The Effects of Protein Source on Appetite Control, Satiety, and Subsequent Food Intake: A Clinical Screening Study

The investigators propose the following acute, randomized crossover study to compare 5, isocaloric yogurt-based preloads containing 20, 30, or 40 g pea protein; 20 g whey protein; and an isocaloric carbohydrate (control).

For 3 consecutive days/pattern, the participants will consume the respective treatment, at home, between 7-9 am, based on their habitual breakfast time. (These days are implemented to allow for the acclimation to the respective preload. Using this approach, the participant becomes familiar with the taste profile along with the practice of consuming a breakfast 'shake' so that the testing day more closely assimilates the habitual effects of the preload on appetite, satiety, and food intake.)

On day 4, the participants will report to the research facility 1 h prior to their habitual breakfast time to complete each 4-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 appetite/satiety and cognitive function questionnaires will be completed. At time 0 min, the respective preload will be provided. Immediately following the first swallow of the preload, the participants will be given a questionnaire assessing the palatability. The participants will consume the preload within 10 min. Afterwards, the participants will continue to complete the questionnaires every 30 min throughout the 4-h postprandial period. In addition to these questionnaires, participants will complete a cognitive function paradigm at -30 min, +90 min, and +180 minutes in order to assess memory, executive function, attention, and reaction time. Throughout the day, the participants will also indicate if/when they would like to eat again. Regardless of their meal timing request, at 4-h post-breakfast, lunch will be provided. The participants will be given 30 min to "consume as much or as little as they wish until comfortably full." Following these procedures, the participants will be allowed to leave the facility. There will be a 3-7 day washout period between testing days.

Inclusion criteria

• Normal weight (BMI: 18.0-24.5 kg/m2)
• No history of smoking
• No metabolic or hormonal conditions/diseases that influence metabolism, appetite, or food intake
• No past history of surgical interventions for the treatment of obesity
• No weight loss/gain (≥10 lb. in the past 6 months)
• No medication that would influence directly appetite or cognition
• No change in any medications (over the past 3 months)
• Not currently/previously on a special diet such as Atkins/Ketogenic, high protein, vegan, vegetarian, etc.
• Habitually consumes breakfast (i.e., of at least 350 kcal on ≥ 5 days/wk prior to 9 am
• Habitually consumes lunch (i.e., of at least 350 kcal on ≥ 5 days/wk approximately 4 h after breakfast
• Not clinically diagnosed with an eating disorder such as anorexia, bulimia, night-eating syndrome
• Displays a score of <4 on the Three Factor Eating Habits Questionnaire (TFEQ)
• No allergies and/or aversions to the food/ingredients included within the study
• No history of drug or alcohol abuse (i.e., >14 drinks/week)
• Willing to maintain current activity dietary patterns throughout the study
• Willing to consume all study breakfast and lunch foods
• Generally healthy, as assessed from the medical history questionnaire
• Rating of ≥ 5 illustrating a minimum of "neither like nor dislike on a hedonic 9 pt taste test of the breakfast preloads

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 >10 lb. over the past 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