Understanding Net Carbs and the Glycemic Response
The ketogenic diet hinges on restricting carbohydrate intake to induce a metabolic state called ketosis, where the body burns fat for fuel instead of glucose. Counting 'net carbs' is a fundamental practice in keto, representing the carbohydrates that your body can digest and convert into glucose. Total carbs, as listed on a nutrition label, include all carbohydrates—both digestible and indigestible. To find the net carb count, you subtract dietary fiber and, crucially, a portion or all of the sugar alcohol content.
The logic behind this subtraction is rooted in how different carbohydrates affect your blood sugar levels. A food's glycemic index (GI) measures how quickly it raises your blood glucose. Regular sugar (sucrose), with a high GI of 65, causes a rapid spike in blood sugar, potentially disrupting ketosis. Sugar alcohols, or polyols, have a chemical structure that the small intestine struggles to absorb efficiently. Consequently, they cause a much smaller and slower rise in blood sugar, if any at all. This is why they are not counted fully toward your daily carbohydrate limit.
Not All Sugar Alcohols Are Created Equal
It is a common misconception that all sugar alcohols are treated the same. Their glycemic impact varies significantly depending on the type. This is a critical distinction for anyone on a strict ketogenic diet. Some, like erythritol, have a negligible effect, while others, such as maltitol, have a more pronounced impact and should be consumed with caution.
The Most Common Sugar Alcohols and Their Keto Friendliness
- Erythritol: With a glycemic index of 0 and very few calories (0.24 calories per gram), erythritol is the most keto-friendly sugar alcohol. It is readily absorbed but excreted largely unchanged in the urine, causing no blood sugar spike.
- Xylitol: Found in many sugar-free gums and candies, xylitol has a lower GI (around 7-13) but can still raise blood sugar slightly. Many keto dieters count half of the xylitol carbs toward their daily total.
- Maltitol: This is the least keto-friendly of the commonly used sugar alcohols, with a GI ranging from 35 to 52. It can significantly impact blood sugar and should be limited or avoided entirely on a strict keto diet.
- Sorbitol: With a GI of 9, sorbitol is a moderate option. It is less sweet and less absorbed than maltitol but can still cause digestive issues.
Comparing Sugar Alcohols and Sweeteners
| Feature | Table Sugar (Sucrose) | Erythritol (Sugar Alcohol) | Maltitol (Sugar Alcohol) | Stevia (Natural Sweetener) |
|---|---|---|---|---|
| Carb Impact | High | Minimal (GI of 0) | Moderate to High (GI 35-52) | None (GI of 0) |
| Calorie Count | ~4 kcal per gram | ~0.24 kcal per gram | ~2.1 kcal per gram | 0 kcal |
| Effect on Ketosis | Disrupts ketosis | Maintains ketosis | Can disrupt ketosis | Maintains ketosis |
| Flavor Profile | Sweet | Mild, cooling aftertaste | Sweet, similar to sugar | Very sweet, sometimes bitter aftertaste |
| Digestive Effect | Easily digested | Well-tolerated in most people | Can cause digestive distress | Generally no effect |
Practical Application for Your Keto Journey
To apply this knowledge, always check the ingredients list of low-carb products. If the only sugar alcohol is erythritol, you can safely subtract the full amount from the total carbs. For products containing other sugar alcohols like xylitol or sorbitol, it is a safer practice to count half the sugar alcohol grams toward your net carb count, or simply consume them in great moderation. Products containing maltitol should be approached with extreme caution or avoided completely, as their glycemic effect can be significant enough to throw you out of ketosis.
Be mindful of digestive side effects. Because sugar alcohols are not fully absorbed, consuming large quantities can cause gastrointestinal discomfort like bloating, gas, and diarrhea, especially with less-absorbed types like sorbitol and maltitol.
Conclusion: Making Informed Choices on Keto
Subtracting sugar alcohols from total carbohydrates is a valid strategy on the keto diet, but it requires an understanding of the specific type of sugar alcohol used. The key reason is their incomplete absorption by the body, which leads to a minimal blood sugar response compared to regular sugars. By distinguishing between different sugar alcohols and being aware of their individual glycemic impacts, you can make smarter, healthier choices. Prioritize options with the lowest GI, such as erythritol, and treat others with more caution. Ultimately, a successful keto diet involves paying attention to the details on nutrition labels to ensure you maintain ketosis effectively and avoid unwanted side effects. For further reading on this topic, a detailed guide on sweeteners for low-carb diets is available from Clean Plates at Are sugar alcohols keto-friendly?.
