Functional dyspepsia

Little known to the general public, functional dyspepsia (FD) is a very common gastrointestinal disorder that is under-diagnosed and still poorly understood today. FD accounts for 3% to 5% of GP visits in North America ¹ !

Functional dyspepsia’s varied symptoms are always associated with a feeling of poor digestion ²:

• feeling full long before you’ve finished your meal 
• the feeling of having eaten too much (stomach feels heavy and bloated), despite having eaten a perfectly reasonable-sized meal
• pain or burning in the upper stomach
• loss of appetite
• belching or hiccups
• nausea or even vomiting

Did you know?

The disorder is called functional dyspepsia since it is not accompanied by any structural abnormality in the digestive organs and tissues. Symptoms cannot be explained by the presence of a lesion in the stomach (no ulcers) or any other organic or structural abnormality: all tests (gastroenteroscopy, ultrasound, CT scan, etc.) come out negative.

How common is the disease? Who is most at risk?

Studies suggest that 10% to 30% of adults and 3% to 27% of children worldwide are affected by functional dyspepsia ². Women, smokers, and users of non-steroidal anti-inflammatory drugs (ibuprofen, ketoprofen) are at greater risk ³.

The consequences for patients are far from negligible: two-thirds of those affected by functional dyspepsia suffer from persistent and irregular symptoms that can affect their quality of life and well-being ¹.

Diet

Increasingly clear is the role played by diet in triggering functional dyspepsia symptoms. The culprits? Above all, fatty foods. But they’re not alone. Carbohydrate-containing foods, milk and dairy products, citrus fruits, spicy foods, coffee, and alcohol, have also been implicated ⁵. However, the results of these studies remain uncertain.

The mind may also play a role, with the memory of a bad experience leading patients to anticipate symptoms and over-experience them when exposed again. Experience has shown that distracting a patient with a cognitive task is enough to make them forget about their symptoms. Conversely, stating that the fat content of a yogurt is higher than it actually is increases the nausea felt by patients

Stress and anxiety

functional dyspepsia patients are often stressed and anxious: one large study showed that anxiety was clearly linked to the disease, and more specifically to postprandial distress; another study of 18,000 Japanese showed that patients with functional dyspepsia symptoms felt more stressed on a daily basis, more often mentioned not getting enough sleep, and complained more of difficulties in falling asleep ⁵.

Lack of physical activity

Functional dyspepsia patients generally report lower levels of physical activity. This is unfortunate since it appears that sport can actually reduce symptoms, and improve transit and gas evacuation in people suffering from bloating ⁵.

Tobacco

A study of 2,560 Swedes shows that smokers are at greater risk of postprandial distress syndrome: smoking 10 to 19 cigarettes a day increases the risk by 42%, while smoking more than a pack a day more than doubles the risk ⁷.

Obesity

Obesity is associated with many gastrointestinal symptoms, including functional dyspepsia. Several hypotheses have been put forward: for example, in obese people, the oral and gut receptors responsible for alerting the body to the presence of fats may be altered, amplifying the gastrointestinal effects in these patients, making them more sensitive to dietary fats ⁵.

Some specialists also point to a reciprocal link between functional dyspepsia and metabolic syndrome (sidenote: Metabolic syndrome Metabolic syndrome, also known as syndrome X, is characterized by the accumulation of several metabolic disorders in the same individual, including a large waist circumference (due to excess abdominal adipose tissue), hypertension, abnormal fasting blood sugar levels or insulin resistance, and dyslipidemia.  ) , with each promoting the other, creating a vicious circle ¹.

Helicobacter pylori bacteria

Since the 1980s, it has been known that the stomach, although highly acidic, is not sterile. It even harbors a community of microorganisms, including the bacterium H. pylori. However, infection by H. pylori appears to lead to the onset and progression of functional dyspepsia: patients with a history of H. pylori infection have a higher risk of developing functional dyspepsia ².

Dysbiosis throughout the digestive system

The digestive tract is home to almost 100 billion microorganisms from over 1,000 different species, which together are known as the gastrointestinal microbiota.

Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes dominate this community, making up more than 98% of the gut microbiota, with Firmicutes predominating, followed by Actinobacteria and Bacteroidetes ². At least in healthy patients. In those suffering from illnesses such as functional dyspepsia, this balance is not found; instead, dysbiosis is observed throughout the digestive system, from mouth to anus ².

