Why Do I Get Phlegm After Eating Certain Foods?

Understanding phlegm

Phlegm is a type of thick mucus produced in the upper airways (throat) and lungs.¹ Phlegm is similar to pulmonary (lung) mucus; both are protective substances that coat the insides of the lung and protect inner tissues from dehydration. 

Healthy and undamaged airways are covered by tiny hair-like structures, cilia; these allow oxygenated air to travel through the airways easily.²  Cilia are covered by goblet cells, cells that normally produce mucus to protect lung linings and trap  irritants, such as germs, dust and chemicals.⁹ Mucus essentially helps to get rid of these irritants through coughing. On the other hand phlegm production is often related to the disease and inflammatory processes. ¹ Excessive production of the thicker phlegm leads to development of so-called wet cough, due to its build-up in the lower lung  and obstruction of the airways. Too much mucus and phlegm prevents normal flow of oxygenated air, thus making breathing more difficult and changing optimal conditions in the lung, increasing risk of pulmonary infection. An excess of thick fluid in the lung is a common sign of various lung diseases, such as chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), bronchiectasis, bronchitis or asthma.²

Learning more about the phlegm, and phlegm triggering events can help to prevent, treat and manage symptoms of excessive mucus production, thus including improving your overall lung function.

Although excess phlegm production has been linked to numerous underlying causes, this article will focus specifically on phlegm-production influenced by a diet and consumption of certain food products.

Types of phlegm

While mucus is a slimy transparent  water-gel containing various immunoglobulins and glycoproteins that hydrate and protect the lung, phlegm usually has a colour and thicker consistency, containing mucus with trapped microorganisms, debris, and inflammatory cells.⁹ Once phlegm is excreted  by a cough, it is called sputum.¹

Phlegm can be classified and differentiated based on its appearance and structure:

• Yellow or green: it indicates presence of  infection by a virus or bacteria, the color change occurs as a result of interaction between an infectious agent with an enzyme produced by immune cells called leukocytes¹
• Clear: No color can be a sign of allergies, excessive mucus secretion and production of anti-allergic histamines⁸
• Red: it can be caused by coloring of the phlegm with blood. The potential causes include an extremely dry nose and throat, but can also be a sign of lung malignancy⁸

Common Causes

Mechanical damage of the vocal cords: clearing the throat,  raising your voice/yelling/ screaming all can cause mini-tears,  inflammation, thus resulting in phlegm.⁶

Tobacco smoke: smoke is itself a strong irritant, it can also contribute to extreme drying of the vocal cords; a clinical study showed that smoking inhibits airway re-hydration for about three hours.  Excessive phlegm is a reaction of the body to cope with dryness and consequent inflammation.¹⁰ 

Infectious diseases and common cold: During such conditions as viral flu, cold, and pneumonia, phlegm is stimulated to maximize elimination of the invading bacteria/virus. Among major associated diseases with bacterial causes is acute bronchitis, which causes massive secretion of phlegm and its reduced clearance; often it requires treatment with an antibiotic.

Allergies: Hay fever, as well as asthma can cause prolonged inflammation of the small airways known as bronchioles, leading to phlegm production and clogging of the airways.

Diet: It has been widely reported that consumption of dairy products can worsen and amplify phlegm production, although this hypothesis remains debatable and needs more clinical evidence. Besides dairy consumption, various other food groups can be linked to coughing and phlegm production. On the other hand, it has been well-established that food rich in fibre can ease the symptoms of excessive phlegm, its buildup in the lung and obstruction of the pulmonary airways.^5,7

Signs and symptoms

As mentioned above, mucus has an important function within a healthy functioning lung, as is constantly being produced. Normally, people are unaware of it, until there is an overproduction and change in consistency of the mucus, usually related to the disease.

The symptoms and signs include:

• Consistency changed: mucus becomes thick and sticky and lines up in the upper respiratory tree, making it harder to breathe²
• Onset of the wet cough: extra phlegm is trapped within the lung, back of the throat and nose, thus contributing to cough in an attempt to get rid of it
• Changed colour and transparency of mucus and phlegm: the appearance of the secreted substance can tell a lot regarding its underlying cause. For instance, cloudy mucus can indicate presence of the proteins released by the immune cells as a response to a trigger, such as pollen, or another allergen. Often people can experience phlegm after eating spicy food⁹

Why do I get phlegm after eating certain foods?

Possible causes of phlegm after eating

Some might experience chesty (wet) coughs after eating a meal, which can be explained by production of phlegm in response to chemically active irritants present in certain food products. Coughing  is a reflex mechanism which helps to clear lungs of thick mucus, or chemical irritants. Short-term cough is not a sign of medical emergency and does not require any treatment.

