ANZCTR - Registration

Registration number

ACTRN12626001125314

Ethics application status

Approved

Date submitted

23/07/2026

Date registered

10/09/2026

Date last updated

10/09/2026

Date data sharing statement initially provided

10/09/2026

Type of registration

Prospectively registered

Titles & IDs

Public title

Effects of a dietary fibre supplement on blood glucose after meals in healthy adults consuming a diet higher in processed foods

Scientific title

Effect of dietary fibre supplementation on postprandial glycaemic response during dietary periods higher in processed foods in healthy adults aged 20–29 years: a double-blind randomised cross-over trial

Additional trial identifiers [1]

Nil known

Universal Trial Number (UTN)

U1111-1341-6462

Trial acronym

OFFSET (Otago Fibre Food SupplEment Trial)

Related trial records

Health condition

Health condition(s) studied:

Postprandial glycaemic response

Cardiometabolic health

Condition category

Condition code

Diet and Nutrition

Other diet and nutrition disorders

Metabolic and Endocrine

Normal metabolism and endocrine development and function

Intervention/exposure

Study type

Interventional

Description of the intervention or exposure

Active dietary fibre intervention during dietary periods higher in processed foods

Trial overview

This is a double-blind, randomised, two-period, two-sequence cross-over trial. Each participant will complete a 14-day active dietary fibre condition and a 14-day matched placebo condition in random order. The two intervention periods will be separated by a washout period of three to six weeks.

The intervention will be undertaken under free-living conditions in Dunedin. Participants will attend five in-person study visits facilitated by trained members of the research team. Blood pressure and other research-team assessments will be conducted in a clinic room on the 9th floor of Dunedin Hospital. Fasting venous blood samples at Visits 2, 3, 4 and 5 will be collected by trained phlebotomists at the Awanui Labs collection site at Dunedin Hospital. Participants are expected to spend approximately two hours in total attending the five visits.

Visit 1 – baseline and screening visit

Visit 1 will occur before the run-in period and will take approximately 30 minutes. A trained member of the research team will explain the study procedures, answer questions and obtain written informed consent. Height, body weight and blood pressure will be measured. Participants will complete the baseline study questionnaires and receive instructions for completing the four-day food diary. A continuous glucose monitoring sensor will be inserted by a trained member of the research team to measure glucose under usual dietary conditions during the run-in period.

Run-in period

Following Visit 1, participants will complete an approximately 14-day run-in period. During this period, participants will continue their usual diet and lifestyle and will not consume either study product or the study-provided processed foods.

Participants will wear a continuous glucose monitoring sensor to obtain glucose measurements under their usual dietary conditions. They will also complete a four-day food diary covering three weekdays and one weekend day. Participants will record all foods and beverages consumed, including food type and brand, preparation method, portion size and time of consumption. The run-in period will provide baseline dietary and glucose data before the first intervention period.

Visit 2 – pre-intervention assessment for Intervention Period 1

Visit 2 will occur immediately following the run-in period and immediately before the first 14-day intervention period. The visit will take approximately 20 minutes. Body weight and blood pressure will be measured, and a fasting venous blood sample will be collected by a trained phlebotomist at Awanui Labs. The run-in continuous glucose monitoring sensor will be removed and its data uploaded for analysis. Participants will complete the study questionnaires, and the research team will review the run-in food diary.

Participants who remain eligible after review of the screening and baseline results will be randomised to their intervention sequence. A new continuous glucose monitoring sensor will be inserted for the first intervention period. Participants will receive their allocated study product in a study container with the dosing record incorporated into its label, together with written instructions. The research team will arrange collection or delivery of the participant's selected processed supermarket foods for the first week of the intervention period.

Visit 3 – end of Intervention Period 1

Visit 3 will occur at the conclusion of the first 14-day intervention period, on or immediately after Day 14, and will take approximately 30 minutes. Body weight and blood pressure will be measured. A fasting venous blood sample will be collected by a trained phlebotomist at Awanui Labs. The continuous glucose monitoring sensor will be removed and its data uploaded for analysis.

