|August 5, 2020

How to Calculate Net Carbs for Keto and Why They Matter

By Spencer Brooks
Reviewed by Emily Gonzalez, ND for Scientific Accuracy

How to Calculate Net Carbs for Keto and Why They Matter

  • If you follow the ketogenic diet, it’s essential that you know how to calculate net carbs: the carbohydrates that your body actually processes and uses for energy.
  • Fiber and certain sugar alcohols don’t count toward your total carbs on keto, so you can subtract them from your daily total—with some important exceptions.
  • Find out how to calculate net carbs, how many you should aim for and why not all sugar alcohols are truly low-carb.

If you’re new to the ketogenic diet, you’re probably asking yourself, “What are net carbs, and why should I care?” On a lower-carb diet, net carbs vs total carbs is actually a big deal.

Every gram of carbohydrate you eat counts, so it’s essential to know how to calculate net carbohydrates correctly so you don’t go over your daily carb limit. This guide explains what net carbs care, why they matter and how to use a manual net carb calculator to figure them out for yourself.

What are net carbs?

Produce aisle in grocery store

There’s more to a food label than just total carbohydrates. That total can also include fiber, sugar and sugar alcohols, which help determine your net carb intake.

What does net carbs mean? Net carbs are the carbohydrates in food that you digest and use for energy.

It might be surprising to hear that your body doesn’t use everything you eat. In reality, your body can’t completely break down and absorb some types of carbs, like fiber and sugar alcohols. They pass through your body without being digested. That’s why most fiber and sugar alcohols can be subtracted from your daily carb total.

On a keto diet, eating too many carbs can kick you out of ketosis. When you calculate net carbs, you’ll have a better idea of how many carbs you’re actually eating in a day.

Carbs vs. net carbs

If you look at the nutrition facts label of most packaged foods in the United States, you’ll see total carbohydrates, dietary fiber and sugar. This information is regulated by the FDA and has an official, legal definition.

Net carbs are different. Food manufacturers came up with the term “net carbs” in the early 2000s when low-carb diets went mainstream. Today, you might even see net carb callouts on the labels of lower-carb and keto foods.

However, there’s no official definition of net carbs, so the way that companies calculate their totals can differ.

To calculate net carbs for keto for yourself, take a food’s total carbohydrates and subtract:

  • Dietary fiber: Although fiber is technically a carb, your body doesn’t have the enzymes to break it down. So, it passes through your digestive system unchanged. This means (for keto, at least) that grams of fiber have zero net carbs and zero calories.
  • Certain sugar alcohols: Sugar alcohols taste sweet, but their molecular structure is slightly different from that of sugar molecules. A lot of sugar alcohols are either partially or entirely indigestible by humans.

Note that certain sugar alcohols do impact your blood sugar, and you should factor them into your keto carb count if you eat a large amount. For details, see the “How to calculate net carbs for keto” section below.

Why is counting carbs on keto so important?

When you keep net carbs low enough—typically under 50 grams of net carbs per day—your body enters ketosis: a metabolic state where you shift from burning carbs for energy to burning fat for fuel.

Getting into ketosis, and staying there, is the whole goal of keto. When you’re in ketosis, you feel lasting energy, a cognitive boost and fewer cravings, to name just a few benefits. Keto can even help you stay at a healthy weight.

The problem is that eating too many carbs can prevent you from reaching ketosis and staying there. That’s why learning how to figure out net carbs is so important.

Go over your carb limit, and you’ll fall out of ketosis and lose out on all the benefits. If you’re not seeing results on keto, our number one recommendation is to look at your macronutrient breakdown (how much carbs, fat and protein you eat daily). This is true whether you follow clean keto or a dirty keto diet.

Regardless of your diet, a high amount of carbs (and especially refined ones, like starches and sugars) can also contribute to the following side effects:

  • Spikes in your blood sugar
  • Inflammation[1][2]
  • Food cravings[3]
  • Disruptive changes to your hormones[4]
  • Shifts in your gut bacteria
  • Health conditions like obesity, insulin resistance and metabolic syndrome[5]

The trick is figuring out what your ideal carb intake looks like.

The reality is, carbs are fine in moderation. But if you’re on a strict keto diet, you have to pay attention to every single gram and how your body responds to different foods.

Net carbs are important, but they’re not the whole picture on keto. Keep reading to find out why.

How many net carbs on keto should I be aiming for?

