Calculating carbs on the ketogenic diet is an important part of being able to stay in ketosis. In this blog, I want to explain what net carbs are and how to calculate them. It is probably a lot easier than you may think, so don’t stress. Of course, there is debate about whether you should count total carbs vs net carbs, but that is up to you to decide.
It is my belief that if you are following the ketogenic diet that you want to know which carbs will have an impact on your blood sugar. I look at net carbs. I will later discuss in this blog that not all carbs should be counted as a carb. Some carbs will not affect your blood sugar equally.
If you are interested in reading some of the negative affects, check out my blog here.
What are net carbohydrates?
To put it in its simplest form, to calculate net carbs you would take the total carbs and subtract the fiber. So net carbs = total carbs – fiber.
The term “net carbs” is not officially recognized or agreed upon by scientists or nutrition experts. Because there are not any official rules or regulations on how companies calculate net carbs, the information on the nutrition facts may not actually reflect the total carbohydrates that your body will absorb. Here is a link to WebMD explaining how they define carbs.
There are different types of carbohydrates and they all act differently in our bodies. Due to these differences, you may want to think differently about them. I also want to point out that not all carbs are bad and should be avoided. Some carbs are actually very good for us and help improve your digestive health.
Digestible carbs
Digestible carbs or impact carbs are many times referred to as net carbs. That is because it is in reference to the carbohydrates that are absorbed into the body. So, any carbs that will actually have an impact on your blood sugar. These carbs are both simple and complex carbs. Both of these can be broken down in your small intestine into a single sugar molecule that our body can use.
Fiber carbs
Unlike some other forms of carbohydrates, fiber can NOT be broken down in your small intestine. So in the small intestine, fiber carbs will simply pass through and will not affect your blood sugar. Fiber comes in two basic forms, soluble and insoluble. Soluble means that it can dissolve in water and insoluble means that it can not dissolve in water. On average, about 2/3 of the fiber you consume is insoluble.
Since insoluble fiber does not get broken down (dissolved) in water, it will pass through the colon and has no impact on your blood sugar. It will also prevent constipation and will give you a bulkier stool.
Soluble fiber on the other hand will be fermented in the colon into short-chain fatty acids. These short-chain fatty acids good for your gut health. Since soluble fiber can be broken down in the small intestine, it will provide some calories, but not enough to greatly affect blood sugar levels. Some studies have even shown that soluble fiber can help with blood sugar control, insulin sensitivity and with the absorption of fewer calories.
Note: If you see a type of processed fiber known as isomaltooligosaccharide (IMO), it is important to know that it will act more like non-fiber carbs and increase your blood sugar. While it is not overly common, it can still be found in some foods labeled “Low carb”.
Both soluble and insoluble fibers will have next to no impact on your blood sugar, which is why we can subtract these from total carbs.
Sugar alcohol carbs
Many of us on the keto diet use erythritol or similar sugar alcohol as as sugar substitute. Sugar alcohols are processed in the small intestine similar to the way fiber is. Most sugar alcohols are only partially absorbed (a range of 2-90%), and some of that is excreted out in your urine. Since there are several types of sugar alcohols, they will all act differently and have different affects on your blood sugar and insulin levels. Below I put together a list of some of the most common sugar alcohols and their glycemic and insulin indexes. How these sugar alcohols act in your body will affect calculating carbs.
| Erythritol | Isomalt | Maltitol | Sorbitol | Xylitol | |
| Glycemic Index | 0 | 9 | 35 | 9 | 13 |
| Insulin Index | 2 | 6 | 27 | 11 | 11 |
Hopefully this chart helps explain why most people that are eating keto recommend erythritol if you choose to use a sugar alcohol as a sweetener. It has the lowest effect on your blood sugar, with a Glycemic Index of 0 and has an Insulin index number of 2. It also has less gastrointestinal side affects as compared to some of the others.
The worst option here is maltitol. Maltitol is found in many processed low carb foods, protein bars and sugar-free candies, and this is one that you want to avoid. It will have a higher impact on your blood sugar than what you would want on the keto diet.
Erythritol will be absorbed in the small intestine (about 90% of it) and will be excreted in the urine. The other 10% of erythritol is fermented in the colon to small-chain fatty acids. It is the best sugar alcohol option because it is essentially carb and calorie free and not very likely to cause digestive problems.
While any sugar alcohol is better than using sugar, their impact on your body will vary. By looking at my chart, you can see that erythritol is the best option and maltitol the worst, and the other 3 are in-between.
Sugar alcohols eaten in large quantities are known to cause upset stomach, gas, bloating and possibly diarrhea.
Whole food carbs
Calculating net carbs in whole foods is as simple as my formula at the beginning of this blog. 
Subtract the fiber form the total carbs to get the net carbs. Since these foods naturally have fiber and no added products, these are very simple to calculate.
Processed food carbs
This is where things can get a bit more tricky. Get your reading glasses out and read the label carefully. If the processed food has fiber listed, then you can subtract all of the fiber from the total carbs. If the food has sugar alcohols, subtract half of the carbs unless it is erythritol and you would subtract all of the carbs.
So the formula here would be something like: net carbs = total carbs – (fiber + (.5X(non erythritol sugar alcohol carbs))) or net carbs = total carbs – (fiber + erythritol carbs)
Takeaway
These formulas are not 100% accurate for calculating carbs, but they will help you get in the ball park. For the most part, figuring out net carbs is pretty easy. Reading some nutritional labels is a real pain in the butt, so you may not be able to determine if there is a sugar alcohol in the product or what type. It should be in the ingredients list, but it seems that some labels are not entirely accurate or they may be using a different terminology.
By calculating carbs in foods, you should be able to keep track of your daily carb intake. While there are differing standards, I most commonly see a range of 20-50 grams of carbs a day in order to stay in ketosis. I am not going to debate how many grams of carbs you should have in a day. I will leave the recommended amount of carbs to be determined by doctors and nutritionists. The important thing that I am hoping you were able to take away from this blog is to know the difference in carbs, how they react differently in your body and how to calculate net carbs.
Some doctors have stated that they believe that you should look at the total number of carbs that you eat, not just the net carbs. Their theory is that our bodies initially will not be able to determine that this carb is not digestible. Our body will think that it is getting more carbs than are able to be absorbed because it simply will not be able to tell the difference until it tries to break the carbs down.
I personally disagree with this ideology, but I am also not a doctor. I don’t think our body will count carbs until they are broken down and able to be used. If we can’t break them down into sugars, our body will process it as any other indigestible food and pass it through our system. Hopefully future research will clarify in more detail how our bodies treat all types of indigestible carbs.
There likely will be continued controversy over different methods of calculating carbs for years to come. Do your best to calculate your carb intake.
