Danger of Low Calorie Diets

dangers of low calorie diets


We are often told that to lose ½ a kilogram or a pound a week that we should eat 3500 calories less than what we burn each week. This works out to 500 calories a day.

We are also told that the average woman burns 2000 calories a day and the average man 2500 calories a day.

This means that many average women end up consuming 1500 calories a day or often less. Because if you eat 1500 calories a day to lose a pound a week then if you eat even less than that you should see results faster, right?

Yes and no.

I do know women who have successfully lost weight on 1200 or even 800 calories a day. I do not know many women who have done this and kept the weight off, had a strong athletic physique, perform well in the gym, have balanced hormones and regular cycles, healthy hair and skin, a positive body image and relationship with food.

I would also say that almost EVERY client I have worked with who has come from a background in restrictive eating has struggled to lose the weight they gained back or reached a stand still at some point that has become very frustrating.

So this blog has been a long time coming. I think there are a lot of women (and men) who deserve to know better, to understand that they can lose weight without punishing themselves but the trade off is perhaps a little bit more patience and a lot more self love.

So let me start at the beginning.


Your metabolism is made up of a few things:

1. your resting metabolic rate – the energy required to maintain your body, its organs, its muscle, bone and fat tissue, at rest

2. the energy expended during physical activities of daily living

3. thermoregulation

4. thermic effect of food – the energy expended when you digest food [protein is particularly thermogenic]


Let’s look at your resting metabolic rate. I put this picture up on social media recently, you might have already seen it. It pretty much spells everything out. Remember, that the numbers are for an average person, not male or female specific. So a smaller female might have slightly lower requirements maybe by 200kcal or so and a bigger male maybe more.



Regardless of this, it is clear to see that the requirements for someone who is exercising, even for a small woman, would sit probably not much lower than 1200 calories per day.


We feed ourselves fuel (food) to maintain functioning organs. The body’s energy currency is glucose or sugar which comes from carbohydrates. This doesn’t mean that we need to eat 1200 calories from carbohydrates a day however. Our body is very efficient at making sugar from fats and proteins. This is because, traditionally, starvation would have been a massive threat to our survival and the ability to break down protein and fats from our stores would have kept us alive in times of famine.

We would have broken down fat from our fat stores but it can actually be easier sometimes to make sugars from proteins and therefore our body will break down non-essential protein tissues to give us the energy we need. We may therefore lose some muscle mass, our organs may shrink. This will contribute to weight loss along with some fat tissue.

So yes, we are losing weight, but we are also losing weight at the expense of our muscle tone and organs which are essential for healthy life.

The most “expensive” organs we have include our brain, heart, kidneys, liver and gut and muscles (even more so when exercising). If we exclude our muscles, these organs make up 6% of our total body mass yet about two thirds of our total daily energy expenditure. If we add our muscle mass we reach about 80% of our total expenditure.

So at the expense of losing some body fat, a small amount of protein loss from organs and muscle mass will significantly reduce metabolic rate. This means that we can easily hit a plateau, potentially driving further restriction or that when we go back to “normal” eating we are more likely to regain body fat.

Under-eating also significantly increases the incidence of binge eating behaviour. This may start as a physiological response due to hunger but, even if the first few times are physiological, it will soon develop into an emotional response as feelings of guilt, failure and lack of self control start to negatively impact the dieters psychology. What starts out as physiological soon becomes psychological. It can then become difficult to distinguish between physical and emotional hunger and the whole thing just gets a bit blurry.


The average energy requirements across a cycle of the female reproductive system are 70 kcals per day. This is the average so what we may see is that needs are lower on some days but much higher around ovulation and menstruation. If you are a woman you have probably experienced this, I know I have. Often I get a couple of days a month when I want to EAT ALL THE FOOD. Then a few days later I have an “ah-ha moment” and I realise that’s why

If we are in major caloric deficit and our body is breaking down organs to create energy, it is unlikely we will be prioritising energy to the reproductive system. This is especially true if we are doing a lot of exercise.

The King Pins of energy demand are the brain, immune system, the muscles and reproductive system. If the brain is taking energy (which it would be if it needs to find food) then the immune system is often not active. If the muscles are taking energy, then the reproductive system is likely not. So exercise and calorie restriction is a likely explanation of infertility.


