Net carbs, sugar, dietary fiber, sugar alcohols, starch … what, where, how? What’s the difference and how do you find them on a nutrition facts label?
In the last 3 parts of this blog series (part 1, part 2 and part 3), we’ve learned pretty much about how a nutrition information panel is built up and what purpose it serves and we had a look at some analysis methods used in this context. In order to obtain appropriate data for a nutrition facts label, you have to break down the food to its individual components first so that you can separately determine the amount of each macronutrient. We’ve learned how to determine the fat content, how to calculate the energy content (’the calories’) on the basis of the total amount of macronutrients and that it’s called physiological energy value and that these values are significantly more accurate and more meaningful than some people might claim.
Today it’s all about a macronutrient that creates a great deal of confusion when it comes to the respective values in a nutrition information panel. Here, people juggle with terms such as ‘usable carbs’ (also called ‘net carbs’), sugar alcohols, sugar, polyols – and what about dietary fiber?
What are carbs?
Firstly, we have to define the term ’carbohydrates’ more clearly. In general terms, ‘carbohydrates’ refer to so-called saccharides. Here, it doesn’t matter whether we’re talking about monosaccharides (e.g. glucose), disaccharides (e.g. sucrose (retail sugar), lactose) or polysaccharides (e.g. starch, dietary fiber) – all of them have at least one saccharide building block (figure 1) and belong to the group of carbohydrates.
However, there are significant differences between those different types of saccharides: e.g. dietary fiber and starch are metabolized in very different ways in the human body. But why is that the case?
Dietary fiber and starch both are polysaccharides, that means, they consist of a huge (mostly thousands!) amount of individual saccharide units which are linked together by a chemical bond. The big difference here is the type of chemical bonding: starch has a different bonding than dietary fiber – and our human body is only able to break up the bonding type in starch. In order to make polysaccharides easily digestible, we have to break the long chains apart to get individual building blocks, the monosaccharides. This is done by our digestive system using enzymes. We can directly sense this effect of enzymes if we chew starchy food, let’s say rice, intensively and for a long time, and suddenly we notice that it tastes much sweeter. Amylase, an enzyme contained in saliva, has broken down the starch into glucose – which has a sweet taste!
The bond in dietary fiber holding together the building blocks can’t be broken by the human digestive system, or at least this proves to be very difficult. For example, we are not able to digest cellulose in grass (which also consists of glucose units!) – in absolute contrast to cows, which as ruminant animals are able to gain even the last remainder of energy from one blade of grass, whereas we’d excrete it undigested.
We’ve already brought up the subject in part 1 of this series. Due to the different level of usability of carbohydrates by the human body, net (usable) carbs and non-usable carbs (dietary fiber) are now considered separately from each other and listed in separate lines on a nutrition facts label. In Europe, the dietary fiber is presented as a separate item on the label. The net carbs are further itemized as sugars and, as the case may be, as polyols (more on this later).
That’s handled differently in the US: here you’ll find the total carbs, which are split up in dietary fiber, sugars and polyols.
Both tables have got a point as the information you can draw from them is of course the same. But you must be aware of the differences, otherwise you’ll wonder with the next journey to the US why the broccoli all of a sudden has much more carbs than in Germany ….
Take a small model calculation and you’ll directly recognize the differences (table 1): Let’s take a food with 50g total carbohydrates. 30g of that is dietary fiber, so there are still 20g left for net carbs. 15g from those net carbs is usable sugar (glucose, fructose, saccharose, lactose …) and the remaining 5g is starch.These 5g starch won’t be shown in the table – but they do exist and are just hidden behind figures.
Both classifications, however, feature some shortcomings, especially where not all values are listed.
In Europe, there are still food labels around where no fiber is listed. It is unclear whether the value given for carbohydrates is just the value corresponding to the net carbs and the dietary fiber may have simply been ‘embezzled’, or whether we’re dealing with the total amount of carbohydrates. The labeling system in the US does not always include the term ’net carbs’; here, you need to calculate the value for net carbs by yourself. The total carbohydrates (in this case 50g) minus dietary fiber (30g) = 20g net carbs. There’s no extra line in this labeling system for starch; if you want to know this value, you have to calculate it anyway: net carbs (20g) minus sugar (15g) = 5g starch. This value, however, isn’t generally an issue on a low-carb diet because ALL net carbs are converted into glucose.
Table 1: Different breakdowns of the carb content in Europe and US
|Europe labeling||US labeling|
|carbohydrates||20 g||carbohydrates||50 g|
|– sugars||15 g||– sugars||15 g|
|dietary fiber||30 g||– dietary fiber||30 g|
|– net carbs||20 g|
Is dietary fiber really not digestible?
For a long time it was thought that dietary fiber cannot be digested at all and is just ‘ballast’ for the human body. An assumption that has long been surpassed.
First of all, one must differentiate between soluble and insoluble fibers.
Soluble fibers include e.g. fructans such as inulin, polyuronides such as pectin, alginate, agar and carragheen, raffinose (in legumes) and polydextroses.
Insoluble fibers include e.g. celluloses (food fibers in vegetables, grain, fruits and nuts), lignin, xanthan and resistant starch, yet some of the celluloses are partly soluble in water.
Whereas insoluble fibers can be metabolized in the human body only very poorly, soluble fibers are fermented in the colon in significant amounts and also provide energy. However, fiber is not broken down into sugar building blocks (which you would have to consider in your carbohydrate count), but into short-chain fatty acids. The physiological energy value of dietary fiber is set to be 2 kcal/g and serves as mean value for the different fiber types. Theoretically, you would have to add dietary fiber to the total fat count and not to the total carb count – although only partially, as one gram of fiber doesn’t yield one gram of fatty acids, but considerably less – the fermentation process additionally produces gases and other metabolites, which cannot be used by the human body.
