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Endo Belly

Perhaps one of the most overlooked symptoms of endometriosis is the aptly named ‘endo belly’. A quick google image or social media search yields numerous examples of this phenomena. Endo belly is the pronounced bloating or swelling of the abdomen, which can often be uncomfortable or painful, often accompanied by a feeling of ‘fullness’ in the abdomen. This bloating may occur at certain points of the menstrual cycle or randomly at other points of the month.

When we talk about symptoms of endometriosis the conversation tends to revolve around the subjects of pain and fertility. This is reasonable, considering that these are the most prominent symptoms associated with endo and the most impactful on people’s lives. However, there are a number of other symptoms also associated with endo that often get overlooked. They may not be as common or severe as some of the pain symptoms, but they are still factors that influence the health and wellbeing of people who suffer with the disease on a day to day basis.

Endometriosis is known to drag along a lot of other symptoms. Gastrointestinal symptoms in particular are reported almost as often as gynaecological symptoms, with some studies reporting up to 85% of women with endometriosis experiencing gastrointestinal symptoms. The same study reported that the top triggers for gastro symptoms (if one was known) were menstruation and stress (you can read the full study on the gastro symptoms of endo here).

This is unsurprising given that studies indicate that a third of women with no history of endometriosis report gastro symptoms around the time of menstruation (I know plenty of women who dread the infamous ‘period poos’), and for women with endo the most severe gastro symptoms are reported to occur in line with menstruation.

When looking at specific gastro symptoms abdominal pain, constipation, bloating, and defecation urgency were significantly more common in women with endo compared to those without, while diarrhoea, and nausea and vomiting weren’t more common in either group of women (unless endo is found on the bowel directly). For this post though I’m going to focus on bloating and the ‘endo belly’ effect as it seems to be the most mysterious of the gastro symptoms.

Another study on women undergoing laparoscopy for suspected endo found that, of the women confirmed to have it, only 7.6% were found to have endo directly involving the bowel, however 81.3% reported gastro symptoms, including 81.6% of women with confirmed endo reporting bloating, which was overall the most common gastro symptom.

Although ‘endo belly’ is well known in patient circles, it seems it isn’t as well known in the medical field. This is exemplified by a study on questionnaire design for measuring the painful symptoms of endometriosis. Patients and clinicians were asked about how valid they thought certain statements were for measuring chronic pain in endometriosis. One of the statements involved asking about “bloating, bloated abdomen during menstruation”. 88.2% of patients agreed this was valid to include in the questionnaire, compared to only 35% of the clinicians.

Perhaps this is why very little research has been done into the phenomena of chronic abdominal bloating in endometriosis. To my knowledge there has only been one study that has focussed on that issue alone. Let’s take a look at that study in more detail.

Firstly the authors recruited three groups of women; those women without endometriosis (a control group consisting of 25 women), a group of women diagnosed with endometriosis who were not taking any medication (12 women), and a group of women diagnosed with endometriosis who were taking some form of medication (14 women).

First of all, before looking at bloating, let’s see how these groups compare in terms of pain symptoms, specifically pain related to menstruation. The graph below shows what percentage of women in this study reported which type of pain associated with menstruation they experienced.

It’s fairly unsurprising that the women with endo have the most severe pain symptoms during menstruation. But what about their bloating symptoms? The patients were asked a series of questions about their bloating, below are the results. First and foremost the most obvious question is; do you experience abdominal bloating?

From this graph alone it comes clear that women with endo, whether they are taking medication or not, experience bloating more than women without endo. A further part of the study looked at perceived severity of bloating in control women and unmedicated endo women as it varied from morning to evening. They found that the endo group had significantly higher bloating severity variation from morning to evening, across all stages of the menstrual cycle.

Speaking of the menstrual cycle, the survey asked the groups of women who did experience abdominal bloating whether it varied in relation to their menstrual cycle, below is what they had to say

A very clear difference there between the women with and without endo. Around 1 in 6 of the control group always experienced bloating linked to some part of their menstrual cycle, compared to over two thirds of either endometriosis group. So a huge number of women with endo experience their bloating in close synchronicity with their cycle. But when during the cycle?

It may come as little surprise that most women in either group experienced bloating before or during their period. For the endometriosis group though (only women with endo not taking any meds were included for this graph), nearly half of the women surveyed said their bloating was both before and during their period, compared to around a third of the control women. There seems to exist a definite ‘bloating window’ directly before and during menstruation where bloating occurs most frequently. Clearly some factor/s influencing or influenced by menstruation play a role in chronic bloating in endometriosis. What these factors are, remains a mystery, but we’ll discuss later what they might be.

