Plain English Summary
Background and study aims
Intermittent (stop-start) energy (calorie) restriction, such as the 5:2 diet, has received considerable interest of late as a potential alternative to the conventional continuous energy restriction approach to weight-loss. Whilst there have been many studies demonstrating the efficacy of intermittent energy restriction as a viable means of weight-loss, little is known regarding its effects on blood sugar and fat breakdown after meals (postprandial glucose and fat metabolism). This is important because impairment to sugar and fat breakdown are important risk factors for type 2 diabetes and cardiovascular disease (e.g. heart disease, stroke). The aim of the study is therefore to compare the effects of intermittent and continuous energy restriction on postprandial glucose and fat metabolism. In addition, the study will compare changes in body composition (e.g. waist circumference and body fat), fuel utilisation (fat and glucose oxidation), resting calorie expenditure, eating behaviour and sleep quality with both diets.
Who can participate?
Healthy, weight-stable overweight/obese adults without significant medical conditions.
What does the study involve?
Participants are randomly allocated to one of two groups. Those in the first group take part in intermittent energy restriction. This involves two days per week of very low energy intake (about 600 calories/day) through using commercially available meal replacement products (Lighterlife) and five days of healthy eating with no calorie restriction. Those in the second group take part in continuous energy restriction. This involves limiting daily intake to 600 calorie/day, following current best practice guidelines. At the start of the study and after participants have lost 5% of weight (as opposed to fixed duration of time), blood samples are taken 6 hours after drinking a test drink (chocolate milkshake) containing carbohydrate and fat to measure postprandial glucose and fat metabolism. In addition, resting calorie expenditure (the amount of calories expended maintaining essential body functions whilst at complete rest) is assessed using indirect calorimetry, which involves placing a plastic hood over the head which samples the amount of oxygen breathed in, is measured and participants undergo a Flanker task, which is a computer based cognitive task designed to assess distraction to sweet/savoury foods. Finally, participants complete a range of questionnaires to assess changes in sleep quality, eating behaviour and mood. Weight of participants is tracked regularly during the study.
What are the possible benefits and risks of participating?
Participants benefit from intensive dietary support by registered dietitian and weight-loss guidance. In addition, if they lose weight then this is beneficial to their general health. The intermittent diet carries a risk of increased hunger, lethargy (sluggishness), insufficient fluid intake/dehydration due to the very low calorie nature of the intervention. Other risks include pain and bruising when blood samples are taken.
Where is the study run from?
Surrey Clinical Research Centre, Guildford (UK)
When is study starting and how long is it expected to run for?
May 2015 to August 2016
Who is funding the study?
Who is the main contact?
Dr Denise Robertson
Comparative effects of intermittent versus continuous energy restriction on postprandial glucose and lipid metabolism following matched weight-loss
The relative reduction (improvement) in incremental triacylglycerol responses will be greater following weight-loss via intermittent energy restriction.
University of Surrey Ethics Committee, 29/01/2015, ref: UEC/2014/140/FHMS
Single-centre randomised parallel trial
Primary study design
Secondary study design
Randomised parallel trial
Patient information sheet
Not available in web format, please use the contact details to request a patient information sheet
Participants are randomised to one of two groups:
Intermittent energy restriction (IER): The study utilises a commercially available IER diet by LighterLife (Essex, UK). On two consecutive days of the week, participants consum four LighterLife Food Packs (2638kJ: 38%, 36% and 26% of total energy as carbohydrate, protein and fat respectively) which delivers approximately 25% of their estimated euenergetic needs. Meal replacement products are provided by study team. On the remaining five days of the week (“feed days”), participants self-select food intake but are asked to aim to consume an euenergetic diet compliant with healthy eating guidelines.
Continuous energy restriction (CER): Participants assigned to the CER diet consum a daily hypoenergetic diet of 2510kJ below their estimated energy requirements compliant with NICE obesity guidelines. Diets are not provided but are self-selected by participants.
In both groups, energy requirements are calculated using the Henry equations for BMR multiplied by an appropriate physical activity factor.
Metabolic and anthropometric assessments are conducted before and after participants attained a 5% weight-loss (as opposed to fixed duration of time). Weight tracked regularly over the course of the study.
Primary outcome measure
1. 6-hour postprandial glucose (glucose, insulin, c-peptide) to a liquid mixed test meal is measured before and after attainment of 5% weight-loss
2. Lipid responses (triacylglycerol, non-esterified fatty acids) to a liquid mixed test meal is measured before and after attainment of 5% weight-loss
Secondary outcome measures
All outcomes are measured before and after 5% weight-loss:
1. Body composition is assessed via tape measure and bioimpedance
2. Rate of weight-loss
3. Fasting substrate utilisation is assessed via indirect calorimetry (respiratory quotient)
4. Postprandial substrate utilisation is assessed via serial blood sampling (3-hydroxybutyrate) for 6 hours after a liquid mixed test meal (400ml Fortisip, Nutricia, Trowbridge, UK: 2510kJ, 74g carbohydrate, 24g protein and 23g fat)
5. Fasting cardiometabolic risk markers (glucose, insulin, lipid profiles)
6. Resting energy expenditure (indirect calorimetry)
7. Sleep quality is measured using the Pittsburgh sleep quality index and Epworth sleep scale
8. Eating behaviour is measured using the Dutch eating behaviour questionnaire
9. Mood is measured using the positive affect negative affect scale
10. Self-efficacy is measured using a self-efficacy questionnaire
11. Hedonic food preference is measured using the Flanker psychometric task and power of food scale
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Overweight and obese participants (BMI ≥25 kg/m2)
2. Aged 18 to 65 years
3. Weight-stable (±2 kg) over the preceding three months
4. No significant medical history
5. To control for the potential influence of the menstrual cycle between visits, female participants were either post-menopausal or taking oral contraceptives
Target number of participants
Participant exclusion criteria
Individuals not meeting the inclusion criteria.
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Surrey Clinical Research Centre
University of Surrey
Funding Body Type
private sector organisation
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Not provided at time of registration
Intention to publish date
Participant level data
Available on request
Basic results (scientific)
1. 2018 results in https://www.ncbi.nlm.nih.gov/pubmed/29508693 (added 24/01/2019)