Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.
Carbs are one of the most controversial topics when it comes to the keto diet. If you’re just starting your keto journey, learning about carbs is vital as they are one of the main things you’ll be constantly on the lookout when making your food choices.
The idea behind net carbs is that certain carbohydrates don’t need to be tallied in your total carb count for the day.
In other words, it’s not just about your carb intake — it’s about what kind of carbs you’re consuming.
In this article, you’ll learn which carbs can keep your blood sugar stable, whether or not calculating net carbs is worthwhile, and how to calculate net carbs if you want to.
An impact carb is any carbohydrate type that has a high impact on your blood sugar level. These carbohydrate varieties are known as high GI (or high glycemic index[*]) carbohydrates and they break down rapidly into glucose, which then makes its way to your bloodstream.
When high-GI carbs enter your bloodstream — unless they are immediately used for physical exercise — they typically contain more energy than your body can successfully use in one go. And everything you don’t use as energy gets stored — sometimes as glycogen in your muscles and liver, but mostly as body fat.
Impact carbs can be very damaging to your health (and waistline) when you consume them regularly in high amounts.
This is why it’s so important to calculate macronutrients specific to your goals, activity level, and health history. You can calculate yours here.
Now, on the other hand, non-impact (or low-impact) carbohydrates are low-glycemic and digest at a much slower rate.. Due to this prolonged release of glucose into your bloodstream, insulin spikes are less likely and you’ll experience more sustained energy levels.
It’s the overconsumption of high-GI carbohydrates that are presumed to cause many of the negative health conditions like obesity and type 2 diabetes — hence, the rise of nutrition plans like the keto and Atkins diets. These plans help your body make the switch from being carb-dependant to being fat-dependent.
Creating a Healthy Carb Balance
The main goal in a low-carb or keto diet is to replace most carbohydrates with healthy fats and protein. But it’s also important to know exactly when you can have high-impact carbs versus low-impact carbs.
You can use high-glycemic carbs, for instance, to help support your workouts or for sports performance.
However, for anyone following a relatively sedentary lifestyle, the energy from high-GI carbs isn’t necessary.
How to Calculate Net Carbs
When it comes to carb counting, one thing that can get a little confusing is the “net” carbohydrate situation. Don’t worry, though — it’s not nearly as difficult as it sounds.
Net carbohydrates are what you’re left with after subtracting the grams of fiber per serving from the total carbohydrate amount per serving. For example, if an item has 20 grams of carbohydrates and it contains 8 grams of fiber, then the amount of net carbs the item contains is 12 grams.
This is a great way to measure the potential “damage” an item could cause you. Since fiber is essential for the successful internal function of the body and contains no calories because it’s not absorbed, what you’re left with is the true caloric content and carbohydrate content.
The keto diet is based on this system, and it allows you to successfully gauge whether you’re taking in enough fiber and eating the right kinds of carbs.
High-GI carbs are typically very low in fiber, so you’re mostly consuming sugar and not anything that will serve a practical purpose in your body when you eat them. You really want to be sure the carbs you eat for energy have a low “net worth” once the fiber has been removed.
Soluble vs. Insoluble Fiber
Fiber is a type of carbohydrate that, unlike other carbs, can’t be broken down into digestible sugar molecules. Therefore, dietary fiber passes through the intestinal tract relatively intact. It is crucial for optimal digestive functions and overall health.
There are two types of fiber:
Soluble fiber is the type of fiber that can be diluted in water, creating a gel-like substance that will make you feel fuller for a longer period of time (helping to promote weight loss).
This happens because this substance slows down the process of absorption of food in the body. Even though it contains a small number of calories, it doesn’t seem to affect your blood glucose levels. Soluble fiber also feeds your gut bacteria, ensuring a healthy microbiota [*].
Insoluble fiber, on the other hand, is the fiber that does not dissolve in water, has no calories, and its function is to help you have healthy and regular bowel movements.
When buying processed goods, reading food labels is extremely important as some manufacturers may place a type of processed fiber in their foods, called IMO.
IMOs or Isomaltooligosaccharides can occur naturally in foods like honey or fermented foods like miso and soy sauce. When manufactured on a commercial scale, IMOs are processed from cereal crops like wheat, barley, oats, tapioca, rice, potato, pulses (peas, beans, lentils), and others.
Studies on IMOs show that they may raise blood sugar levels[*]. Even though the FDA is petitioning to grant them fiber status, the EU prohibits health claims for oligosaccharides, so take that into consideration when reading nutrition labels.
Learn more about the almighty fiber in this podcast episode with Dr. Michael Ruscio.
Sugar Alcohols and Carb Count
Sugar alcohols, also known as polyols, are comprised of sugar molecules and alcohol molecules. They do not, however, contain ethanol, the compound that makes you tipsy after a few drinks.
Sugar alcohols are naturally occurring in a vast number of fruits and vegetables but they’re mostly used as alternative sweeteners. The most well-known ones are sorbitol, erythritol, xylitol, and maltitol and they are commonly found in sugar-free foods.
Even though they are considered alternatives to sugar, keep in mind that these polyols do contain calories and some of them might affect your blood sugar and insulin levels.
Learn how to calculate sugar alcohols net carbs here.
Calculating Net Carbs in Whole Foods
When your goal is to lose weight and your tool of choice is a low-carb diet like the keto diet, whole foods are your best friend. Why?
Because to calculate net carbs in whole foods is the easiest thing in the world.
As whole foods are comprised of a percentage of naturally-occurring fiber, all you have to do is subtract the grams of fiber from the grams of total carbs. And voilà!
Take an avocado, for example. It’s one of the most important whole foods in a keto diet not only for its dense nutrient content, but also for the immense quantity of healthy fats it contains (such as omega-3s and omega-6s).
A medium avocado contains:
• 21 g fat
• 2.7 g protein
• 12 g carbs of which 9.2 g is fiber
• 12g carbs – 9.2g fiber = 2.8 grams of net carbs
Here’s a great tool provided by USDA, which contains all the nutrition information about thousands of whole foods and more, to help you on your keto journey.
Now that you know the difference between carb types, you can use this information to integrate them into your daily diet and form a plan that will keep you in ketosis.
Completely removing any nutrient from your diet is never the best way to ensure overall vitality. However, maintaining a balance, especially if you’re very physically active, is the key to getting your nutritional needs met.
Learn more about how to start a keto diet and get the detailed, scientific-based information you need for a healthy lifestyle.