How To Count Carbs, and Other Nutrition Label-Reading Skills

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Low-Carb Guide to Food Labels

Shop assistant and customer looking at food label.
Betsie Van Der Meer/Taxi/Getty Images

When you start a low-carb diet, half the battle is learning what exactly counts as a carb beyond white potatoes and chocolate chip cookies, and how many carbs in a given item qualify as "low-carb." Plus, there's the small but important matter of learning how to read and understand a nutrition label. Is it the total carbohydrate per serving that matters when counting carbs? Or is it the total sugar content? What about sugar alcohols? 

Learning to read nutrition labels is an invaluable skill in life, and particularly while on any specialized diet, especially low-carb. It provides crucial information about the food we eat and can make all the difference in not only our weight but also our overall health.

While the ideal low-carb diet will be a health-promoting one that includes plenty of foods that don't come with a label—whole foods such as vegetables, meats, fruits, and other fresh foods that are naturally low in carbs and sugars—it's virtually impossible never to eat out of a package. After all, nutritious foods such as raw almonds and frozen vegetables come in packages! So it's best to learn to be a savvy nutrition label reader. 

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Serving Size

Serving Size
Serving Size on a Nutrition Label. Image © Emily Dolson

Serving size is a very important element of the label. In the first place, a "serving size" according to a package may bear little resemblance to the amount of the food which most people eat at a time. If a package says a serving size is ¼ cup, it's best to actually measure some out to get a clear idea of how much that is, as it's very easy to underestimate the amount we're actually eating. When it comes to snack foods, you might want to separate a larger package into smaller bags that are the amount of food you want to eat.

Sometimes, as in the label pictured, the serving size is by weight. If you don't have a scale handy, pay special attention to the number of servings in the package.

When we are counting grams of carbohydrate, it's important to look out for so-called "rounding error" when it comes to serving size. For example, if a label says that 1 tablespoon of a food has one gram of carbohydrate, that could be anything from .51 grams to 1.49 grams. That’s not a big deal if you are eating one serving. But there are 16 tablespoons in a cup, so the error could be as much as 8 grams in either direction if you are using that much in a recipe.

A common example of this issue is heavy cream. One tablespoon of heavy cream has slightly less than half a gram of carbohydrate, which labeling regulations say is "zero." This has led some low-carb dieters to believe that they can use several tablespoons at a time. But those "zero carbs" can add up pretty fast.

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Total Calories

calories
Calories on a Nutrition Label. Image © Emily Dolson

We don't generally count calories on a low-carb diet, as part of the idea is that our appetites will normalize to reflect our body's needs. Still, many people find that at some point it's helpful to at least keep an eye on calories.

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Fats

fats nutrition label
Fats on a Nutrition Label. Image © Emily Dolson

The amount of fat in a food isn't generally an issue on a low-carb diet, but the type of fat can be. Some diets such as the South Beach and Zone diets limit saturated fat, and everyone should stay away from trans fats. Although not usually labeled, choosing foods where most of the fat is monounsaturated is a good guide. In the context of a low-carb diet, total fat intake has not been shown to be a risk for heart disease. The same is true for dietary cholesterol.

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Carbohydrates

carbohydrates food label
Carbohydrates on a Food Label. Image © Emily Dolson

There are several parts to the carbohydrate section of the nutrition label, and it's important for anyone who counts carbohydrates or is sensitive to sugar to understand each one.

The main thing that people on low-carb diets are concerned about is the impact of the carbs we eat on our blood sugar (blood glucose). We aim for blood sugar impact that is both low and slow. What we want to avoid are high peaks in blood glucose, and there is quite a bit of information on the label that can help us.

Total Carbohydrates

The grams of total carbohydrate is the first thing to look at. If it's very high, you can almost always put that food right back on the shelf. Even if the carbohydrates are coming from a "good" (nutritious) source, too much carbohydrate at once will shoot blood glucose up. The exact amount that is "too much" for you will depend on your own body's ability to tolerate glucose, and the particular diet you are on.

Beneath the Total Carbohydrates line in this section, there will be two or three other lines - fiber, sugars, and sometimes sugar alcohols. You may notice that these figures do not add up to the total. This is because starch is not listed on food labels. Therefore, any missing carbohydrate can be assumed to be starch. In processed foods, starch (which is made up of long strands of glucose) generally raises blood glucose as much or more than sugars, because the processing makes the carbohydrate more glycemic.

