Fact-checked by Dr. Anthony Gustin, DC, MS.
Written by Emily Ziedman
Sugar alcohols are popping up on nutrition labels everywhere as a sugar alternative that won’t spike blood sugar and have fewer calories. This is especially true for keto and other low-carb food products.
You may see sugar substitutes like erythritol, xylitol, mannitol, and others on everything from low-carb snacks to protein powders. And most keto experts say that sugar alcohols don’t count toward your total carb count.
But what exactly are sugar alcohols? How does your body process these sugar substitutes, what are they actually doing to your blood sugar, and are there side effects to eating too much?
When it comes to living a ketogenic lifestyle, the quality of your food is just as important as your macronutrient ratios.
Read on to find out what sugar alcohols are all about, and whether or not they deserve a place in your healthy keto diet.
If you’ve been following a ketogenic diet for a while, then you’ve most likely come across some food products containing sugar alcohols.
Also known as polyols, these sugar substitutes are widely used in the food industry to reduce the amount of added sugar in low-carb or low-sugar products.
Sugar alcohol is a bit of a misnomer — they are neither sugar nor alcohol, but a hybrid that creates a whole new type of carbohydrate compound. You can think of them as a carbohydrate with an alcohol attached.
To clear this up right off the bat — sugar alcohols do not contain ethanol (the chemical in boozy drinks that gives you a buzz). So you’re not going to get drunk off your sugar-free hard candies.
Sugar alcohols occur naturally in some fruit and vegetables, but the majority are man-made from starch, glucose, and sucrose. They tend to be a bit less sweet than sugar, and often create a cooling effect in the mouth.
For this reason, manufacturers often combine sugar alcohols with either artificial sweeteners or other low-calorie sweeteners to round out the taste[*].
Before we jump into glycemic response, let’s do a quick review of blood glucose and insulin.
How Your Glycemic Response Works
Your glycemic response is the effect that a specific food has on your blood sugar.
Eating a meal rich in sugar and sugar-containing sweeteners will trigger a large glycemic response — aka, sugar in your bloodstream.
Eating a meal low in sugar and higher in fat and protein will trigger a much smaller glycemic response — not as much sugar in the blood.
Having a lot of sugar in your blood is not a good thing. This is where insulin comes in. The more blood sugar present, the more insulin you need to shuttle that sugar out of your blood and into energy-hungry cells.
If you’re on a low-carb diet or are avoiding sugar because you have diabetes, the main benefit of a low-carb diet is controlling the amount of sugar in your blood and keeping insulin from working too hard.
This is where sugar replacements like sugar alcohols can help.
How Sugar Alcohols Work
Unlike sugar and sugar-containing sweeteners, sugar alcohols are not completely absorbed by your body.
When sugar alcohols reach your small intestine, instead of being rapidly absorbed and entering circulation, they are only partly absorbed — and pretty slowly at that.
The remaining unabsorbed sugar alcohol moves on to your large intestine, never making it into your bloodstream.
Depending on the specific sugar alcohol, the amount absorbed vs. sent to the large intestine can range from 0-80%[*][*]. Sorbitol is the most likely absorbed, and erythritol has the lowest absorption rate[*][*].
Eighty percent may seem like a large amount of absorption. But, once in circulation, not all sugar alcohols are broken down and used for fuel.
In fact, it’s been shown that up to 20% of absorbed sorbitol and xylitol, and 40% of absorbed mannitol are excreted in the urine, untouched by your metabolic process.
The sugar alcohols that do get metabolized do so with the help of insulin. But the insulin response is much lower than when you’re consuming sugar[*].
The one exception is maltitol, which may raise blood sugar and elicit a higher insulin response[*]. However, other studies have found maltitol to have a minimal effect on blood sugar[*][*]. It might depend on the person.
Overall, sugar alcohols tend to produce a lower glucose response than fructose, sucrose, or glucose (the most common nutritive forms of sugar).
However, there is still debate as to whether the amount of sugar alcohols used will actually give you a net reduction in calories or not. This is especially dependent on the type of sugar alcohol[*].
Below is the glycemic index for some common sugar alcohols. Of course, the amount you eat and your own digestion come into play[*]. (Low-glycemic is considered anything less than 55)
|Sucrose (table sugar)||65.0|
As you can see, erythritol, mannitol, and isomalt have a minimal (if any) effect on blood sugar, while maltitol has the most significant impact.
Net Carbs in Sugar Alcohol
So what does this all mean when it comes to counting net carbs?
Since a certain percentage of the sugar alcohols listed on your food items aren’t even absorbed or metabolized, having a strategy in place for when you come across certain sugar alcohols is essential.
