The Effects of 24-hour Fasting or Carbohydrate Restriction on Postprandial Metabolic Responses

Most individuals spend the majority of the day in a fed state, making postprandial blood glucose and lipid regulation a central component of metabolic health. Short periods of fasting or reduced carbohydrate intake can occur frequently in daily life, whether through intentional dietary practices (e.g. intermittent fasting), cultural or religious traditions, or unstructured eating patterns. These periods can induce measurable metabolic changes, but the acute effects of a single 24-hour period of fasting or carbohydrate restriction on postprandial metabolism upon refeeding remain poorly characterised.

This study will examine how 24 hours of either complete fasting or low carbohydrate intake without energy restriction influence postprandial blood glucose and lipid concentrations, as well as related metabolic markers, in healthy adults, in comparison to a habitual high carbohydrate control diet. Participants will complete all three conditions in a randomised order, consuming a standardised meal test after each 24-hour condition. Repeated blood sampling and gas exchange measurements will be carried out to assess postprandial metabolic responses.

The aim of this study is to characterise whether acute periods of fasting and low carbohydrate restriction elicit distinct or comparable alterations in postprandial metabolic responses. A clearer understanding of these acute physiological effects can help inform how variations in eating patterns influence glucose and lipid handling in individuals without metabolic disease.