Sugars

By now you may have figured out that the amount of sugar in a food is not a very reliable indicator of how much the food will affect blood sugar, because starches, and sometimes sugar alcohols, have similar effects.

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Fiber

fiber on a food lable
Fiber on a Food Label. Image © Emily Dolson
Fiber is one type of carbohydrate that does not raise blood glucose. In fact, the presence of fiber can slow down the impact of the other carbohydrates in a meal. Therefore, when counting carbs, we subtract the grams of fiber from the grams of total carbohydrate. This gives a number which is variously called effective carbs, or usable carbs, or net carbs, or impact carbs. This figure is the amount of carbohydrate in a food that affects blood sugar.

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Sugar Alcohols

sugar alcohols on a food label
Sugar Alcohols on a Food Label. Image © Emily Dolson

Sugar alcohols can be tricky ingredients to interpret. A product can be called "sugar-free" and contain sugar alcohols. In that case there must be a separate line for them on the nutrition label (products that aren't labeled sugar-free are not required to have this line).

Manufacturers would like us to believe that sugar alcohols have very little affect on blood sugar, but in fact it depends a lot on which sugar alcohol is in the product. The chart at the bottom of this article about sugar alcohols has a lot of information about this. Note especially that many of the sugar alcohols aren't as sweet as sugar, so more must be used to get the same sweetness. Also note that many sugar alcohols (most notoriously maltitol) can cause gas and other adverse intestinal reactions.

Erythritol is the only commonly-used sugar alcohol that I feel comfortable recommending not counting in the total carb count. I don't eat maltitol at all, but it could be counted as having 3/4 of the stated carbs. Sorbitol can be counted as half of the stated carbs -- and so on, according to the chart.

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Protein

Protein on a Food Label
Protein on a Food Label. Image © Emily Dolson

It's important to eat enough protein, partially because our bodies use it to make needed glucose if we aren't getting enough from carbohydrates. Usually, our appetites tend to regulate getting the right amount of protein. Still, if you aren't someone who tends to eat much protein, it doesn't hurt to keep an eye on this. The National Academy of Sciences recommends that we get 10% to 35% of our calories from protein. 

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Vitamins and Minerals

Vitamins and Minerals on a Food Label
Vitamins and Minerals on a Food Label. Image © Emily Dolson

There isn't a whole lot of information about vitamins and minerals on nutrition labels, but information is required for Vitmins A and C, and the minerals iron, calcium, and sodium. Except for sodium (which we sometimes need to limit), the exact amount isn't required to be listed, but rather the approximate percentage of the total daily recommended intake. People on low-carb diets sometimes don't get enough calcium, so low-carb authors sometimes advise paying attention to this and taking a supplement if needed.

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Ingredients

Ingredients on a Food Label
Ingredients on a Food Label. Image © Emily Dolson

You should be wary of some ingredients. Most of these have to do with blood sugar and will give you a clue as to the glycemic impact of the carbohydrates.

1. Refined and processed carbohydrates, including both sugars and refined grains. "Sugar" can go by a lot of different names, (e.g. high fructose corn syrup), many of which are signs of a highly processed food. Here is a list of ingredients which essentially mean "sugar." Note that on this label we see "evaporated cane juice" - another name for sugar.

Processed starches often take the form of wheat or other flours. Processing grains or grinding them into flour makes them more glycemic. Note that the first ingredient in the sample label is "wheat flour." This almost always means "white flour," otherwise it would say "whole wheat flour". If the label doesn't say the grain is "whole" you can assume it isn't.

2. Sugar Alcohols - As noted previously, carefully check which sugar alcohol is in the ingredient list. This label has erythritol, which is a truly low-impact sugar alcohol, so that's a good one from the standpoint of low-carb eating.

3. Special Low-Carb Ingredients - There are some other special ingredients that are put into low-carb products to maintain taste or texture without raising blood sugar, such as artificial sweeteners. On this label we see inulin and wheat gluten. Wheat gluten is the protein part of the wheat. Inulin provides sweetness and texture. It's a good idea to get familiar with some of these special ingredients.

4. Partially hydrogenated oils are trans fats. Avoid any food with this ingredient.

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