General Health
Burning fat
Continuing his series on weight management, Jimmy Tang explores the energy
system and the energy equation for weight loss.
T
o understand the effects of
exercise on the body’s system,
we need to analyse how the
body creates energy for exercise and
how the different forms of exercise
place different demands on energy
production. In other words, in order
to understand the most effective way
of burning fat, we need to understand
how our body acquires energy in the
first place.
Jimmy Tang
is a GDP and Level 3 personal trainer
with a special interest in postural
dysfunction and lower back problems.
68 The Dentist April 2016
All functions of the body require
energy and this energy comes
from the breakdown of adenosine
triphosphate (ATP). There is a limited
store of ATP within the muscle and
it only lasts for approximately one
or two seconds. Re-synthesis of ATP
comes from either the breakdown of
phosphocreatine or macronutrients
in the diet, such as carbohydrate, fat
and protein.
Creatine is produced in the liver
from amino acids and it is transported
in the blood to muscle cells where
it is combined with phosphate to
make phosphocreatine. Creatine can
be obtained in the diet from fish.
Vegetarians have no dietary source.
The following three energy systems
use different fuels to convert ADP
back into ATP:
1) Creatine phosphate (CP) or
phosphocreatine system – The CP
system is anaerobic and does not
require oxygen, fat or carbohydrate.
Adenosine triphosphate can be
regenerated almost immediately
using creatine phosphate, but again,
this only lasts for a very short period
of time due to the limited creatine
phosphate store. The CP system is
exhausted after a maximum of 10
seconds. This energy system is used
during activities requiring maximal
exertion and when muscles need to
generate a lot of force very quickly,
for example, a 100m sprint. Creatine
phosphate and ATP stores are 50 per
cent restored after 30 seconds and
fully restored after about five minutes
of rest.
2) Lactate system – The lactate
system uses intramuscular glycogen
(carbohydrate) to make ATP.
Glycogen is broken down into
glucose without oxygen. One
glucose molecule produces two ATP
molecules along with lactic acid (a
General Health
waste product). This system is used
when near maximal exercise lasts
longer than CP sources can provide
(beyond 10 seconds) or when the
intensity during aerobic activity
starts to demand more energy than
the aerobic system can provide.
When the production of lactic
acid exceeds the body’s ability to
disperse it, there will be a build up
of lactic acid – onset of blood lactate
accumulation (OBLA). Targeted
interval training improves this lactate
tolerance. Anaerobic training uses
up the intramuscular glycogen store
after one to three minutes. Recovery
should be active (for example
walking between running intervals) to
aid the return of blood to the liver.
3) Aerobic system – This involves the
production of ATP from the complete
breakdown of carbohydrate, fat and
protein in the presence of oxygen.
This system is active when there is
sufficient oxygen in the cells to meet
the energy production requirements,
such as when the body is at rest and
the intensity of the activity is low
to moderate. Carbohydrate is the
preferred energy source as it will
release energy a lot faster (although
it releases less energy per molecule
than fat). The aerobic system
70 The Dentist April 2016
produces ATP, carbon dioxide, water
and heat from the breakdown of fat
and carbohydrate.
It may surprise you that the best
way to burn fat is actually with
light, easy exercise (60 to 70 per
cent of your maximum heart rate.
This will typically burn much higher
percentages of fat. Fat burns slowly
as fuel and requires oxygen to burn
properly. So, if the oxygen gets to
the muscles, you can burn more fat.
That being said, lighter exercises also
burn fewer overall calories. A person
who performs more intense exercises
will lose more calories, but without
sufficient oxygen getting to their cells,
they won’t lose fat quite as quickly
and will instead lose carbohydrates.
Whilst it is convenient to describe
the systems as separate concepts,
during actual exercises, all three
systems interweave to produce the
desired performance outcome. It
is the intensity of the exercise that
dictates which one will be used to
supply the majority of the energy.
