by Kathrynne Holden, MS, RD

From: Issues in Vegetarian Dietetics, Summer 2000; Vol. 9(4):1-6

Kathrynne Holden, MS, RD, is the author of "Eat Well, Stay Well with Parkinson's Disease" and "Parkinson's Disease: Guidelines for Medical Nutrition Therapy." You may visit her website at:

The nature of Parkinson's disease

Parkinson's disease (PD) afflicts about one to one and one-half million people in the United States [1]. PD is a progressive neurological disorder that results in the death of dopamine-producing cells in the brain. Loss of dopamine affects movement, both of skeletal muscle and the smooth muscle of the gastrointestinal (GI) tract. This can result in slow, shuffling gait, resting tremor, and/or slowed peristalsis. Individuals with PD may experience frequent falls [2, 3], difficulty handling cooking and eating utensils, and such GI-related problems as slow stomach emptying, gastroesophageal reflux, and chronic constipation [4, 5, 6, 7].

Nutrition-related problems

Individuals with PD have been found to have a higher incidence of bone thinning and fractures than age-matched control groups [8, 9, 10, 11, 12, 13, 14]. Loss of the olfactory sense and sense of taste are frequently present [15, 16], along with xerostomia (dry mouth) [17] and sometimes loss of appetite [18]. These, along with other factors, may contribute to the high rate of unplanned weight loss in this population [19, 20, 21].

There are also indications that B vitamin deficiencies may be of concern, although the causes are not clearly understood. In 1979, Bender et al. reported the possibility that users of levodopacarbidopa (Sinemet, Sinemet CR, medication used to treat the symptoms of PD) could be at risk for both niacin and vitamin B6 deficiencies [22]. Long-time users of levodopa-carbidopa have since been found to have increased levels of serum homocysteine [23, 24] implicating vitamins B6, folate, and B12. In attempts to determine the etiology of PD, Hellenbrand et al. compared the dietary habits of patients vs a control group; patients were found to have consumed significantly less niacin than controls [25]. In a more recent Swedish study researchers noted that consumption of niacin-containing foods appeared to reduce risk for PD [26]. Finally, in an unpublished study, pellagra was discovered in several patients using levodopacarbidopa [27]. Thus, patients could have increased risk for vascular disease, pellagra, and other conditions resulting from deficiencies of B vitamins.

Constipation is very common due to the disease and/or to the medications used to treat PD [4, 28, 29]. Because chronic constipation can raise the risk for fecal impaction [30] and colon cancer [31, 32], safe methods of controlling constipation are desirable. Furthermore, PD brings with it a food-medication interaction that has been generally underaddressed by dietetics professionals. Levodopa, the primary medication used to treat PD, competes with the five large neutral amino acids for carriers, both in the gut and at the blood-brain barrier[33]. Thus, levodopa absorption is effectively blocked if taken with meals.

A Vegetarian diet and Parkinson's Disease

While research has failed to conclusively show a link between diet and PD, nevertheless, the fiber, protein, and nutrients found particularly in plants are excellent reasons to choose among the various vegetarian and plant-based eating plans. Animal foods are often high in protein and lack fiber, whereas plants generally have a high proportion of carbohydrate and moderate amounts of protein. Plants also contain fiber and many phytochemicals, which animal products do not.

Fiber. A plant-based diet is generally richer in fiber, which can alleviate constipation and thereby reduce risk for fecal impaction and colorectal cancer. In a pilot study, McIntosh and Holden found that while 21 out of 24 patients reported frequent constipation, analysis of three day food diaries showed that 18 patients reported intake of fewer than 25 grams of dietary fiber daily [29]. Education in the need for greater fiber intake, and its benefits to health, is necessary for PD patients. Additionally, a high-fiber eating plan may promote bioavailability of levodopa. Astarloa et al. found a correlation between a diet rich in insoluble fiber and plasma levodopa concentration, and postulate that the improvement of constipation may have a positive effect upon levodopa availability [34]. While there is no research as yet on benefits of a vegetarian diet for people with PD, it appears possible that the higher fiber content of a vegetarian or plantbased diet may be helpful for people with PD.

Unplanned weight loss. To combat weight loss, patients must consume more calories. Yet delayed stomach emptying, if present, may require moderate use of fatty foods, while those using levodopa may need to control their use of protein. Such restrictions sometimes necessitate small, frequent meals and snacks, and a diet high in carbohydrates. A vegetarian diet adapts very well to such an eating plan, as it can be both high in carbohydrates and low in fat, whereas animal foods are often high in fat and protein.

Chewing/swallowing difficulty. Patients in mid-to-late stages of PD may experience difficulty chewing food and/ or moving the tongue to position food properly for swallowing. The normal esophageal peristalsis may be slowed, resulting in choking. While a swallowing evaluation should be performed, along with education in safe swallowing techniques, it should be noted that plant foods may be easier to chew than many meats; plant foods also can be chopped, mashed, or pureed easily to provide the best consistency for the individual's needs while retaining valuable fibers and phytochemicals.

Nutrients. Plant foods are rich in magnesium and vitamin K, important to bone health. This should be emphasized, as PD patients, due to the nature of the disease, may be prone to falls [8, 9, 10, 11, 12, 13, 14] and therefore more susceptible to fractures [2 ,3]. Good sources of calcium and vitamin D must be highlighted, also, as there may be a greater need for these in this population; in a controlled study, Sato et al. found increased incidence of vitamin D deficiency and reduced bone mass in individuals with PD [14].

A vegetarian or plant-based diet can provide excellent amounts of the B vitamins (with the possible exception of B12), especially folate. Education regarding need for B vitamins is important. The vegan patient may require a supplement of vitamin B 12 and if deficiencies are suspected, a B complex may be required, at least temporarily It should be noted that large amounts of vitamin B6 (over 10 mg per day) may reverse the effects of levodopa; therefore, supplements should be taken with meals, with levodopa taken at least 30 minutes prior to meals, to avoid this food-medication interaction.

Protein-levodopa interactions. As stated before, protein breaks down in the gut to individual amino acids, with which levodopa must compete for carriers across the intestinal wall. For this reason, patients must take levodopa at least 30 minutes prior to meals or snacks. As the disease progresses, individuals often begin to experience fluctuations in their response to levodopa, resulting in the "on-off' phenomenon, a condition wherein a dose of levodopa wears off before the next dose is due. Without levodopa, the individual may be able to move only very slowly, or not at all, and is effectively disabled.

To cope with these motor fluctuations, it has long been advised that patients avoid protein during the day, limiting intake to no more than ten grams prior to the evening meal. The bulk of protein needs is met at the evening meal, allowing the patient optimal use of levodopa during the daytime hours. However, this often means that the patient cannot move all night long, which can be very frustrating and even frightening, as s/he cannot turn over in bed, get up to use the bathroom, or adjust the bedclothes. If diabetes, hypoglycemia or other conditions are present, this protein restriction is even less desirable.

Although less widely understood, a high-carbohydrate eating plan consisting of a ratio of five parts carbohydrate to one part protein, or higher, can be very effective [35]. Once in the bloodstream, the high ratio of carbohydrates causes an insulin rush that also removes amino acids from the blood, thereby allowing levodopa to reach the blood-brain barrier unobstructed [see 36, 37]. A plant-based diet is an ideal way to achieve a high-carbohydrate meal plan, as plant proteins are often found in a carbohydrate-to-protein ratio of 3:1 or higher, whereas meats have virtually no carbohydrate. Legumes, seeds, and nuts are excellent foods, and can easily be incorporated into a meal consisting of a 5:1 or higher ratio.

Most patients gain improved "on" time with some form of protein adjustment. Some find they can reduce the amount of levodopa needed. Reduction of levodopa may result in lessened side effects, such as hallucinations and dyskinesia (unwanted twisting or writhing movements). Much more research is needed in this area, to document reduction in medications, improved "on" time, lessened dyskinesia, and reduced adverse effects of medications.

Sample high-carbohydrate menu -- Ratio 5:1

  • 1-1/2 cups split pea or lentil soup
  • 1 oz whole-grain crackers
  • 1 TB peanut butter
  • 8 oz cranberry juice
  • 1/2 cup grapes

(694 calories, 122 g carb, 24 g pro, 16 g fiber, 66 mg Calcium)

For more infromation, including snacks, breakfast, lunch, and evening meal plans in 5:1-10:1 ratios, refer to Eat Well, Stay Well with Parkinson's Disease, by Kathrynne Holden.


It is important to assess nutrition risk, and a three-day food diary can be of great help in determining whether fiber and nutrient intake is adequate. Information intake via interview is also important, paying particular attention to weight changes and risk for bone thinning. If unplanned weight loss has occurred, determine whether this is due to depression, excessive calorie expenditure because of tremor, dyskinesias, rigidity, inability to self-feed at a normal pace, chewing or swallowing problems, or other condition. Small, frequent meals and snacks are often preferable to the usual three meals a day. To assess delayed stomach emptying, inquire whether the individual experiences heartburn or acid reflux, often a sign of slowed peristalsis; also find out how long it takes for medications to "kick in." If the patient is using levodopa, and taking it at least 30 minutes prior to meals without feeling the onset of antiparkinson effects, delayed stomach emptying is a possible factor. Again, small meals and snacks, moderate in fat, may be an effective way to counter delayed stomach emptying.

If the individual uses levodopa and motor fluctuations occur, consider protein adjustment. The simplest, and often very effective method, is to estimate individual protein needs, and divide the protein equally among meals. If weight loss or slowed stomach emptying is present, suggest small meals with low-protein snacks between meals. This provides the most natural eating plan. If the person is protein-sensitive, it maybe helpful to increase carbohydrates. Try a ratio of 5:1 initially, as this provides the most protein and therefore a more natural eating plan. After two to three weeks, the individual should notice improved "on" time; if not, increase the ratio to 6:1 or 7:1. This eating plan is often harder to teach; it may be necessary to provide ready-made menus for meals and snacks. NOTE: it is difficult to provide a 7:1 eating plan having less than 1800 kcal per day This may be too much food for some people, especially small women. If a 7:1 ratio works well for the person, s/he may wish to use it throughout the day in small meals and snacks, then add additional protein at the evening meal. This will provide for a smaller number of calories and offer sufficient protein, while still allowing for better levodopa absorption during the day.

Again, it is important to be aware of the increased risk for bone thinning and need for vitamin B12. It may be necessary for patients to use vitamin/mineral supplements, especially of calcium, vitamin D, and vitamin B 12. In some cases, a vitamin B complex may be needed as well. Patients who use levodopa should take supplements containing large amounts of vitamin B6 with meals, at least 30 minutes after taking levodopa, in order to avoid the interference of vitamin B6 with levodopa absorption.


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