FODMAPs and Gastroenterology (Part 2)

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FODMAPs and Gastroenterology


Why does this diet actually help?

This three-part blog series is based largely on an article published in December 2012 in Practical Gastroenterology, “A FODMAP Diet Update: Craze or Credible?” Series editor: Carol Rees Parrish, M.S., R.D. Article authors: J. Reggie Thomas, DO, Banner Good Samaritan Medical Center. Rakesh Nanda, MD, FACP, FACG, Phoenix VA Health Care System. Lin H. Shu, MS, RD, Phoenix VA Health Care System, Phoenix, AZ.

That journal is published for people who read at the MD or PhD level. This blog series is an attempt-to-translate for the rest of us!

Part Two: More About FODMAP Sugars

The previous post concluded that it’s vital to make sure most of the sugars we eat will be absorbed in the SMALL intestine.

This post will provide more information about all those different sugars: Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols…a.k.a. FODMAPs.

First, the fermentable oligosaccharides: these are molecules made up of chained-together sugars. Fructans is an important one for us, because it’s a chain of fructose (remember fructose!) molecules with a glucose molecule on the end. And here’s the problem, quoting the article: “fructans are not transported across the epithelium [intestinal lining] or absorbed at all. Studies have shown that 50-90% of ingested fructans can be recovered from stool output of patients with an ileostomy.” In other words, this molecule is NOT well absorbed in the small intestine, so it can be a major troublemaker farther down the line.

The biggest source of fructans in the North American diet is … brace yourself … WHEAT. I suspect that a high percentage of people who feel better when they give up wheat (including people who test negative for celiac disease) are not bothered by gluten at all, but by fructans! That’s why a tiny piece of bread (e.g. taking Communion) might be tolerated, instead of creating a full-blown allergic reaction…and this could be one reason some people feel better on a gluten-free diet.

The other oligosaccharide (chained-together sugar) that’s important to FODMAPers is galactans. They’re chains of the sugar galactose, with a fructose molecule on the end, and they behave just like fructans. Foods such as beans and brassicas (cabbage and its kin) are high in galactans. Even the general population notoriously has problems with galactans. Remember the song, “Beans, beans, the musical fruit…”?

The second major group of sugars that’s discussed in the article is “disaccharides and monosaccharides,” the DM part of the FODMAP acronym, and this is where fructose (remember fructose!) comes in. Two fructose molecules linked together is called “sucrose” (we know sucrose as common table sugar), but when the body breaks it down, one of them becomes glucose. Interestingly, the fructose and glucose can be absorbed together into the bloodstream by one of the “transporters” I mentioned in the previous post.

If you’re starting to feel overloaded by all this chemistry, don’t worry. Here’s the essence, quoting once more: “Therefore malabsorption of fructose occurs when fructose is present in excess of glucose. Some foods rich in fructose are honey, prunes, dates, apples, pears, and papaya.… It is also often added to commercial foods and drinks as high fructose corn syrup.” Ah, HFCS. Our least favorite food, and among the hardest to avoid.

And then there’s lactose. It can also cause FODMAP-related symptoms. Lactose is in most dairy products. The article also says it can be found in beer (who knew?) and prepared soups/sauces (READ YOUR LABELS).

Third group: polyols (and there’s the final “P” in FODMAP). They’re present in most artificial sweeteners. Eating them together with glucose does not help their absorption. Instead, “A few studies have found that sorbitol and fructose ingested together cause worsening IBS symptoms” (my emphasis)

Besides diet soda and other artificially sweetened foods, watch out for polyols in toothpastes, mints, sugar-free chewing gum, and liquid cough/cold or pain relief medicines. If an artificial-sounding ingredient ends with –ol, it’s probably a polyol: mannitol, xylitol, and sorbitol are among the commonest.

Ugh. That’s a lot to digest (ha ha) in one blog post. A hopeful note: Trying the low-FODMAP diet does not necessarily mean giving up ALL these sugar molecules for the rest of your life! That will be discussed in Part Three of this blog series.

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