Understanding FeNO and the Impact of Diet
Fractional exhaled nitric oxide, or FeNO, is a measurement of the level of nitric oxide (NO) in a patient's exhaled breath. It serves as a biomarker for airway inflammation, particularly eosinophilic inflammation, which is often associated with allergic asthma. Medical professionals use FeNO testing to help diagnose and manage asthma, assess a patient's response to corticosteroid treatment, and monitor disease severity. While FeNO is a useful tool, its accuracy can be influenced by various external factors, with diet playing a significant and immediate role. Specifically, consuming foods rich in nitrates can lead to a temporary spike in FeNO readings, potentially skewing the test results.
The Conversion Process: From Nitrates to FeNO
The link between certain foods and an increase in FeNO is rooted in the body's conversion of dietary nitrate into nitric oxide. This process is distinct from the nitric oxide produced by the lungs due to inflammation.
Here is how the dietary pathway works:
- Ingestion: A person eats a food high in nitrates, such as spinach or beetroot.
- Absorption: The nitrate is absorbed into the bloodstream via the gastrointestinal tract.
- Salivary Circulation: The nitrate is concentrated in the salivary glands and excreted back into the mouth with saliva.
- Oral Bacteria: Bacteria in the mouth convert the nitrate into nitrite.
- Reduction to NO: The nitrite can then be reduced to nitric oxide through non-enzymatic pathways.
- Systemic Circulation: The newly formed NO enters the systemic circulation, where it can transiently affect the levels measured in exhaled breath during a FeNO test.
Foods That Temporarily Increase FeNO
For patients preparing for a FeNO test, it is crucial to know which foods contain high levels of nitrates. The primary culprits are leafy green vegetables and beetroot, but other items can also have an effect.
- Leafy Green Vegetables: This category is one of the highest in dietary nitrates. Common examples include spinach, kale, lettuce, arugula, celery, cabbage, and leek. Consuming these in a salad or cooked can elevate FeNO levels.
- Beetroot and Beetroot Juice: Numerous studies have highlighted the potent FeNO-increasing effect of beetroot. One study noted that participants who drank beetroot juice saw their FeNO levels increase by more than 20% within an hour.
- Cured and Processed Meats: Many processed and cured meats, such as bacon, ham, and sausages, contain nitrates as preservatives. While the concentration may vary, it is wise to avoid them before a test.
- Dairy Products: Some sources suggest that certain dairy products may contain nitrates that could influence test results.
- Fish: Like cured meats, some fish preparations may use nitrates, and it is best to avoid them prior to testing.
Factors That Can Decrease or Alter FeNO Levels
While some foods increase FeNO, other substances can have the opposite effect, potentially lowering the reading and providing a misleading result.
- Caffeine: Caffeinated beverages, including coffee, tea, and energy drinks, are known to temporarily decrease FeNO levels.
- Alcohol: Excessive alcohol consumption can cause a reduction in FeNO levels.
- Tobacco: Both short-term smoking and long-term tobacco use have been shown to significantly lower FeNO levels.
- Vigorous Exercise: High-intensity physical activity should be avoided for at least an hour before a test, as it can affect FeNO readings.
Comparison of Dietary Impacts on FeNO Test Results
| Feature | Foods That Can Increase FeNO | Substances That Can Decrease FeNO |
|---|---|---|
| Mechanism | Dietary nitrates convert to nitric oxide via oral bacteria, increasing exhaled NO. | Pharmacological effects or physiological changes in the body temporarily alter NO levels. |
| Examples | Leafy greens (spinach, kale), beetroot, celery, cured meats, some fish. | Caffeine (coffee, energy drinks), alcohol, tobacco (smoking). |
| Preparation | Avoid for at least 3 hours before a FeNO test. | Avoid for at least 1 hour before a FeNO test. |
| Primary Impact | Can cause a falsely elevated reading of airway inflammation. | Can cause a falsely low reading, potentially masking inflammation. |
How to Prepare for a FeNO Test
To ensure your FeNO test provides the most accurate reflection of your airway inflammation, it is critical to follow specific dietary and behavioral guidelines.
- Avoid High-Nitrate Foods: For at least three hours before your appointment, do not consume nitrate-rich items like leafy greens, beetroot, or cured meats.
- Skip Caffeine and Alcohol: Abstain from caffeinated beverages and alcohol for at least one hour before the test.
- Hold the Smoke: Do not smoke or use tobacco products for at least one hour prior.
- Limit Exercise: Avoid strenuous exercise for at least one hour before testing.
- Maintain Medications: Continue taking your regular medications as prescribed, including asthma inhalers, unless your doctor advises otherwise.
- Consult Your Doctor: Inform your healthcare provider about any substances you have consumed that might impact the results, allowing them to interpret the score correctly.
Conclusion Dietary choices can have a direct and temporary effect on the fractional exhaled nitric oxide (FeNO) test, a key diagnostic tool for asthma. Foods rich in nitrates, such as leafy greens and beetroot, can significantly increase FeNO levels, while substances like caffeine, alcohol, and tobacco can decrease them. By understanding the link between these items and FeNO readings, and by following simple pre-test instructions to avoid them, patients can help ensure their test results are as accurate as possible. This accuracy is vital for proper asthma diagnosis and management, allowing healthcare providers to determine the most effective course of treatment for each individual.
For more detailed information on how food and other factors can influence FeNO test accuracy, you can visit the NIOX.com website, a manufacturer of FeNO testing devices. NIOX.com provides further details on how food affects FeNO test results.
