About 20% of people with PD lose weight, especially people with advanced PD. This weight loss can be marked, with patients losing 10–20% of their body weight over a short time (six months to a year).
Before assuming the weight loss is from PD, you should be evaluated by your doctor for other causes of weight loss such as AIDS, diabetes, cancer, colitis, hyperthyroidism, kidney or liver disease, malabsorption, and tuberculosis. The weight loss in these disorders is like starvation: you break down and lose both fat and muscle, whereas in PD, you just break down fat. If your weight loss is thought to be related to PD, there are several reasons for it:
Decreased Appetite. Decreased appetite may be caused by anti-Parkinson drugs such as levodopa/carbidopa. This can usually be treated by supplementing each dose of levodopa/carbidopa with more carbidopa, which will decrease the nausea and loss of appetite that may accompany your treatment.
Decreased appetite might be caused by loss of your sense of smell with a corresponding loss of sense of taste. This can usually be treated by using condiments and spices to make your food more appealing.
Anxiety and/or Depression. If you’re anxious or depressed you may lose your desire to eat, and you may no longer take pleasure in eating. Treatment of your anxiety and/or your depression may result in regaining your lost weight.
Increased Physical Activity. If you have a high amplitude, marked tremor of both hands that is present most of the time, it may cause you to lose weight. The typical resting tremor that affects only one hand and is not constantly present does not result in weight loss. Likewise, if you develop marked dyskinesias while on levodopa/carbidopa, you will lose weight. Generally, you will only break down body fat and eventually your weight will stabilize.
Hypothalamus Malfunction. The hypothalamus sits above the pituitary gland, in front of the thalamus, and in the center of your ANS. The hypothalamus regulates your appetite by coordinating the actions of three hormones. One hormone is secreted by the stomach before you eat and increases your appetite, another is secreted by your fat cells and tells you that you’re full, and the third is secreted by the hypothalamus and both increases food intake and decreases physical activity.
The hypothalamus is affected in PD and it is theorized (but not proven) that the hypothalamus is “reset,” so that you burn more calories than you take in, and thus lose weight.
Difficulty Swallowing. Significant difficulty swallowing, enough to cause you to lose weight, occurs late in PD. Symptoms of difficulty swallowing include taking longer to eat, coughing or choking while you eat, and drooling. If you have significant difficulty swallowing, you’ll take longer to eat, you’ll feel full and you’ll eat less.
If it’s thought that your weight loss is related to difficulty swallowing and the loss is significant, you may require a feeding tube. However, in my experience it is rare for a patient to need a feeding tube due to weight loss from difficulty swallowing.
If you have lost a significant amount of weight you should be evaluated by your doctor.