Understanding Sugar Alcohols on a Ketogenic Diet
Sugar alcohols, also known as polyols, are a type of carbohydrate used as a sugar substitute in many low-carb and keto-friendly products. Unlike regular sugar, they are only partially digested by the body, which means they have a reduced impact on blood sugar levels and contribute fewer calories per gram. This makes them appealing to those on a ketogenic diet, which requires severely restricting carbohydrate intake to induce a metabolic state called ketosis. However, the key to success lies in understanding that not all sugar alcohols are created equal, and your approach to counting them must be adjusted accordingly.
The Importance of Net Carbs
On a keto diet, the most important metric for tracking carbohydrates is 'net carbs,' not 'total carbs'. Net carbs represent the digestible carbohydrates that actually affect your blood sugar. To calculate them, you subtract fiber and certain sugar alcohols from the total carbohydrate count listed on a product's nutrition label. The core of the confusion around sugar alcohols stems from the fact that different types have different glycemic indexes (GI), a measure of how much a food raises blood sugar. A sugar alcohol with a higher GI will affect your blood sugar more significantly than one with a very low or zero GI.
Which Sugar Alcohols to Subtract
The 'Full Subtraction' Rule: Erythritol and Allulose
Erythritol is widely considered the gold standard for keto sweeteners. With a glycemic index of 0-1, it is almost completely absorbed in the small intestine and then excreted in the urine without being metabolized. This means it does not affect blood glucose or insulin levels, making it a true zero-net-carb option. Similarly, allulose is a rare sugar that the body cannot metabolize, so its carbs can be fully subtracted from the total count.
The 'Partial Subtraction' Rule: Xylitol, Sorbitol, and More
For most other sugar alcohols, the answer to "do you subtract sugar alcohol when doing keto" is only partially. These polyols are only partially absorbed, and while their impact on blood sugar is far less than regular sugar, it is not zero. For products containing xylitol, sorbitol, isomalt, or mannitol, many keto dieters subtract only half of the grams of sugar alcohol listed on the label to get a more accurate net carb count. This partial absorption accounts for the fact that some of the carbohydrates will still enter the bloodstream and impact ketosis. For example, if a product has 10 grams of sorbitol, you would count 5 net carbs from that source.
The 'No Subtraction' Rule: Maltitol
Maltitol is the major exception to the subtraction rules and is often considered one of the least keto-friendly sugar alcohols. With a relatively high glycemic index (GI of 35-52), it can cause a significant blood sugar and insulin response. Therefore, if a product lists maltitol as an ingredient, it is often best to count the entire maltitol content towards your total carbohydrate count to avoid risking ketosis. This is particularly important for maltitol syrup, which can have an even higher glycemic index.
Side Effects and Best Practices
Excessive consumption of sugar alcohols, even the keto-friendly ones, can lead to digestive distress such as bloating, gas, and diarrhea. This is because the unabsorbed portions are fermented by bacteria in the large intestine. To minimize these side effects, it is recommended to consume them in moderation and to observe how your body reacts to different types.
Comparison of Common Keto Sugar Alcohols
| Sugar Alcohol | Glycemic Index (GI) | Subtraction Rule | Notes |
|---|---|---|---|
| Erythritol | ~0 | Subtract 100% | Excellent for baking; minimal digestive impact. Some recent research raises questions about potential risks at high doses. |
| Allulose | ~0 | Subtract 100% | Does not affect blood sugar; a newer and popular choice. |
| Xylitol | 7-13 | Subtract 50% | Popular in gum and baked goods; higher GI than erythritol; toxic to dogs. |
| Isomalt | 2-9 | Subtract 50% | Used for hard candies and decorations; lower GI, but still requires partial counting. |
| Sorbitol | 4-9 | Subtract 50% | Naturally found in fruits; can have higher GI impact and more laxative effect than some others. |
| Maltitol | 35-52 | Subtract 0% | Higher glycemic impact; best avoided or treated as a full carb. |
How to Check Your Product Labels
To apply these rules, you must be a savvy label reader. First, find the 'Total Carbohydrate' count. Below this, the label may list 'Dietary Fiber' and 'Sugar Alcohol.' You also need to scan the ingredients list to see which specific sugar alcohols are used. For instance, if a label shows 20g Total Carbs, 5g Dietary Fiber, and 10g Erythritol, your net carbs would be 20 - 5 - 10 = 5g. However, if that same product listed 10g of Maltitol, your calculation would be 20 - 5 - 0 = 15g net carbs. It is also important to check for hidden ingredients and other fillers, as some manufacturers may combine different sweeteners. For an in-depth look at different sweetener types, you can consult a resource like this keto sweetener playbook.
Conclusion
In summary, the question "do you subtract sugar alcohol when doing keto?" has a nuanced answer based on the specific type you are consuming. The blanket subtraction of all sugar alcohols is an inaccurate practice that could lead to inadvertently exceeding your daily carb limit and falling out of ketosis. Erythritol and allulose can generally be subtracted entirely. For other sugar alcohols like xylitol and sorbitol, it is safer to subtract only half to account for their partial absorption and moderate glycemic impact. Maltitol, due to its higher glycemic index, should be counted as a full carbohydrate. Always remember that moderation is key, and paying close attention to product labels and your body's individual response is crucial for success on a ketogenic diet.
