Energy requirements
(calories) will vary depending on a number of factors: age, bodyweight,
gender, your resting energy expenditure or resting metabolic
rate (REE or RMR), the thermic effect of feeding (or diet induced
thermogenesis) and physical activity levels. Within this your
RMR can vary as it is directly related to the amount of metabolically
active tissue you possess at rest, your heart, liver, kidneys,
lungs and brain are more metabolically active than muscle tissue.
So your husband, being a foot taller than you, will have larger
metabolically active organs which in turn will require more energy
than your own organs, even before beginning to exercise! Individuals
with a greater muscle mass in comparison to body fat will have
a higher RMR. Yet again women usually lose out typically
having 5-10% lower RMR compared with men, mainly due to our larger
stores of hormone-related fat.
Working out precisely how many calories an individual needs is
fraught with problems and is usually left to the scientific laboratories.
If there is no weight gain or weight loss, i.e. energy balance,
one can assume that energy intake equals energy expenditure.
In doing this, estimates of dietary intake can be validated.
One way is by direct measurement, called direct calorimetry,
where subjects are put in a large, expensive room and the amount
of heat produced (and therefore calories) under certain conditions
can be measured; another way more commonly used in sport science
laboratories is by indirect calorimetry. This is where a lightweight
portable analysers can be used to look at how much oxygen is
used up (and carbon dioxide produced) a good measure of how much
energy is being used up can be calculated. Another, very expensive
method, is to give someone some water, specially labelled (non-radioactive)
to be measured when given off on the breath or as sweat or urine.
| Organ |
% of resting metabolic rate for
65kg man |
| Liver |
21 |
| Brain |
19 |
| Heart |
7 |
| Kidneys |
10 |
| Skeletel Muscle |
19 |
| Remainder |
19 |
| |
100 |
So is there an easy
way to calculate your calorie requirements? No, not accurately.
However you can estimate requirements using formula based on
metabolic rate, predicted from weight (measured in kilograms),
using data collated by Schofield et al (1985).
| 18-29
years |
|
| male |
Metabolic
rate = 15.1 x wt + 692 |
| female
|
Metabolic
rate = 14.8 x wt + 487 |
| 30-59
years |
|
| male |
Metabolic
rate = 11.5 x wt + 873 |
| female |
Metabolic
rate = 8.3 x wt + 846 |
So for a 32 year old
female weighing 70kg (11 stone), her estimated metabolic rate
would be:
8.3
x 70kg + 846 = 1,427 kcal a day
A 32 year old male
weighing 113kg (around 18 stone) would have an estimated requirement
of:
11.5
x 113 + 873 = 2,173kcal a day
Simply by being 7 stone
heavier, an additional 746kcal extra each day is needed to maintain
vital organ functioning at rest. Once you and your husband start
moving around, using skeletal muscle yet more energy is needed
to fuel you, and again he will need more!
To cover a general
sedentary lifestyle, dietitians and nutritionists will multiply
the metabolic rate by a physical activity factor (PAL).
This is usually a factor of 1.4. So, our example 11 stone woman
would have a total estimated daily requirement of 1,427 x 1.4
= 1, 9998kcal a day i.e. around 2,000kcal a day; the example
man would need 2,173 x 1.4 = 3,042kcal i.e. around 3,000kcal
a day.
The estimated calorie
cost of various activities (in relation to your bodyweight) can
be found in a number of nutritional and sports science text.
By using reference text, and knowing what you are doing each
hour of any 24hour period, you can approximate your calorie requirements.
(see also paper by Ainsworth et al, Medicine and Science in Sports
and Exercise, vol 25 no.1, 1992)
© j.boorman 2001
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