Keto chopped salad with creamy dressing

On the standard ketogenic diet, you might eat as few as 20 grams of net carbs per day, or 5-10% of your total calorie intake. However, the “right” number of net carbs really depends on you.

Some people can eat slightly more carbs and stay in ketosis. Others need to stay on the lower end of the spectrum. Here are three examples:

  • You’re highly active: Let’s say you exercise three to four times per week, and you’re in the gym for about an hour. You’re more likely to burn through your glycogen stores and stay in ketosis. You might notice improvements in your workouts when you bump up your carb intake.
  • You’re pretty sedentary: You spend most of your day sitting down at a desk or in the car, and you want to lose some body fat. Keep your net carb intake on the lower end, around 5% of your total calories.
  • You’re feeling tired: Other people feel more energized and sleep better when they bump their net carb intake up to 6% of their total calories, a style of eating also known as “modified keto.” If you’re dealing with poor sleep and fatigue that just won’t quit, your body might be asking for more carbs.

How to calculate net carbs for keto

Wondering how to count carbs and stay in ketosis? Use this manual net carb calculator:

Grams of total carbs – fiber – sugar alcohols = Net carbs

Here’s one important element to factor into your net carb formula: Not all sugar alcohols are truly carb-free.

Some sugar alcohols can actually kick you out of ketosis because they have a high glycemic load. However, certain manufacturers selling “low-carb” or “sugar-free” foods will subtract those sugar alcohols from the total carb count. This makes products appear lower-carb than they actually are. Yikes.

On the other side of things, manufacturers will sometimes list sugar alcohols that don’t affect your blood sugar as if they were normal carbs, making net carb counts seem higher than they actually are.

So, how are you supposed to calculate net carbs for keto? Know your sugar alcohols.

Sugar alcohol on the keto diet

First up, what is sugar alcohol? It’s a type of carbohydrate that tastes sweet. On a molecular level, it looks like sugar and alcohol (hence, the name). Some sugar alcohols naturally occur in fruits and vegetables, and others are made by processing sugar.

But your body doesn’t treat it the same as sugar. Your body processes regular sugar pretty easily. Sugar alcohols aren’t as easily digested or absorbed, which is why they’re used in sugar-free and lower-carb foods.

So, do sugar alcohols count as carbs? It depends on the type.

The following sugar alcohols do not count toward net carbs for keto. If you’re eating something with these sweeteners, you don’t need to include them in your carb count:[6][7][8]

  • Erythritol
  • Xylitol
  • Mannitol
  • Lactitol

Exception: These sugar alcohols below do count (at least partially) toward net carbs:[9]

  • Maltitol
  • Sorbitol
  • Isomalt
  • Glycerin

Each gram of maltitol, sorbitol, isomalt or glycerin counts as about half a gram of carbs for keto.

Although sugar alcohols are not digestible carbs, your gut bacteria can ferment them, creating gas and bloating in your small intestine. For this reason, be wary of mannitol, maltitol and sorbitol—you may end up with digestive discomfort.

Here’s a good rule of thumb: Whether or not you follow the keto diet, avoid eating more than roughly 15 grams of sugar alcohols at a time, and pay attention to how you feel after eating them.

How to calculate sugar alcohol on a low carb diet

If you’re eating something that contains one of these sugar alcohols, use a slightly different formula to calculate total net carbs.

Take the number of grams of the sugar alcohol, divide by 2 and add it to your carb count. For example:

Grams of total carbs – fiber – sugar alcohols + (maltitol / 2) = Net carbs

Additional considerations when counting carbs on keto

We’ve established that you should always read the nutrition facts on your foods, and when you eat carbs that don’t raise your blood sugar, you can take them out of your net carb total.

You also want to avoid highly insulinogenic carbs, which are food choices that trigger a blood sugar response in the body. These foods are higher on the glycemic index (GI)—a numerical score that indicates how a food will affect your blood sugar.

On keto, you want to avoid foods with a high GI, which means it will have a larger effect on your blood sugar. The GI score also explains why you should avoid foods like potatoes, carrots and legumes—even though they contain fiber, they’re more likely to mess with your insulin levels and kick you out of ketosis.

Net carbs can feel like a confusing topic, but what it really means is that you have flexibility in your carb total. That’s good news if you want to leave room in your macros for other foods and drinks, whether you’re drinking alcohol on keto or enjoying a slightly higher-carb meal.

After all, flexibility and moderation are keys to a lifelong relationship with a healthful diet. Consider this information even more reason to scope out those nutrition labels, and keep rolling with the diet that works for you.

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This article has been updated with new content.