Medical Reasons You’re Not Losing Weight

I’ve found over the years that many people think there may be an underlying medical reason as to why they are gaining weight, or are having difficulty losing it. In this post, I’m going to take you through the common and not so common medical reasons why people struggle to lose weight. 

I find it really helps to think of these as problems with some of the different hormonal systems within the body. Let’s start with one of the most common hormonal reasons why people have weight problems.

Table of Contents

Thyroid Hormone Problems

The thyroid hormones are an important regulator of our metabolism. I like to think of them as acting like the accelerator (gas) pedal in a car, controlling the speed of many of the body’s functions. If the thyroid is overactive everything speeds up. If it’s underactive, everything slows down.


This is by far the most common cause of issues with weight loss that I see. Approximately 5% of people have a problem with their thyroid gland and an estimated 60% of those are undiagnosed and untreated.

I’ve compiled a list of some of the symptoms of hypothyroidism, and to show you what I mean about the role of the thyroid as a controller of the body’s metabolism I’ve included the symptoms of hyperthyroidism too.





Slow Heart Rate (Bradycardia)Fast Heart Rate (Tachycardia)
Low Mood / IrritabilityAnxiety / Agitation
Memory Loss 
Hair Loss  
Cold IntoleranceHeat intolerance

Thyroid problems are VERY common and frequently missed

Tests for thyroid disorders are among the first tests that I order for my patients who are struggling to lose weight, or who are experiencing unexpected weight gain.

Hypothyroidism is really common, easy to test for, easy to treat and frequently undiagnosed

So if you’re experiencing some of the symptoms mentioned above, then it’s probably a good idea to ask your doctor to consider testing for these.

Cortisol (Stress) Hormone Problems

Cortisol is one of the main hormones that helps us respond to stressful situations.

It has some very useful short-term effects, such as:

1.Increasing blood sugar levels
2.Increasing our attention
3.Decreasing sensitivity to pain
4.Increasing our blood pressure

If you’re being chased by a lion, these are all pretty useful things to happen! 

The problem with cortisol is when these effects become prolonged, such as when someone is always stressed out!

medical reasons for not losing weight

Chronic Stress

Ongoing (chronic) stress is definitely VERY bad for our health.

Persistently raised cortisol causes:

  • Persistently raised blood glucose levels (think diabetes)
  • Persistently raised blood pressure (think heart disease and strokes)


  • Decreased immune system (people who are chronically stressed frequently get more minor infections)
  • Decreased serotonin (the happy chemical) production (think depression).

The excess glucose levels caused by consistently raised cortisol cause weight gain and will also cause cravings for sugary, high-carb foods.

In fact, there is a disease that also causes excessive cortisol secretion, which gives us an extreme version of what happens if we are chronically stressed.

Cushings Disease

A rare (usually benign) tumour that causes excessive secretion of cortisol, which leads to:

  • Weight gain, typically around the abdomen
  • Red, puffy, rounded face
  • Easy bruising
  • Purple stretch marks
  • Mood issues.

Anxiety & Depression

Persistently raised cortisol is also something people with anxiety and depression can experience, so it’s not hard to see why people who are suffering from these mental health issues often gain weight. 

Some medications used for anxiety and depression also cause weight gain. We will discuss medications later…

Leptin Issues

What is leptin?
Leptin is a hormone that is produced by our fat cells. High levels of it tell our brain that we don’t need to eat… so it reduces our appetite!

Sleep Problems

signs you're in ketosis
When sleep goes down, weight goes up.

Sleep is an important regulator of our metabolism, and therefore our weight. There are a couple of ways in which it goes about doing this:

1.Sleep deprivation leads to reduced levels of leptin. So you’re simply more hungry after a bad night’s sleep.

2. And to top that off… a tired brain doesn’t make such well-reasoned judgements about nutrition. In fact, you’re far more likely to be impulsive and give in to the desire for junk food after a bad night’s sleep!

A study from Finland showed that women who had six hours or less sleep gained on average an extra 5kg (11 pounds) over a 7-year period compared to those who slept longer!

Leptin Resistance

As I mentioned before, leptin is produced by the fat cells to send a signal to your brain.

So why do obese people get hungry AT ALL?

Think about it. If you are obese, you have a lot more fat cells that are producing leptin, so you are producing lots of it…this should, in turn, reduce your appetite so that your weight normalises again. 

But something is clearly going wrong.


In the same way that an alcoholic becomes resistant to the effects of alcohol (and requires more booze to get intoxicated), our brains can also become resistant to the effects of leptin.

This is leptin resistance, and is one of the key hormonal problems that hinders you in your progress towards losing weight.

This is probably not a condition that you will find regularly diagnosed by your doctor, but it is one of the key hormonal problems that causes weight issues!

Insulin Problems

Insulin has many roles in the body, but one of the key roles is the regulation of glucose levels in the blood.

I talked about how understanding the role of insulin in the body is key to understanding weight loss in this video.

If our pancreas senses that blood glucose levels are elevated (such as after a meal that was high in carbohydrates), then it will release insulin into the bloodstream.

Insulin allows blood glucose to be taken up by the cells (mainly fat cells and muscle cells).

Insulin Resistance

Much like with leptin resistance, where the brain stops listening to the signals from leptin, insulin resistance also occurs.

In someone with insulin resistance, more insulin is needed to deal with the same amount of glucose. This means that raised insulin levels exist long after someone has had a meal.

If you’ve never heard of insulin resistance before – it’s one of the key hormonal abnormalities in all of the following conditions:

  • Obesity
  • Pre-diabetes
  • Type 2 Diabetes
  • Polycystic Ovary Syndrome (PCOS)

Remember, insulin is the hormone that tells your body to store fat… and if it’s raised above its normal level, then you’re going to have issues with weight (easy to gain, hard to lose).

Other Medical Reasons

There are a few other medically important reasons why people have weight issues.


various medications spilling onto the table

Many of the reasons that people gain weight while on various types of medication. This is often down to the actions that those medications have on the hormonal symptoms described above.

  • Insulin (or any drug that tells the pancreas to produce more insulin) will cause weight gain.
  • Steroid medications – these are essentially synthetic versions of cortisol. We are usually given them in order to suppress the immune system, but they have all the other same effects as chronic stress too.
  • Many antidepressant tablets also cause weight gain for a variety of different reasons (beyond the scope of this article).


Finally, there is one other condition that many doctors have never heard of. 

Lipoedema is a long-term (chronic) condition where there’s an abnormal build-up of fat cells in the legs, thighs and buttocks (and occasionally the arms too). It almost exclusively affects women. 

People with this condition really struggle to lose the weight from those areas, and in fact, may lose weight off the upper body quite well. 

If you have a significant disproportion of fat distribution around your lower half, and you find it very difficult to lose weight from these areas, then this is something you may wish to look into further.


If you’ve identified something in here that you think needs assessing then definitely go and have a chat with your doctor.

You’ll probably realise that all of these disorders have a hormonal basis.

  • Thyroid hormones
  • Cortisol
  • Leptin – appetite
  • Insulin (resistance)

Often in people who are struggling with their weight, there is a mixture of these different problems going on. For example, leptin resistance and insulin resistance commonly co-exist.

So it’s not too much of a leap to say that weight problems are far more about hormones than about calories.