Some studies found that certain chemicals, called tussive agents, activate receptors on cells lining the inner airways, triggering initiation of the inflammatory response/severe allergic reaction and leading to coughing. One common example is the initiation of extreme mucus production by the capsaicin, an active chemical ingredient derived from chili peppers.¹³ Capsaicin was found to stimulate sensory nerves present both in bronchial airways and the oral cavity, leading to activation of certain receptors that sense mechanical and chemical irritants, stimulation of inflammatory and immunological mediators, eventually resulting in increased production of mucus, and the cough reflex.⁷

It is clear that individuals with common airway diseases such as COPD,  asthma, and bronchitis usually experience more severe obstruction of the airways due to phlegm. Similarly conditions such as gastro-oesophageal reflux disease (GORD), ulcerative colitis and irritable bowel disease (IBD) can cause extra production of phlegm.¹² Studies suggest that there is a link between ulcerative colitis and a decline in lung function, defined with inflammation of the lung and airway tissues, changes seen in bronchial mucosal cells and non-resolving chronic cough.¹²

The extent to which it is caused by certain products and underlying mechanisms is still not fully understood and requires more in depth studies to differentiate between mechanisms leading to coughing in different diseases.

Types of foods to avoid to prevent phlegm formation

Dairy products

Milk products have been thought to increase in mucus production, contributing to mucus becoming thicker and leading to mucus build-up within the throat.¹¹ In fact, the hypothesis that dairy intake can directly increase the actual mucus generation has been proven wrong. However, sufficient clinical evidence indicates that consuming dairy products can result in difficulty swallowing and thickening of mucus and saliva. Lactose-containing products, such as heavy cream and yogurt were found to increase feelings of difficulty breathing in individuals with head cold and irritation in a sore throat.

Food allergens

Some products are highly likely to cause allergies in a large proportion of people.¹¹ These foods contain chemicals that can trigger increased mucus production. Such food groups include dairy products, gluten-containing breads and pasta and soy products, like tofu.

In case GORDis suspected, it is strongly advised to avoid irritation-causing food, such as alcohol, spicy and fried foods, chocolate, tomatoes, or citrus fruits.

Caffeinated beverages

Caffeine-containing drinks, such as tea and coffee, may thicken mucus or worsen phlegm production due to their dehydrating effects.

Ways to prevent phlegm after eating

Bringing certain changes into one’s diet can help to manage increased phlegm production. More importantly professionals encourage a balanced diet, rich in low-fat sources of proteins and high in fibre. ⁵ Fibrous fruits have shown a significant beneficial effect for pulmonary health in individuals affected by COPD, fruits containing such nutrients as vitamin C, flavonoids, carotene, vitamin A, and vitamin E.⁴

Avoiding excessive consumption of certain food groups can also help to prevent phlegm production and coughing after eating. It is important to keep in mind that complete elimination is not only unnecessary but can cause a nutritional deficiency in essential vitamins and minerals. For instance, dairy products are important sources of vitamin D and calcium. 

Some general advice includes:

• Try to choose complex carbs, rather than simple carbs. Firstly, it will allow you to consume less volume of food that will keep you satisfied and satiated for longer. Good examples of complex carbohydrates is vegetables, fibrous fruits, and whole grains⁷ 
• Try to limit consumption of simple carbohydrates, such as sugar, sweets, and regular soft drinks
• Aim to consume 20-30 grams of fibre daily⁷ 
• Eat protein, as it helps to replenish daily needs of muscles and to maintain strong respiratory muscles 
• Eat mono- and poly-unsaturated fats. Unlike cholesterol-containing fats, these are “healthier” fats that come from plant sources, such as sunflower, canola, sesame, and a mix of vegetable oils
• Avoid trans fats and saturated fat. Be sparing with foods packed with cholesterol-containing fats, such as butter or shortening 
• Drink water- Staying hydrated is important to keep mucus thin and your airways sufficiently lubricated. Daily recommendation of the water intake is around 8 fluid ounces daily⁷ 
• Limit consumption of caffeine-containing drinks as it can lead to mild diuretic effects and increase risk of dehydration
• In critical weather make sure to use an air humidifier as it can help to reduce mucus and phlegm production and nasal congestion¹

When to seek medical attention

If symptoms do not improve with short-term nutritional changes, seeking help from a health care provider is highly recommended. In fact, if a person experiences a constant chesty cough, runny nose  lasting more than 3 weeks or lung congestion coupled with a fever it is critical to seek professional help as it can be manifestation of a serious condition.

Summary

To summarise, changes in lung mucosa and phlegm can be caused by various pulmonary and non-pulmonary diseases, but can also occur due to the unbalanced inappropriate nutrition. Diet can directly influence the severity of the associated symptoms, and eating a balanced nutritious diet can help to resolve production of excessive phlegm and ease chesty cough after the meal.

Certain products can predispose to the worsening of the phlegm production and therefore consumption of these should be adapted and limited. In case the symptoms fail to resolve by implied nutritional changes and are worsened over the period of time, it is important to contact a healthcare professional.