Participants will complete the end-of-period questionnaires and return the study product container with its completed dosing record and any unused study product. The research team will review the participant's four-day intervention-period food diary. A semi-structured interview of approximately 15 minutes will be conducted by a trained member of the research team to explore the participant's experience of the study foods and study product.

Participants will then commence a washout period of three to six weeks, during which they will return to their usual diet and will not consume either study product or the study-provided foods.

Visit 4 – pre-intervention assessment for Intervention Period 2

Visit 4 will occur at the end of the washout period and immediately before the second 14-day intervention period. The visit will take approximately 10 minutes. Body weight and blood pressure will be measured, and a fasting venous blood sample will be collected by a trained phlebotomist at Awanui Labs. Participants will complete the study questionnaires.

A continuous glucose monitoring sensor will be inserted for the second intervention period. Participants will receive the alternative study product in a study container with the dosing record incorporated into its label, together with written instructions. The research team will arrange collection or delivery of the same selection of processed supermarket foods provided during the first intervention period.

Visit 5 – end of Intervention Period 2

Visit 5 will occur at the conclusion of the second 14-day intervention period, on or immediately after Day 14, and will take approximately 30 minutes. Body weight and blood pressure will be measured. A fasting venous blood sample will be collected by a trained phlebotomist at Awanui Labs. The continuous glucose monitoring sensor will be removed and its data uploaded for analysis.

Participants will complete the end-of-period questionnaires and return the study product container with its completed dosing record and any unused study product. The research team will review the participant's four-day intervention-period food diary. A second semi-structured interview of approximately 15 minutes will be conducted by a trained member of the research team.

Approximately eight weeks after Visit 5, participants will complete an online follow-up session with a member of the research team to determine whether they have returned to their usual dietary pattern. Dietetic support will be arranged if a participant reports difficulty returning to their usual diet.

All study visits and intervention-related contacts will be conducted individually rather than in a group setting.

Provision of processed supermarket foods

At baseline, each participant will select up to eight commonly consumed processed supermarket foods from a predefined list. The same selection of foods will be provided during both intervention periods.

The foods will be supplied twice during each 14-day intervention period: once at the beginning of Week 1 and again at the beginning of Week 2. Participants may collect the foods from a designated supermarket or have them delivered to an agreed address. The research team will coordinate the supermarket orders and will contact participants midway through each intervention period to confirm whether any additional study-provided foods are required.

Participants will be instructed to use the study-provided foods to replace some foods within their usual dietary pattern where appropriate. The study-provided foods are not intended to replace the participant's entire dietary intake, and participants will not be instructed to increase their total food intake.

Active dietary fibre condition

During the active condition, participants will receive No.2 Kiwi Berry Good Gut Fibre in a 200 g study container. Participants will be instructed to mix one teaspoon, weighing approximately 4–5 g and providing approximately 2.9–3.7 g of dietary fibre, with one cup of water and consume it three times daily, preferably with the three main meals, for 14 days. Participants will also be instructed to maintain adequate fluid intake throughout the intervention period.

Assessment of adherence to the study product

Adherence to the active study product or matched placebo will be assessed using the dosing record incorporated into the study product container label. Participants will record each of the three prescribed daily doses on the label throughout each 14-day intervention period.

The research team will review the completed dosing record at the end of each intervention period. Adherence will be calculated as the proportion of prescribed doses recorded as consumed. Participants will also return the study product container and any unused study product.

Monitoring consumption of the study-provided processed foods

Consumption of the study-provided processed foods will be monitored but will not be assessed as a separate quantitative adherence outcome. During each intervention period, participants will complete a four-day food diary covering three weekdays and one weekend day. The diary will record the type, brand, amount and timing of all foods and beverages consumed, including the study-provided foods.

Trained researchers will review each food diary for completeness and clarity and will contact the participant to clarify missing or ambiguous entries where necessary. The midway check-in during each intervention period will also be used to confirm whether additional study-provided foods are required.

Intervention code [1]

Treatment: Other

Intervention code [2]

Lifestyle

Description of the comparator or control

Matched placebo condition

During the placebo condition, participants will receive a maltodextrin-based placebo matched to the active dietary fibre supplement in appearance, flavour and sweetness, although not necessarily in viscosity. The placebo and active study product will be packaged in identical 200 g study containers to maintain blinding.

