Common Science PNG Logo

The appeal of fad diets is easy to understand. It is increasingly clear that something has gone horribly awry with our health in the United States.   Obesity is on the rise and everywhere we look people are beset with diseases related to gastrointestinal system such as diabetes, irritable bowel syndrome, and an ever-increasing array of food allergies. In the face of these problems, it’s tempting to look for a silver bullet solution to them all. So, we cut carbs or meats or fats from our diets. We consider whether genetically modified foods are to blame and we worry about high-fructose corn syrup. Over the last couple of years, the villain of choice has been gluten, a protein contained in wheat, barley, and rye. As a result, millions of Americans have gone gluten free.

Let’s explore whether we have finally found the silver bullet by starting with a simplified model of the gastrointestinal system. The primary jobs of your teeth and stomach are to grind up the food you eat into small pieces. These small pieces head to your small intestine where they are broken down further through the action of specialized proteins called enzymes. As it the case for all proteins, the enzymes that you make are determined by which genes you have. We will return to that point later. Specific types of enzymes break down specific types of food molecules. Most of the extraction of energy and nutrients from the food you eat occurs as the metabolites generated by the enzymes are absorbed through the lining of the small intestine. Generally speaking, the enzymes in the small intestine are produced in your own human cells rather than from the cells of the bacteria that live within your body.

The story changes in the large intestine.   Your large intestine is the home of a staggeringly large number of a great variety of different species of bacteria. So numerous are the bacteria in your large intestine that bacterial cells within your body outnumber human cells by a ratio of 10-to-1. Food molecules that are not digested and absorbed in the small intestine proceed to the large intestine where they are broken down by enzymes produced by these bacteria. The bacteria themselves use some of these metabolites for the energy and nutrients while other metabolites are absorbed through the lining of the large intestine and used by you.

To summarize, digestion in the small intestine is governed by enzymes produced by human cells and digestion in the large intestine by enzymes produced by bacteria cells. This distinction is quite important when considering gluten/wheat sensitivity.

In order to explore potential wheat and wheat gluten sensitivities and diseases, lets follow some wheat through the digestive system.   Wheat contains both proteins such as gluten and a variety of fiber molecules. When gluten reaches the small intestine it is first modified by a human enzyme called transglutaminase. In the 1% of people in the United States with Celiac’s Disease, the modified gluten prompts an immune response. The immune response causes inflammation and eventually damages the lining of the small intestine such that the absorption of energy and nutrients are reduced. In addition, Celiac’s patients usually suffer from other gastrointestinal distress such as constipation and/or diarrhea.

95% of people with Celiac’s Disease have a specific mutation in the gene that makes their transglutaminase. What this means is that the transglutaminase enzyme that they make is slightly different than everyone else’s. This is what prompts the immune response.

The fiber portion of the wheat proceeds mostly intact to the large intestine. Many species of bacteria in your large intestine produce enzymes that break down fiber molecules and use the metabolites for food and nutrition. Generally speaking a diet which is high in fiber makes for a happy and healthy population of bacteria in the large intestine. As I have written about numerous times of late, maintaining a healthy population of bacteria in the large intestine – the gut microbiome – is extremely important to maintaining your overall health. This dynamic is at the heart of why fiber is an important part of a healthy diet.

Now let’s highlight another important difference between the enzymes of the small and large intestines. Since the enzymes in your small intestine come from your human genes, the full slate of enzymes that you can make were determined the moment the sperm fertilized the egg from which you arose. In contrast, since the enzymes in your large intestine come primarily from your resident bacteria and the population of those bacteria can and does change over time due to changes in medications and diet, the digestive performance and behavior or your large intestine also changes over time. This transient behavior of the large intestine has a strong influence on how we respond to different foods at different times.

For example, let say you think that you make have heightened sensitivity to wheat and decide to run your own experiment by going gluten free. It is likely that this change will significantly reduce the amount of fiber in your diet. As a result, the population of bacteria in your large intestine that make the enzymes to break down fiber will drop. At some point, your gluten-free diet is likely to become tiresome and you will break down and have a big piece of birthday cake or a large serving of pancakes. This will send a torrent of fiber to your now unprepared large intestine resulting in discomfort and bloating. And presto! your self-diagnosed wheat sensitivity is confirmed.

I should note that there are people who do have sensitivity to wheat who do not have Celiac’s disease, but this is rare, far rarer than the number of people who are eating gluten free and making the authors of gluten free diet books very rich. If you think you may be sensitive to wheat, check with your doctor before removing it from your diet. As for the rest of us, whole grain fiber is an important part of healthy diet, so go have some toast.

Jeff Danner discussed this week’s column on WCHL with Aaron Keck.


Have a comment or question? Use the interface below or send me an email to Think that this column includes important points that others should consider? Share a link to this column on Facebook or Twitter. Want more Common Science? Follow me on Twitter on @Commonscience.