By Sarah Bloor, Clinical GI Physiologist
IBS is characterized by symptoms of abdominal pain, bloating and a change in bowel habit, especially after eating certain foods. Food sensitivity tests are popular, but are they useful? Here we understand the latest research into food induced IBS symptoms.
A study conducted by a Belgium research group was recently been published in Nature to understand the link between irritable bowel syndrome (IBS) symptoms and food. This is an important topic as up to 20% of people develop gastrointestinal symptoms after eating a meal.
It is well known that a previous gut infection (3-36%) can lead to the development of IBS and 17% of IBS patients report their symptoms started after a gut infection. However, the reason why is unclear.
To understand this, the researchers used mice with a prior bacterial gut infection. The mice were then exposed to ovalbumin, the protein in egg white. The researchers detected specific antibodies to ovalbumin in their colon, even though the mice did not show an allergic reaction to the egg protein. This indicates that the immune response they had was local to the colon rather than the whole body. When the mice were reintroduced to ovalbumin, it caused diarrhoea and gut pain in the mice.
This study also looked at the impact of other food antigens in IBS and healthy patients. They were injected with antigens from soy, wheat, gluten and milk into the colon. All the IBS patients had a mucosal reaction to at least one of the food antigens tested, whereas only 25% of the healthy participants had a mucosal reaction. Importantly, none of the participants had an allergy to any of the antigens tested, so the reaction may also be specific to the intestine like with the mice.
Interestingly, the researchers looked at IgE antibodies. IgE is an indication of hypersensitivity whereas most commercial “food sensitivity” tests look at IgG antibodies. IgG is a secondary response usually associated with a previous exposure to an antigen. All foods contain antigens, so if you ate a lot of something recently, it is likely your body will produce IgG antibodies to it, which could then lead to a fall positive result. There is no evidence that commercially available food sensitivity tests are scientifically credible.
The two most established ways to understand if IBS symptoms may be caused by food intolerances are hydrogen and methane breath testing (HMBT) and elimination diets. HMBT measures the levels of gases produced by bacteria in the colon following ingestion of suspected food. For example, the most common lactose, the sugar food in dairy. People who do not produce enough of the enzyme lactase required to breakdown lactose will produce an increase in hydrogen gas as the undigested lactose reaches their colon and is fermented by the bacteria.
Elimination diets are the best way to find out which foods may be causing IBS symptoms. This involves cutting out all the most common symptom-provoking foods, and then slowly reintroducing certain food groups every few days to find the culprits. However, this can be challenging and stressful, so is best performed under guidance of a trained dietitian.
In conclusion, a bacterial gut infection can cause increased sensitisation to antigens in food leading o intolerance. This means that after an infection, foods that individuals could previously eat with no gastrointestinal symptoms, could trigger abdominal pain due to increased gut hypersensitivity and a change to pain signalling from the gut to the brain.
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Figure 1: The proposed method by the researchers as to food induced abdominal pain. A bacterial gut infection trigeers a change to the pain signalling pathway, meaning food antigens trigger pain.
- Aguilera-Lizarraga, J. et al. Local immune responses to food antigens drives meal-induced abdominal pain. Nature https://doi.org/10.1038/s41586-020-03118-2 (2021)