Previous studies suggest that limiting how many carbohydrates we eat (from foods like pasta, bread, potatoes and sugar) can help with weight loss and improve certain aspects of health, such as blood sugar and fat levels. It is still unknown whether shorter periods of restricting carbohydrates can have similar effects.

The study from the Centre for Nutrition, Exercise and Metabolism aims to compare two diets that temporarily limit carbohydrate intake at different time frames to see if they work and, if they do, understand how. We also hope to learn whether a new mobile phone application is useful in following diets like these and tracking progress.

Laboratory visit 1 (around 1 hour):

Body measurements, a scan to measure body composition, and a 15-minute treadmill walk while measuring your heart rate and breathing.

Monitoring phase (2 weeks):

Monitoring of your current lifestyle through wearable devices (such as a smartwatch, activity monitor and a continuous glucose monitor), food diaries and mobile applications.

Laboratory visit 2 (around 7.5 hours):

Body measurements, collection of breath samples and a measure of blood pressure. A fat and optional muscle sample will then be collected. You will then be asked to drink a glucose (sugar) drink, after which we will regularly collect blood and breath samples for 3 hours. We will then provide you with a meal for lunch, after which we will carry out the same measurements for 2 hours.

Dietary phase (4 weeks):

We will ask you to follow one of the following diets for 4 weeks: 1) Restriction of carbohydrates on two days in a row each week 2) Restriction of carbohydrates after 4pm each day 3) No changes to your current diet You will also be asked to continue monitoring your lifestyle throughout.

Laboratory visit 3 (around 8 hours):

Identical as visit 2 except a body composition scan will be included.

Digital phase (4 weeks):

We will ask you to test out a mobile health-tracking application (‘Metabolism’) that provides education and recommendations tailored specifically to you, while continuing to monitor your lifestyle.

Laboratory visit 4 (around 6 hours):

Body measurements, a body composition scan, collection of breath samples and a measure of blood pressure. You will then be asked to consume a drink of glucose, after which blood will be sampled for 3 hours. Afterwards, we will carry out a 30-minute interview about your experience using the mobile health application.

At the end of your participation, you will gain lifetime access to the ‘Metabolism’ app, which enables you to collect information on your physical activity, sleep and blood sugar from your wearable devices, and provides you with individualised lifestyle recommendations and education that can help build healthy habits.

You will also receive detailed feedback on your body composition, markers of metabolic health (e.g. blood sugar and cholesterol levels), physical activity levels and dietary intake. We will present your results alongside the recommended ranges (where possible) and explain what they mean.

For example, you will receive information on the following:

• basal metabolic rate – How many calories your body burns at rest
• activity energy expenditure – How many calories you burn through physical activity
• body composition – How many kilograms of muscle and fat you have in your body
• energy intake – How many calories you eat/drink per day
• nutrient intake – How many grams of key nutrient to consume per day
• blood sugar, fat and hormonal responses – How your body handles the nutrients you eat (i.e. sugar, fat)