Calorie restriction can be associated with low levels of oestrogen which is an important bone building hormone. Additionally, bone is another structure that may be sacrificed for the energy demands of more essential organs when food intake is low. Osteoporosis, bone health and even the integrity of the discs between the spine can become under threat. An athlete may become at greater risk for bone as well as joint injuries or muscle tears.


Calorie restriction often comes hand in hand with reduced diversity in the diet. In an attempt to control or manage intake it is often perceived to be easier to eat the same things over and over again because certain foods are considered “safe” or to avoid the risk of temptation. I have written a more comprehensive article on the impact of reduced diversity in the diet but ultimately this can have a negative impact on gut health, not to mention that lower carbohydrate intake often accompanies poor fibre consumption, which can lead to constipation. As a side, constipation can also be a sign of a slower metabolism or under-active thyroid.


Common signs that you may be under eating / over restricting?

  • The scales won’t budge despite attempts to restrict intake and exercise harder
  • Poor recovery after exercise, poor performance, constantly aching muscles and joints
  • Cravings and hunger
  • Obsessing about food
  • Increased incidence of binge eating
  • Loss of a regular menstrual cycle or increase pre-menstrual symptoms
  • Low mood, anxiety, feeling emotional
  • Loss of sex drive
  • Feeling cold
  • Hair loss or stunted hair growth
  • Poor relationship with food and fear of social situations
  • Poor energy and/or dizziness (especially when moving from sitting to standing)
  • Digestive imbalances
  • Feelings of “puffiness” and “inflammation”



Is you recognise that this could be you, what do you do about it?

It is much easier when working with individuals to assess their personal situation and identify key areas which need addressing.

It is really important to acknowledge that often if someone is undereating and/or excessively exercising it may on the surface look like the pursuit of vanity. It is often more deeply rooted in a deeper issue. A bad relationship with food, poor body image and ultimately the pursuit of something else, confidence, control or happiness.

I usually ask clients to identify how their current food and exercise choices are affecting them in five areas of their life (now is time to get a pen and paper). Write down the impact you are experiencing…

Physically (how you feel physically – performance, energy, sleep)

Emotionally (your feelings about your body, your energy, your performance etc)

Mentally (what you think about yourself, your body, etc)

Socially (how your under-eating affects you socially)

Sexually (how under eating is affecting your sex life)

I then ask clients to rate these 1-5 in order of the biggest impact to smallest impact. We then address each of these areas over a period of time starting with the smallest and working towards the biggest.

We start with the smallest as it is the least threatening for someone to change, it is also more likely to produce success which creates a positive belief and confidence to then tackle other areas which may be more challenging.


I would normally start by getting someone to increase their food intake slowly. Maybe as little as 50 to 100 calories at a time. It is about seeing that you can eat more and not gain weight so step by step we increase food intake aiming to keep weight stable. It does depend on where the client is coming from but ultimately this could be more carbohydrate, especially after exercise, more good quality fats and sometimes more proteins.

It is also important that we rebalance stressors in the individuals life. If excessive amounts of exercise is a problem, reducing activity to a level that the individual is comfortable with (this is often very difficult to negotiate) can be so helpful.

You may like to refer to my most recent blog on parasympathetic and sympathetic balance.


In the case of under-eating, especially if coupled with over-exercising, digestive imbalances, adrenal imbalances and thyroid imbalances are common. Therefore, as food intake increases, nutrients and foods which support these systems can be extremely beneficial. The following foods are some of my favourites:

  • Fermented foods: provide beneficial flora for the gut
  • Sea vegetables and seaweed: nourish the thyroid gland
  • Eggs: provide choline for healthy cell membranes and cholesterol for steroid hormones (sex and stress hormones)
  • Oily fish: provide essential omega 3 for healthy cell membranes and manage inflammation
  • Dark chocolate: provides magnesium for health energy cycles
  • Liver: nature’s multi-vitamin containing good levels of B-vitamins for health energy cycles
  • Brazil nuts: provide selenium for the thyroid gland
  • Olives, olive oil, avocado, macadamia, flaxseed and hemp: beneficial fatty acids


It may be appropriate to get additional test done to address any underlying problems. Again, favourites include:

  • Adrenal Stress Test
  • Comprehensive Digestive Stool Anaylsis to address gut issues
  • Thyroid panel including T3
  • Sex Hormone Profile

Based on test results I would often personalise a supplement program to rebalance underlying health concerns.


Want to work with me-


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