If as part of a health resolution you’re planning on trying out a crash diet you should
definitely reconsider. A crash diet is when you try and achieve very quick weight loss, often
by drastically reducing your daily total amount of calories. Crash diets and the dieting
philosophy that comes with them actually often result in weight gain, alongside distorted
eating behaviours (binge-eating, overeating), unpleasant emotional states (guilt and eating-
related stress) as well as poor metabolic and body composition effects.
Crash diets are appropriately named as they are bound to cause a ‘crash’ (emotionally) and
burn (of muscles). When you try to outsmart your body it outsmarts you back, so when you
start eating less your body adapts and ‘burns off’ less energy through:
- The ‘thermic effect’ (energy your body uses to digest food) goes down as you are
eating less.
- Your resting metabolic rate decreases as you weigh less.
- Non-exercise activity production of heat (thermogenesis) decreases as you eat less.
- You absorb the full spectrum of the calories you consume although in a normal state
you wouldn’t absorb 100% of the calories you ingest.
- Your hunger signals start accumulate and push food cravings through the roof.
12 hours - Early signs
In the first 12-18 hours on a crash diet your body is preparing to get into ‘starvation’ mode
and is utilising as much of its stored energy (glycogen) as possible.
24 hours - Feeling cold and bloated
As your energy stores are reduced due to the lack of energy intake, cortisol levels rise which
can cause your body to hold onto more water and make you feel ‘bloated’ and less ‘lean’ than you actually are. Also at this stage your natural response to keep your core temperature stable (thermogenesis not related to activity) decreases which might manifest as shivers and feeling cold.
48 hours - Metabolism slows down
At this stage your body’s energy stores are most likely completely depleted. As your body
can’t tell the difference between food scarcity and starvation, it slows your metabolism in
order to conserve energy. The body has an amazing ability (survival instinct) to reduce
energy expenditure in an attempt to conserve energy. This ultimately causes sluggishness and makes the body great at storing fat!
72 hours - Bye-Bye Muscles
At this point your metabolism slows WAY down, and you burn fewer calories. As your
metabolism has been decreased and your body is preferentially storing fat (fat has more
energy), lean tissue (which is mostly muscle) starts being burned off. Furthermore, as your
thyroid function is affected, adrenaline secretion is reduced which makes you feel mentally
and physically run down.
1-2 weeks - Missing nutrition
By the first couple of weeks, there is a great chance that at least 50% of your weight loss is
lean muscle. From this stage onwards you are also likely to start missing out on important
nutrients (such as protein, B12, iron) compromising your immune system, mental ability and
overall health. Food obsession is likely to start affecting your personal and social life, as you
can’t stop thinking when your next meal will be, what and how much you are allowed to eat.
You may well spend all day obsessing about food.
As the days go on, your food and sugar/fat cravings are through the roof as there is a build-up
of appetite-stimulating hormones in your system (ghrelin etc) and binge-eating episodes are
more likely to happen.
1 month - HANGRY
By now you are a ‘hangry’ person. Your appetite hormones are through the roof and you are
also in a constant bad mood because you had ‘green tea and a rice cake’ for breakfast so you
get in a viscous cycle of being hungry and moody.
There is a good chance that there have been some ‘breakout; cases at this point where you
gave in your body’s constant ‘nagging’ for energy and consumed everything you found in
front of you.
6 months - Danger, danger
If you’ve made it this far without being hospitalised or having irreparably damaged your
metabolism and health, you are likely to be a moody, walking cluster of bones. Next stop:
rebound weight gain!
As you have been trained in an ‘all or nothing’ mentality for months, you are probably going
all out on all the ‘forbidden foods’. Having lost most of your muscle mass, your body will be
a fat-absorbing machine as priority will be to replenish the energy stores. Our body’s fat cells
have great memory, and the original body fat levels can be reached much faster following a
crash diet and are in many cases surpassed!
So your take-away present from months of struggle will be:
- A decreased metabolism
- A higher chance of developing blood sugar related diseases like diabetes as you have
spiked your insulin sensitivity
- You are now storing fat more efficiently
- Your muscle mass is very low affecting your health, body composition, posture and
confidence
- Your relationship with food is damaged and you may be a closer to having a food
disorder
- Likely social implications such as isolation