While it is rather common for people to blame themselves for being overweight, this might not always be the case. In most cases weight gain is indeed caused by consuming more calories than the body will burn during the day due to a combination of eating too much unhealthy foods and a lack of physical exercise. With this in mind, it seems that the idea that healthy diet and active lifestyle are the only way to achieve and maintained desired weight is rather well founded. Again, this is indeed the case for a vast majority of cases – majority, but not all. So, what else can cause weight gain?

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There are some situations when otherwise unexplained weight gain can actually be tracked to already existing health problems or even medications that are used for the treatment of the given condition. Here we will consider which exact condition can cause weight gain as a related symptom while exploring the mechanisms leading to weight gain.


Hypothyroidism, also known as thyroid hormone deficiency is a medical condition caused by the underperformance and overall lower levels of hormones produced by the thyroid glands. These naturally produced compounds are tasked with managing the body’s metabolism so it comes as no surprise that any problems with thyroid gland will manifest through problems with metabolism. More commonly diagnosed in women than men, the symptoms of hypothyroidism can take many years to manifest and they tend to be closely associated to weight gain in a majority of cases.

Don’t confuse the condition with hyperthyroidism, which is the opposite – a condition marked by overactive thyroid gland and the subsequent production of excess hormones.

Located just below the Adam’s apple in the throat, the thyroid gland is ductless gland that is tasked with the production of hormone thyroxine (also known as T4) which is later transformed in the triiodothyronine (or T3) in the kidneys and the liver. Both T4 and T3 play a crucial role in managing body’s metabolism by causing a chain of chemical reactions that break down the molecules in the food, subsequently converting them into energy. This process is of essential importance for health and proper functioning of the organism, keeping the organs working properly and helping the body repair itself in the case of an injury.

When hypothyroidism is diagnosed, it means that the thyroid gland cannot produce enough thyroxine to satisfy the body’s needs, causing the body to eventually become ‘run down’ in a sense. The common symptoms will include:

  • Unexplained weight gain
  • General fatigue
  • Heightened sensitivity to the cold
  • Depression
  • Feeling constipated
  • Disruption of the menstrual cycle
  • Drowsiness
  • Feeling less focused or alert
  • Dryness of the hair and skin
  • Aches and stiffness in the muscles and joints

If left untreated, the condition can cause various heart illnesses, problems with fertility, mental health issues as well as nerve damage. In most cases, hypothyroidism is caused by damage to the thyroid gland, caused by the injury to the gland. The injury can occur during surgery, but is much more commonly caused by the body’s own immune system due to so-called autoimmune thyroiditis. There are also some indications that viral infections can also cause short term damage to the thyroid gland.

While weight gain is a very common and well known side effect of hypothyroidism, the amount of weight gained because of this problem is relatively limited, peaking at 5 to 10 pounds, reaching 20 pounds in much rarer cases. Following treatment, the patient can lose as much as 10% of his or her body weight, with the weight loss being significantly decreased if the condition has been untreated for a long time.

Polycystic ovary syndrome

Polycystic Ovary Syndrome, often abbreviated to PCOS is a relatively common condition affecting roughly one in five women in the United Kingdom. While many of those don’t experience any symptoms, those who do will usually notice problems in their late teen years or early 20s. There are some indications that this condition is linked to a kind of resistance to the hormone insulin and imbalance in levels of male sex hormones called androgens.

PCOS is marked by difficulties in the development of eggs in the ovaries due to high levels of male sex hormone testosterone. The excess presence of this hormone will cause the eggs to remain trapped in the follicles during ovulation.

The usual symptoms that serve as earliest hints that there might be some problems include excess hair growth, hair loss and acne.

The link to insulin is made due to the fact that high levels of insulin present in the body tend to cause difficulties with transformation of glucose into energy, thus contributing to weight gain. In many cases, this will create a feedback loop where extra weight gained will encourage the body to produce even more insulin, leading to further weight gain. At the same time, the excess presence of male sex hormones in women can cause those affected to accumulate the excess weight around the waist, thus increasing the risk of heart conditions and problems such as type 2 diabetes.

As of now, PCOS cannot be efficiently cured, but it can be managed with significant success through certain lifestyle changes, medications or, more commonly, the combination of both. Losing weight with physical activity and healthy diet can greatly improve your overall health and wellbeing, with the loss of just 5% of total body weight leading to significant improvements of general health, including the symptoms of PCOS.

Depression and anxiety

Roughly one in four people in the UK gets diagnosed with a mental health issue each year. And while a significant portion of those affected tends to experience weight loss, the symptoms of these mental health problems can actually cause others to gain weight. Regardless of the direction the weight change eventually takes, it can have serious health implications.

Problems with insomnia, lack of energy and motivation as well as feelings of hopelessness that accompany both depression and anxiety can cause those affected to begin avoiding physical and outdoor activities, instead staying at home and consuming fat and sugar-rich foods for comfort. If weight gain follows, many will experience further loss of self-confidence as well as decrease in the feelings of self-worth, leading to a vicious cycle of poor diet and weight gain.

There are numerous approaches to managing mental health problems, and the research into the topic has shown that aside from therapies and medication, things such as exercise or just spending time with friends and family can help.

Fluid retention

Oedema, colloquially known as fluid retention, refers to the accumulation of fluids under the surface of the skin, between areas of tissue and in the body’s organs is exceptionally common, especially when it manifests in the feet and lower leg. In some cases, this condition can be short-term, usually caused by long periods of standing, but in other cases it can be a symptom of a more serious medical condition.

In addition to weight gain, fluid retention is usually accompanied by soreness of the muscles, joints and limbs, as well as in the changes in the colour of the skin. While these symptoms might eventually disappear on their own, if they prove to be difficult to deal with, you should definitely visit the doctor to check if oedema might be a symptom of an underlying medical condition.

Cushing’s syndrome

Cushing’s syndrome is a very rare medical condition marked by excess of the cortisol hormone. Most commonly, this condition is caused by prolonged use of corticosteroid medicine, but it can also be linked to tumour growth in the pituitary gland in which case, the condition is classified as endogenous Cushing’s syndrome or Cushing’s disease.

Weight gain caused by this condition will lead to the accumulation of fat in the face and middle section of the body, with characteristic hump between the shoulders and the back of the neck. People affected will also notice the fragility of their skin (easy bruising), high blood pressure, brittle bones and problems with fertility and depression.

Due to the fact that the early symptoms of Cushing’s syndrome can be easily misdiagnosed as symptoms of hypothyroidism or high blood pressure.