Along with all its demonstrated and potential benefits,
calorie restriction may result in a range of negative
side effects.
Those interested in the calorie-restricted lifestyle should
be aware of the following potential issues:
List of disadvantages
Physical effects
Tissue loss
The body's response to low dietary energy levels involves
burning off any existing resources.
The body's least important tissues are dispensed with first
- but their absence can still have some side effects...
Less fat
Body fat is burned as fuel during CR's weight-loss phase.
This results in reduced thermal and mechanical insulation -
and depleted fuel reserves...
Reduced thermal insulation
Reduced body fat and decreased body temperature can make
practitioners more sensitive to prolonged cold temperatures.
As a result, unexpected, prolonged cold exposure can become more
dangerous - such as after a car failure on the highway in winter.
Also, reduced subcutaneous fat may increase the hazard
represented by local heat and burns - by removing an
insulating layer and exposing the more important and
sensitive tissues beneath.
Reduced mechanical insulation
Less insulation due to fat results in external objects
getting closer to your skeletal structure. This can result
in tissue near the (smaller) contact point getting squashed.
This can result for example, in discomfort in the buttocks
while sitting on a hard surface.
Similarly, collisions with external objects are less likely
to be decelerated by a protective insulating layer - and are
more likely to reach underlying tissues - such as bone.
The result can be that the energy from a more rapid
deceleration is concentrated in a smaller area - and there
is a greater chance of breaking the skin and doing damage to
underlying structures.
Reduced energy reserves
Fat deposits represent the body's primary energy reserves.
These can be drastically depleted during CR.
Energy is widely and abundantly available in the modern
world - and that shows few signs of changing any time soon -
but there are still a few cases where resource availability
could cause problems.
Being unexpectedly stuck on a boat, locked in a
room or lost in a wilderness are all scenarios where
resource reserves may be important.
It is theorised that some "wasting" diseases may deplete
energy reserves - by interfering with metabolism and making
it harder to use dietary energy. Intestinal parasites might
produce such an effect.
It is also theorised that some flu-like disorders
characterised by fevers may make energetic demands on the
body which can be best met by existing fat reserves.
Drained states and weakness can sometimes result if
activities requiring stamina are performed for extended
periods of time.
Less muscle
Muscle tissue is often burned as fuel during CR's weight-loss phase.
This saves energy overall - since muscles need energy to maintain them.
The result is often reduced strength and stamina...
Reduced strength
CR is likely to result in reduced muscle mass and
lower strength.
This could cause problems under circumstances where strength
is needed.
For example, strength can be needed when attempting to
absorb a blow - from something like a falling heavy object -
or when preventing damage from a fall onto the ground.
Reduced stamina
A combination of reduced muscle mass and lower stores
of energy means that CR practitioners are likely to
be unable to repeat exercises as many times - and lack
stamina.
This could cause problems under circumstances where
stamina is needed - for example, if engaged in a chase.
Less bone
Reduced bone mineral density
Weight loss is often accompanied by reduced bone mass -
which is likely to place the practitioner at a somewhat
greater risk of certain sorts of fracture.
Smaller organs
CR will often reduce the size of other bodily organs -
besides muscle and fat tissue.
Smaller organs of digestion
The liver is involved in detoxifying the blood, and a
smaller liver may be become overloaded more easily
- under some conditions.
Smaller brain components
Though studies suggest brain size is not reduced in organisms
doing adult-onset CR, one
study
of rhesus monkeys found parts of the brains of
the CR'd individuals reduced in size. More study can be
expected to clarify the existence of this effect.
Smaller testicles
One study
of rats found their testicles shrank by 20% when they
were on CR. More study can be expected to clarify the
existence of this effect.
The liver is involved in detoxifying the blood, and a
smaller liver may be become overloaded more easily
- under some conditions.
A smaller pancreas is less able to secrete large volumes of
insulin. This may result in reduced ability to tolerate
large loads of glucose.
The size of the stomach can limit how much food it is
possible to eat at once. This could make brief,
rapid refeeding more difficult.
Cosmetic problems
CR can affect the appearance of those who pursue it.
This can affect how others regard practitioners and behave towards them...
Reduced attractiveness
Among women, a certain level of fat is widely regarded as
sexually attractive. Some degree of fat on thighs, buttocks
and breasts is believed to act as a signal of fertility.
Similarly among men, a certain degree of muscular
development is perceived as being indicative of
health, freedom from disease, strength and stamina.
As a result of their dietary practices, practitioners
sometimes find some of their friends and family think they
are "too thin".
Percieved weakness
Extremes of slenderness are sometimes associated with disease states.
As a result of this, there is a link in the minds of many
people between extreme slenderness and illness.
Consequently some people may assume that because
practitioners are thin they are also ill.
Percieved lack of strength might also make practitioners
targets for criminal elements of society who seek to take
advantage of others weaknesses for their own benefit.
Down-regulation of non-essential functions
CR can interfere with bodily functions not of immediate
relevance to survival...
Reproductive problems
Low energy intake can temporarily shut down reproductive function...
Libido reduction
More extreme CR can result in reduced interest in sexual
activity - and reduced levels of desire.
Menstrual irregularity
A very low calorie intake can sometimes interfere with
menstrual function in women - and can cause amenorrhea -
a cessation of menstruation.
Reduced fertility
In rodents, CR appears to reduce fertility, reduces sperm
motility, and increases the proportion of sperm that are
abnormal.
Low BMI is widely regarded as a risk factor in pregnancy.
It can result in ovulatory dysfunction and thus infertility.
Underweight mothers have higher levels of preterm delivery -
and more low birth-weight infants.
Women planning to get pregnant soon, should not initiate CR
until after having (and weaning) their offspring.
Those already practicing CR should seriously consider increasing
their calorie intake if contemplating reproductive activity.
Slower growth
Growth processes are often suppressed in CR'd organisms.
They are rarely urgently necessary - and can demand resources...
Slower wound healing
Wounds heal more slowly among CR practitioners.
This could be a complicating factor if facing any major
operations, and may increase risk after traumatic injury.
Tissue adaptation
Some tissues respond with growth to demands made by usage.
This can happen with muscles, bones and teeth.
Muscles normally grow in strength when demands are made on them;
Bones increase in density and strength when forces are applied to them;
However CR makes growth processes more difficult - making
these processes less likely to happen.
Thermoregulation
Heating the body can be expensive. CR turns down the heat...
Cold extremities
CR lowers the core body temperature of practitioners.
A reduced heating budget also seems to make it more likely
for the body to go into a mode where circulation in the
extremities is restricted to keep warm blood near the core
of the body.
This can leads to discomfort in the extremities, loss of
feeling and motor competence - and in extreme cases -
cell death due to asphyxiation, or frostbite.
Lifestyle effects
Psychological effects
CR can influence things such as mental outlook and emotional function...
Psychological issues
CR interferes with a basic drive - the
consumption of food.
This can have psychological repercussions...
Hunger
Hunger and craving for food are widely regarded as
unpleasant sensations. However for some practitioners, they
are a regular part of their practice of CR.
Hunger - and having your thoughts constantly returning to
the subject of food - can represent distractions that
interfere with other activities in a debilitating manner.
Obsession
To a certain extent, a preoccupation with food is
healthy - given its significance to health and well being.
The optimal diet is certainly an interesting and important
subject - and CR is a powerful instrument for postitive
change that many individuals should understand and explore.
However, the fact that many CR'd individuals are
constantly having their thoughts dragged back to
food by hunger can - contribute to them spending
more time and energy thinking about food and diet
than perhaps is rational or healthy.
Mood changes
Some have reported that their mood alters in a negative way
when their energy intake goes too low.
The reported symptoms appear to be rather similar to
depression.
Others have reported feelings of detachment; a lack of
emotion.
Studies of the effects of starvation have reported dramatic
increases in preoccupation with food, difficulty in
concentrating - and a range of emotional, social and sexual
changes in those deprived of a substantial share of their
normal food intake for extended periods.
Social issues
Eating food is often a social phenomenon.
CR can sometimes interfere with conventional social practices...
Family meals
Eating is often a communal activity, and a time for
socialising with members of the family. CR can present some
problems in this area:
Some CR practitioners try to eat less frequently than is usual;
CR diets may not be suitable for all family members;
Such factors can work to divide and isolate family members -
unless active steps are taken to combat their effects.
Social events with food
Many other types of social event also often involve eating:
Eating out at restaurants and bars;
Hosts often offer food to visitors;
Workplace lunches;
Food and socialising are often intertwined; and not
eating - or following unorthodox diets - can interfere
with some aspects of a normal social life.