Some people choose to count all sugar alcohols as if they were carbs. Although this is definitely playing it on the safe side, people with diabetes have a more balanced way of counting.
If you do choose to subtract sugar alcohols from net carbs, subtract half the amount of sugar alcohols from the total carbohydrate count to get the net carb count[*].
An example would be:
20 grams of total carbohydrate
10 grams of sugar alcohol =
Net carb count
DIvide sugar alcohol in half (5) subtracted from total carbohydrate (20) = net carbohydrates (15)
Different sugar alcohols have varying amounts of calories per gram. Some sugar alcohols are sweeter than others when compared to table sugar.
Here are some of the most commonly used sugar alcohols, with their calories per gram and comparison of their sweetness to sucrose (table sugar).
Sorbitol clocks in at 2.6 calories per gram, with 50-70% sweetness of sucrose. It’s typically used in chewing gums, sugar-free candies, and frozen desserts. It has a cooling effect on the mouth, with no aftertaste[*][*].
With 2.1 calories per gram and 75% the sweetness of sucrose, maltitol is widely used in hard candies, and can also be found in chewing gum, chocolates, ice cream, and baked goods. Of all the sugar alcohols, maltitol is the most likely to cause a blood glucose response[*][*].
Xylitol has 2.4 calories per gram and 100% the sweetness of sucrose. Xylitol has been extensively studied for its benefits on oral health[*]. It’s commonly found in chewing gum, toothpaste, mouthwash, as well as hard candy and gum drops[*].
Erythritol has 0-.2 calories per gram and 60-80% the sweetness of sucrose. It has the least impact on digestive health as it’s not fermented by your gut bacteria[*]. It’s commonly used as a sweetener in lower calorie foods, especially products that come from health-conscious manufacturers[*].
Mannitol contains 1.6 calories per gram, and has 50-70% the sweetness of sucrose. Mannitol is often used as an ingredient for chocolate-flavored coatings found in ice cream and other confections. It’s poorly reabsorbed by the kidneys so it may have a diuretic effect[*][*].
Isomalt has 2 calories per gram and is 45-65% sweetness of sucrose. Isomalt is frequently found in toffee, lollipops, cough drops and wafers[*].
Other sugar alcohols include lactitol and hydrogenated starch hydrolysates.
Sugar alcohols offer more than just a healthier stand-in for sugar.
#1: Oral health
One of the biggest culprits in tooth decay and cavities is sugar. When you eat sugar, it reacts with the bacteria in your mouth and creates an acid. This acid acts on your enamel and slowly erodes your pearly whites until they collapse and form cavities.
Xylitol not only replaces sugar, but it also inhibits the growth of harmful bacteria in your mouth[*].
By halting the acid-producing process, xylitol triggers a protective mechanism for oral health. Erythritol may also have a balancing effect on the bacteria in your mouth, playing a role in the inhibition of cavities[*].
The process of tooth decay and cavities starts with the loss of mineralization and enamel. Xylitol assists in the remineralization of both your enamel and cavities that have already formed[*]. This is why you’ll commonly find xylitol as an ingredient in your mouthwash, toothpaste, and chewing gum.
Prebiotics are a type of carbohydrate that are not fully absorbed in the small intestine. They travel further down your digestive tract and end up in your large intestine, where they can become food for good bacteria.
Since sugar alcohols are only partially absorbed in your digestive tract, they can act as prebiotics to feed the good bacteria in your gut. Xylitol, for instance, has a prebiotic effect and may also contribute to reducing blood glucose, triglyceride, and cholesterol levels[*].
Isomalt is one of the sugar alcohols with the lowest amount of absorption in the small intestine. Because it’s not taken up into circulation, a greater amount of isomalt ends up in the large intestine.
Scientists were curious if the isomalt that ended up in the large intestine would act as a prebiotic and create beneficial shifts in gut bacteria. To determine the effect of isomalt, study subjects were split into two groups — one consuming isomalt and the other consuming sucrose.
When scientists compared the gut bacteria between the two groups, they found a positive shift in the bacteria of the isomalt group, indicating prebiotic activity[*].
#3: Bone density
In animal studies, xylitol has been used as a protective measure against bone loss. Although research in humans is lacking, osteoporosis prevention was seen in rats fed a diet consisting of xylitol[*].
In another study, an increase in bone mineral density and bone mineral content was found when rats were fed a continuous and moderate amount of xylitol[*].
#1: They May Cause Digestive Issues
Sugar alcohols are only partially absorbed by your body. What doesn’t get taken up by your small intestine gets sent to your large intestine.
