As a clinical dietitian working with patients with Parkinson's Disease (PD), I had many queries about the potential value of protein restriction with PD. I hope this article will offer insight into the risks, benefits, and indications for use of this dietary therapy.
Levodopa is the most common medication used to treat symptoms of PD. Dietary-derived large neutral amino acids compete with levodopa for transport into the brain across the blood/brain barrier. High protein intake may result in inadequate levels of levodopa in the brain, resulting in unpredictable fluctuations in motor performance. Studies of people who experienced severe, unpredictable fluctuations in motor performance while taking levodopa (the on/off phenomenon) who consumed protein-restricted diets during the day (when motor skills were most needed) and then ate enough protein in the evening to meet their dietary requirements, showed that some people experienced some benefit from the diet. Concerns arose about subjecting a nutritionally vulnerable patient population to a restricted diet over the long term (1). The availability of controlled release preparations of levodopa and the use of surgical interventions have reduced the need for protein restriction (2), which is unfortunately still widely promoted by many health professionals.
There is no justification for the use of a protein-restricted diet patients with PD who neither use levodopa nor experience unpredictable motor fluctuations in association with use of the medication. Use of a protein-restricted diet may increase the already substantial risk for malnutrition. Weight loss and poor protein status indicated by reduced muscle mass and law serum albumin are common. To compound concern about dietary restriction, in trials with protein-restricted diets, suboptimal intakes of several nutrients, including calcium, were observed. Many people expressed concern about hunger, lack of variety in the diet, and decreased palatability of low protein food (3). Some patients have noticed that protein intake influences the effectiveness of their medication. Rather than advising a low protein diet, these individuals should be encouraged to redistribute their protein intake to avoid taking high protein foods and levodopa simultaneously. Taking medication 15-30 minutes before meals may be helpful; however, this is not always feasible, as many individuals take their medication with food to prevent nausea (4).
The decision to try out a modified diet should be made in consultation with a neurologist and a dietitian. Patients starting the diet must be carefully monitored, as detrimental side effects of levodopa including nausea, vomiting, dyskinesias and hallucinations are more likely with enhanced uptake of the drug. Those most likely to benefit from the restriction are often at the end-stage of the disease and are already nutritionally compromised. Following a restricted diet may further diminish their nutritional status (5).
Any therapy that holds promise for controlling PD symptoms may be attractive. Patients should be informed that protein intake modification has been shown to help only those who experience severe "on/off" fluctuations in association with levodopa use. Patients who opt to try the diet should be monitored by a neurologist, and advised on optimizing dietary intake, including discontinuing the diet if no benefit is observed after one week. Any potential benefits should be noted almost immediately.
[Reference]
1. Tsui JKC, Ross S, Poulin K, et al. (1989).The effect of dietary protein on the efficacy of L-Dopa: a double blind study. Neurology, 39(4), 549-552.
[Reference]
2. Calne DB, Calne S. (1997). Treatment of Parkinson's disease. in: Ancil RJ, Holliday SG, Mithani AH (Eds.), Therapeutics in Geriatric Neuropsychiatry. Chichester: John Wiley, & Sons Ltd., 1-12.
3. Pare S. Barr S, Ross S. (1992). Effect of daytime protein restriction on nutrient intakes of free-living Parkinson's disease patients. American Journal Clinical Nutrition, 55: 701-707.
[Reference]
4. Carter J, Nutt J. (1995). Dietary issues in Parkinson's disease. In holler W, Paulson G (Fds.), Therapy of Parkinson's Disease (2rcd edj. New York: Marcel Dekker, 443-461.
5. Olanow CVV; Koller W. (1998). An algorithm (decision tree) for the management of Parkinson's disease: treatment guidelines. Neurology, 50: SI-557.
[Author Affiliation]
Contact Information:
Meredith Cushing; RDN
meredithcushing@hotmail.com
Meredith was formerly a clinical dietitian at UBC Hospital, Vancouver and is embarking on graduate studies in Indianapolis, IN.
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