The Effects of Protein Source on Appetite Control, Satiety, and Subsequent Food Intake

The Effects of Protein Source on Appetite Control, Satiety, and Subsequent Food Intake

The investigators propose a randomized, tightly-controlled breakfast trial in normal to overweight adults that will test whether the consumption of various types of protein-rich meals, containing ~24g of protein, will differentially alter food intake and meal initiation through proposed appetite and satiety mechanisms.

Aim 1: To examine whether the consumption of protein-rich meals that vary in protein quality (source) effect:

1. postprandial feelings of hunger, fullness, desire to eat, prospective food consumption
2. postprandial fluctuations in key appetite and satiety hormones
3. eating initiation (i.e., motivation to eat (again))
4. food cravings

Aim 2: To examine whether the consumption of protein-rich meals that vary in protein quality (source) effect:

1. energy intake and food choice within the breakfast meal
2. energy intake and food choice at the next eating occasion
3. energy intake and food choice across the entire day

Experimental Design: For 3 consecutive days/pattern, the participants will consume the respective treatment, at home, between 7-9 am and refrain from eating or drinking anything other than water until 12:00pm. On day 3, the participants will consume a standardized dinner at home the night before testing. On day 4, the participants will report to the research facility between 6-8 am to complete each 5-h testing day. Upon arrival to the facility, each participant will become familiarized with the testing day procedures. At time -15 min, a baseline set of computerized questionnaires (and/or blood samples) will be completed. At time +0 min, the respective breakfast treatment will be provided. Immediately following the first swallow of the breakfast meal, the participants will be given a questionnaire assessing the palatability. The participants will consume the breakfast within 20 min. After breakfast, the participants will continue to complete the questionnaires (and/or blood samples) every 30 min throughout the 5-h postprandial period. Throughout the day, the participants will also indicate if/when they would like to eat again. Regardless of the participants' meal timing request, at +240min post-breakfast, the participants will be provided with an ad libitum lunch. For the lunch meal, the participants will be given 30 min to "consume as much or as little as possible until comfortably full." Following these procedures, the participants will be allowed to leave the facility. The next day, a dietary recall will be performed to assess daily energy intake across the previous day. Lastly, on day 5 (at home), the participants will be provided with their respective breakfast along with additional carbohydrate and/or fat foods. Once the treatment breakfast is consumed, the participants can select and consume as much of the additional foods as they wish to consume within the breakfast time period (30 minutes).

Inclusion Criteria:

• Males and females
• All ethnicities
• Age: 20-40y
• BMI/BMI Percentile: 18.5-29.9 kg/m2
• Consumes breakfast (>110 kcal prior to 10 am) at least 5 days/week for the past year
• Never smoked or used other tobacco products
• Willing to consume the study breakfasts
• Generally healthy (as assessed by Medical History Questionnaire)
• Health conscious as determined by answering yes to 3 pre-screening health & lifestyle questions
• Rating of ≥ 5 illustrating a minimum of "neither like nor dislike on a hedonic 9 pt taste test of all testing treatments

Exclusion Criteria:

• Clinically diagnosed with an eating disorder
• Metabolic, hormonal, and/or neural conditions/diseases that influence metabolism or appetite
• Currently or previously on a weight loss or other special diet (in the past 6 months)
• Gained/lost ≥4.5kg over the past 6 months
• Donated (or plan to donate) blood through the American Red Cross within the past 6 months (or future 6 months)
• Taking medication that would directly influence appetite (weight-loss drugs or antidepressant, steroid, or thyroid medication, unless dosage has been stable for at least 6 months)
• Not willing or able to complete all study testing procedures
• Clinically diagnosed with a sleeping disorder