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Pistachio Intake and Macular Pigment; a Randomized Controlled Trial

Pistachios and Neural Macular Pigment; a Randomized Controlled Trial

Eye diseases
All genders
person-wave 40-70
Recruiting now
More information  


Principal Investigator: Tammy M. Scott, PhD

Age-related macular degeneration (AMD) is a disease that affects the retina, an integral part of the eye responsible for sensing light and relaying images to the brain. In the United States, AMD is the leading cause of irreversible vision loss as people age. Previous studies have shown that the nutrients lutein and zeaxanthin can help protect against AMD in middle aged and older adults. These nutrients form a pigment in the retina (macular pigment) that helps protect the retina from light damage. The more macular pigment in the retina, the better protection it offers.

Lutein and zeaxanthin are found in foods such as leafy green vegetables, broccoli, peas and avocados. They are also found in pistachio nuts, a bioavailable source of these nutrients. Since most people do not eat pistachio nuts daily, we are trying to see whether eating 2-ounces of pistachio nuts a day can help increase the density or amount of macular pigment in the eye.

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Clinical and Translational Research Center

Study details

Inclusion Criteria
  • Adult men and women, aged 40 - 70 years
  • Body Mass Index (BMI): 20.0 - 36.9 kg/m2
  • Low lutein and zeaxanthin intake at baseline (<2 mg/d)
Exclusion Criteria
  • History of self-reported:
    - Tree nut allergies
    - Eye disease, including macular degeneration and cataracts
    - Any conditions (celiac disease, Crohn's disease, atrophic gastritis, high cholesterol, or triglycerides, etc.) surgeries (small bowel resection, intestinal tract surgery, etc.), or medications that interferes with fat absorption.
Study Requirements

The research study will take place for approximately 12 weeks. If you consent and agree to participate in the study, you will be randomly assigned to one of two groups.

One group will receive pistachio nuts in two-ounce packs; this group will consume one pack every day over the course of the 12-week study. The other group (the control group) will not receive pistachio nuts and will be asked to make no changes to their diet (e.g., continue to eat their regular diet). Both groups will be asked to not eat any pistachio nuts outside of what is assigned and make no changes to their diet.

For both groups, the study will involve four visits, a screening visit and three study visits.  During the screening visit, we will assess study eligibility by obtaining participant’s medical history, height and weight, macular pigment density (a non-invasive procedure which does not require dilation of the pupils) and food intake. Participants will also perform a nut allergy challenge  (consume 2-oz of pistachio nuts) to determine whether a severe allergy exists. Following the screening visit, if eligible, participants will return to perform baseline (visit 1) measures: a fasting blood draw (10 ml, or about 2 teaspoons), macular pigment density measurement, weight measurement, and food intake measurement. Participants will then be randomized into either the pistachio or control group. If a participant is randomized into the pistachio group, they will be given pistachio nut packs to take home. During the week-6 (visit 2) and week-12 (visit 3) study visits, participants will be weighed, have their macular pigment density measured, and be asked about the food that they’re eating. During the week-12 visit, participants will have another fasting blood draw (10 ml, or about 2 teaspoons). Most visits will take approximately 1.5 hours.

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