Metabolic Effects of Almond in the Longer-term Study

Experiment protocol and measurements

i) Oral glucose tolerance test (OGTT) sessions

At baseline, participants attended a session where a standard OGTT with drinks containing 75 grams dextrose was performed following an overnight fasting. Serum glucose and insulin concentrations were measured at 0 and 120 minutes of the session. During the same session, height, weight (Tanita), body fat (air displacement plethysmography, BOD POD), waist circumference, and blood pressure were measured. Participants also completed a 24-hour dietary recall using a multi-pass interview method and standard questionnaires that assessed personality, eating behavior and habitual physical activity levels during the OGTT session. After the completion of this session, participants were asked to record their hourly appetite sensations, measured as "hunger", "fullness" and "desire to eat" on visual analog scales, during waking hours for a day before attending the next (clinical) visit. Participants repeated this session after four weeks of almond consumption.

ii) Acute feeding sessions

Within a week following the OGTT session, participants returned for an acute-feeding session, after an overnight fasting of at least 10 hours. This session began between 7:00 am and 8:00 am, and lasted for approximately 515 minutes. Upon arrival, an indwelling arm catheter was placed in the upper arm for blood sample collection. Participants rested for 15 minutes after catheter placement, before a baseline blood sample was drawn. Immediately after the first blood sample collection, a standard breakfast was served, and participants were instructed to consume the entire portion within 10 minutes. Subsequent blood samplings were performed at 15, 45, 60, 90, 120, 180, and 240 minutes after the breakfast, before a standard lunch was provided to the participants. Again, participants were given 10 minutes to consume the lunch, before blood samples were taken at similar intervals again (at 265, 295, 310, 340, 370, 430, and 490 minutes of the session). Participants randomized into the BF and LN groups received 43 grams of almonds together with their meals, while the MS and AS groups consumed 43 grams of almonds 120 minutes after breakfast and lunch respectively. Participants also recorded their "hunger", "fullness", and "desire to eat" sensations when blood samples were taken. During the acute-feeding session, activities that may alter appetite sensations (e.g. sleeping and watching movies containing food cues) were prohibited. Postprandial glucose, insulin and triacylglycerol concentrations were measured for all 15 samples collected from each participant. Participants in all almond groups group were also asked to rate their likings for the almonds they ingested using a general label magnitude scale, and their action responses to almonds using the "food action rating scale", a visual analog scale ranging from "I would eat the almonds only if I were forced to" to "I would eat this food every opportunity I had" anchored to the 2 extremes. This session was repeated again after four weeks of almond supplementation.

iii) Weekly follow-ups

Following the baseline acute-feeding session, participants were asked to consume 43 grams of almonds every day at times based on their group randomization. The CL group was instructed to avoid all nuts and seeds in the diet during the study period. All almonds were dry-roasted and lightly salted, and were pre-weighed and per-packaged for convenience. Except for the permission to adjust dietary intake due to almond supplement, participants were asked to maintain their dietary intakes and physical activity levels. A ruse (breath analysis) was introduced in order to enhance the compliance of participants to consuming almonds at the designated times of day. Compliance to almond consumption was assessed through fasting plasma α-tocopherol. Participants attended weekly visit (week-1, 2 and 3) after an overnight fasting, during which body weight was recorded and compliance to study protocol reinforced. During the week-2 visit, participants were also asked to complete a 24-hour dietary intake assessment using the multi-pass interview method and appetite sensation ratings on VAS at every waking hour for a day. On week-4, participants returned for OGTT and acute-feeding sessions as described above. The study protocol was approved by the Purdue University Institutional Review Board.