A sugar molecule is the basic building block of every carbohydrate. The body uses carbohydrates to break it down to glucose (blood sugar), which is the source energy for the cells, tissues and organs of most living things. The glucose can be used immediately or stored in the liver and muscles to be used later, when needed. The most common forms of carbohydrates are sugars, starches and fibers.
Starch carbs are found in all cereal grains, as well as roots and tubers. Starchy foods include: bread, pasta, rice, noodles, couscous, tapioca, potatoes, sweet potatoes and yams.
Dietary fiber carbs are found in most plant foods, like fruits, vegetables, legumes and whole grain cereals.
The digestive system handles all carbs in the same way - by breaking them down into single sugar molecules so they are small enough to absorb into the bloodstream. Fiber is an exception because it can't be broken down into sugar molecules by the human digestive enzymes and as a result passes through the body undigested. Simple carbs are digested very quickly whereas complex carbs take longer to digest and are usually packed with fiber, vitamins and minerals.
There are two types of dietary fibers: soluble (dissolves in water) and insoluble (doesn't dissolve in water). Soluble fiber binds to fatty substances in the intestines and carries them out as a waste and insoluble fiber helps push food through the intestinal tract, which promotes regularity and helps prevent constipation.
Soluble fiber is found in the following: oatmeal, oat bran, nuts and seeds, most fruits (e.g., strawberries, blueberries, pears, and apples), dry beans and peas.
Insoluble fiber is found in the following: whole wheat bread, barley, brown rice, couscous, bulgur or whole grain cereals, wheat bran, seeds, most vegetables, and fruits.
Digestible or Net Carbs
It is common to see the phrase "Digestible Carbs" or "Net Carbs". This refers to the total amount of carbs in a particular food that can be absorbed and digested in the intestinal tract, which excludes dietary fiber, as they cannot be digested.
Sugar alcohols are carbs that we do not completely absorb. The most common ones are sorbitol, xylitol, mannitol, and maltitol. These sugar alcohols can cause increased bloating, gas and diarrhea since the unabsorbed components end up fermenting in the intestine. Sugar alcohol has also been advocated as a low calorie sweet substitute. One unique beneficial side effect of the Xylitol is it inhibits bacterial growth in the mouth, and reduces the chance of tooth decays. The easiest way to calculate the net carbs in a food is to subtract the dietary fiber and sugar alcohol content from the total carb content.
Total Carbs: 30g
Dietary Fiber: 5g
Sugar Alcohol: 15g
Net Carbs: 10g (30 - 5 - 15 = 10)
Also, remember that in general not to eat carbs before bedtime as it triggers insulin and this initiates fat storage, which is probably counterproductive when it comes to weight loss.
A DS Carb Primer
By Kelly L.
All carbohydrates (carbs) begin digesting in the mouth when it comes in contact with the enzyme amylase. Even complex carbs begin the process of breaking down into simpler types at this point. Since monosaccharides need no further digestion to be absorbed, the body begins absorbing, a very small percentage of the total, them as soon as they hit the mouth.
Enzyme activity continues in the stomach but it is slowed by the contact with stomach acids.
When carbs enter the small intestines this is where DS may assist in preventing some absorption of the more difficult to digest polysaccharides (starches). This reduced absorptive capacity is because of the separation of the secreted enzymes by the pancreas and the liver, from the food that is being delivered for breakdown. A type of enzyme, amylase, is secreted by the pancreas into the duodenum that cuts carbs down into simple sugars. As it passes further, more enzymes break the carbs down into even smaller bits until they are eventually converted to glucose and absorbed by the mucosa lining, villi, of the small intestinal walls.
Because of the switch portion of the DS, the amount of time that a polysaccharide is in contact with pancreatic enzymes is reduced. This is probably why many people have gastrointestinal issues when eating starches.
Also, glucose is absorbed by the villi in the intestine, so those with shorter common channels and those earlier out will also absorb less. As the body adjusts to the DS, a patients villi becomes thicker and more efficient to counteract the malabsorption; this may be a component of some weight regain years after DS.
Carbs and Gas
By Diana C.
Fruits comprise simple carbs (primarily fructose, which is a monosaccharide and doesn't have to be digested at all) so they are fully absorbed in the small intestine, and fiber, which is indigestible by both our guts and our bacterial symbionts.
Flour products contain starches, which are made up of long chains of monosaccharides -- thus, polysaccharides -- which are only partially digestible by our rearranged guts with the diminished contact with digestive enzymes. This results in some of the starch ending up in the colon where it is digested by our bacterial symbionts to produce gas. The more whole grain-y the complex carbs we put in our guts, the higher the fiber (indigestible) to starch ratio, and the less likely to cause issues.
Other things that cause gas are specific starches that are indigestible in our guts, which our colon bacteria are happy to process, such as raffinose, inulin (the offensive starches in beans, broccoli, etc.) and retrograded starch, which is caused by cooking then cooling of amylose. The primary starch in white flour products, which produces a form of amylose is indigestible in our small intestine, but can be digested by our colon bacteria. This of course is a worse problem for DS patients who digest starches even less than others.
For more information on gas and flatulence-producing foods: