There are a few findings from the current study worth exploring in greater detail.

Flaxseed oil and vitamin E

A single trial found that a combination of flaxseed oil and vitamin E improved insulin sensitivity (as assessed using QUICKI). Furthermore, this improvement seemed to be of a clinically meaningful magnitude.^[1]

Interestingly, although whole flaxseeds have been found to improve insulin sensitivity,^[2]^[3] most studies have failed to find evidence that either flaxseed oil^[2] or vitamin E^[4]^[5]^[6] affect insulin sensitivity.

Research is being done on insulin sensitivity in the context of PD because some researchers have proposed that poor insulin sensitivity may increase the risk of PD. People with type 2 diabetes appear to have an increased risk of developing PD, and some evidence suggests people with PD have insulin resistance occurring in their brain.^[7]

It’s also worth mentioning that supplementation with flaxseed oil and vitamin E reduced disease symptoms, although this was found in only one trial, so it’s important to view these findings with caution.

Essential amino acids

In one trial, supplementation with all 9 of the essential amino acids improved insulin sensitivity (also assessed using QUICKI). This improvement appeared to be clinically meaningful.

This improvement in insulin sensitivity with amino acids could be due to the fact that some amino acids (i.e., methionine and lysine) are used to make L-carnitine,^[8]^[9]^[10] a nutrient that can improve insulin sensitivity by supporting fat metabolism and the clearance of metabolism byproducts.^[8]^[8]^[9]^[10]

Psyllium

Another supplement of note was psyllium, which smoothed out blood concentrations of L-DOPA (the main medication used to manage PD), reducing the number of peaks (high points of blood concentrations) after taking the drug. Psyllium also reduced factors like the maximum L-DOPA peak, and absorption rate, but these changes didn’t reach statistical significance. The effects of psyllium husk on L-DOPA are similar to what fiber (the main component of psyllium) does to carbohydrates: smoothing out blood concentrations, reducing peaks, and slowing the absorption rate.^[11] In addition, psyllium supplementation seems to be fairly safe for people with PD.^[12]

Curcumin

In one trial, curcumin improved sleep quality and quality of life in people with PD, a finding consistent with some preliminary research in populations without PD.^[13]^[14]^[15] It’s certainly possible that improved sleep quality directly improves quality of life.^[16] For how curcumin might have these neurological benefits, it appears curcumin can cross the blood-brain barrier, where it can act as an anti-inflammatory agent and improve neurological functioning.^[17]

Fish oil

One trial found that fish oil supplementation reduced depression symptoms in people with PD. This makes sense because this finding has been observed in other studies, although the effect is usually very small.^[18] Fish oil seems to improve depression if used at doses of 1–2 grams per day with at least 60% of the omega-3s consisting of EPA. This is consistent with the trial in participants with PD, which used a dose of 1.2 grams per day, of which 60% was EPA.^[19] Fish oil likely has a similar mechanism to curcumin in that it acts as an anti-inflammatory agent in the brain.^[18]^[20]

Caffeine

Caffeine reduced daytime sleepiness in participants with PD in studies. This is an intuitive and unsurprising finding and is well documented in other research.^[21] This finding was also observed in another study that was not included in the current systematic review, though that study was extremely small, as it had only 4 participants.^[22] Broadly speaking, caffeine works to inhibit fatigue by blocking the binding of adenosine, a byproduct of the breakdown of energy molecules (ATP or adenosine triphosphate), to adenosine receptors.^[23]

Dietary patterns

A wide variety of diets were studied, and the macronutrient (carbohydrates, proteins, and fats) ratios varied greatly. Low-fat, ketogenic (high fat, low carbohydrate), low-protein, high-protein, and the well researched Mediterranean diet were all examined. Each diet seemed to improve PD scores, so it’s helpful to determine the commonalities between these diets to determine what may help to explain these effects.

One variable seems to be a likely explanation. Most of these studies reported that there was either a lower calorie intake and/or weight loss in the group that achieved improved PD scores. In other words, if the people consuming the diet lost weight or ate a lower number of calories (which will usually result in weight loss), then their PD scores improved. Note that weight loss also typically improves insulin sensitivity.

There are unique aspects to some of these diets, like the Mediterranean diet, that might confer additional benefits beyond calorie restriction and/or weight loss. The Mediterranean diet typically has higher intakes of health-promoting fats (EPA and DHA from fatty fish, monounsaturated fatty acids from olive oil), fiber, and various phytonutrients and antioxidants from a variety of sources.

In the Mediterranean diet study, the participants’ UPDRS scores decreased by 4.8 points compared to the traditional Iranian diet after 10 weeks. Although there is a large amount of variability in PD progression from person to person and even throughout a person’s disease course with PD (people tend to progress much more slowly during the first stage of PD), a person with PD might increase their PD score by 4.0 points per year, suggesting that following a Mediterranean diet for 70 days was equivalent to reversing over a year of disease progression.^[24]

Conclusion

Ultimately, there is preliminary evidence to suggest that some supplements may have certain benefits in PD with respect to insulin resistance (which might be involved in the disease process of PD), mood, and sleep. Furthermore, diets that produce lower calorie consumption and/or weight loss may have some beneficial effects on PD symptoms. Individual dietary choices should come down to sustainability, because being able to stick to a diet is the best way to maintain the potential resultant benefits for PD.

Supplements, foods, and dietary patterns for Parkinson’s disease Original paper