for people ages 25-65 (full criteria)
Healthy Volunteers
healthy people welcome
at UC Davis
study started
estimated completion
Principal Investigator
by Carl L Keen, PhD (ucdavis)



A randomized, double-masked and cross-over dietary intervention study to investigate the effects of diet supplementation with cocoa flavanols on arterial stiffness in healthy adult human subjects.


Cocoa flavanols (CF) are plant-derived compounds commonly present in the human diet. Examples of flavanol-containing foods and beverages are apples, chocolate, tea, wine, berries, pomegranate and nuts. Flavanols encompass a group of different compounds, and the final profile of flavanols in foods will depend on multiple factors including plant origin, time of harvesting, storage, food processing, and cooking techniques. The term "cocoa flavanols" (CF) as used here refers to the particular profile of flavanols and procyanidins naturally found in cocoa beans, and CF mainly consist of the monomeric flavanol (-)-epicatechin and its oligomeric derivatives (procyanidins) containing up to 10 monomer subunits. Accumulating data resulting from dietary intervention studies suggest that the intake of diets rich in flavanols can exert a beneficial cardiovascular health effect in humans. However, most of these investigations have been conducted with patients with diverse health complications (e.g. hypertension, diabetes and coronary heart disease) rather than healthy subjects. Thus, the interpretation of these data in the context of nutrition, primary prevention, and dietary recommendations is limited. In the current study, the investigators propose to investigate the effects of cocoa flavanol intake on arterial stiffness in a healthy population of adults. The investigators submit that this investigation will provide novel insights into the potential health benefits of dietary flavanols and procyanidins in the context of cardiovascular health in humans. The data resulting from this study will be key to the design of larger scale studies in this context, which are needed to comprehensively study the role of dietary flavanols and procyanidins with regard to potential dietary recommendations and public health.


Healthy flavanol cocoa flavanols arterial stiffness blood pressure step test Cocoa flavanols I Cocoa flavanols II


You can join if…

Open to people ages 25-65

  • 25-65 years old
  • BMI 18.5 - 34.9 kg/m2
  • Weight ≥ 110 pounds
  • Previously consumed cocoa and peanut products, with no adverse reactions
  • Having completed physical exercise similar to 5 MET within the last 2 months without having any physical limitations [e.g. i) Brisk walking (at 4 mph); ii) Mowing lawn; iii) Bicycling-light effort (10 mph) and iv) Playing tennis-doubles.]

You CAN'T join if...

  • Adults unable to consent
  • Individuals who are not yet adults (infants, children, teenagers)
  • Pregnant women
  • Prisoners
  • Non-English speaking*
  • BMI ≥ 35 kg/m2
  • More than 150 minutes of moderate-intensity aerobic activity or 75 minutes of vigorous-intensity aerobic activity weekly and more than two days a week of muscle strengthening activities that work all major muscle groups (CDC recommended physical activity guidelines for adults)
  • Allergies to nuts, cocoa and chocolate products
  • Active avoidance of coffee and caffeinated soft drinks
  • A history of cardiovascular disease, stroke, renal, hepatic, or thyroid disease
  • History of clinically significant depression, anxiety or other psychiatric condition
  • History of difficult blood draws
  • History of Raynaud's disease
  • Indications of substance or alcohol abuse within the last 3 years
  • Current use of herbal, plant or botanical supplements (multi-vitamin/mineral supplements are allowed)
  • Blood Pressure >140/90 mm Hg
  • Blood Pressure < 100/60 mm Hg, or heart rate < 50 bpm (due to limitations in the assessment of arterial stiffness
  • GI tract disorders, previous GI surgery (except appendectomy)
  • Self-reported malabsorption (e.g. difficulty digesting or absorbing nutrients from food, potentially leading to bloating, cramping or gas)
  • Diarrhea within the last month, or antibiotic intake within the last month
  • Vegetarian, Vegan, food faddists, individuals using non-traditional diets, on a weight loss diet or individuals following diets with significant deviations from the average diet
  • Metabolic panel results or complete blood counts that are outside of the normal reference range and are considered clinically relevant by the study physician
  • Cold, flu, or upper respiratory condition at screening
  • Currently participating in a clinical or dietary intervention study
  • *Non-English speaking volunteers will be excluded for safety reasons, as we do not have staff that can adequately provide interpretation services that can explain and answer questions with regard to study procedures.


  • Ragle Human Nutrition Research Center, Department of Nutrition at UC Davis accepting new patients
    Davis California 95616 United States

Lead Scientist at University of California Health

  • Carl L Keen, PhD (ucdavis)
    Professor, Nutrition. Authored (or co-authored) 548 research publications.


accepting new patients
Start Date
Completion Date
University of California, Davis
Study Type
Last Updated