EP.374/ Study Spotlight: What Is the Research on Dairy and Endometriosis?

Podcast

6 Dec

Okay, so today we’re continuing with our Study Spotlight Series on ‘Dietary Modifications and Supplement Use for Endometriosis’.

And today we’re looking at dairy.

Now, before we dive in, this episode is going to be significantly shorter and less detailed than the others I’ve done so far in this series, and that’s because I did a huge 4 or 5 part series on endometriosis symptoms and dairy earlier this year, and in that series I really go into all the reasons as to why dairy may worsen pain for some of us, so I am going to link to the episodes in the show notes.

So, the ‘Dietary Modifications and Supplement Use for Endometriosis’ found that out of those who tried removing dairy, 45% reported a reduction in pain.(1)

Now, just like all of the other times we’ve discussed this study; there are of course variables to consider. Each individual would have tried their own method for dairy removal, some may have removed it for a day, some a month, others six months and so on.

And then there’s the placebo affect to consider, which we’ve explored a lot on this series, but just to remind you, it’s a real phenomena where we feel better because we expect something to make us feel better; so there’s a chance that for some who experienced improvements, it may be to do with having heard other people’s stories about removing dairy and feeling better, and then expecting to feel the same.

And lastly, we also have to remember that this study relied on participants to remember accurately whether removing dairy did or didn’t help them - and honestly, that could really swing either way, I’ve had some clients say something hasn’t helped symptoms, but then when we actually start scoring their symptoms and comparing them, they realise it had, but the opposite can be true as well.

Now, aside from this study, do we have any other studies on dairy and endo?

Yes, we do, but frustratingly they are much more focused on endometriosis risk and dairy, not endometriosis symptoms and dairy.

And you might be surprised by the findings.

A 2025 umbrella review on diet and endometriosis, which is essentially a review of all of the major reviews (in short!), found that a higher consumption of dairy was associated with a lower risk of endometriosis, except for butter, which showed an increased risk with regular consumption.

Just like many other studies and reviews that came before this, the researchers concluded that the reduced risks are likely to do with the levels of vit D and calcium found in dairy, and their positive effects on inflammatory markers and growth factors associated with endo development, such as interleukin-6 (IL-6).They also acknowledged the positive microbiome alternations that can come with probiotic dairy, and theorised that this may benefit gut reactivity that then furthers pain.(2)

And in 2021, a systematic review and meta-analysis of 120,706 participants found that total dairy products intake was associated with a reduced risk of endo, in a dose dependent manner, meaning the more dairy consumed, the lesser the risk of endo. They also observed that there was a significant reduction in endo risk when dairy consumption exceeded 21 portions per week.(3)

And in 2022, there was another meta-analysis and review of all observational studies, looking at food groups and nutrients consumption and endo risk, and again, a higher intake of dairy products was associated with reduced endo risk.(4)

It’s worth noting that researchers did admit to limitations and variables, for example, in the 2022 meta-analysis, the researchers shared that there were significant differences in how some of these studies were obtaining and analysing data, for example, one looked at diary consumption the year prior, whereas another looked at dairy consumption in adolescence.

I also wanted to mention, some studies have found the opposite. For example, one study from 2010 analysing 12 years of data from the Nurses Health Study II, found that a higher intake of palmitic acid (a type of fat found in meat and dairy products) was associated with a significantly higher risk of endometriosis.(5)

However, remember that meta-analyses and systematic reviews looked at all the data from all the studies, and they concluded that a higher intake of dairy was protective, and as we have discussed in previous episodes in this series, the Nurses Health Study, whilst large, still has limitations.

Finally, a mini review from 2023 observed that the influence of oestrogen present in meat and dairy could potentially influence disease risk (now, before you throw meat completely out the window, I will be doing an episode on meat in this series too, so hold fire on that, or you can just download my Nutrition Masterclass if you want to learn about meat and endo now).(6)

So that’s endo risk and dairy, but what about the management of endometriosis symptoms?

A 2021 observational study looked 157 endometriosis patients, with 46.5% of them reporting using dietary methods for management and increasing vegetables, reducing gluten, dairy or soy, were reported as being the most effective changes made. 71.3% of the dietary changes tried were reported to reduce pain symptoms. On a score of 1-5, with 5 being the most effective, complete removal of dairy was reported at just over 3 on the scale (with only the complete removal of gluten exceeding it) and limited consumption of dairy received a score of about 1.5 or 1.7.(7)

It’s interesting to note here that the diets of endometriosis patients were compared to those without endo, and the quality of diet in endo patients was found to be lower based on the Dutch Healthy Diet 2015 Index Food Frequency Questionnaire. However, what’s really interesting is despite the concern that dietary changes for endo can reduce quality of diet (which we hear from many doctors and researchers), the endo participants who did make dietary changes, had a higher score on diet quality, often because of increased vegetable, fruit, nuts and fish intake.

In a 2019 online survey study of 484 respondents, dietary changes were listed as the third most helpful self-management strategy, with cannabis/CBD and heat being cited as most effective, with dietary changes scoring 6.39 out of 10(8). Some of the most frequent diets reported were vegan, paleo and the low FODMAP diet; the vegan and paleo are dairy free, whilst the low FODMAP reduces some forms of dairy. The researchers theorised that the high rates of IBS and gastrointestinal issues within our community likely contributes to some of the pain and symptoms we experience with endo, and so the removal of certain food groups can ease some of these gastro symptoms, improving pelvic and abdominal pain, bloating, etc. Indeed, the participants also reported improvements in gastrointestinal symptoms, nausea and vomiting.

