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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Type of registration
Prospectively registered

Titles & IDs
Public title
Comparative effects of protein-rich ‘preloads’ on appetite and energy intake in healthy young and older individuals - role of gastrointestinal mechanisms
Scientific title
Effects of oral protein-rich 'preloads', on energy intake, appetite, antral area, gastric emptying, amino acids, hormones, glucose and blood pressure in healthy young and older individuals
Secondary ID [1] 285029 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Anorexia of ageing 292538 0
Condition category
Condition code
Diet and Nutrition 292844 292844 0 0
Other diet and nutrition disorders
Oral and Gastrointestinal 292845 292845 0 0
Normal oral and gastrointestinal development and function

Study type
Description of intervention(s) / exposure
A total of 15 healthy young (18-35 years) and 15 healthy older (>65 years) subjects with a body mass index (BMI) of 22-30 kg/m2 will be recruited. Each subject will be studied on 4 occasions, with a randomised intervention order, separated by at least 3 days. Bolus oral consumption of preloads containing the following amounts of calories and energy percentage (%) protein/carbohydrate/fat; i) control 0 kcal, ii) ‘pure protein’ 280 kcal and 100/0/0 energy % (70/0/0 g), or iii) ‘low-caloric protein-rich’ 280 kcal 20/40/40 energy % (14/28/12.4 g); or iv) ‘high-caloric protein-rich’ 504 kcal 56/22/22 energy % (70/28/12.4 g). The drinks will be equivolaemic (~450 mL) and matched for taste, texture and appearance. The drinks will contain different quantities of food-grade whey protein isolate powder (Fonterra Australia Pty Ltd, Mt Waverley, Australia) dissolved in varying amounts of distilled water, sodium chloride and low-calorie lime cordial (Bickford’s ‘diet lime’ cordial). 0.1 g 13C sodium acetate will also be added to the nutrient-containing solutions to enable the measurement of gastric emptying through excretion of 13CO2 in the breath. Gastric emptying rate and intragastric meal distribution are determined using 3D ultrasound.
Appetite sensation questionnaires in the form of a Visual Analogue Scale (VAS) are measured and blood samples are collected for concentrations of gut hormones, amino acids and glucose.
A standard buffet meal is provided at 180 minutes following the preload and the participant has 30 minutes to eat until comfortably full. The weight of the foods will be recorded before and after it is offered to the subjects and energy intake and macronutrient composition calculated subsequently using commercially available software (Foodworks 3.01, Xyris Software, Highgate Hill, QLD, Australia).
Intervention code [1] 289860 0
Comparator / control treatment
Placebo: a single 450mL water and diet lime cordial preload.
Control group

Primary outcome [1] 292714 0
Macronutrient and total energy intake of a standard buffet meal (quantified using Foodworks software).
Timepoint [1] 292714 0
Buffet meal is presented at 180 minutes following the last ultrasound measurement and the subject is allowed to freely consume food until comfortably full for 30 minutes (until t= 210 minutes).
Primary outcome [2] 292715 0
Appetite sensations using a Visual Analogue Scale (VAS) (nausea, hunger, fullness, desire to eat, thirst).
Timepoint [2] 292715 0
VAS is administered at time points: -15 minutes, 0 minutes and every fifteen minutes thereafter until 180 minutes. The final VAS is administered at 210 minutes after the buffet meal has been consumed.
Primary outcome [3] 292716 0
Plasma concentrations of gut hormones (e.g. cholecyctokinin (CKK), glucagon-like peptide-1 (GLP-1), peptide YY (PYY), gastric inhibitory polypeptide (GIP), ghrelin, glucagon and insulin), glucose and amino acids.
Timepoint [3] 292716 0
Blood samples are taken at t= -15, 0, 15, 30, 45, 60, 90, 120, 150 and 180 minutes.
Secondary outcome [1] 309545 0
Gastric emptying rate assessed by three-dimensional (3D) ultrasonography and 13C Octanoic Acid Breath Test.

3D ultrasound defines the fraction of the meal emptied from the stomach, including 50% emptying time (T1/2), during the study.

The 13C Octanoic Acid breath test assesses gastric emptying of the protein drink through measurement of 13CO2 in the breath via mass spectrometry. Half-emptying time and gastric emptying coefficient will also be calculated and compared to those obtained using 3D ultrasonography.
Timepoint [1] 309545 0
Ultrasound measurements for assessment of gastric emptying will be taken at -15, 0, and every 15 minutes thereafter until 180 minutes.

Breath samples are collected for assessment of 13CO2 immediately before meal ingestion, and every 5 minutes for the 30 minutes following meal ingestion. Breath samples are then collected every 15 minutes until 180 minutes.
Secondary outcome [2] 309547 0
Blood pressure and heart rate are determined using an automatic sphygmomanometer.
Timepoint [2] 309547 0
Blood pressure and heart rate are measured prior to the drink (i.e. baseline mean of three samples, t = -9, -6, -3) and at 3 minute intervals from t = 0 – 180 minutes and after the buffet meal t = 210 min.

