Sucrose and Enzymes

Making the Connection Between Sucrose and Sucrase

Like many sucrose-intolerant individuals, your road to diagnosis has likely been long and tumultuous. For months or even years, you have endured moderate to severe gastrointestinal discomfort. You have undergone test after test, only to rule out diseases like inflammatory bowel disease, celiac disease, and gastrointestinal infections. As a last resort, perhaps you were diagnosed with irritable bowel syndrome or possibly even told that it’s “all in your head.” So, when your doctor finally diagnosed you with Sucrose Intolerance, also called Congenital Sucrase-Isomaltase Deficiency (CSID), you were probably so relieved and overwhelmed that you don’t remember much of what was said after that. To reiterate, your doctor likely explained that individuals affected by Sucrose Intolerance have an absence or low activity of the digestive enzymes sucrase and isomaltase. But if you don’t know what enzymes are, that explanation doesn’t help clarify things a whole lot. Let’s break things down so that you can gain a better understanding of your new diagnosis.

What Are Enzymes?

Enzymes are specialized agents that help cells speed up various chemical reactions, allowing the cells to do their jobs more efficiently. There are 37.2 trillion cells in your body working tirelessly to make your tissues and body function as they should. Each cell contains thousands of specialized enzymes, responsible for catalyzing (stimulating) various chemical reactions. In fact, chemical reactions in cells occur 100 million to 10 billion times faster with enzymes than they would without an enzyme. For example, a chemical reaction that happens in milliseconds with an enzyme could take anywhere from several days to hundreds of years without an enzyme. Clearly, your cells and tissues couldn’t function without enzymes.

Enzymes are proteins manufactured by cells, based on your genetic code, your DNA. These proteins consist of long chains of amino acids bound together in different ways to make a wide variety of enzymes.

This figure shows the sucrase-isomaltase enzymes. Though they may look like tangled balls of string, enzymes have very precise shapes that help them facilitate specific chemical reactions. Many enzymes are involved in digestion, the chemical process of breaking down nutrients. Each enzyme has an active site (the lock) that is perfectly designed to fit only a certain type of molecule (the key). For example, a sucrose (sugar) molecule is the key that snugly fits into the active site, the lock, of a sucrase enzyme. The sucrase enzyme then places pressure on the sucrose bonds that hold the sugar together, making it much easier to break sucrose apart. The figure below shows this enzymatic reaction.

Sucrose and Enzyme Reactions

Enzymes and Sugar Digestion

If you have Sucrose Intolerance, your enzymes sucrase and isomaltase are either absent or insufficient. But what are these enzymes and why do you need them?

  • Sucrase helps break down sucrose (from the French word “sucre,” meaning sugar). Sucrose is plain table sugar, and it is also found in many fruits and vegetables.
  • Isomaltase helps break down a complex form of maltose (from the word “malt,” which is germinated grain). Maltose is a sugar found in grains and starchy foods like potatoes, rice, and bread.

The sugars sucrose and maltose are disaccharides, which means that they are made up of two sugar molecules (monosaccharides) bound together. Sucrose is made up of one glucose molecule and one fructose molecule, while maltose is made up of two glucose molecules. Disaccharides are too big to be absorbed directly into the bloodstream and, therefore, must first be broken down into their constituent components.

This breakdown is important since glucose is the primary fuel source for every cell in the human body. In fact, red blood cells and some neuronal cells rely solely on glucose as an energy source. Therefore, it is vital that sucrose and maltose be broken down, so glucose can make it out of the small intestine and into the bloodstream.

The sucrase and isomaltase enzymes are located in the cells that line the wall of the small intestine. They are tethered to tiny microvilli — also known as the brush border — that extend like tiny fingers from each cell into the inner, open tube of the small intestine to interact with the food that has been consumed. The left-hand side of the figure below shows a cross-section of the small intestine and the location of the villi. The right-hand side shows a close-up of the villi.

Many foods contain sugar (sucrose) and starch (maltose). For example, when you eat a cookie or a cracker, sucrose and maltose pass through the stomach and into the small intestine. There, sucrose and maltose attach to the enzymes in the cell walls of the intestinal brush border and are broken down into the smaller molecules, glucose and fructose, as shown in the previous figure titled “Enzymatic Reaction.” Glucose and fructose then pass freely into the small intestinal cells and on into the bloodstream to fuel the cells in your body.

Enzymes and Sucrose Intolerance

Due to variations in the DNA blueprints of the compound sucrase-isomaltase enzyme, an individual with Sucrose Intolerance has little or no functional enzyme activity from sucrase or isomaltase enzymes in the brush border. Consequently, after a meal, sucrose and maltose pass right through the small intestine without being digested or absorbed and into the large intestine.

The large intestine contains a wealth of gas-producing bacteria, both good and bad. These bacteria are supposed to dine only on foods that are high in fiber or resistant starches, foods that can’t be fully digested in the small intestine. Bacteria slowly break down the tough fibers and resistant starches by the process of fermentation, which produces small amounts of gas as a byproduct.

Sugars, on the other hand, are very easy for the bacteria to digest by fermentation, resulting in a higher level of gas that is produced faster than when fiber is fermented. A meal of sucrose and maltose is like a bag of Halloween candy for the bacteria in your large intestine. They attack it with gusto and simultaneously produce a lot of gas very quickly, leading to painful bloating, excessive gas, diarrhea, feelings of nausea, or upset stomach.

So, now you have a better understanding of Sucrose Intolerance, or CSID, and what is causing your painful symptoms. Because CSID is a genetic disease, it is lifelong and it is unlikely you will ever be able to produce a suffcient amount of the enzymes sucrase and isomaltase. Though it is difficult to do, eliminating sugar from your diet goes a long way toward easing your symptoms.

Sucrose Intolerance May Be More Common Than You Think