACTOR |
MALES |
FEMALES |
| Burns (<10%) | 1.2 | 1.2 |
| Minor surgery | 1.3 | 1.3 |
| Respiratory failure | 1.5 | 1.5 |
| Multi trauma/major surgery | 1.5 | 1.5 |
| Major sepsis | 1.6 | 1.6 |
| Burns (>50%) | 2.0 | 2.0 |