Effects of Dual-Source Carbohydrate Intake and Liver Glycogen Repletion After Overnight Fasting.

This study is looking at whether eating a breakfast which has two different sources of carbohydrates, glucose and fructose (found in foods like honey and fruits), can increase how much glycogen can be stored in the liver. Glucose is a type of sugar that the body uses to provide energy during exercise. When it is not circulating in the blood, it is stored in the muscles and liver. The stored version of glucose is often referred to as glycogen. When the body needs energy, for example, it will break down glycogen into glucose so that it can be used as fuel.

Muscle and liver glycogen stores are vital in providing energy during prolonged exercise, and strenuous activity can rapidly deplete these stores, leading to increased fatigue and a decline in performance. Liver glycogen, however, is particularly important because it controls blood glucose levels. This is important because the brain and other organs are constantly relying on the supply of glucose to function properly.

When sleeping, the body goes through a natural period of fasting. During this period, the liver gradually breaks down its glycogen stores to release glucose into the bloodstream. Because of this, following sleep, liver glycogen stores are automatically low (which is why having breakfast is important). There is research to suggest that eating a high-carbohydrate breakfast can prevent further declines in liver glycogen; however, it is not known if eating different types of carbohydrates within the breakfast (glucose and fructose together) will affect the liver's ability to store glycogen. This research will aid in understanding optimal ways to increase liver glycogen stores before performing exercise, which may influence exercise performance.

Therefore, the main aim of this study is:

1\. Investigate whether a high fructose breakfast will increase liver glycogen storage

To achieve this, participants will be recruited to complete a randomised crossover study where they will undertake three different conditions. All laboratory trials will take place at the Manchester Metropolitan University Institute of Sport.

1. No breakfast (Control) 2. 3 g/kg of body mass of carbohydrate (of which contains 0% fructose) 3. 3 g/kg of body mass of carbohydrate (of which contains50% fructose)

Liver glycogen stores will be measured using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). The investigators will measure liver glycogen content, liver volume, and stomach volume. Blood samples will also be taken to measure different metabolic hormone responses.