Participants will be instructed to mix one teaspoon of the placebo with one cup of water and consume it three times daily, preferably with the three main meals, for 14 days. Participants will receive the same personally selected processed supermarket foods during the placebo and active dietary fibre conditions. The food-supply procedures, participant instructions, research-team contact and adherence-assessment procedures will be identical in both conditions.

Placebo adherence will be assessed using the dosing record incorporated into the study product container label. Participants will record the time of each meal-related dose over the 14-day intervention period. The research team will review the completed label, and participants will be asked to return any unused study product at the end of the intervention period.

Each participant will complete both intervention conditions in randomised order and will therefore act as their own control.

Control group

Active

Outcomes

Primary outcome [1]

Mean 120-minute postprandial interstitial glucose incremental area under the curve (iAUC), expressed as mmol·h/L.

Timepoint [1]

This is the average postprandial glycaemic response from all meals(maximum 3 meals a day) identified using continuous glucose monitors over the whole 14 day period. Each postprandial glycaemic response is measured by the incremental area under the curve (iAUC), which will be calculated over 0–120 minutes, using the glucose concentration immediately before the excursion as the baseline. These values over the 14 days are then averaged to determine a mean and standard deviation per participant per intervention.

Secondary outcome [1]

Body weight in kilograms.

Timepoint [1]

At baseline (Visit 1), immediately before each 14-day intervention period (Visits 2 and 4), and at the end of each intervention period (Visits 3 and 5).

Secondary outcome [2]

Body fat percentage.

Timepoint [2]

At baseline (Visit 1), immediately before each 14-day intervention period (Visits 2 and 4), and at the end of each intervention period (Visits 3 and 5).

Secondary outcome [3]

Systolic blood pressure, measured in mmHg.

Timepoint [3]

At baseline before the run-in period (Visit 1), immediately before each 14-day intervention period (Visits 2 and 4), and at the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [4]

Fasting low-density lipoprotein cholesterol concentration, measured in mmol/L.

Timepoint [4]

Immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each intervention period (Visits 3 and 5).

Secondary outcome [5]

Mean daily energy intake, measured in kilojoules per day.

Timepoint [5]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [6]

Composite total physical activity score, measured in metabolic equivalent-minutes per week.

Timepoint [6]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [7]

Composite Craving Control subscale score, measured on a 0–10 scale.

Timepoint [7]

At baseline and immediately before and at the end of each intervention period (Visits 1-5).

Secondary outcome [8]

Overall Diet Satisfaction Score, a composite outcome calculated as the mean of the 10 item responses and reported on a scale from 1 to 5.

Timepoint [8]

At baseline and immediately before and at the end of each intervention period (Visits 1-5).

Secondary outcome [9]

Composite Food Noise Questionnaire total score, calculated as the sum of the five item responses and reported on a scale from 0 to 20.

Timepoint [9]

At baseline and immediately before and at the end of each intervention period (Visits 1-5).

Secondary outcome [10]

Abdominal pain domain score from the Gastrointestinal Symptom Rating Scale, measured on a scale from 1 to 7.

Timepoint [10]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [11]

Adherence to the prescribed study product.

Timepoint [11]

Recorded daily throughout each 14-day intervention period and assessed at the end of each intervention period (Visits 3 and 5).

Secondary outcome [12]

Participant-reported acceptability of the dietary intervention.

Timepoint [12]

At the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [13]

Plasma concentrations of potential biomarkers of dietary intake - exploratory outcome

Timepoint [13]

Samples will be collected immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each intervention period (Visits 3 and 5). Laboratory analyses will be conducted after study completion.

Secondary outcome [14]

Diastolic blood pressure, measured in mmHg.

Timepoint [14]

At baseline before the run-in period (Visit 1), immediately before each 14-day intervention period (Visits 2 and 4), and at the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [15]

Fasting high-density lipoprotein cholesterol concentration, measured in mmol/L.

Timepoint [15]

Immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [16]

Fasting total cholesterol concentration, measured in mmol/L.