Resource management
CR can affect how practitioners allocate their resources...
Time and money
As medicine costs go, CR can be an inexpensive intervention.
It saves time eating food - and reduces the time spent digesting it. However...
Time
CR can be a time sink in several ways. In particular it can
cause some practitioners to spend time:
...preparing meals (more than they would otherwise do);
...swapping notes with other practitioners over the internet.
...educating themselves about how best to practice CR;
...monitoring their health;
...seeking out a variety of foods and nutrients;
...preparing packed meals when travelling;
...growing their own food;
All these activities consume time - and that time needs to
be budgeted for - and balanced against the other things in
life that deserve attention.
Money
CR is fundamentally a low cost intervention. Indeed, it's
theorised that the reason it results in health benefits is
because it activates an adaptation "intended" for dealing
with resource shortages.
However, it can involve expense on:
...eating high quality foodstuffs;
...supplements;
...health monitoring equipment;
...consulting with physicians;
Prospective practitioners should not necessarily assume that
CR will result in saving them money - it may have the
opposite effect.
Reduced stamina;
...may all interact synergetically to increase the risk of
practitioners drowning if they fall into deep water.
Exercise
Reduced strength ...and...
Reduced stamina;
...can combine to adversely affect:
Exercise programs;
Sporting activities;
Some recreational activities;
Note also that low levels of strength and stamina can create
the following vicious circle:
Reduced levels
of exercise
=>
<=
Reduced strength
and stamina;
I.e.
Less exercise being done can lead to reduced strength and stamina;
Reduced strength and stamina can lead to less exercise being done;
Flesh wounds
Reduced insulation against mechanical damage ...and...
Slower would healing;
...can result in the presence of an increased number of
scabs and scars, if the practitioner is not cautious.
Falls
Risk from falls is influenced by many factors - and more than
one of them is in the above list of disadvantages of CR:
Strength is reduced - so the ability to cushion blows
due to falls using arm strength may be reduced;
Impact forces may be transmitted more directly into
bones - due to a lack of cushioning fat;
Bone density can be reduced - and this might result in
increased fracture risk - see the "broken bones" section, below;
Note that there are other points likely to reduce
the risk of falls - the practitoner may have a better sense
of balance, be more alert, have better reactions, and any
forces applied to their limbs by their body weight are
likely to be reduced.
Broken bones
Reduced bone density can make the bones of CR practitoners
more brittle.
While it also reduces body weight (reducing body inertia and
making some bone injuries less likely) reduced body weight
does not protect against all bone injuries (for
example those cause by being crushed under a car).
This can represent a hazzard - in conjunction with reduced
padding resulting in external forces more directly impacting
bone tissue locally.
Being thin increases the risk of hip fracture for this
reason - the impact force is more concentrated due to
a lack of insulating padding.
CR may also produce slower bone regrowth resulting
in increased recovery times.
Violent crime
Lack of physical strength may make some sorts of violent
crime more likely - since lack of physical strength can be
advertised by a slight frame - and may attract some sorts of
attackers seeking victims lacking the ability to resist.
A combination of percieved weakness, lack of actual physical
defenses, and a lack of protection from blows may mean that
the risks associated with personal attack are somewhat
greater for CR practitioners.
There may be some compensating benefits - in the form of
improved abilities at dodging blows and running away.
Work in progress
The long-term physical and psychological effects of CR are
not yet all known or understood - it remains relatively
"uncharted territory".
This means that there may be disadvantages that are not yet
properly appreciated or understood.
An example of one area where this might happen, consider
plagues:
Many of the animal lifespan studies which have established
CR as an intervention which extends lifespan have taken place
in a disease-free environment.
Humans live in an environment which is very different from
this.
There are many studies about the effect of CR on the immune
system - and many are very positive: CR apparently improves
immune function in many cases.
However, anecdotal reports suggest that - while infections
are rare - those that succeed in establishing themselves can
be more difficult to shake off.
There is very little information about how CR affects
mortality from causes such as AIDS, SARS, and pneumonia.
A future version of this page may give a more prominent
position to the hazard represented by infectious diseases
when the situation is better understood.
Disclaimer
The information on these pages is intended for educational
use only - and practitioners are recommended to consult with
a qualified medical advisor before making any dietary
changes.