In functional dyspepsia patients, studies have found, for example:

• a higher abundance of Firmicutes, streptococcus (associated with symptoms in the upper stomach), Bifidobacterium and Clostridium
• a lower abundance of Prevotella (accompanied by more symptoms of discomfort after eating)

The role of microbial metabolites

The microbiota’s role in functional dyspepsia is far from limited to the bacteria present, since each of these bacteria secretes various active molecules, both beneficial and harmful, that are closely linked to host health and to the onset and progression of numerous diseases ^2,3. For example: 

• some bacterial metabolites have a beneficial effect (e.g. short-chain fatty acids (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. )  produced by Firmicutes) 
• while others are harmful to the host (e.g. pro-inflammatory sphingolipids produced by Bacteroidetes and Prevotellacae) ³

While many gray areas remain, researchers believe that the mechanisms behind functional dyspepsia are likely to be multifactorial and vary from patient to patient ⁸. Thus, a range of mechanisms are involved in functional dyspepsia:

Disruption of the gut barrier

In normal circumstances, food passing through our digestive system remains isolated from our body by a barrier, the intestinal mucosa. This barrier is semi-permeable: it allows nutrients to be absorbed but bars passage to the various harmful substances and pathogens ingested along with our meal ². 

In functional dyspepsia patients, the integrity of this mucosa is compromised, so much so that it performs its filtering role less effectively

Disruption of gut immunity

In functional dyspepsia patients, there appears to be an excessive immune response: 40% of patients present inflammatory cells infiltrated into the duodenum, while a proliferation of bacteria (particularly oral bacteria) ⁹ is frequently observed in the small intestine, which may activate this immune response. Indeed, some researchers believe that a greater focus on the microbiota of the small intestine (sidenote: Small intestine Section of the digestive system between the stomach and the large intestine (i.e. the colon) essential for the digestion and absorption of nutrients. Measuring 21 to 23 feet, it is the longest portion of the digestive tract, comprising the duodenum, then the jejunum, and finally the ileum.  ) is required in order to better understand the pathogenesis of functional dyspepsia ⁹.

Deregulation of the gut-brain axis

There are complex interactions between the gut microbiota, the digestive system, and the central nervous system. This microbiota-gut-brain axis explains why stress can cause stomach ache, or why changes in the gut flora can alter intestinal motility and “inform” the brain, which in turn can regulate the gut. However, functional dyspepsia has been shown to be closely linked to gastrointestinal motility disorders (which are under cerebral control) and to gastrointestinal hypersensitivity, all of which are linked to the gastrointestinal microbiota ². From here to suggesting that everything is linked is only a short step...

An abnormal response to food ingestion

The presence of nutrients in the interior of the digestive tract produces signals that alter digestion. For example, a high-fat meal emains in the stomach longer, since gastric emptying is delayed. In functional dyspepsia patients, food ingestion may be associated with exaggerated signals from the gastrointestinal tract. This results in a whole series of symptoms which bear no relation to reality, such as feeling full when a meal has only just begun, hypersensitivity to gastric distension, and so on. ⁵

Diet

Logically, since diet is thought to play a role in functional dyspepsia, adapting it may improve symptoms. However, there is a dearth of studies highlighting the effects of specific diets. Nevertheless, experts believe that a large proportion of patients would benefit from a lower-fat diet and smaller meals eaten more often. In fact, functional dyspepsia patients are already doing so in practice: they have a slightly reduced dietary fat intake and tend to eat smaller meals more frequently ⁵.

Other patients would benefit more from avoiding spicy or acidic foods (tomatoes, citrus fruits, etc.) or foods rich in fiber or FODMAPs, which cause bloating. However, these restrictions should be managed with care so as to avoid an unbalanced diet ².

Proton pump inhibitors

Proton pump inhibitors (PPIs) are drugs used to reduce gastric acid secretion. They are prescribed by doctors to treat gastroesophageal reflux disease (GERD) and peptic ulcers.

In the short term, proton pump inhibitors (PPIs) may improve functional dyspepsia symptoms. However, their long-term use seems to go hand in hand with an increase in Streptococcus and, thus, a harmful dysbiosis ¹³.

Antibiotics to eradicate H. pylori

According to the American College of Gastroenterology and the Canadian Association of Gastroenterology, functional dyspepsia patients under 60 years of age should first be screened for H. pylori. If the test proves positive, antibiotics should be prescribed to eradicate the bacteria.

However, this strategy has its limits: only 1 in 10 patients will experience an improvement in their symptoms, while the remainder will see their symptoms worsen ¹⁴.

Probiotics

Since dysbiosis of the gastrointestinal microbiota is closely linked to the onset and progression of functional dyspepsia, regulating the gastrointestinal microbiota has logically been put forward as a potential treatment ². The role of probiotics may be multifactorial ¹⁵ :

• restoration of commensal flora eliminated by pathogens
• restoration of gut barrier permeability
• reduction of visceral hypersensitivity
• local and systemic anti-inflammatory action
• regulation of intestinal motility

All these benefits are thought to reduce symptoms of functional dyspepsia ¹⁵.

Alternative therapies

Various alternative therapies have been recognized as safe and effective treatments for functional dyspepsia:

• cognitive behavioral therapy, commonly used to treat stress and anxiety, helps the patient identify the thoughts or behaviors that lead to or exacerbate the expression of symptoms
• hypnotherapy, where the patient, in a state of hypnosis, is more receptive to therapeutic suggestions
• The potential of virtual reality is also being explored ¹⁴.