Timepoint [16]

Immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [17]

Fasting triglyceride concentration, measured in mmol/L.

Timepoint [17]

Immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [18]

Mean daily dietary fibre intake, measured in grams per day.

Timepoint [18]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [19]

Mean daily carbohydrate intake, measured in grams per day.

Timepoint [19]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [20]

Mean daily protein intake, measured in grams per day.

Timepoint [20]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [21]

Mean daily total fat intake, measured in grams per day.

Timepoint [21]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [22]

Mean daily saturated fat intake, measured in grams per day.

Timepoint [22]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [23]

Mean daily total sugars intake, measured in grams per day.

Timepoint [23]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [24]

Mean daily sodium intake, measured in milligrams per day.

Timepoint [24]

During the run-in period, using a four-day food diary completed on three weekdays and one weekend day selected within the period; and during each 14-day intervention period, using a four-day food diary completed on three weekdays and one weekend day selected within that intervention period.

Secondary outcome [25]

Composite Craving for Sweet subscale score, measured on a 0–10 scale.

Timepoint [25]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [26]

Composite Craving for Savoury subscale score, measured on a 0–10 scale.

Timepoint [26]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [27]

Reflux domain score from the Gastrointestinal Symptom Rating Scale, measured on a scale from 1 to 7.

Timepoint [27]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [28]

Indigestion domain score from the Gastrointestinal Symptom Rating Scale, measured on a scale from 1 to 7.

Timepoint [28]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [29]

Diarrhoea domain score from the Gastrointestinal Symptom Rating Scale, measured on a scale from 1 to 7.

Timepoint [29]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [30]

Constipation domain score from the Gastrointestinal Symptom Rating Scale, measured on a scale from 1 to 7.

Timepoint [30]

At baseline and immediately before and at the end of each 14-day intervention period (Visits 1–5).

Secondary outcome [31]

Participant-reported feasibility of implementing the dietary intervention under free-living conditions.

Timepoint [31]

At the end of each 14-day intervention period (Visits 3 and 5).

Secondary outcome [32]

Exploratory untargetted plasma metabolomic profile.

Timepoint [32]

Samples will be collected immediately before each 14-day intervention period (Visits 2 and 4) and at the end of each intervention period (Visits 3 and 5). Laboratory analyses will be conducted after study completion.

Eligibility

Key inclusion criteria

Participants must meet all of the following criteria:

1. Healthy adults aged 20-29 years.

2. Body mass index (BMI) between 18.5 and 27.0 kg/m².

3. Willing to provide venous blood samples.

4. Willing to wear a continuous glucose monitoring sensor during the study.

5. Willing to consume the study-provided foods and dietary fibre supplement or matched placebo.

6. Habitually consume a healthy diet, defined as a Healthy Dietary Habits Index score of 37 or higher.

7. Usually consume three main meals per day or be willing to adopt a three-meal eating pattern for the duration of the study.

8. Willing and able to complete the required online questionnaires and smartphone-based food diaries.

Minimum age

20 Years

Maximum age

29 Years

Sex

Both males and females

Healthy volunteers

Yes

Key exclusion criteria

Participants will be excluded if they meet any of the following criteria:

1. Current or previous diagnosis of metabolic or cardiovascular disease, or another condition that may affect metabolism, including cancer, hypertension, dyslipidaemia or diabetes.

2. Current or previous diagnosis of an eating disorder, or another condition considered by the investigators to be incompatible with safe and successful participation.

3. A gastrointestinal disorder, including irritable bowel syndrome or inflammatory bowel disease.

4. Use of prescription medications or other substances that may affect metabolism, including lipid-lowering medications, weight-loss medications, antihypertensives, psychiatric medications, corticosteroids or other medications considered unsuitable by the investigators.

5. Pregnancy or lactation.

6. Regular use of dietary fibre supplements.

7. Regular use of tobacco products.

8. Limited control over usual food intake, including living in catered accommodation or a residential hall where meals are provided.

