Thoughts on the low FODMAP diet

I haven’t quite abandoned the low FODMAP diet but I know it hasn’t worked for me. Briefly, for those unfamiliar with FODMAPs, they are types of carbohydrate that aren’t digested well, if at all, by the body but are feasted on by bacteria. They are found in a variety of types of food, including some fruit and vegetables. A diet low in FODMAPs has been shown to improve symptoms in IBS patients and is now seen by many as the primary dietary intervention for treatment of IBS.

I tried to follow the low FODMAP diet religiously for eight weeks to see if it improved my flatulence. Logically it made good sense: cutting out the foods that bacteria feast on means there’s less for them to digest and consequently they’ll produce less carbon dioxide and other intestinal gases that make their way into our farts. But, as Anthony Trollope said, seldom is it that theories stand up to the wear and tear of practice.

On a positive note, almost immediately I found that the IBS symptoms that I did experience (urgency, diarrhoea) all but disappeared. Later on in the diet I found I  experienced these occasionally but not to the same extent. However, rather than improve my flatulence, I found it actually made things worse. This isn’t supposed to be a post theorising why that might be the case, though. Rather, it is to highlight some of the problems I faced, and concerns I have, with the diet.

The cost

I wouldn’t say that I spent more or less money following the diet, although some staples I came to rely on, like gluten-free bread and pasta, aren’t cheap compared to their wheat-based cousins. And to people on tight budgets, I fear the low FODMAP diet may be less affordable. For me, though, the biggest cost was paying for a dietician, which certainly wasn’t cheap. Nor am I convinced a dietician was good value for money.

The dietician

Obviously dieticians differ in quality. Some will be superb, others will be inexperienced, and most don’t know anything about the low FODMAP diet anyway! However, the general advice is that you should only go on the low FODMAP diet under the supervision of a dietician to make sure you’re still getting the right balance of nutrients.

That said, the only reason my dietician spotted I wasn’t getting enough fibre was because I’d kept a fastidious food diary on my own volition. There is so much information out on the Internet about the low FODMAP diet now, I fail to see what value the dietician can add unless they are helping you adjust your existing diet or trying to find affordable options for people struggling with cash. And unless the low FODMAP diet, and managed dietary intervention in general, are better recognised by the NHS in general, and GPs in particular, as a treatment for IBS, I don’t see how people less well off would be able to get access to this support.

The portion sizes

I think the majority of dieticians who recommend the low FODMAP diet in the UK have been trained by King’s College, London. As such, patients are often given King’s guide ‘Reducing fermentable carbohydrates the low FODMAP way’. They might also get the book ‘Suitable products for the low FODMAP diet’. These are both simple books to follow (although it might be helpful to have a single page summarising all the ingredients you can eat).

However, the one thing I struggled with understanding was portion sizes. The guidebook helpfully suggests portion sizes in grams for some fruit but on other occasions it gave portions in tablespoons. Now, there are different sizes of tablespoon in every cutlery canteen, and these are a lot bigger than the tablespoon measure I use for baking. So what exactly does a tablespoon of sweet potato, fennel or peas look like? Or a slice of beetroot? I think some clarity here would certainly make the advice easier to follow.

The lack of fibre

It’s all very well advising patients to make sure they have enough fibre but it’s a bit impractical getting them to work out how much they are consuming and how this will change on the low FODMAP diet (an area where the dietician could really help). However, I’m the sort of person who would do such a thing and I worked out that I was probably getting between 2 and 4 grams less fibre a day on the diet than I would have normally, largely because of the vegetables and fruit I was cutting out. I found that oatcakes and linseeds helped plug some of this gap. Indeed, I found that my flatulence improved marginally when I was less constipated.

The side effects

As the diet progressed, I found I was getting more and more depressed. This was probably for a variety of reasons:

• the diet was the most promising solution to my problem and it wasn’t working
• it was pretty exhausting trying to work out things to make for lunch and dinner every day, even for a person who enjoys cooking
• changes in the gut microbiota

Studies have shown that dietary changes alter the balance and proportion of bacteria in the gut and that microbial colonies can alter mood and personality. In a significant number of patients, the low FODMAP diet has been shown to reduce the proportion of Bifidobacteria in the gut proving that it too has an effect on the gut microbiota. What effect this might have on mood, though, hasn’t been studied. However, I found that when I did have a slightly higher FODMAP dinner one evening after I’d given up on the diet, although my symptoms got a little worse, I did feel happier.

There’s another thing about the drop in Bifidobacteria, though. This genus of bacteria doesn’t produce carbon dioxide so, if it is reduced, there is less competition faced by its gas-producing cousins. In fact, for a short while after my eight week trial of the diet, I maintained the regime as best as I could but introduced the prebiotic Bimuno IBAID, which has been shown to selectively increase Bifidobacteria, and saw some improvement in my flatulence.

The unknown

Perhaps the key thing about the low FODMAP diet is that no one knows what the long term effects of the low FODMAP diet are. Are there yet unidentified, long term iatrogenic effects that may cause more serious problems in the future, and would these risks be acceptable for relief in the present?

The reintroduction of FODMAPs

Patients who find that the diet works for them are encouraged to reintroduce different FODMAPs one at a time to identify which ones they are sensitive to. As I hadn’t had adequate relief from the diet I didn’t go through this but I did find that on eating some foods after the diet I experienced more severe symptoms than previously the first couple of times I ate them although these subsided after a while. I first thought that this meant I wouldn’t be able to eat that food again – indeed, anecdotal evidence suggests that some people who try the diet and find it doesn’t work as well as hoped for still stay with it for this very reason. However, I found that my body did adjust once again.

Of course, once you settle into the diet for the long term, it’s not clear how you keep up to date with new information about high and low FODMAP foods. It’s not unheard of for food that was once thought to be low in FODMAPs to be shown to be high in one of them and vice versa, for instance.

The future, FODMAPs and me

I still avoid eating much wheat – sticking to a single burger bap at BBQs I’ve been to recently for instance – don’t touch beans (green beans seem to be okay), and I’m slowly identifying high FODMAP foods that seem to be more consistently correlated with worse symptoms. Since ending the diet properly, I have had improved symptoms and worse symptoms. It is simply proving impossible for me to gauge what my triggers are: they really are unpredictable. I will continue to use FODMAPs as a guide for what to avoid, but my symptoms are clearly a lot more complicated than that.