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How certain foods affect FeNO testing results
FeNO (fractional exhaled nitric oxide) testing can help clinicians to support asthma diagnosis. It is important to be aware that several factors may influence a patient’s FeNO levels, including age, sex, weight, and height.1
In this article, we will discuss how certain types of food affect FeNO and what information clinicians can give patients to ensure reliable results.
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How does a FeNO test work?
A FeNO test is quick and easy to perform with an electrochemical device. Some devices, like NIOX VERO®, are equipped with a breathing handle that filters out any ambient nitric oxide present in the air. This ensures an accurate and reliable result.
After inhaling through the handle, the patient exhales steadily for 10 seconds. Visuals on the device screen help the patient to exhale at the right air flow rate. The device analyzes the exhaled breath and around one minute later, the result is displayed on the screen.
How should clinicians interpret the result? The American Thoracic Society (ATS) has published a guideline dedicated to the interpretation of FeNO testing.1 Their recommendations state that levels above 50 ppb (35 ppb in children) indicate that Type 2 inflammation is likely. FeNO lower than 25 ppb (20 ppb in children) indicates that Type 2 inflammation is unlikely.1
Nitrate-rich foods increase FeNO levels
It is important to be aware of any factors that may influence a patient’s FeNO levels. For best results, patients should be advised to avoid certain types of food a few hours before a FeNO test.
Patient with their doctor completing a NIOX VERO® Test
Studies have shown that nitrate-rich foods, especially leafy vegetables such as lettuce, spinach and kale, but also beetroot, can increase FeNO.2,3 In a study by Kroll et al. clinicians measured 38 patients’ FeNO levels before and after drinking a nitrate-rich beetroot juice.2 45 minutes after the intake, the measured FeNO levels increased on average by 21.3%. After 90 minutes, they still measured an average increase of 20.3%.
During a case study by Kerley et al. in 2016, a similar test was performed in a 12-year-old boy with cystic fibrosis.3 His FeNO levels had increased by about 150% 90 minutes after drinking a nitrate-rich beetroot juice.
Caffeine, alcohol, and tobacco may decrease FeNO levels
Other types of food can have the opposite effect. In a recent study, caffeine was shown to decrease FeNO levels significantly.4 However, it is good to know that other studies have reported different results and concluded that caffeine does not need to be considered.5,6
Whereas coffee potentially affects FeNO levels in the short term, other food and lifestyle habits can have a lasting effect.7 A study by Afshar et al. pointed out that excessive alcohol consumption causes a reduction in FeNO levels. Even though they concluded that further studies are needed, they suggest that patients’ drinking habits should be taken into account during a FeNO test.7
Tobacco has also been found to influence FeNO levels both in the short and the long term.8,9,10 In a study by Kougias et al. researchers analysed the effect of smoking one cigarette immediately before measuring FeNO, and saw a significant decrease in FeNO levels.9 Malinovschi et al. looked at the long-term effects of tobacco and concluded that both current and ex-smokers have lower FeNO levels.10
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Conclusion: Ask your patients about their food consumption
It is safe to say that certain types of food may affect a patient’s FeNO levels. It is recommended that clinicians communicate this clearly to their patients and stress that it is important to make sure that they get the best possible treatment. This way, patients will know to avoid tobacco, caffeine, and nitrate-rich food a few hours before a FeNO test, and that they should provide the necessary information about their alcohol and tobacco habits.
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References
1.Dweik RA et al. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FeNO) for clinical applications. Am J Respir Crit Care Med. 2011;184(5):602-15.
2. Kroll JLet al. Acute ingestion of beetroot juice increases exhaled nitric oxide in healthy individuals. PLoS ONE. 2018;13(1): e0191030.
3. Kerley CP et al. Dietary nitrate acutely and markedly increased exhaled nitric oxide in a cystic fibrosis case. Clin Med Res. 2016;14(3-4):151-155.
4. Bruce C et al. Caffeine decreases exhaled nitric oxide. Thorax. 2002;57: 361–363.
5. Taylor E et al. Effect of caffeine ingestion on exhaled nitric oxide measurements in patients with asthma. Am J Resp Crit Care Med. 2004;169(9):1019-21,
6.Yurach M et al. The effect of caffeinated coffee on airway response to methacholine and exhaled nitric oxide. Resp Med 2011;105(11);1606-1610.
7. Afshar M et al. Exhaled nitric oxide levels among adults with excessive alcohol consumption. Chest. 2016; 150(1): 196–209.
8. Jacinto T et al. Differential effect of cigarette smoke exposure on exhaled nitric oxide and blood eosinophils in healthy and asthmatic individuals. J Breath Res. 2017 21;11(3):036006.
9. Kougias M et al. The acute effect of cigarette smoking on the respiratory function and FeNO production among young smokers. Exp Lung Res. 2013;39(8):359-64.
10. Malinovschi A et al. Effect of smoking on exhaled nitric oxide and flow-independent nitric oxide exchange parameters. Eur Respir J. 2006;28(2):339-45.