Key inclusion criteria
Body Mass Index (BMI): 22-30 kg/m2

Weight stable (<5% fluctuation in body weight in previous 3 months)

Age young group: 18-35 years
Age older group: >65
Minimum age
18 Years
Maximum age
No limit
Both males and females
Can healthy volunteers participate?
Key exclusion criteria
Significant gastrointestinal symptoms, disease, or surgery.

Current gallbladder or pancreatic disease; diabetes mellitus; epilepsy; cardiovasculr or respiratory diseases; any other illnesses as assessed by the investigator (including chronic illnesses not explicitly listed above).

Impaired cognitive function.


Use of prescribed or non-prescribed medications (including vitamins and herbal supplements) which may effect gastrointestinal function or appetite.

Lactose intolerant or other food allergies; intolerance or allergy to paracetomol.

Individuals with low ferritin levels or who have donated blood in the 12 weeks prior to taking part in the study.

Current intake of >2 standard drinks on >5 days per week.

Current smokers of cigarettes/cigars/marijuana.

Current intake of any illicit substance.

Experience claustrophobia in confined spaces.

Unable to comprehend study protocol.

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Volunteers are asked to visit the clinic for a screening visit. A series of screening questionnaires are answered by the volunteer, and a blood sample is taken for determination of ferritin and HBA1C levels. Eligibility is determined based on the inclusion/exclusion criteria. A signed informed consent form is obtained and study dates are established. Eligible volunteers are assigned a subject number and randomised into a treatment for each study visit using a randomisation table. Randomisation involves contacting the holder of the randomisation table (study assistant) to inform them of the subjects details and study dates. The unblinded study assistant is therefore responsible for allocating a random treatment to the subject and preparing the preload on each study day.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
The randomisation table was created using
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s
The people administering the treatment/s
The people assessing the outcomes
The people analysing the results/data
Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 2760 0
The Royal Adelaide Hospital - Adelaide
Recruitment postcode(s) [1] 8459 0
5000 - Adelaide

Funding & Sponsors
Funding source category [1] 289640 0
Name [1] 289640 0
Royal Adelaide Hospital Research Foundation - Clinical Project Grant
Address [1] 289640 0
North Terrace
Adelaide, SA 5000
Country [1] 289640 0
Primary sponsor type
Stijn Soenen
Discipline of Medicine, University of Adelaide
Attn.: Stijn Soenen
Level 6 Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Secondary sponsor category [1] 288329 0
Name [1] 288329 0
University of Adelaide
Address [1] 288329 0
North Terrace
Adelaide, SA 5005
Country [1] 288329 0

Ethics approval
Ethics application status
Ethics committee name [1] 291380 0
Royal Adelaide Hospital Research Ethics Committee
Ethics committee address [1] 291380 0
Level 3, Hanson Institute, North Terrace
Adelaide, South Australia, 5000
Ethics committee country [1] 291380 0
Date submitted for ethics approval [1] 291380 0
Approval date [1] 291380 0
Ethics approval number [1] 291380 0

Brief summary
Ageing is associated with a physiological reduction of appetite and energy intake, which has been called the “anorexia of ageing”. Dietary supplementation with liquid protein preparations is now used frequently to increase energy and protein intake in older adults in both institutionalized and community-dwelling populations. Although the latter would appear a logical approach, evidence for success of increased energy intake in older individuals is limited. It is well established that the ingestion of nutrients induce a number of changes in gastrointestinal (GI) function, which are associated with the modulation of appetite and energy intake. These changes include the slowing of gastric emptying, which sustains gastric distension and is associated with proximal gastric relaxation. Urgent investigation is warranted to determine the optimal load of protein that can be incorporated into their diet to assist in sparing muscle mass without reducing their appetite.

The study aims to characterise in healthy older individuals, absolute and in comparison to young individuals, the effect of different oral protein-rich loads on energy intake, appetite, antral area, gastric emptying, plasma concentrations of amino acids, hormones (i.e. CCK, PYY, ghrelin, GLP-1, GIP, glucagon and insulin) and glucose, and studies the relationship between the suppression of appetite and energy intake by protein with ‘intragastric’ mechanisms.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 50106 0
Dr Stijn Soenen
Address 50106 0
Discipline of Medicine, University of Adelaide
Attn.: Stijn Soenen
Level 6 Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 50106 0
Phone 50106 0
+61 8 8313 3638
Fax 50106 0
+61 8 8223 3870
Email 50106 0
Contact person for public queries
Name 50107 0
Dr Stijn Soenen
Address 50107 0
Discipline of Medicine, University of Adelaide
Attn.: Stijn Soenen
Level 6 Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 50107 0
Phone 50107 0
+61 8 8313 3638
Fax 50107 0
+61 8 8223 3870
Email 50107 0
Contact person for scientific queries
Name 50108 0
Dr Stijn Soenen
Address 50108 0
Discipline of Medicine, University of Adelaide
Attn.: Stijn Soenen
Level 6 Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 50108 0
Phone 50108 0
+61 8 8313 3638
Fax 50108 0
+61 8 8223 3870
Email 50108 0

No information has been provided regarding IPD availability
Summary results
Have study results been published in a peer-reviewed journal?
Other publications
Have study results been made publicly available in another format?
Results – basic reporting
Results – plain English summary