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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
Effects of protein on gastric emptying and hormones, and appetite and energy intake in healthy older individuals
Scientific title
Effects of oral protein load, on energy intake, appetite, antral area, gastric emptying, amino acids, hormones and glucose in healthy older individuals
Secondary ID [1] 281134 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Ageing 287304 0
Condition category
Condition code
Diet and Nutrition 287638 287638 0 0
Other diet and nutrition disorders
Oral and Gastrointestinal 287639 287639 0 0
Normal oral and gastrointestinal development and function

Study type
Description of intervention(s) / exposure
The participant receives a single 450mL preload per study visit (separated by at least 3 days) in a randomised, crossover fashion of: i) 30 grams Whey Protein Isolate with diet lime cordial flavouring ii) 70 grams Whey Protein Isolate with diet lime cordial flavouring or iii) Water control with diet lime cordial flavouring. All preloads contain 100uL of 13C Octanoic acid to enable measurement of gastric emptying via 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 buffet meal consists of 300ml orange juice, 600ml water, 375ml iced coffee, 4 slices white bread, 4 slices brown bread, 100g deli leg ham, 100g virginian chicken, 4 slices cheese, 100g tomato, 100g cucumber, 100g lettuce, 2 portions mayonnaise, 2 portions margarine, 1 medium apple, 1 medium banana, 200g chocolate custard, 150g fruit salad, 200g strawberry yoghurt, and a 14g milky way bar.

Each volunteer receives one of each of the 3 treatments on each of the 3 study days. Each study visit is separated by no less than 3 days. Each visit lasts approximately 4 hours.
Intervention code [1] 285594 0
Comparator / control treatment
Placebo: a single 450mL water and diet lime cordial preload.
Control group

Primary outcome [1] 287887 0
Macronutrient and total energy intake of a standard buffet meal are quantified using Foodworks software.
Timepoint [1] 287887 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] 287888 0
Plasma concentrations of gut hormones (cholecyctokinin (CKK), glucagon-like peptide-1 (GLP-1), peptide YY (PYY), gastric inhibitory polypeptide (GIP), ghrelin, glucagon and insulin), glucose and amino acids.
Timepoint [2] 287888 0
Blood samples are taken at t= -15, 0, 15, 30, 45, 60, 90, 120, 150 and 180 minutes.
Primary outcome [3] 287889 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 [3] 287889 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 [1] 298991 0
Appetite sensations using a Visual Analogue Scale (VAS) (nausea, hunger, fullness, desire to eat, thirst).
Timepoint [1] 298991 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.
Secondary outcome [2] 298992 0
Blood pressure and heart rate are determined using an automatic sphygmomanometer.
Timepoint [2] 298992 0
Blood pressure and heart rate are measured at -15 minutes, 0 minutes and every fifteen minutes thereafter until 180 minutes. The final measurement is at 210 minutes after the buffet meal has been consumed.

Key inclusion criteria
Body Mass Index (BMI): 20-30 kg/m2

Weight stable (<5% fluctuation in body weight in previous 3 months).
Minimum age
65 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.

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 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?

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)

Funding & Sponsors
Funding source category [1] 285915 0
Government body
Name [1] 285915 0
National Health and Medical Research Council Grant
Address [1] 285915 0
Level 1 16 Marcus Clarke Street
Canberra ACT 2601
Country [1] 285915 0
Primary sponsor type
Dr Stijn Soenen
Level 6 Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Secondary sponsor category [1] 284737 0
Name [1] 284737 0
University of Adelaide
Address [1] 284737 0
North Terrace
Adelaide, SA 5005
Country [1] 284737 0
Secondary sponsor category [2] 284738 0
Name [2] 284738 0
Royal Adelaide Hospital
Address [2] 284738 0
North Terrace
Adelaide, SA 5005
Country [2] 284738 0

Ethics approval
Ethics application status
Ethics committee name [1] 287944 0
Royal Adelaide Hospital Research Ethics Committee
Ethics committee address [1] 287944 0
Level 3, Hanson Institute, North Terrace
Adelaide, South Australia, 5000
Ethics committee country [1] 287944 0
Date submitted for ethics approval [1] 287944 0
Approval date [1] 287944 0
Ethics approval number [1] 287944 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, the effect of different oral protein 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 to determine the relationship between the suppression of appetite and energy intake by protein with ‘intragastric’ and ‘small intestinal’ mechanisms.
Trial website
Trial related presentations / publications
Giezenaar C, Trahair LG, Rigda R, Hutchison AT, Feinle-Bisset C, Luscombe-Marsh ND, Hausken T, Jones KL, Horowitz M, Chapman I, et al. Lesser suppression of energy intake by orally ingested whey protein in healthy older men compared with young controls. Am J Physiol Regul Integr Comp Physiol 2015;309(8):R845-54.
Public notes

Principal investigator
Name 34649 0
Dr Stijn Soenen
Address 34649 0
Discipline of Medicine, University of Adelaide
attn.: Dr Stijn Soenen
Level 6, Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 34649 0
Phone 34649 0
+61 8 8313 3638
Fax 34649 0
Email 34649 0
Contact person for public queries
Name 17896 0
Dr Dr Stijn Soenen
Address 17896 0
Discipline of Medicine, University of Adelaide
attn.: Dr Stijn Soenen
Level 6, Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 17896 0
Phone 17896 0
+61 8 8313 3638
Fax 17896 0
+61 8 8223 3870
Email 17896 0
Contact person for scientific queries
Name 8824 0
Dr Dr Stijn Soenen
Address 8824 0
Discipline of Medicine, University of Adelaide
attn.: Dr Stijn Soenen
Level 6, Eleanor Harrald Building,
Frome Road,
Adelaide, SA 5000
Country 8824 0
Phone 8824 0
+61 8 8313 3638
Fax 8824 0
+61 8 8223 3870
Email 8824 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