People with Parkinson’s disease (PD) may lose a considerable amount of weight in the later stages of the condition. This may be due to a combination of factors, including low appetite and high energy expenditure.

Weight loss is a common symptom of PD. However, the American Parkinson Disease Association (APDA) emphasizes the importance of ruling out any potential underlying causes of the weight loss first.

This is because weight loss can be the result of many medical conditions, so it may not always be due to PD.

This article examines the link between late stage PD and weight loss. It also looks at why weight loss might occur, when to contact a doctor, and the available treatment options.

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Evidence indicates that weight loss is a symptom that people have reported throughout all stages of PD.

Research from 2017 suggests that, on average, those with PD may experience mild to moderate weight loss in the first 6 years following a diagnosis. However, a person’s weight loss is likely to become more significant as the condition progresses.

Additional reports indicate that many people lose weight in the years before they receive a PD diagnosis. The authors also note that the duration and severity of PD may further increase weight loss symptoms.

This suggests that although weight loss can occur at any stage of PD, it may be more prominent or severe in the later stages of the condition.

As with other stages of PD, weight loss in late stage PD may be due to a combination of factors. These include:

Low appetite

In late stage PD, a person may develop a low appetite as a result of the following:

  • Decreased sense of smell: About 80–96% of people with PD have an olfactory impairment that affects their sense of smell. Smell plays an essential role in food appeal and taste perception. Those with a poor sense of smell may find food less appealing, which can affect their appetite.
  • Depression and other mood conditions: Depression, which can result in a decreased appetite, affects about 35% of people with PD. People with PD may also experience apathy, which is a state of emotional indifference. This is a common symptom of PD, and it can result in a decreased interest in eating or preparing meals.
  • Nausea: Many people with PD may experience nausea and vomiting as a side effect of some PD medications. Nausea can reduce a person’s appetite.

High energy expenditure

Several involuntary movements associated with PD, such as tremors, dyskinesia, and rigidity, can increase energy expenditure and promote weight loss:

  • Tremor: Tremor is an uncontrollable rhythmic muscle contraction in one or more body parts, leading to high energy consumption and, potentially, excessive weight loss. At the onset of PD, the first symptom may be a barely noticeable tremor in just one hand. Over time, the symptoms worsen and progressively spread to other body parts.
  • Dyskinesia: Dyskinesia refers to involuntary muscle movements. Frequent, involuntary physical exertions such as dyskinesia can burn more calories for a person with PD and make gaining or maintaining weight difficult.
  • Rigidity: People with PD may feel involuntary stiffness and tightness in the muscles of the arms, legs, neck, and back. These symptoms might even affect the face. Tight and rigid muscles can increase the body’s energy expenditure.

Gastrointestinal problems

People with PD may lose weight due to gastrointestinal issues that prevent the body from absorbing and using sufficient nutrients:

  • Constipation: A person may have constipation if they have fewer than three bowel movements per week. This is one of the most common gastrointestinal symptoms, affecting between 24.6% and 63% of people with PD. It may be due to malnutrition or the slow movement of digestive waste products in the colon.
  • Dysphagia, or difficulty swallowing: People with dysphagia have difficulty swallowing certain foods or liquids. Some people are unable to swallow at all. Although health experts consider dysphasia to be a late complication, it can sometimes develop early in the course of PD. The inability to swallow may cause low food intake, resulting in weight loss.
  • Gastroparesis: This partial paralysis of the stomach muscles affects the normal movement of food from the stomach to the small intestine. It can affect 70–100% of people with PD and may occur in the early or advanced stages of PD. Gastroparesis may cause other gastrointestinal issues, including nausea, bloating, vomiting, and abdominal discomfort, which can also contribute to weight loss.

The APDA notes that weight loss can be a sign that the disease is progressing. For example, it could be a result of difficulty swallowing, worsening mobility, and impaired gut function.

Weight loss can also lead to malnutrition and vitamin deficiencies. As a result, a person may be more susceptible to:

  • infection
  • fatigue
  • frailty

Individuals who are underweight have an increased chance of osteoporosis, or fragile bones. This can mean that the bones are more likely to fracture if a person falls over.

Weight loss and malnutrition may influence the progression of PD. According to a study in Frontiers in Aging Neuroscience, this weight loss and malnutrition may lead to:

  • involuntary muscle movements
  • cognitive decline
  • orthostatic hypotension, which is a type of low blood pressure that occurs when a person stands after sitting or lying down

If a person with PD is unable to maintain a moderate weight, they or their caregiver should contact a doctor.

A doctor can help in several ways, such as:

  • evaluating the person’s ability to swallow
  • referring the person to a dietitian, who can provide information on high calorie and nutritious foods
  • adjusting PD medications
  • treating depression or other conditions affecting a person’s mood

An accurate diagnosis is usually the first step toward treating and managing weight loss in late stage PD.

Although there are no clinical guidelines on treating and preventing weight loss in late stage PD, the doctor will evaluate a person’s symptoms, weight, and nutritional status to rule out any underlying causes.

After diagnosing the condition, the doctor may adjust a person’s PD medication dosage or treat any underlying condition that is responsible for the weight loss.

The Parkinson’s Foundation notes that a doctor may also recommend:

  • eating small, frequent meals every 2–3 hours
  • eating favorite foods
  • incorporating a dietitian’s tips on how to eat a high calorie, nutritious diet
  • taking a doctor-approved nutritional supplement
  • increasing the consumption of whole grains
  • avoiding filling up on tea, coffee, or clear soup
  • keeping easy-to-prepare foods on hand
  • choosing foods that are easy to chew, such as smoothies, ground meat, and other soft proteins
  • seasoning foods with herbs, spices, and sauces to help stimulate a person’s appetite

Weight loss is a common symptom of PD. Although it can happen at any stage, a person’s weight loss may be more significant during the later stages of the condition.

There are many reasons why people with PD typically experience weight loss. These include nausea, a decreased sense of smell, depression, and medication side effects. Certain PD symptoms, including dyskinesia, tremor, and difficulty swallowing, can also lead to weight loss.

People should contact a doctor if they are not able to maintain a moderate weight. Weight loss can result in malnutrition and put a person at higher risk of complications.

A doctor will be able to rule out any underlying causes and provide tips on how a person can increase their appetite and gain weight safely.