When I first began maintaining a ketogenic diet, I thought “I’ll just eat sugar-free candy!” without doing the research. BIG MISTAKE.
Most sugar-free candy, especially those from big candy manufacturers, usually use sugar alcohols as sweeteners. Sugar alcohols include Xylitol, Erythritol, Maltitol, Mannitol, and Sorbitol. Unfortunately, eating too much sugar alcohols can seriously upset your stomach, causing digestive issues such as gas, bloating, cramping, and diarrhea. Sugar alcohols’ laxative effects are so pronounced that they can be found in many over-the-counter laxatives. I’m personally only able to eat maybe one piece of candy per day that contains sugar alcohols without beginning to notice digestive symptoms.
What are sugar alcohols you ask? An excerpt from the page on sugar alcohol at Wikipedia states:
Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, that comprise a class of polyols. Contrary to what the name may suggest, a sugar alcohol is neither a sugar nor an alcoholic beverage. They are white, water-soluble solids that can occur naturally or be produced industrially from sugars. They are used widely in the food industry as thickeners and sweeteners. In commercial foodstuffs, sugar alcohols are commonly used in place of table sugar (sucrose), often in combination with high intensity artificial sweeteners to counter the low sweetness.
As a group, “sugar alcohols” are comprised of many compounds. The ones commonly used as sweeteners in foods are isomalt, mannitol, sorbitol, xylitol, and hydrogenated starch hydrolysates. These compounds commonly come from sweet plants such as berries and fruits where the carbohydrate found in these plants undergoes a chemical process. Mannitol for example can be created via a hydrogenation process using Raney nickel catalysts. Some sugar alcohols such as mannitol occur naturally, however for industrial purposes sugars frequently undergo this or similar processes so as to be able to be produced at scale for production.
When used as a sugar substitute, sugar alcohols provide somewhat fewer calories than table sugar (sucrose), primarily because the body does not digest them well and they are not well absorbed. Because of this, sugar alcohols can have a laxative effect.
So, how do sugar alcohols affect ketosis?
The Joslin Diabetes Center’s page on sugar alcohols states:
Many so-called “dietetic” foods that are labeled “sugar free” or “no sugar added” in fact contain sugar alcohols. People with diabetes MISTAKENLY think that foods labeled as “sugar free” or “no sugar added” will have no effect on their blood glucose. Foods containing these sugar alcohols need to have their calorie and carbohydrate contents accounted for in your overall meal plan, as it is carbohydrate that raises blood glucose levels. Since many people typically overeat “sugar free” or “no sugar added” foods, their blood glucose may be significantly elevated.
Because the body needs to burn fat for energy rather than glucose in order to stay in ketosis, sugar alcohols in any significant amount can be problematic. It is helpful that in contrast to sugars they are not well digested and not well absorbed, but when consuming more than a very small amount, these carbohydrates still add up. If you’re going to consume sugar alcohols, be sure to limit your intake to minimal levels in order to maintain ketosis, just as you would with regular sugars and carbohydrates.