Motor Improvement in Parkinson's with Lower Protein Intake

By Dr. Sean M Wells, DPT, PT, OCS, ATC/L, CSCS, NSCA-CPT, CNPT, Cert-DN

Parkinson's Diseases (PD) is a chronic, progressive neurodegenerative disease that significantly impacts movement. Many patients seek the expertise of physical therapists (PTs) to help improve their movements, balance, and quality of life. Exercise is most certainly the mainstay treatment, with resistance training, boxing, HIIT, and balance exercises being some of the top choices. Some clients of my practice have improved their condition so much they no longer use their rolling walkers, need help with transfers, and some even reduce their meds.

Other than exercise, nutrition is another key area that Doctors of Physical Therapy ought to be aware for their clients with PD. Nutrition is intimately related to the causality of PD. From heavy metals in foods like fish to severe alterations in the gut-biome, many nutrition researchers are finding that diet plays a major factor in developing the disease. Consumption of fruits rich in polyphenols, teas high in flavonoids, and peppers rich in nicotine-like compounds, a predominantly plant-focused diet seems to greatly reduce the odds of getting PD -- this is all good information that PTs can provide those clients who are worried about getting PD.

But what about patients who already have PD -- can dietary changes help them? The simple answer is that diet changes can help patients improve their motor function. In several studies using lower-protein diets, patients reported marked improvements in motor responses. In brief, patients with PD on levodopa, the most common PD medication that improves motor function, can have significant interactions with dietary protein. The main driver of this interaction is related to the large neutral amino acids (LNAA), like tyrosine and tryptophan, in protein-rich foods (e.g. meat). These LNAAs compete with levodopa for absorption in the gut lining and at the blood-brain barriers; such competition decreases levodopa from reaching its target in the brain, thus negatively affecting motor responses.

How much motor interaction are we talking about? Specifically in this cross-sectional study, researchers noted:

Almost 80 % of patients with protein-interactions with levodopa either had decreased efficacy of their levodopa dose, or wore OFF from a prior dose after protein ingestion. Let's break the 80% down into what each patient reported:
50 % of those with an interaction reported decreased efficacy of levodopa after protein intake,
29 % reported that protein intake led to wearing OFF of a previously effective dose,
17 % reported dose failures when levodopa and protein were taken concurrently, while one patient each reported delayed time to motor improvement (ON state) and decreased length of ON state time after protein

A great review article summarizes much of the data around protein, levodopa, and PD. The authors found that such protein interaction with levodopa appears about 13 years after the onset of motor symptoms or 8 years after the initiation of levodopa therapy, and correlates with higher severity of motor fluctuations. Data show that a lower protein diet may actually cause hyperkinetic responses, lower body mass index, and lower diet adherence. Hyperkinetic responses may be unwanted and demand the PT to work with the neurologist to better dose levodopa. A lower body mass index can also pose a problem, especially for patients at risk for falling and maintenance of muscle mass. Most lower protein diets for PD patients have been done in the 0.5-0.8g protein/kg body mass per day. Note that 0.8g/kg is the USDA RDA, and less body mass loss was seen when protein was kept closer to the RDA number versus 0.5g/kg. Malnutrition was rarely seen in any of the protein reduction studies. Lastly, dietary adherence can be difficult for a low protein diet as many humans have become accustomed to eating meat throughout the day at all 3 meals.

Another way to manipulate protein and levodopa interactions is to shift protein to later in the day, also known as a protein restricted diets (PRD). By eating mostly carb and fat rich foods in the morning and afternoon the patient with PD will have good availability for most of the day to function without motor impairments. Once dinner comes along, the patient with PD can consume protein (either meat or plant-based alternatives), which will impair some of the levodopa for the evening, when patients may not need it as much. The PRD is a good option for someone not wanting to ditch meat altogether, and some data suggest it may ameliorate some of mass loss seen in full protein restricted diets. Moreover, PRD may be more easy to adhere to compared to full protein restricted diets. The obvious downside to PRD is the worsening of motor responses in the evening, which can be fixed by possibly shifting the protein-rich food to another time in the day.

As PTs, clinical rehab specialists, and movement specialists, we all have seen our patients with PD have "off" days or invariably have to increase the levodopa dose overtime. It is likely due to multiple factors but one strong potential cause is excessive dietary protein. Data consistently show that Americans consume far more protein than many other developed countries -- patients with PD are likely to be no different.

As such, physical therapists need to encourage their patients to explore protein restricted diets or limit their protein intake to help optimize levodopa uptake. PTs educated in nutrition may be able to help clients on their own; or, some PTs may need to seek guidance and assistance from licensed dieticians -- either way, the discussion of dietary protein and levodopa is vitally important to keeping patients with Parkinson's moving optimally!

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