The FODMAP Diet: An IBS diet based upon peer-reviewed science

I’m extremely lactose intolerant. What this means, biologically, is that I no longer produce enough lactase to process lactose sugar. Because I can’t process lactose in my small intestine, it moves on intact to my large intestine where bacteria eat the sugar. The byproduct of their digestion, gas, causes bloating, pain, cramping and, well, you know the rest.

What is IBS and what causes it?

Irritable Bowel Syndrome (IBS) is an incredibly common malady, affecting 6-46% of the population, depending upon the study. It’s a diagnosis resulting from the lack of a diagnosis; it’s diarrhea, bloating, stomach pain, and cramping that can’t be explained by celiac disease, lactose intolerance, fructose intolerance, or other understood gut disorders.

IBS is thought to be caused by visceral hypersensitivity, or over-sensitivity to pressure on the intestines. Imagine two people eat broccoli and get a bit gassy: the person with IBS would feel pain and discomfort while the other person might be bloated but otherwise fine.

It’s often implied that IBS is psychological as much as physiological. Anxiety and depression are common in people with IBS. In my experience, the perceived psychological component, the lack of simple treatments, and the lack of life-threatening consequences can lead doctors to be blasé about IBS. They recommend fiber, exercise, and routine, and shrug if that does little. Small wonder that people might feel blue. But gut science is improving, and the FODMAP approach is a new and widely successful strategy for reducing the symptoms of IBS.

What is the FODMAP approach, and what is different about it?

The FODMAP diet is based upon known biochemistry and the hypothesis that visceral hypersensitivity causes IBS. There are many molecules that, like my undigested lactose, tend to be digested in the large intestine and produce gas. The FODMAP diet eliminates a wide range of such molecules.

FODMAP, introduced in 2005 by Monash University, is a peer-reviewed diet based upon a concrete biological hypothesis supported and improved by scientific trials. It is not a weight-loss diet. FODMAP stands for Fermentable Oligo- Di- and Mono- Saccharides And Polyols. Catchy, right? But the concept is simple—FODMAPs are short-chain sugars that we know most people digest poorly (meaning bacteria digest them), and you avoid FODMAPs on the FODMAP diet. (For the biochemists, that means avoiding fructans (oligosaccharide), lactose (disaccharide), fructose (monosaccharide), and all sugar alcohols such sorbitol (polyols).)

Many other diets have questionable scientific bases and are profit driven. The Atkins Diet was published by a cardiologist who never published any peer-reviewed work, but several books. The Paleo Diet was published by an “exercise scientist untrained in paleobiology”. This is not to say that these diets cannot be beneficial in any way. But they have not been tested and refined in the way the FODMAP diet has been, and their fundamental science is hazier. Putting the cart before the horse, they have been developed first for profit, and then researched afterwards, often with mixed results. To be fair, the scientific process is slow and contentious and doesn’t always lend itself well to studies as broad and complex as diet. But FODMAP was developed, tested, and improved using the scientific process. If you’re skeptical of diets, as I am, you can read up and convince yourself that this diet has a reasonable basis and good results.

What’s a FODMAP diet like?

If you are considering a FODMAP diet, you will have to do some research, and be able to prepare food often from scratch. The internet is a phenomenal tool, and there are even some dieticians you can consult online. FODMAP sensitivity is not the same thing as an allergy. You don’t have to absolutely eliminate FODMAP foods, you simply must aim to minimize them for a period of time.

To follow the FODMAP diet, you avoid FODMAP-laden foods for two weeks to two months (different sources vary in their recommendations, and provide rationales). After this time, you re-introduce foods in a controlled manner to identify trigger foods. Most IBS-sufferers are not sensitive to all FODMAPs. Many people report benefits within a few days of starting the diet, and 70% of IBS patients in peer-reviewed studies reported improvements following the diet. I personally had much less bloating within a few days. Following a FODMAP diet revealed that some of my symptoms are due to gastritis, which I’m now treating. I see now that I’ve had gastritis symptoms for a while, but I was unable to separate various gastrointestinal symptoms before this diet. I remain on the full FODMAP diet after three months, but I have eliminated one side issue.

What foods are and aren’t allowed?

Following the most basic level of the FODMAP diet, one avoids all garlic, onion, and gluten-containing foods. It is not a gluten-free diet, but grains containing gluten overlap almost perfectly with grains containing the FODMAP fructan. Beer happily is the major exception; it is FODMAP-free due to the fermentation process.

I consider the FODMAP approach an alternative way of categorizing foods. There is a common perception that vegetables and fruit are healthful, and grains and meat are less healthful. At least from the perspective of IBS, that is not a useful framework. On the FODMAP diet, meats are okay. Roughly half of grains, dairy, vegetables and fruit contain FODMAPs, and these are avoided on the diet. Specifically, greens and squash are okay, but broccoli, leeks, and  brussels sprouts aren’t. Citrus and melon are okay, but peaches, cherries, and figs aren’t. Lactose-free milk and hard cheeses are okay, and ice cream, fresh cheeses, and sour cream aren’t.

For those considering the diet, this is my favorite exhaustive list of allowed and disallowed foods.

TL;DR

In short, the FODMAP diet requires research and it’s a pain to follow, but it offers real promise to the numerous people suffering from IBS. If you’re considering the diet yourself, good luck. I hope this provided a better explanation of the topic than the sources I encountered when trying to understand this diet. To others, maybe this will help explain why your friend has such a fiddly diet, and why you should support them.

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