Let’s move away from talking about food and FODMAPs for a second, and put our public health hats on for a change!
Do the words ‘prevalence’ and ‘incidence’ sound familiar to you? What do they mean, and how are they related to IBS?
‘Prevalence’ and ‘Incidence’ are two terms that are commonly used to describe population-based health studies (1), particularly in epidemiology. Epidemiology is the analysis or study of disease occurrence in a given population.
Prevalence measures the number of existing cases in a specified population at a given time. It tells you the proportion of the population affected by a condition.
Incidence measures the number of new cases in a particular population at a given time.
The bathtub analogy is often used to describe the differences between the two. Prevalence is the amount of water currently in the bathtub, and incidence is the amount of ‘new’ water flowing into the bathtub, say, from a faucet.
The prevalence of IBS varies depending on the criteria used for diagnosis. One meta-analysis found a global IBS prevalence of 14.1% in 2006-2024, using the Rome III and IV criteria (2). This number supports the observation of 1 in 7 of the population having IBS. Another 2021 study by the Rome Foundation Global Foundation found an IBS prevalence of 3.8% and 10.1%, when the ROME IV and III criteria were used, respectively (3).
On the other hand, the incidence of IBS is relatively challenging to quantify.
IBS is not diagnosed using objective tools and markers, such as blood tests or biopsies.
Instead, IBS diagnosis relies on symptom manifestation, measured by the ROME IV criteria. IBS is also a condition often with no clear onset, and symptoms can fluctuate or come and go over time. People with IBS symptoms also seek medical help or diagnosis at different timepoints from when symptoms first appear. These factors make it difficult to measure the true incidence of IBS, from when symptoms first appear, versus when the condition is formally diagnosed by a doctor (4).
That being said, one US study used the first occurrence of IBS symptoms in the community to estimate the incidence of IBS, and found that 9% had developed symptoms over the year, an incidence rate of 67 per 1,000 person-years (5). Person-years is another way of saying ‘if 1,000 people were followed for a year, 67 of them would develop IBS’. Other studies that measured incidence using IBS diagnosis by a physician found a relatively conservative incidence of 2 per 1,000 person-years (6), and 38.5 per 10,000 person-years (7).
As evidenced by these numbers, IBS is affecting the wellbeing of millions worldwide. The commitment to optimising symptom control, quality of life and nutritional adequacy of these IBS patients is what has kept our team going over the years. Together with ongoing research and the delivery of clinical care in institutes around the world, we will be continuing to provide accurate and accessible dietetic science information and translating it into real-life applications.
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