We’ve established who gets bloating and when, but what about the effect it has on the people who experience it?

Again from these results, it is clear that, bloating has a far greater impact on the day to day life of women with endo. In particular those women with endo taking medication. There are several answers for why this might be the case, women taking medication for endo are likely to have more severe symptoms anyway, or it could be that some of the side effects from medications cause bloating (opiates in particular are known to cause gastro problems).

A further way in which the authors measured the effect of bloating on women’s lives was to ask whether it was necessary to wear loose fitting clothing

Whereas just over a third of control women needed to wear loose clothing, roughly 80-90% of women with endo needed to. I think this highlights an important aspect of living with endometriosis; that the disease can restrict you in so many ways that other people may not think of. Being in pain is restrictive in itself, but what about not being able to wear what you want, when you want, for a good portion of every month? Or having to plan activities around a restrictive symptom you know will come each month? These all add up to the way in which endometriosis negatively impacts a sufferer’s life.

What could be the cause of these symptoms? Direct endometriosis involvement with the bowel is a fairly obvious answer, certainly, women with endo on the bowel or in close proximity to the bowel (such as the recto-vaginal septum) report more severe bowel symptoms. Yet, gastro symptoms are still common in women with all types of the disease and regardless of where the disease is located.

The natural place to start when looking at problems that might involve the gastrointestinal system, is to ask about food. The authors of this study did ask whether bloating was worse after meals.

Although the control group had roughly the same proportion of yes/no answers, the endo groups had a much higher proportion of yes’s to no’s. This was particularly pronounced for the medicated endo group, with over 80% getting bloated after meals. The next logical question would be to ask whether the participants thought any particular food triggered this reaction

Most seem to agree that there is a dietary component to their bloating, however there are also fairly large portions of the endo groups who said ‘no’ or ‘don’t know’. This in combination with the bloating linked to menstruation means there is clearly more to it than just food.

Other studies into gastro symptoms and the menstrual cycle have found a clear link between the two, with one study finding a third of women experiencing gastro symptoms of some kind during their period. This number rose to half in women who also had irritable bowel syndrome (IBS). IBS is fairly common, with almost half of the women reporting pelvic pain having symptoms suggestive of it. However, IBS is also one of the most common misdiagnoses of endometriosis, with one study showing a third of women with endo were originally misdiagnosed with IBS resulting in their true diagnosis being delayed.

That said, studies into women who have been diagnosed with both endometriosis and IBS suggest that dietary modification, such as low FODMAP can be helpful at reducing the gastro symptoms.

Are there other reasons that gastro symptoms, like bloating, could occur in women with endo? There is some evidence from animal studies that the good bacteria that help maintain a healthy digestion are altered in endometriosis, and that gut bacteria help regulate estrogen in the body, but this very speculative at present and far more research is needed before we make any judgements.

Something we do know very well is that endo is a disease characterised by chronic inflammation. During menstruation the uterus produces a number of inflammation promoting factors, such as certain prostaglandins and interleukins (signalling molecules that tell tissues when to become inflamed). These help control the breakdown, shedding and regrowth of the endometrium. The production of the inflammation promoting factors is a tightly controlled process in the body. However, this process is dysregulated in endo, with endometriotic lesions continually producing the inflammatory factors leading to localised and chronic inflammation around the pelvic organs, which is thought to contribute to the painful symptoms of endo.

With the relentless initiation of inflammation in the pelvic area of women with endo, it would be unsurprising if the organs close to the endometriotic lesions were also affected by this inflamed environment. If you were to look at any high school biology textbook diagram of the female reproductive system you would see that the bowel lies very closely to where endometriosis is usually found. Therefore, it may be that the inflamed pelvic environment caused by endo leads to irritation and bloating of the nearby gut, and the surge of inflammatory factors during menstruation only serves to worsen this effect.

I need to point out these are educated guesses at the moment, hypotheses at best. There is still much more work to be done to understand why bloating is such as common feature of endometriosis and the ways it can be treated. In any case endo belly is a phenomena distinct and unique to women with endometriosis, (to give it a clinical description I hereby name it Endometriosis-Associated Chronic Abdominal Bloating [EACAB]), its presence should be taken seriously by clinicians and needs to be the focus of future research.

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Dr Matthew Rosser

I have over 15 years experience researching endometriosis, endometrial cancer and fibroids. During this time I have       noticed that whilst research is regularly published on               endometriosis very little is reported accurately to the public in mainstream media. This blog aims to educate and inform anyone who wishes to learn more about the science and research into endometriosis.


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