What's the Deal with Net Carbs, and How Do You Calculate Them?
Nutrition experts break down how to calculate net carbs — and the pros and cons of doing so. Spoiler: It's not the best idea for everyone.
While scanning the grocery store shelves for a new protein bar or pint of ice cream to try, your brain is likely bombarded with dozens of facts and figures that are meant to clue you in on a food's health status. The usual suspects: Calorie counts, grams of protein, and amount of fiber. (If you need to, now's a good time to brush up on how to read a nutrition label.)
But some products' packaging now touts a little something called net carbs — and it's a totally different number than the one listed in the "carbohydrates" section on the nutrition facts panel. So what does this number actually mean — and does it even matter? Here, registered dietitians give the lowdown on what net carbs are, why you should (or shouldn't) pay attention to them, and whether it's worth knowing how to calculate net carbs or not.
What Are Net Carbs, Anyway?
Essentially, net carbs are the carbohydrates in food that can be absorbed by your body and that have an impact on your blood sugar levels, says Jennifer McDaniel, M.S., R.D.N., C.S.S.D., L.D., owner of McDaniel Nutrition Therapy.
But to truly understand what that means, you need to know the gist of carbohydrates in general and their effect on your body. Carbs are one of three key macronutrients found in food (the others: protein and fat). Carbs are found in fruits, veggies, dairy, and grains. When you wolf down a slice of toast or baked potato, your body breaks down the food's carbs into glucose (aka sugar) — the main source of energy for your body's cells, tissues, and organs, according to the National Library of Medicine — which then enters the bloodstream. As your blood sugar levels rise, your pancreas produces insulin, a hormone that tells cells to absorb that sugar for energy, which in turn helps blood sugar levels fall and return to homeostasis, according to the Harvard School of Public Health.
However, not all carbohydrates can be broken down to provide the body energy. Fiber, a component in plant foods, can't be digested and doesn't raise blood sugar levels, according to the Harvard School of Public Health. The same goes for sugar alcohols — sweeteners (such as sorbitol, xylitol, lactitol, mannitol, erythritol, and maltitol) that are slowly and incompletely absorbed into the blood, so they have a smaller impact on blood sugar than other carbohydrates, per the U.S. Food and Drug Administration.
And that's exactly what net carbs attempts to account for. While there isn't a formal definition (yet) from any large governing body such as the Food and Drug Administration, net carbs are typically thought of as the carbohydrates that can be absorbed and have an impact on the body's blood sugar levels, says McDaniel. "These are calculated to indicate how many carbohydrates in a certain product will cause an increase in blood glucose," she explains.
There isn't one set-in-stone recommendation for the amount of net carbs — or even total carbs — to consume daily, says Molly Kimball, R.D., C.S.S.D., a New Orleans-based dietitian at Ochsner Fitness Center and host of the podcast FUELED Wellness + Nutrition. In fact, the United States Department of Agriculture advises consuming 45 to 65 percent of your total calories in the form of carbohydrates (amounting to 225 to 325 grams of carbs on a 2,000-calorie diet). On the other hand, the American College of Sports Medicine recommends those who exercise moderately (think: an hour a day) consume 2.3 to 3.2 grams of carbohydrates per pound of body weight each day (amounting to 391 to 544 grams for the average 170-pound woman, for example). So if you want to know the best balance of macros for your unique needs — and if it's beneficial for you to be calculating your net carbs in the first place — schedule some time to chat with a registered dietitian or your medical provider. (More here: How Many Carbs Should You Eat Per Day?)
How to Calculate Net Carbs
While some packaged foods are now labeled with their net carbs, that's certainly not true for all foods. Great news: You don't have to be a math wiz to calculate net carbs yourself. (That said, if you don't feel like breaking out your notepad to calculate net carbs on your own, MyFitnessPal premium members can track their net carbs through its mobile app.)
Simply put, net carbs is the total amount of carbohydrates per serving, minus the amount of fiber and sugar alcohols. For a clear picture of what this exactly looks like, turn to this breakdown of how to calculate net carbs:
Net carbs (g) = total carbs – fiber – sugar alcohols*
1. Look at the amount of total carbohydrates per serving. Let's say a serving of ice cream has 20 grams of carbs.
2. Look at the amount of fiber per serving. If that ice cream has 5 grams of fiber, subtract it from the 20 total grams of carbohydrates. You're now left with 15 grams of net carbs.
3. *Look at the amount of sugar alcohols per serving (if needed). This is where things get a bit tricky. (If the food you're looking at doesn't contain sugar alcohols, you can skip this step.) To calculate net carbs, you'll need to know the number of grams of sugar alcohols in a food; however, the FDA requires food manufacturers to call out the amount of sugar alcohols per serving on nutrition facts labels only when the label features a claim about sugar alcohol, total sugar, or added sugars (i.e. marketing something as "sugar-free"). Luckily, you'll often see food products that tout low net carb counts voluntarily listing sugar alcohol contents. Regardless of whether they're called out separately, sugar alcohols will always be counted in the "Total Carbohydrate" section.
If the package shows the number of grams of sugar alcohols inside, then you'll want to look at the type of sugar alcohol listed in the ingredients list, says Kimball. While standard sugar and other carbohydrates typically have 4 calories per gram, some sugar alcohols — including sorbitol, lactitol, mannitol, and maltitol — have about 2 calories per gram, so they're almost like "half-strength carbs," says Kimball. As such, you'll only subtract half the amount of these sugar alcohols from your total carbohydrates. If that ice cream has 20 grams of carbs, 5 grams fiber, and 10 grams sorbitol, a serving would boast 10 grams of net carbs.
