'Sick Enough': The Complications of Undereating in Eating Disorders
- Talia Cecchele
- 3 days ago
- 5 min read
Written by Talia Cecchele, Highly Specialist Dietitian and TCN Founder
If you’ve ever thought…“I’m not sick enough to need support.” You’re not alone.
This belief shows up time and time again in the work we do as eating disorder dietitians, and it’s one of the biggest barriers to people getting the help they deserve.
At the TCN Clinic, we support people through nutritional rehabilitation to both prevent medical complications of undereating and for the reversal of symptoms to improve nutritional wellbeing.
Sadly, the reality is that undereating impacts your body in ways that aren't visible, so even though you might feel "fine" your body is likely working hard to protect you.
You Don’t Need to “Look Sick” to Seek Support
One of the biggest misconceptions around eating disorders and undereating is that it's only serious when you can "see" that someone is unwell. As a mental health illness, this is a worrying position many people are put in due to stigma, medical gaslighting and inequalities in accessing healthcare.
The reality is, that in the UK, 94% of people seeking support for an eating disorder are not underweight. If your relationship with food is impacting your life any way (physically, mentally, or emotionally), that is enough of a reason to seek support.
You can listen to Talia and Dr Gaudiani (author of Sick Enough) on the Food Is Food podcast where they explore what “sick enough” really means… and more importantly, what often gets missed.
The Complications of Undereating in Eating Disorders
When the human body isn't receiving enough energy, the body responds by slowing metabolic processes in an attempt to conserve energy. This is a biological response to survival that has evolved over the millennia.
Let’s cover some of the most common complications of undereating in eating disorders (and disordered eating).
1. Heart Health
When your body isn’t getting enough energy, it adapts. One of the ways it does this is by slowing your heart rate to conserve energy — a state known as bradycardia.
As a result, you might notice:
Low heart rate (pulse less than 60 bpm)
Feeling dizzy or lightheaded
Fatigue
Feeling cold often, even in warmer temperatures
Having cold hands and feet
Reduced exercise tolerance
It is important not to confuse a malnourished heart with a 'fit' heart. One has weakened muscle and needs to work hard even at low intensity, while the other is strong and therefore doesn't need to work as hard to pump blood around the body.
2. Bone Health
When the body is in energy conservation mode, bone marrow production can reduce as the body tries to save energy. This can lead to:
Reduced bone density (osteopenia or osteoporosis)
Increased risk of fractures
Hormonal disruptions
Reduced production of blood cells (red cells, white cells, platelets) due to bone marrow suppression
3. Blood Tests or Biochemistry
This can be a result of nutritional deficiencies or signs of a body conserving energy (and different organs under stress). The impact of undereating can show up as:
Low white blood cell count (due to bone marrow suppression)
Anaemia (due to bone marrow suppression or low iron intake)
Electrolyte imbalances (commonly a result of compensatory behaviours such as vomiting and laxative misuse, and also in refeeding syndrome)
High cholesterol due to the liver cells breaking down (where cholesterol is stored) and releasing cholesterol into the blood
Elevated liver function tests (e.g. ALT)
Low thyroid function (e.g. T3) as the hypothalamus conserves energy
It is also really important to note that some people might be severely undereating, however their blood results come back normal. This comes down to genetics and how human bodies respond differently to undereating. Just because your blood test results come back normal, it doesn't mean that everything is "fine."
4. Brain Health
Your brain is the hungriest organ in your body, using approximately 20%-25% of energy at rest. When you are undereating, the brain senses this as a threat of famine and our primitive survival instincts kick un (remember, humans are animals too).
You might experience:
Hypervigilence (scanning for threat constantly)
Difficulty concentrating
Increased anxiety or irritability
Rigid or obsessive thinking
Low mood
5. Digestive Issues
Most people experiencing disordered eating and/or undereating will experience digestive issues. Many people think that food is to blame and further restrict their intake (or go on a Low FODMAP diet for IBS) when axtually the two main causes are increased anxiety and a digestive system that is working more slowly due to the body trying to conserve energy.
When digestion is slowed, this can lead to:
Bloating
Constipation or diarrhoea
Feeling full quickly (early satiety)
Nausea
Bloating
Abdominal pain
Instead of eating less (which helps to reduce abdominal pain), symptoms will only improve in the long term if the body is receiving adequate nutrition for all metabolic processes to return to normal. Following a restrictive diet might worsen digestive symptoms and reduce the good bacteria in your gut.
6. Metabolism
When you undereat, metabolic processes slow down. This doens't mean that your metabolism is broken, your body is just doing what it is meant to for survival. When you eat adequately, your metabolic processes will return to normal.
Some people will experience hypermetabolism. We have a blog post dedicated to this topic here.
Why You Might Feel “Fine” (Even When You’re Not)
One of the most confusing things, is that you might be eating less than you need but still feel energised, productive and "fine." If we take this back to our primative response to survival, you wouldn't be able to go and find food if you were exhausted and sleeping all day. Your body and brain are trying to do whatever is possible in order to help you survive.
Your body is always communicating with you. Even when things look “normal” on the outside, there can be a lot happening beneath the surface.
Need Support?
If you need support in your recovery, we offer 1:1 nutrition counselling at the TCN Clinic to help you overcome food rules and build a more positive relationship with food. You can find out more about how we can support you here.
Talia Cecchele
TCN Director and Lead Specialist Dietitian
Talia Cecchele Nutrition (TCN) is a virtual clinic with a team of registered dietitians specialising in eating disorders and disordered eating. Our services include 1:1 consultations, group meal support and group programs to support you to break free from food rules and chronic dieting and find food freedom. Talia and her team work by incorporating a compassion-led, non-diet and weight inclusive. To enquire about a private consultation please fill out a contact form.
REFERENCES:
Gaudiani, J (2025). Sick Enough: A Guide to the Medical Complications of Eating Disorders and Undernutrition.
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