From the Guidelines
Exercise Before Fasting and Its Impact on Laboratory Results
It is generally recommended to avoid strenuous exercise for at least 12 hours prior to fasting labs, especially if the labs include measurements of glucose, insulin, or lipid profiles, as exercise can induce acute endothelial dysfunction and affect vascular function 1.
- Mild to moderate exercise, such as walking or light stretching, may be acceptable, but high-intensity exercise, such as running or weightlifting, should be avoided due to its potential to cause transient hyperglycemia and affect glucose uptake into active muscles 1.
- Preanalytical conditions, such as avoiding vigorous exercise the day before collection, fasting overnight, and adhering to laboratory guidelines, are crucial to minimize measurement error and ensure reliable results 1.
- Additionally, factors such as time of day for blood collection, fasting status, and pre-blood draw exercise activity should be recorded to facilitate downstream interpretation of results, as they can impact blood biomarker levels 1.
- Patients taking medications such as beta-blockers or certain blood thinners should consult with their healthcare provider for specific guidance on exercise prior to fasting labs, as these medications can affect the vasculature and interact with exercise-induced changes 1.
- In all cases, it is best to consult with a healthcare provider for individualized advice on exercise and fasting labs, as the impact of exercise on laboratory results can vary depending on the specific tests being performed and the individual's health status.
From the Research
Effect of Exercise on Laboratory Results
- Exercise before fasting can affect laboratory results, particularly those related to glucose and lipid metabolism 2, 3, 4.
- Studies have shown that exercise in a fasted state can increase fat oxidation and improve cardiovascular risk factors 5, 3, 4.
- However, the impact of exercise on laboratory results can vary depending on the type and intensity of exercise, as well as the individual's health status and dietary habits 6, 2.
Glucose and Lipid Metabolism
- Exercise in a fasted state has been shown to increase glucose variability and hyperglycemia in individuals with type 1 diabetes 2.
- In contrast, exercise after a meal can improve glucose tolerance and reduce the risk of hypoglycemia 6.
- Exercise has also been shown to improve lipid profiles, including reductions in triglycerides and increases in high-density lipoprotein (HDL) cholesterol 5, 3.
Fat Oxidation and Metabolism
- Prior exercise can increase whole-body fat oxidation during submaximal exercise compared to overnight fasting 3.
- Fasted resistance exercise has been shown to rely more heavily on fat metabolism than carbohydrate metabolism 4.
- Exercise can also increase the levels of fatty acids and succinate in the blood, indicating increased fat oxidation and metabolism 3.