Here’s where things can get a little dicey — some sugar alcohols are fermented in the large intestine by your bacteria. If you eat a large amount of sugar alcohols or the wrong type, you can end up with a lot of gas and digestive discomfort[*].
Everyone’s body will respond differently to sugar alcohols, but it seems as though maltitol, isomalt, and sorbitol are the biggest offenders. All three of these sugar alcohols have been found to cause significant diarrhea and gas[*][*].
Poor absorption of compounds like sugar alcohols in the large intestine can disrupt normal water and electrolyte absorption. This causes an increase in water being held in the colon and ultimately leads to diarrhea.
The fermentation of excessive amounts of sugar alcohols also contributes to the digestive discomfort with gas, cramping and bloating[*].
Erythritol is one sugar alcohol that doesn’t seem to cause much digestive discomfort. The majority of the erythritol you consume actually gets absorbed by your small intestine, and never makes it to the large intestine. In fact, only about 10% of erythritol goes on to the large intestine[*].
So wouldn’t this mean that it would cause an increase in blood sugar? Not really.
Once absorbed, the majority of erythritol remains unmetabolized by your body and gets excreted in your urine. And that small amount that does make it to your large intestine doesn’t get fermented by your gut bugs[*].
#2: They Can Raise Blood Sugar
Maltitol is a disaccharide, meaning it is made of two sugar units bonded together. One of the sugar units is glucose.
When your digestive enzymes get to work on maltitol, it breaks the bond and liberates that glucose. The small intestine easily absorbs free glucose, and therefore causes an increase in blood sugar[*].
If your aim is to stay in ketosis, you should definitely avoid maltitol. Even though the blood sugar spike isn’t as large as if you ate pure sugar, it’s not worth the risk of raising insulin.
#3: They May Inhibit Weight Loss
You, like many others, may be considering switching out your sugar for some sugar alcohols if you’re trying to lose weight. In theory, this makes sense.
However, the research is still up in the air as to whether sugar alcohols can actually help with weight loss when used in place of sugar.
Since most sugar alcohols need to be used in higher concentrations, it’s possible the net calories end up being similar to what you would get with your standard table sugar[*].
You’re also more likely to indulge in processed foods if you know they are sugar-free, which can easily lead to overindulgence in foods that don’t support weight loss and overall health[*].
#4: High Doses Potentially Associated With Cancer Risk
High doses of xylitol in rats was shown to increase abnormal cell growth and tumor progression[*].
While it’s unlikely you’d ever consume as much xylitol as these rats — which were given 10-20% of their total calories in the form of xylitol — it’s best to keep your consumption low.
#5: Xylitol is toxic to dogs
If you have a furry friend at home, make sure to keep the xylitol stashed away with a tight lid.
Xylitol is a known toxin to dogs and can quickly send them into a state of “liver melt.” It’s suggested that the toxic effect is attributed to increased insulin secretion leading to severe hypoglycemia[*],[*].
Keeping blood sugar stable is paramount for a keto diet, but you shouldn’t ignore food quality and the long-term potential effects of things like sugar alcohols.
Although some sugar alcohols won’t necessarily affect your blood sugar, there are still too many unknowns to determine whether or not they are part of a healthy ketogenic diet.
They don’t contain any important nutrients and may trigger unwanted digestive issues. More research is needed when it comes to the long-term effects of consistently high doses.
But this doesn’t mean you can’t enjoy some sugar substitutes now and then. In fact, keeping your keto diet exciting is vital to sustaining keto long-term.
What to Use Instead
There are a couple of sugar substitutes that have stood the test of time.
Whether you’re whipping up a keto treat at home, or looking for a snack among the ever-growing keto products out there, check the label for the sugar substitutes listed.
The Takeaway on Sugar Alcohols
Sugar alcohol is a name given to a group of very diverse compounds. Although there are definitely benefits to using sugar alcohols in place of sugar, there are significant downfalls a well.
Maltitol is the worst of the bunch and can trigger the highest glycemic response. It not only causes an increase in blood sugar, but it’s also very hard on your digestion.
Sorbitol and isomalt are also hard on digestion, while xylitol and mannitol may cause digestive discomfort in some.
Erythritol is one sugar alcohol that doesn’t seem to spike blood sugar and is also pretty easy on digestion. It does, however, remain largely unmetabolized by your body even though it has a high absorption rate.
This means your kidneys have to work extra hard to excrete any erythritol you consume. This, in combination with the lack of nutrients, makes it a neutral option at best.
Opting for tried and true sugar substitutes like stevia and monk fruit is a safe, an equally delicious, bet.