Effects of an Evening Snack Containing Avocado on Risk Factors for Diabetes in a Prediabetic Population

The study is a single-center, randomized, single-blinded, 3-arm, and cross-over study design. Participants will be randomized to receive three eventing snack in randomized order: low-fiber, low-fat control snack (low-fat yogurt); whole avocado snack; or control snack + fiber supplement + vegetable oil, which will be consumed in the evening before the clinic visit. Twelve hours (12 h) after snack intake (based on subjects typical evening snack and morning breakfast routine), participants will report to the clinic for fasting blood draws, followed by a standard meal with a minimum of 50 g available carbohydrate, and repeated blood collection for 3 hours. On the day of "snack" intervention (ie., 24 h before standard meal testing), subjects will be guided to follow their typical dietary pattern in consultation with staff. Food diaries with a general plan will be used as a tool to help with dietary compliance.

STUDY PROCEDURES: SCREENING VISIT:

Interested subjects will be asked to come to the Clinical Nutrition Research Center (CNRC) on the IIT Campus, Chicago, IL, where the study will take place for a screening visit to determine if they are eligible to participate in the study. The screening visit will take 2 hours. Prospective subjects must read, sign and date a written Institutional Review Board (IRB) approved Informed Consent Form prior to performing any study procedure.

At the on-site screening visit, subject will be asked to arrive after overnight fasting for 10-12 hours and be well-hydrated. Subject will be instructed to aim for a water intake of at least 8-10 cups for the 24 hours before the screening visit. Determining eligibility to participate includes having subjects to complete a series of questionnaires related to their health, medication use, dietary habits, and physical activity history. Anthropometrics (height, weight and waist circumference), body composition, ear temperature, and vital signs (blood pressure and heart rate) will be measured. For women under the age of 60 years, a pregnancy test will be conducted. Body mass index (BMI) will be calculated from height and weight measurements. Fasting blood glucose level by capillary blood from finger prick will be tested. For vital sign measurements, subjects will sit in a comfortable chair, feet uncrossed and on the floor and will be asked to rest quietly for 5 minutes before measuring blood pressure and heart rate. Arm vein will be assessed using a vein access scale test. Subject will be instructed to complete a 24-hour food recall.

Based on the results of the questionnaires, BMI calculation, and health evaluation, subjects who meet the inclusion and exclusion criteria will be invited to participate in the study. Eligible subjects will be trained and instructed to record all food and beverages consumed for a 24 hour period on food record diarie using ASA24. Subjects will be asked not to take any allergy medications and/or any pain medications such as Aspirin, Excedrin, Ibuprofen (Advil, Motrin, Nuprin), Naproxen, or Aleve within 48 hours of each scheduled study days. Tylenol is allowed. If they need to take allergy/pain medication 48 hours prior to their study day, we will ask them to let the study investigators know so they can be rescheduled. Before leaving the CNRC, subjects will be provided with written instruction for "how to prepare for your study visit". This will include instructions for eating a standardized dinner meal the night before the study day, consume the assigned study snacks, fasting overnight (10-12 hours), avoidance of vigorous physical activity, alcoholic and caffeinated beverage consumption for at least 24 hours preceding a study day, maintain regular sleep pattern and usual diet except for the guidance provided for "foods and beverages to avoid or limit". If subject did not get enough sleep during the night preceding a study day, we will ask them to let us know so we can reschedule their study day.