With both these studies, there are limitations, such as relying on participants to accurately self report which can lead to both overestimating or underestimating improvements - but as you may well know by now, whilst I of course think it’s important to acknowledge these limitations, I also don’t see these as sufficient enough reasons to dismiss what endo patients tell us has or hasn’t worked for them.

In a placebo-controlled intervention study, dietary changes that included a 30% reduction in dairy products resulted in a significant decrease in pain but also a reduction in inflammatory markers such as CA-125 and even levels of that sneaky inflammatory prostaglandin PGE2, which we know is elevated in endo and causes pain.(9)

Now, it’s important to note that the reduction in dairy was only one change of many here. Gluten, alcohol, caffeine, chocolate, meat, butter and more were reduced. Fibre was increased and participants were also given a supplement containing a mix of curcumin, quercetin, omega 3, amongst other nutrients.

We also have a study from Dec 2023, which allowed endo patients to follow either the low FODMAP diet, no diet at all or “the endometriosis diet” (10). The “endometriosis diet” involved removing red meat, cow’s dairy, gluten, added and refined sugars, phytoestrogen foods like soy and limited caffeine. Both diet groups reported better pain scores and quality of life in contrast to the non diet group after six months, and less pain with sex, urination, less bloating and tiredness.

Of course, given that participants were not randomly assigned to a diet and could choose a diet themselves, there was a risk of bias/placebo effect. We can see that both diets limited some dairy products, but the study didn’t limit dairy in isolation, so we don’t know if the improvements came from the specific dairy changes or not.

Finally, we also have a qualitative interview study, which we talked about recently in the context of gluten and endometriosis (11). This study interviewed 12 endometriosis patients who had made dietary changes, these patients removed or lowered gluten, dairy and increased fruit, vegetables and fish. The patients reported a decrease or entire disappearance in pain, and improvements in gut health, with patients reporting more normalised bowel habits, a calmer gut, and a reduction in swelling and gas. They also reported better energy levels, better sleep, shared that they could do more normal day to day tasks, they felt healthier overall and more “normal”, had better mental health, took less sick days from work and also had a reduction in allergic type symptoms like nasal congestion and rashes.

Obviously the reduction of dairy was just one change of many in this study, and it was also a small study with a risk of bias, however, the reports from the participants involved are really compelling, for example, one participant shared “…(The dietary change) enabled me to actually continue to work and…live a decent normal life…”

So now I want to cast the net a bit wider to look at more general nutrition trends with endo, and whether we can learn anything about the impact of dairy from them.

A systematic review of dietary interventions for endometriosis symptoms from 2021 concluded that despite needing better quality studies and a high risk of bias, nearly all studies - aside from one on vit D supplementation - showed improvements in pain with endometriosis (12). Now, there wasn’t a mention of dairy in this, but they did look at the studies performed on the low FODMAP diet and endo, and did acknowledge that the low FODMAP diet was low lactose.

Whilst they reiterated the need for higher quality studies, they actually ended the review by suggesting a clinical approach of exploring the Mediterranean diet and/or 6 months of antioxidant supplementation with endo patients or the low FODMAP diet for those with endo and IBS issues.

And additionally, there is also a research paper from 2022(13) and another systematic review from 2020 (14), that both conclude that whilst quality of evidence is poor, dietary interventions show promise for pain and symptom reduction with endo, and that diets of an anti-inflammatory, antioxidant nature or low in FODMAPS, should be considered and further researched.

Now again, these reviews don’t specifically highlight dairy as the removal of dairy wasn’t heavily present in many of these studies, but as we just discussed, the low FOMDAP diet is lower in lactose.

Finally, a scoping review from 2024 also concluded that dietary interventions did show pain improvements, but that the quality of the research, on the whole, was poor (15). However, because of the high rate of interest in dietary interventions from endo patients, they did outline recommendations such as the Med diet and healthy eating in general, the low FODMAP diet for those with gut issues and ideally, working with a trained practitioner, to name a few of their concluding recommendations.

I do want to point out here, that throughout all these research papers I’ve listed today, there were several mentions of the Med diet, and the amount of dairy consumed in the Med diet varied from study to study; some calling for a high intake of low fat dairy, others suggesting moderate dairy, and then one, a reduction in dairy. So I think it’s hard for us to work out how much dairy is actually consumed in the recommended Med diet for endo, and whether any of the benefits of the Med diet studies come from increasing or decreasing certain dairy types.

So, a few things to consider based on these reviews (aside from the obvious fact that we need better quality studies) is that we don’t have a huge amount of research on endo symptoms and the removal or lowering of dairy, and secondly, people reported improvements in dietary interventions that didn’t eliminate dairy or didn’t focus just on dairy specifically. So, this suggests that symptom improvement is possible for some, with or without dairy removal, yet we must also acknowledge that some studies, like the one we’re talking of today, reducing intake can provide relief for some endo patients.

Okay, so I think I have covered all the research I could find, so now the question is, why does removing or lowering dairy help for some people?

So, to answer that question, I am actually going to point you in the direction of another podcast series. Last year, I did a significant deep dive on endo and dairy, and symptom relief. I summarise all my findings in one single episode, so you can start there if you’d like, but for fuller, more scientific explanations, I would go to the individual episodes, and I’ve linked to all of those in the show notes.

But to give you a taste, from my research and experience, I suspect the root cause varies amongst individuals, for some, it could be a lactose intolerance, others a histamine issue, A1 casein reactivity and more!

So, check out that series to understand those areas.

Of course, it goes without saying that if you’re planning to make dietary changes like possibly reducing dairy, it’s best to work with your doctor or a nutritional practitioner. The series I just mentioned does offer guidance on how to test whether dairy is an issue for you in a systematic and considered way, so you could listen to that to get started.

Okay, I hope this episode has been insightful and helpful. I’ll see you next week!

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