Is Diet Coke (caffeine-free carbonated beverage) acceptable to consume before fasting laboratory tests?

From the Guidelines

It is not recommended to consume Diet Coke before fasting labs due to its potential impact on test results, particularly glucose readings and hormone levels. While the study by 1 focuses on the diagnosis of diabetes, it emphasizes the importance of fasting for at least 8 hours before blood tests to ensure accurate results. Although Diet Coke contains no calories, its artificial sweeteners and caffeine may still affect the body's metabolic processes. The artificial sweeteners in Diet Coke might trigger insulin responses in some individuals, potentially altering glucose readings [ 1 ]. Furthermore, the caffeine in Diet Coke can influence cortisol levels and other hormones being measured. To minimize any potential interference with test results, it is best to stick to drinking only plain water during the fasting period.

Some key points to consider when preparing for fasting labs include:

• Consuming nothing except plain water for 8-12 hours before the blood draw
• Avoiding any substances that could potentially affect test results, including artificial sweeteners and caffeine
• Discussing any concerns, such as caffeine withdrawal symptoms, with a healthcare provider beforehand to determine the best course of action. Given the potential risks of inaccurate test results, it is crucial to prioritize caution and follow the recommended fasting guidelines to ensure the most accurate and reliable outcomes [ 1 ].

From the Research

Diet Coke Consumption Before Fasting Labs

• There is no direct evidence to suggest that consuming Diet Coke before fasting labs is okay or not okay.
• However, studies have shown that artificially sweetened beverages, such as Diet Coke, may be associated with an increased risk of type 2 diabetes 2, 3.
• A study published in 2018 found that diet soda consumption was positively associated with incident diabetes, even after adjusting for body mass index (BMI) and calorie consumption 3.
• Another study published in 2021 found that consuming more than seven servings of sugar or artificially sweetened beverages per week was associated with an increased risk of chronic kidney disease 4.
• It is generally recommended to avoid consuming any beverages that may affect blood sugar or insulin levels before fasting labs, as this can impact the accuracy of the test results.
• If you are scheduled to undergo fasting labs, it is best to consult with your healthcare provider for specific instructions on what to eat and drink before the test.

Artificially Sweetened Beverages and Health Risks

• Artificially sweetened beverages, such as Diet Coke, have been linked to several health risks, including type 2 diabetes and chronic kidney disease 2, 3, 4.
• A systematic review and meta-analysis published in 2021 found that consuming sugar or artificially sweetened beverages was associated with an increased risk of chronic kidney disease 4.
• Another study published in 2015 found that artificially sweetened beverages were associated with a greater incidence of type 2 diabetes, although the findings were likely to involve bias 2.

Intermittent Fasting and Diabetes

• Intermittent fasting has been shown to be effective in improving glycemic control and reducing insulin resistance in adults with type 2 diabetes 5, 6.
• A review of the literature published in 2021 found that intermittent fasting was an effective non-medicinal treatment option for type 2 diabetes, and that it may be able to reverse the need for insulin therapy in some patients 6.
• However, more research is needed to fully understand the effects of intermittent fasting on diabetes management, and patients should consult with their healthcare provider before starting an intermittent fasting regimen 6.