Study finds pistachios may help prevent vision loss

A study found that a dietary intervention using pistachios was effective in increasing macular pigment optical density (MPOD) in healthy adults.

study: Pistachio intake increases macular pigment optical density in healthy adults: a randomized controlled trial. Image credit: Peter Hermes Furian/Shutterstock.com

recent nutrition journal The study conducted a randomized controlled trial to evaluate the effect of a pistachio dietary intervention on macular pigment optical density in healthy adults.

background

Lutein and zeaxanthin (L/Z) are dietary xanthophylls that cross the blood-brain barrier and accumulate exclusively in the macular region of the human retina. In this region, these xanthophylls are called macular pigments (MPs), which protect against light damage as blue light filters and antioxidants.

Higher levels of MP protect against vision loss caused by: age-related macular degeneration (AMD) and enhance visual function. Studies have shown that L/Z intake increases MP levels, which can be measured with MPOD.

As L/Z is a fat-soluble phytonutrient, the bioavailability of L/Z depends on the food source. For example, L/Z found in egg yolk is three times more bioavailable than L/Z found in spinach or dietary supplements.

Pistachios contain large amounts of L or Z and are a source of fat, primarily monounsaturated and polyunsaturated fats. This potentially makes pistachios a highly bioavailable source of lutein. It would be interesting to quantify the improvement in MPOD after pistachio dietary intervention.

About research

This study conducted a single-blind, randomized, controlled trial in healthy adults to evaluate the effect of consuming 2 ounces of pistachios daily on MPOD. The intervention lasted 12 weeks and results were compared with those of the usual diet (UD) group.

We compared MPOD and serum L/Z in middle-aged to older healthy adults across the UD and pistachio intervention (PIS) groups.

The sample size consisted of 36 individuals with habitually low L/Z intake and low baseline MPOD. Exclusion criteria included diseases of the liver, kidneys, and pancreas, hyperlipidemia, bleeding disorders, and diverticulitis.

The mean age of subjects at baseline was 59.5 years, and 58% were female. The proportions of Asian, Black, and White participants were 14%, 8%, and 78%, respectively. The average body mass index (BMI) was 25.6, and the average daily L/Z intake was 1.1 mg/day.

Utilizing heterochromatic flicker photometry, MPOD was measured at four retinal eccentricities: 0.25°, 0.50°, 1.00°, and 1.75°. Higher eccentricities reflect peripheral measurements, and lower eccentricities reflect more central macular MPOD measurements.

Measurements were taken during baseline, week 6, and week 12 study visits. Serum L/Z was analyzed using high performance liquid chromatography (HPLC).

Research results

At baseline, there were no significant differences in macular pigment optical density (MPOD) between the pistachio intervention (PIS) and usual diet (UD) groups at any eccentricity. After 6 weeks, the PIS group showed a significant increase in MPOD compared to baseline, which was maintained at 12 weeks. However, no further increase was observed between 6 and 12 weeks. The UD group showed no change in MPOD over the 12-week study.

Changes in serum lutein concentration followed the same pattern as MPOD. Serum lutein concentrations increased from baseline to week 12 in the PIS group, whereas they remained stable in the UD group. Zeaxanthin and cystultein levels did not change in either group. Furthermore, at all four eccentricities, changes in serum lutein concentrations were associated with changes in MPOD.

Several limitations should be considered when interpreting these results. First, this was a single-blind study without a true placebo group, determined by the nature of the intervention, although serum analyzes and dietary data showed that participants complied with study instructions. Second, a blood lipid profile was not performed, although this may be relevant given the role of lipoproteins in carotenoid transport. Third, the pistachio dose was higher than recommended by the nut's qualifying health claim, suggesting that it should be investigated in future studies. efficacy of lower doses.

Finally, the generalizability of this study may be limited because participants started with low baseline MPOD and dietary lutein/zeaxanthin intake. It remains unclear whether the effects of pistachio interventions are comparable in other populations.

conclusion

In summary, this study showed that dietary intervention with pistachios was effective in increasing MPOD. This finding is relevant given the low intake of tree nuts in the United States compared to FDA-approved health claims.

In the future, dose-response and efficacy in other diverse populations should be studied.