On the flip side, the sugar alcohol erythritol contains just .002 calories per gram, so you can subtract the entire amount of it (in grams) from your total carbs. If that same ice cream contained 10 grams of erythritol, a serving would contain just 5 grams of net carbs. Likewise, a fiber-like sweetener called allulose isn't digested, nor does it impact blood sugar, so you can subtract the total amount of allulose from the total carbohydrate count as well, explains Kimball.
Why You Might Want to Care About Net Carbs
For the average person, there's no real need to pay attention to net carbs. The only perk is that calculating net carbs can help get you in the habit of looking for fiber — a nutrient that plays an essential role in improving gut health, weight management, and reducing the risk of chronic disease, says McDaniel. "When we pay attention to certain characteristics of a food label, like carbs, it has the ability to increase overall awareness of the quality of the food," she adds.
If you fall into one of these other categories, though, looking at net carbs might be more worthwhile.
People with type II diabetes may benefit from learning how to calculate net carbs and keeping an eye on their intake, as understanding the impact certain carbs will have on blood sugar can help them better manage their levels, explains McDaniel. What's more, "if someone is watching their carbs, they might think that they 'shouldn't' or 'can't' have certain items, but looking at net carbs can really open up the door," adds Kimball. For example, someone with diabetes might typically pass on cookies, but if they know how to calculate net carbs, they could find out that a treat made with erythritol and fiber-packed whole grains and nuts may have a lower amount of net carbs — and thus a smaller impact on blood sugar — may be a better fit within their diet than a standard sugar-filled one. (Related: What You Need to Know About the Latest Alternative Sweeteners)
People who exercise a ton or are looking to add more carbohydrates to their daily diet to ensure they properly fuel up and replenish their bodies (think: endurance runners) may also want to calculate and reference their net carb intake, says Kimball. Since they're exercising for several hours at a moderate- to high-intensity every single day, these folks may need to consume up to 5.4 grams of carbohydrates per pound of body weight daily to amp up their glycogen stores (the glucose stored in cells for later use), according to the American College of Sports Medicine. Nosh primarily on foods with a low amount of net carbs, and you might not give your body the glucose it needs to power through those tough workouts. By paying attention to net carbs, these athletes can ensure they're properly fueling up on carbohydrates that can be used for energy — not just ones that move through their systems undigested. (Related: Here's Why Carbs Are Actually So Important for Your Workouts)
People on the keto diet should also keep net carbs top of mind. The keto diet — a high-fat, low-carb diet —as spikes in blood sugar can throw you out of ketosis, the state in which your body uses fat, not stored glucose, as fuel. While on the diet, you'll want to consume fewer than 35 grams of net carbs per day to stay in ketosis, but that the exact number will be different for everyone, Toby Amidor, M.S., R.D., C.D.N., a registered dietitian, previously told Shape.
The Downsides of Paying Attention to Net Carbs
Though knowing how to calculate net carbs can help you better understand how your body is going to use a particular food for energy, some folks might not want to make a habit of tracking them. "For some, focusing on 'macros' or specific nutrients of a food can fortify an unhealthy relationship with food," says McDaniel. People who have a history of, a predisposition for, or actively have disordered eating behaviors will want to be careful with counting net carbs, as well as any other nutrients and numbers involved in their diet, adds Kimball.
Even if you don't have this history of disordered eating, being a bit obsessive about your health stats (think: constantly checking your steps) calls for caution, says Kimball. "I think [tracking net carbs] takes away from the food itself, and it makes food more of a science than a pleasure," she explains. "What I would say in this case is maybe it's fine to assess it, to see what the net carbs are and how that can fit into your normal day, but then not continuing to count or have this running tally of your day in your head." In either instance, consider talking over your decision to calculate your daily net carb consumption with your healthcare provider or a registered dietitian before you get started.
Aside from the potential risks involved with tracking and calculating net carbs, focusing on one single aspect of your food oversimplifies how it interacts with your body, says McDaniel. "We don't just eat 'net carbs' — we eat foods that also offer fats, proteins, micronutrients, and phytochemicals," she says. "It's limiting to define the health or quality of a food by only one nutrient."
By making your food choices solely based on the amount of net carbs, you might end up loading your plate with only highly processed, highly refined ingredients — not nourishing whole foods, adds Kimball. "Sometimes food makers jack up the fiber count and manipulate the ingredients so that their net carbs are low, but when you look at the quality of these ingredients, it's like all these weird starches and isolated fibers," she explains.
For example, some food manufacturers add inulin (aka chicory root) to amp up the fiber content, and although there aren't any major drawbacks of the ingredient on its own, you should consider the other ingredients included along with it, says Kimball. A granola bar made from whole grains and a little inulin has a different nutritional profile than a bar made from tapioca starch, potato flour, and inulin, she explains. "The reason registered dietitians say to aim for 25 to 35 grams of fiber a day for whole-body health isn't because we want all these isolated fibers," says Kimball. "It's because the things that give you that fiber — all these vegetables, fruits, and whole grains — are really rich in other nutrients."
So, Should You Calculate Net Carbs?
Considering the handful of drawbacks for the average eater, McDaniel typically recommends calculating net carbs only to those who are diagnosed with diabetes. "Unless you've been advised otherwise, net carbs should have little to no weight in how much you should be eating of a certain food," she adds.
That said, there's nothing wrong with knowing how to calculate net carbs and taking a peek if you're curious — just like every other stat on a food's nutrition label. "The numbers, such as net carbs and protein, are definitely relevant," says Kimball. "For instance, we would want to steer clear of things that have a lot of added sugar or are all carbohydrates and no protein or fats, which won't be a sustaining meal. We want to be really mindful of letting the numbers be a guide, but not letting the numbers be the sole gauge for what you're choosing."