9. Dietary restrictions incompatible with the study protocol, including a vegan diet or relevant food allergies.

10. Inability to provide informed consent.

11. Lack of internet access or an appropriate device for completing online study procedures.

12. Inability or unwillingness to complete the smartphone-based food diary.

13. Insufficient English proficiency or literacy to complete the study questionnaires and food diary.

14. A screening low-density lipoprotein cholesterol concentration of 3.0 mmol/L or higher, or another screening result considered inconsistent with safe participation as a healthy young adult.

Study design

Statistical methods / analysis

The sample size calculation was based on the primary outcome of 120-minute postprandial interstitial glucose incremental area under the curve (iAUC). The within-participant standard deviation was estimated as 0.56 mmol·h/L and the within-participant correlation was assumed to be 0.46 based on published data. A mean between-treatment difference of 0.30 mmol·h/L was considered clinically meaningful.

Using a two-sided significance level of 0.05 and 80% power, 32 participants are required for a two-period, two-sequence cross-over design. Allowing for 15% attrition, the target sample size is 38 participants. This calculation assumes no carryover effect.

Continuous outcomes will be analysed using regression methods appropriate for the cross-over design, with treatment effects estimated using within-participant comparisons and presented with 95% confidence intervals. The primary analysis will follow the intention-to-treat principle and include all available data.

Recruitment

Recruitment status

Not yet recruiting

Date of first participant enrolment

Anticipated

14/09/2026

Actual

Date of last participant enrolment

Anticipated

14/06/2027

Actual

Date of last data collection

Anticipated

30/11/2027

Actual

Sample size

Target

38

Accrual to date

Final

Recruitment outside Australia

Country [1]

New Zealand

State/province [1]

Otago

Funding & Sponsors

Funding source category [1]

Other Collaborative groups

Name [1]

Riddet Institute Centre of Research Excellence

Country [1]

New Zealand

Primary sponsor type

University

Name

University of Otago

Country

New Zealand

Secondary sponsor category [1]

None

Name [1]

Country [1]

Ethics approval

Ethics application status

Approved

Ethics committee name [1]

University of Otago Human Ethics Committee (Health)

Ethics committee address [1]

https://www.otago.ac.nz/council/committees/committees/humanethicscommittees

Ethics committee country [1]

New Zealand

Date submitted for ethics approval [1]

16/06/2026

Approval date [1]

14/08/2026

Ethics approval number [1]

H26/0176

Ethics committee name [2]

University of Otago Human Ethics Committee (Health)

Ethics committee address [2]

https://www.otago.ac.nz/council/committees/committees/humanethicscommittees

Ethics committee country [2]

New Zealand

Date submitted for ethics approval [2]

Approval date [2]

Ethics approval number [2]

Summary

Brief summary

Diets high in processed foods are often low in fibre and may contribute to poorer cardiometabolic health, but it is not clear whether adding fibre can lessen these effects. This study will investigate whether a dietary fibre supplement reduces the rise in blood glucose after meals when healthy adults aged 20–29 years consume study-provided processed foods as part of their usual diet. In this randomised, double-blind crossover study, 38 participants will complete two 2-week intervention periods in random order, separated by a washout period of at least three weeks; they will take a fibre supplement during one period and a matched placebo during the other. We expect that the fibre supplement will reduce the rise in blood glucose after meals compared with placebo. The study will also examine other measures of heart and metabolic health, appetite, food cravings, gastrointestinal symptoms, dietary intake, physical activity, adherence, and participants’ experiences of the intervention.

Trial website

Public notes

Contacts

Principal investigator

Name

Prof Sheila Skeaff

Address

Department of Human Nutrition, University of Otago, PO Box 56, Dunedin 9054

Country

New Zealand

Phone

+64 3 479 7944

Email

[email protected]

Contact person for public queries

Name

Sheila Skeaff

Address

Department of Human Nutrition, University of Otago, PO Box 56, Dunedin 9054

Country

New Zealand

Phone

+64 3 479 7944

Email

[email protected]

Contact person for scientific queries

Name

Andrew Reynolds

Address

Department of Medicine, University of Otago, PO Box 56, Dunedin 9054

Country

New Zealand

Phone

+64 3 470 9916

Email

[email protected]

Trial Review

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