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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Date results information initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
High-Protein vs Low-Carbohydrate Diets for Weight Loss
Scientific title
Higher-protein vs lower-carbohydrate energy-restricted diets: effects on eating behaviour, weight loss, and body composition in obese females.
Secondary ID [1] 297258 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Obesity 311332 0
Appetite control 311335 0
Condition category
Condition code
Diet and Nutrition 309972 309972 0 0

Study type
Description of intervention(s) / exposure
Participants will be randomised to follow either a High-Protein Normal-Carbohydrate (HPNC), High-Protein Low-Carbohydrate (HPLC), Normal-Protein Normal-Carbohydrate (NPNC) or Normal-Protein Low-Carbohydrate (NPLC) Low-Energy Diets (LED) for 8 weeks. The target macronutrient compositions are: (i) 50/40/10 en% of protein/carbohydrate/fat for HPNC; (ii) 50/28/22 en% of protein/carbohydrate/fat for HPLC; (iii) 35/40/25 en% of protein/carbohydrate/fat for NPNC; and (iv) 35/28/38 en% of protein/carbohydrate/fat for NPLC. Furthermore, the LED is aimed to provide approximately 40% of their daily energy requirements estimated using the Harris-Benedict Equation to generate an energy deficit for weight loss. The LED will be achieved through the consumption of 2 servings Cambridge Meal Replacements in combination with 2 home-prepared meals (breakfast and dinner) every day for a period of 8 weeks. This trial will provide the Cambridge Meal Replacements to the participants at no cost but the participants are required to buy the food ingredients to prepare their home-prepared meals while adhering to our meal plans.
The participants will attend a face-to-face group consultation at the Human Nutrition Unit, University of Auckland with a Registered Dietitian (RD) before the intervention is commenced and once every two weeks (Week 2, Week 4 and Week 6 after the intervention is commenced) to promote adherence to the diets.
The participants will also complete a 4-day food diary and a 24-hour urine collection at baseline, 4 weeks after the intervention is commenced and 8 weeks after the intervention is commenced to check for compliance.
Intervention code [1] 313512 0
Treatment: Other
Intervention code [2] 313619 0
Comparator / control treatment
All 4 treatments (HPNC, HPLC, NPNC and NPLC) are active to induce weight loss. The treatments will be compared among each other to explore the differential effect of macronutrient composition on weight loss. The High-Protein Diets (HPLC and HPNC) will be compared against the Normal-Protein Diets (NPNC, NPLC), and the Low-Carbohydrate Diets (HPLC and NPLC) will be compared against the Normal-Carbohydrate Diets (HPNC and NPNC).
Control group

Primary outcome [1] 318878 0
Change in body weight as assessed using a calibrated digital scale.
Timepoint [1] 318878 0
We are primarily interested in the difference between baseline and 8 weeks after intervention commenced. However, we also collect the body weight data at 4 weeks after the intervention commenced.
Secondary outcome [1] 366310 0
Objective markers of appetite as assessed using plasma concentration of appetite-related biomarkers (CCK, GLP-1, PYY)
Timepoint [1] 366310 0
At baseline and 8 weeks after intervention commenced.
Secondary outcome [2] 366311 0
Subjective feelings of appetite as assessed using Visual Analogue Scales (VAS)
Timepoint [2] 366311 0
At baseline and 8 weeks after intervention commenced.
Secondary outcome [3] 366312 0
Change in body composition (fat mass and fat-free mass) as assessed using a DEXA scan.
Timepoint [3] 366312 0
At baseline and 8 weeks after intervention commenced.

Key inclusion criteria
i. Females aged between 18 and 65 years.
ii. Obese (BMI 30 kg/m2 - 45kg/m2) with a maximum body weight of 130kg
iii. Otherwise healthy
Minimum age
18 Years
Maximum age
65 Years
Can healthy volunteers participate?
Key exclusion criteria
i. Recent body weight loss/gain >5% within previous 3 months
ii. Currently taking part in an active diet program
iii. Current medications or other conditions known to affect body weight and appetite
iv. Previous bariatric surgery
v. Diagnosed with impaired liver or kidney function
vi. Significant current disease such as type 2 diabetes, cardiovascular disease, or cancer; or digestive disease including inflammatory bowel syndrome/disease (IBS/D), ulcerative colitis (UC), Crohn's disease
vii. Systolic blood pressure greater than or equal to 160 mmHg and/or diastolic blood pressure greater than or equal to 100mmHg
viii. Depression or any other anxiety disorder known to affect appetite
ix. Unable to consume food items included in the study, or hypersensitivities or allergies to these foods (based on Food Preference Questionnaire)
x. Smokers or ex-smokers who have given up smoking for less than 6 months
xi. Pregnant or breastfeeding women
xii. Unwilling/unable to comply with the 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)
Allocation not concealed
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Simple randomisation using a randomisation table created at
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
Power calculation is performed based on the data from a similar study conducted in The Netherlands (Soenen et al., 2012). The HP diet in this study resulted in a mean body weight reduction of 14kg over 12 weeks, with a standard deviation of 4kg. By applying these data, a sample size of 32 participants per diet arm is required to detect a difference of 2.8kg (20% of 14kg) in body weight between two diet groups (HP vs LC) with 80% power and a 5% level of significance. Assuming a dropout rate of 10%, we target recruitment of 35 participants per diet arm. Since there are 4 intervention diets (HPNC, HPLC, NPNC, and NPLC) in this study, a total of 140 participants will be recruited.
Differences between intervention arms will be tested using ANCOVA, whereas the differences of parameters between baseline and post-intervention within each intervention arm will be tested using paired T-test.