Regardless of the fermentation process in the colon and the use of energy in the body, fibers increase the volume of the food mass (chyme) in the intestinal tract, they delay insulin response after a meal and increase the feeling of satiety, so that on the whole it can be assumed that they have a positive impact on health. 
Current nutrient calculations consider the energy value of fiber and include it in the total energy value of the respective food item. 
To sum up: Even though fibers can be partly converted into energy in the human body, they are not included in the total amount of net carbs.
Problem case polyols (sugar alcohols):
If sugar alcohols such as maltitol, sorbitol, xylitol, isomalt or erythritol are used in foodstuffs, a further subitem has to be listed as part of the carbohydrates, which is mostly referred to as ‘polyols’ or ‘polyhydric alcohols’. Here, the European food labeling regulation is not ideally suited as the different sugar alcohols are metabolized in a very different way by the human body. While maltitol and sorbitol are quickly absorbed through the intestinal walls and strongly affect the blood sugar level, xylitol is only very little metabolized and erythritol is not metabolized at all. Depending on which type of sugar alcohol is used in the product, the value for sugar alcohol can be either subtracted from the total carbohydrate count or not, or only partly. Some producers have recognized this problem and list the value for net carbs separately. So always look at the list of ingredients first and find out which type of sugar alcohol is contained. If you read erythritol, you can subtract its value given from the total carbohydrate count as a whole.
How is the carb content analyzed?
Whereas the content of protein and fat in food is always calculated absolutely (e.g. fat is isolated and weighed later on), this is not easy to be done with carbohydrates. If a complete analysis of the nutrients in a food is carried out, you determine all absolute values per 100g of specimen first (fat, protein, sodium nitrate, ashes, water content). We’ve already learned about how to analyze fat. After that, the sum of all absolute values is deducted from the 100g and what you get (as the difference) is the value for the total carbohydrates – including dietary fiber. In our example in table 1 this would total to 50g. But this value is not sufficient for us, after all, we wish to know how big the amount of net carbs is.
Now things start to get exciting: As we’ve just learned, dietary fibers and net carbs are very similar when we look at their structure and differ only in the type of bonding. This means, it’s very difficult to break them apart. There are, nevertheless, some analysis methods which are suited to further split up the total carbohydrates:
- HPLC analysis of sugars: monosaccharides and disaccharides differ from starch and fiber in size and this knowledge has been put to use for lab work. In an HPLC analysis, the dissolved sample is supplied through a specific pipe with a porous layer on the inner surface. This process separates the molecules from each other according to their size so that they can be quantified. So that’s where the value for ‘sugar’ originates from on a nutrition facts label. It includes in general glucose, fructose, saccharose and lactose.
- Enzymatic breakdown to analyze dietary fiber: according to this method, we take advantage of the fact that the strong bonds of saccharides in fiber cannot be split off by some enzymes, though, this works perfectly with starch. Here, we use exactly the same enzyme as our bodies use to break down starch: amylase. You simply add amylase to a solution of total carbs in a given sample. Then sit back and wait while the enzymes are busy doing their job and have finally broken down the long chains of starch molecules into small monosaccharides. The smaller molecules can be separated again and the amount of the residual fiber can easily be determined.
The second method, though, reveals some shortcomings and has been revised again and again in recent years [2, 3]. For example, certain soluble fibers such as inulin and oligofructoses are included to some rather poor degree: if foods contain significant amounts of those fibers, the value for dietary fiber is too low using this traditional analysis method – and the value for carbs (net) turns out to be too high.
A good example to illustrate this problem is the carb content in sunflower seeds containing inulin.
If you have a closer look at the nutrition facts of different manufacturers, you’ll find values for net carbs that vary from 2g – 20g!
Newer, more accurate analyses cover all types of fiber in a food and show, however, that sunflower seeds in general include very few net carbs, which are between 2 – 4g / 100g depending on the type.
This also applies to many other seeds, and to oilseeds in particular!
We have frequently been asked how come that our LCHF Seed Wonder contains virtually ZERO carbs (according to lab results < 0.1 g, which means that the carb content is below the detection limit), even though one of the main ingredients (sunflower seeds) does contain 20g carbs. Putting aside the fact that we chose a German accredited laboratory to carry out the food analysis of our bread (analysis see product image), here the figures once again in black and white –
Nutrition facts of sunflower seeds, measured according to a newer, more accurate method (in German):
If you take a look at some more seeds with even fewer carbs (flax seed) and consider the water content in bread and the measuring limits of the analysis methods, the value for our LCHF Seed Wonder cannot be put in doubt at all.
The carb content on nutrition panels has the greatest potential for confusion. However, if you know the systematics behind and possible country-specific differences, you can obtain the information needed relatively fast.
When following a low-carb diet, only the amount of carbs is of interest that generates an insulin response in our bodies. According to the European regulation for food labeling, we normally get this value directly from the total carbohydrate count, whereas in the US, this value is shown as ’net carbs’ on a nutrition facts label.
When it comes to sugar alcohols, it very much depends on the specific type of sugar alcohol. While erythritol has no impact on the blood sugar level, other sugar alcohols have to be partially taken into account.
Although dietary fibers contribute, in a roundabout way, to the body’s energy balance, they can be neglected in the carb count.
In the next part of this series, we’ll learn something about the last items on a nutrition facts label: the protein and salt content. In addition, we take a closer look at how we can best benefit from the data given on a nutrition facts label to follow an optimal diet and how best to handle contradictory manufacturer’s data, and moreover, how we can manage to keep track of our macronutrient intake with as little effort as possible and, lastly, what role a calorie deficit plays when trying to lose weight.