Unintentional Weight Loss – Common Causes and Symptoms

Physiological or Intentional Weight Loss

Loss of body weight can be intentional or unintentional. With intentional weight loss, the person undertakes certain changes in their lifestyle which results in a loss of body weight. This may also be referred to as physiological weight loss which may be a result of :

  • Low food intake – dieting, fasting or starvation (voluntary).
  • Increased physical activity – exercise, sports, manual work.
  • Old age – loss of appetite, impaired nutritional intake due to various physical (frail), pathological (chronic/terminal disease), psychiatric (senility, dementia, depression), or even socioeconomic factors.
  • Medication – chronic drugs, scheduled and over-the-counter medicines is used over a long period of time.
  • Medical weight loss – supervised program for losing weight including the use of weight loss drugs or after weight loss surgery.

These causes will explain a drop in body weight and should first be corrected or moderated to assess if the body weight will increase or return to normal. If this does not occur or if there are signs and symptoms of some disease then the causes of weight loss may be pathological, meaning that it is a result of disease which is usually chronic in nature.

Any loss of weight that is more than 5% of the normal body weight over a 6 month period or less, which is not intentional, should be investigated.

Pathological or Unintentional Weight Loss

Disease Weight Loss

With unintentional weight loss, the reduction in body weight may be due to a disease. This is also referred to as pathological weight loss. At times, a patient may be unaware of an underlying condition that may be contributing to the loss of weight because the presenting signs and symptoms are ignored or not evident as yet. The most common cause of weight loss due to disease is a result of a lack of appetite, nausea or limited calorie intake. Malabsorption may be another factor.

Any chronic condition may lead to weight loss if the ailment is causing significant physical and psychological distress which may lead to a loss of appetite that is not a feature of the disease itself. Some of the causes may be a result of decreased mobility thereby preventing or hampering food preparation and intake.


Cachexia is a medical term for weight loss and muscle wasting seen in systemic infections like AIDS, organ failure and cancer. In cachexia, the weight loss is due to catabolism which is the increased metabolic rate as a result of cytokines released by immune cells and proteolytic enzymes which break down protein. The weight loss in the early stages of these diseases may be due to a lack of appetite, nausea and malabsorption. Cachexia is often described as the terminally ill patient ‘wasting away’ and not every case of pathological weight loss will be due to cachexia.

Causes of Unintentional Weight Loss

The conditions and diseases below are some of the common causes of pathological weight loss. Not all the symptoms or clinical features listed for each cause may be evident. There are a number of other causes which should also be considered in the event of unexplained weight loss.


Food may be deprived by the abuser (starvation) or lack of appetite may be due to fear, anxiety or depression. Signs of physical or sexual abuse may also be present.

  • Poor self esteem.
  • Nervous disposition.
  • Behavior changes.


Weight loss is a common feature of most types of addiction, including alcoholism, narcotic drug abuse and prescription medication addiction. Nicotine may also play a part in suppressing appetite.


A malignancy may often be missed until the latter stages of the disease. Unexplained weight loss and fatigue may be the only signs in the early stages.

Chronic pain

May be due to conditions like fibromyalgia or pain due to unknown causes.

  • Limited movement.
  • Difficulty sleeping
  • Irritable.
  • Depressed.


Both diabetes mellitus and diabetes insipidus may result in weight loss.

  • Frequent/excessive urination (polyuria).
  • Increased thirst (polydipsia).

Eating Disorders

Weight loss is a common feature in most types of eating disorder, particularly anorexia nervosa. This should be suspected in teenagers and young adults, particularly females and especially in those with a preoccupation with food or meal time.

  • Avoiding food.
  • Binge eating.
  • Purging.
  • Poor self esteem.
  • Obsession with body weight or shape.

Gastrointestinal Infections

May be due to viral, bacterial, fungal or parasitic infectious agents. Human intestinal parasites may remain unnoticed for long periods of time.


Infection with the human imuunodeficiency virus (HIV) or the onset of AIDS may lead to weight loss with cachexia often noted in the latter stages.

  • Night sweats.
  • Fevers.
  • Fatigue.
  • Repeated infections like the common cold or seasonal flu.


Also referred to as thyrotoxicosis, the weight loss is due to an overactive thyroid gland and igh levels of thyroid hormones which increases the basal metabolic rate.

  • Intolerance to heat.
  • Excessive or abnormal perspiration.
  • Tremors.
  • Protruding eyeballs (exopthalmos).

Mental Illness

This may vary from depression to bipolar disorders, dementia and schizophrenia.

  • Poor self esteem
  • Delusional
  • Impaired cognitive abilities or perception
  • Irrational behavior.
  • Abnormal patterns of behavior in terms of daily activities and social interaction.


Active infection with Mycobacterium tuberculosis may result in weight loss. Tuberculosis (TB) primarily affects the lungs but other sites may also be affected without any lung involvement.

  • Night sweats.
  • Fevers.
  • Fatigue.
  • Chest pain, shortness of breath (dyspnea), coughing up blood (hemoptysis), persistent coughing in pulmonary tuberculosis (lung TB).


Mental or emotional stress may result in weight loss due to a lack of appetite and decreased food intake. Usually the person is either preoccupied with an activity or past event but hormonal causes (stress hormones) may also be involved for the lack of appetite. Apart from work stress or financial worries, recent traumatic incidents like death, divorce or post traumatic stress (war, acts of crime) may result in temporary loss of appetite and weight loss.

  • Irritable.
  • Weepy.
  • Panic attacks.
  • Insomnia.
  • Nightmares.

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