Involuntary Weight Loss: Why Does It Occur?

Involuntary weight loss is more common than is generally believed. Most of its causes are natural, but psychological disorders and other diseases are among the possible origins.
Involuntary Weight Loss: Why Does It Occur?

Last update: 10 September, 2021

Involuntary weight loss is when a person reduces their body volume without trying to do so. In other words, this individual isn’t undergoing a deliberate treatment or a specific diet to shed these pounds. Doctors consider this situation to be a warning sign of many possible conditions.

When a patient consults a doctor regarding involuntary weight loss, the professional immediately look for underlying causes to rule out malignant processes and serious life-threatening diseases.

It’s important to clarify that not all involuntary weight loss is extremely serious, as long as it doesn’t persist over time. Therefore, a professional evaluation is important in each case to determine the steps that must follow.

Strictly speaking, the health team should be on alert if the patient loses more than 5% of their previous weight in 6 months. If the drop in pounds is at the limit of that percentage, it’s possible to wait up to one year.

Who’s most at risk and why?

There are population groups more prone to suffer involuntary weight loss than others. In a healthy adult, it’s rare, although it can appear spontaneously. The situation is different in those over 60 years of age, among whom the symptom can appear with a frequency of more than 10%.

With hospitalizations, there’s a constant of 2% of hospitalized patients losing weight during hospitalization. However, if this hospitalization is long or turns to institutionalization, then the prevalence increases up to 50 %.

Involuntary weight loss leads to an increase in morbidity, and in patients with a previous disease, it worsens the prognosis. In the case of cancer, it’s a sign of progression and poor response to treatment.

An elderly woman in a hospital with an oxygen mask over her face.
Prolonged hospitalizations cause involuntary weight loss in almost 50% of patients.

The causes of unintentional weight loss

One reason for involuntary weight loss that escapes medicine is socioeconomic reasons. Lack of money and lack of accessibility to nutrients due to social barriers lead to unwanted malnutrition. At the same time, we have three main groups of causes that we’ll see below: Organic causes, psychological causes, and drug-related causes.

The organic origins of unintentional weight loss

There are many organic causes of this symptom, from systemic disorders such as neoplasms to hormonal modifications such as diabetes. Sometimes they represent a real diagnostic challenge.

In cancer, we often speak of a constitutional syndrome, which is a combination of involuntary weight loss, asthenia (lack of strength), and anorexia (lack of appetite). Although it manifests itself in various malignant illnesses, it’s more typical of stomach cancer.

Gastrointestinal disorders result in lower weight because patients eat smaller amounts to avoid symptoms. This is true in celiac disease and Crohn’s disease.

Among the hormonal variations that alter appetite and nutrient absorption is adrenal insufficiency, the maximum expression of which is Addison’s disease. Diabetics suffer from different pathways, linked to changes in taste and smell perception, as well as variations in insulin.

In patients with neurological diseases, there’s a behavioral alteration that explains eating problems and, consequently, weight loss. In Parkinson’s, Alzheimer’s, and vascular dementia, patients refuse food when it’s offered to them.

Psychological causes

Depression is a cause of involuntary weight loss that can be masked by other pathologies. Depressed individuals eat less, but often hide it and attribute their thinness to external or external factors.

Anorexia nervosa, characterized by the refusal to eat, sometimes due to the impossibility of swallowing, without a specific obstruction of the digestive tract, leads to thinness with serious health risks. It’s a disorder that tends to appear more frequently in young women than in the rest of the population.

Finally, addictions to alcohol and other more potent drugs, such as cocaine, displace eating habits. Addicts don’t respect lunch and dinner schedules and don’t ingest the nutrients the body needs to build its body mass.

A woman turning down a plate of pasta.
Lack of appetite may be caused by an underlying psychological disorder.

Find out more: Natural Remedies for Children with Poor Appetite


Several drugs have involuntary weight loss among their adverse effects. When prescribed for another symptom or another illness, they cause, in the background, a decrease in pounds.

Levothyroxine prescribed for hypothyroidism accelerates metabolism and, in high doses, consumes kilocalories. Levodopa for Parkinson’s disease also causes unintentional weight loss, as do digoxin and liraglutide.

Don’t let time go by with unintentional weight loss

Both people who notice an abrupt drop in weight and physicians who are consulted for this symptom need to be vigilant. The appropriate complementary tests must be performed to get a diagnosis and treat the source of the problem so that it doesn’t get worse.

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  • Suárez-Ortega, Saturnino, et al. “Síndrome constitucional: entidad clínica o cajón de sastre.” Revista Médica del Instituto Mexicano del Seguro Social 51.5 (2013): 532-535.
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