Recruitment status
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment outside Australia
Country [1] 21239 0
New Zealand
State/province [1] 21239 0

Funding & Sponsors
Funding source category [1] 301817 0
Name [1] 301817 0
The Riddet Institute, Center of Research Excellence (CoRE)
Address [1] 301817 0
Riddet Institute
Massey University
Tennent drive
Palmerston North
New Zealand
Country [1] 301817 0
New Zealand
Primary sponsor type
The University of Auckland Research Office
Level 10, Building 620
49 Symonds St
Auckland 1010
New Zealand.
New Zealand
Secondary sponsor category [1] 301561 0
Name [1] 301561 0
Address [1] 301561 0
Country [1] 301561 0

Ethics approval
Ethics application status
Ethics committee name [1] 302521 0
Northern A Health and Disability Ethics Committee
Ethics committee address [1] 302521 0
Ministry of Health
133 Molesworth Street
PO Box 5013
Wellington 6011
New Zealand.
Ethics committee country [1] 302521 0
New Zealand
Date submitted for ethics approval [1] 302521 0
Approval date [1] 302521 0
Ethics approval number [1] 302521 0

Brief summary
Maintaining a healthy body weight is important as obesity is linked to diseases such as diabetes, heart disease, kidney disease, liver disease, and some cancers. In theory, weight loss can be achieved by simply reducing food intake and increasing exercise. In reality, many people struggle to maintain a healthy body weight. Many people find following a weight-loss regime to be very difficult in the long term when feelings of hunger and the desire to eat increase during periods of dieting. While there are plenty of weight-loss diets being advertised, there are two which are particularly popular with the general public: (i) the ‘high-protein diet’ and (ii) the ‘low-carbohydrate diet’. A high-protein weight-loss diet has been claimed to reduce hunger, increase energy expenditure, and retain muscle mass while helping to lose body fat. However, pushing up the protein content of your diet, means that you have to decrease either the carbohydrate or fat content, otherwise you will start to overeat, and possibly even gain weight. While the success of the ‘high-protein diet’ has been well documented in scientific articles, it has puzzled many researchers as to whether it is increasing to high-protein or decreasing to low-carbohydrate/low-fat that actually promotes the weight loss. Therefore, this study is designed to compare the difference in weight loss achieved using a ‘high-protein’ or a ‘low-carbohydrate’ low-energy diet for 8 weeks.
Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 90502 0
Prof Sally Poppitt
Address 90502 0
Human Nutrition Unit
University of Auckland
18 Carrick Place
Mt Eden
Auckland 1024
New Zealand.
Country 90502 0
New Zealand
Phone 90502 0
+64 096305160
Fax 90502 0
Email 90502 0
Contact person for public queries
Name 90503 0
Mr Jia Jiet Lim
Address 90503 0
Human Nutrition Unit
University of Auckland
18 Carrick Place
Mt Eden
Auckland 1024
New Zealand.
Country 90503 0
New Zealand
Phone 90503 0
+64 096301162
Fax 90503 0
Email 90503 0
Contact person for scientific queries
Name 90504 0
Mr Jia Jiet Lim
Address 90504 0
Human Nutrition Unit
University of Auckland
18 Carrick Place
Mt Eden
Auckland 1024
New Zealand.
Country 90504 0
New Zealand
Phone 90504 0
+64 096301162
Fax 90504 0
Email 90504 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
This is in accordance to our ethical application that all data generated will only be used for this study only. However, if this is necessary, additional consent will be sought from the participants to allow the use of the data for other studies.
What supporting documents are/will be available?
Study protocol
Informed consent form
Ethical approval
How or where can supporting documents be obtained?
Type [1] 1256 0
Study protocol
Citation [1] 1256 0
Link [1] 1256 0
Email [1] 1256 0
Other [1] 1256 0
Type [2] 1257 0
Informed consent form
Citation [2] 1257 0
Link [2] 1257 0
Email [2] 1257 0
Other [2] 1257 0
Informed Consent Form is attached to the Participant Information Sheet.
Type [3] 1258 0
Ethical approval
Citation [3] 1258 0
Link [3] 1258 0
Email [3] 1258 0
Other [3] 1258 0
We received ethical approval on 18 December 2018. However, we have amended the study protocol and PIS recently. This is the reason why the protocol and PIS in the attachments were dated later than the date when we received ethical approval.
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