Diet
The total amount of calories
should be divided across each of
the macronutrients to achieve the
following ratios:
 Minimum of 50 per cent of total
calories from carbohydrates.
 Maximum of 35 per cent of total
calories from fats.
 Minimum of 55g of protein per day
(nine to 12 per cent of total calories).
The key to successful fat loss
is to cut your fat to between 20
and 25 per cent of total calories
and to reduce carbohydrates by
only a modest amount. Ideally,
carbohydrates should continue
to contribute 50 to 60 per cent of
your total calories. Reducing your
calorie intake by 15 per cent - a
relatively modest reduction - will
avoid the metabolic slowdown that is
associated with more severe calorie
reduction. The body will recognise
and react to a small deficit by
oxidising more fat. If you cut calories
more drastically, you will not shed
fat faster. Instead, it will cause your
body to lower its metabolic rate in
an attempt to conserve energy. It will
also increase protein oxidation and
glycogen depletion. The end result is
likely to be the loss of lean muscle
tissue, low energy levels and extreme
hunger.
It is therefore recommended that
you eat more frequently and do not
skip breakfast – every time we
General Health
eat, the metabolic rate increases
by approximately 10 per cent
for a short while afterwards, due
to the thermic effect of food.
Furthermore, frequent eating keeps
blood sugar and insulin levels
more stable.
Stress
Dentistry is well known for being
a stressful job. Problems can
include patients turning up late
or not attending, unexpected
incidents, staff problems, or CQC
compliance and so on. Cortisol,
the primary corticosteroid released
from the adrenal cortex, helps to
provide reserves in the body for
managing stress. It is a catabolic
hormone which promotes the
breakdown of carbohydrates,
proteins and fats to provide
energy for the body during
stressful periods. It offers support
during short term bouts of stress.
Long term chronic stress and the
resulting excess cortisol can lead
to deterioration in health due to
an unbalancing of the endocrine
system. Apart from causing
muscles to break down, cortisol
also causes the body to hold
on to fat and boost appetite. It
encourages fat to be stored around
the middle and it is known that fat
in this area is associated with an
72 The Dentist April 2016
increased risk of heart disease and
diabetes.
Effective stress management
techniques include meditation and
good time management.
Diet and exercise
Before exercise
Eat between two to four hours before
training as this leaves enough time for
your stomach to settle so that you feel
comfortable and not too hungry.
If fat loss is your main goal,
exercising on an empty stomach –
such as first thing in the morning
– may encourage your body to burn
slightly more fat for fuel. The problem
is that you may fatigue sooner due
to deprivation of your intramuscular
glycogen, or drop your exercise
intensity and therefore end up
burning fewer calories.
You should consume 2.5g
carbohydrate/kg of body weight
approximately three hours before
exercise.
During exercise
For activities lasting less than an hour,
drinking water would be sufficient.
For activities longer than an
hour at moderate to high intensity,
consuming carbohydrate during
your workout can help delay fatigue.
Consuming a drink containing
protein as well as carbohydrate
during exercise may minimise
protein breakdown following
exercise.
After exercise
The best time to replenish your
glycogen store is during the first
two hours after exercise, using
carbohydrate with a moderate
or high GI. Eating carbohydrate
stimulates insulin release which
in turn increases the amount of
glucose taken up by your muscle
cells from the bloodstream.
Furthermore, post exercise, the
muscle cell membranes are
more permeable to glucose
so that they can take up more
glucose than normal. Combining
carbohydrate with protein has
been shown to be more effective
in promoting glycogen recovery
than carbohydrate alone. One
part of protein to three parts of
carbohydrate promotes faster
glycogen refuelling, muscle repair
and growth compared to an intake
of carbohydrate alone.
Summary
The key to successful fat loss is to
cut your total calories by reducing
fat consumption but to reduce
carbohydrates by only a modest
amount; eat more frequently and
do not skip breakfast.