FODMAPs and Gastroenterology (Part 1)

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 One : One Cause of Our Symptoms

When doctors don’t see anything structurally wrong with the appearance of our insides, they refer to our problems as “functional” instead of “structural.” One of the commonest “functional” gastrointestinal diagnoses is Irritable Bowel Syndrome or IBS, essentially meaning the doctors haven’t known what’s actually wrong—and it affects about 15% of the world’s population!

Research in the early 2000s suggested that FODMAP sugars make IBS worse in one of three possible ways: 1) food allergies, or hypersensitivity, 2) something those sugars did to the intestines, or 3) what they called “luminal distension,” which translates to “gas stretching the intestines and making them hurt.”

This journal article starts by explaining how carbohydrates—sugars, and food molecules that can be broken into sugars—are absorbed into the body. This is crucial for people with IBS, because it’s the sugars that are NOT absorbed (“absorption” happens in the small intestine) that get dumped into the large intestine, creating symptoms for people who are FODMAP-sensitive.

FODMAP sugars will be explained in the next post.

There is some chemistry involved in what happens in the small intestine, because “sugar” comes in several molecular forms. Our bodies have different ways of recognizing and dealing with the different kinds of molecules. In our small intestines, research has found three different “transporter” molecules that help sugars cross through intestinal cells into the bloodstream.

One kind of molecule transports the sugars glucose and galactose. One transports only fructose (remember “fructose”!). The third carries the sugars glucose, fructose, and galactose—but it’s best at carrying fructose if there is glucose or sucrose present in the food it’s trying to digest.

Let me quote the article briefly: “Symptoms of FGID [functional gastrointestinal disorders] can result from the malabsorption of fructose and sucrose that occurs when the activity of one of these transporters is altered… [translation: if something happens to our bodies’ production of one of those “transporter” molecules, we can’t absorb those sugars as well as we used to] … When the small intestine is unable to absorb fructose, it is transported into the large intestine where it is fermented by colonic flora [bacteria].” In other words, the unabsorbed sugars go where they do us no good at all. Even harm! Also  load of indigestible sugars creates an “osmotic effect” that draws water out of the body into the large (lower) intestine. Increased water in the lower intestine causes diarrhea. This is how some laxatives work.

This first section of the article is pretty convincing evidence that it’s vital to make sure that most of the sugars we eat will be absorbed in the small intestine, so they don’t pass downstream to the large intestine and overfeed those colonic bacteria.

Part Two coming soon!