Learn the science behind:
Yes, you can determine the nutritional value of a product, by sending it to a laboratory. But, there are other (cheaper) ways to do so. For instance, you can use some simple math, as well as trustworthy literature sources.
- Why determine the nutritional value of food?
- What is the nutritional value?
- Keep in mind: foods are variable
- Determining the nutrient content in three ways
- Determining energy content is a simple calculation
- Getting started
Why determine the nutritional value of food?
Aside from being legally required on a food label in most countries worldwide, the nutritional value also serves to help customers make choices around the products they want to buy.
Some people may be in search of products high in protein, or can’t handle high amounts of sugar. The nutritional value label on a product tells a consumer exactly what is in a product. A consumer can literally determine what the nutritional value of a food is for their body. Does it provide energy? Or does it provide certain components that are crucial for their health?
Legislation differs between countries as to what has to be included on a nutritional value label and how such a label should look like. In the EU the 1169/2011 directive describes requirements with regards to labelling.
What is the nutritional value?
The ingredient list simply tells you which ingredients a food contains. The nutritional value digs a little deeper. It then analyzes what these ingredients are made up of and groups these components.
First of, a nutritional value states how much energy a product contains. This is the amount of energy that a human body can get out of these ingredients. We all need energy on a daily basis to function properly.
Secondly, the nutritional value states which types of molecules are present in the food and how many. These molecules are split into functional groups. The most common molecules are:
These are macromolecules. Almost every food and drink contains at least one of these (except for pure water for instance). We humans need them to live. These ingredients are also the main energy source of foods.
Carbohydrates and fats can be split up into smaller groups of molecules. For instance, carbohydrates might be split into sugars, and fats can be split into saturated and unsaturated fats.
Want to learn more about carbohydrates, fats and proteins? We cover them in far greater detail in our Food Chemistry Basics course.
There’s more to good food than just proteins, carbohydrates and fats. We also need certain vitamins and minerals. These can also be found on labels.
Keep in mind: foods are variable
Before attempting to determine the nutritional value of a product, keep in mind that foods are highly variable. The less processed a product is, the more this is the case.
- An unripe vs. a ripe apple can make a huge difference with regard to the amount of sugar in the apple.
- Cow’s milk has a different composition in summer than it does in winter.
- Beef from a fat cow is different from that of a skinny cow.
- Cocoa harvested from one species can be quite different from that of another species.
- The leg of a chicken has quite a different fat content than the breast does.
- Broccoli stems contain different components that the flowers do.
As such, it is almost impossible to give very precise correct nutritional values for food. There will almost always be some variations, simply because you can’t analyze every apple from a batch and give it a different value. Often nutritional values are averages for a specific product.
That does not mean nutritional values are useless. They still provide clear differences between products, just be aware that it is not as exact a science as you might think it is.
Determining the nutrient content in three ways
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Determining the nutritional value starts by determining how much of each of the components your food contains. So how much proteins, carbohydrates, fats, vitamins, etc. does your food contain?
There are three main ways in which you can determine these:
- The analytical route
- The literature route
- Using some math
1) Analyze the contents in a lab
There exist a wide range of analytical methods that can be performed on foods to determine their nutritional value. Methods exist to determine the types and amounts of sugar, fats, etc. Laboratories will state which methods are required to get a full nutritional profile of a product.
All of the analyses required are chemical analysis techniques. These techniques tend to only use very small amounts of sample to make a determination. Knowing how variable products can be, it is important to make sure that this small sample size is actually representative of the product you’re testing.
Once you’ve prepped the sample, let’s have a look at the possible analytical methods involved. Keep in mind that there may be more options than the ones mentioned below.
Protein analysis – Determining nitrogen content using Kjeldahl
Foods tend to contain a lot of different proteins. It is virtually impossible to analyze how much there is of each protein, nor does it provide a lot of added value. That’s why most labels only require the overall protein content.
Proteins are some of the only molecules in food that contain nitrogen. As such, by analyzing how much nitrogen a product contains, you can calculate the overall protein content. There are two main analysis techniques used for this: the Kjeldahl method and the Dumas method.
Depending on where you live, you might also need to take into account the quality of the protein. Some proteins are more ‘complete’ than others. Some countries require you to correct the overall protein content with a separately determined factor (e.g. a PDCAAS score).
There exist a lot of different carbohydrates, from small to large. Unlike proteins, they don’t contain a unique atom. On the contrary, it is quite similar to fats. It’s why in a lot of cases, the carbohydrate content is etermined by taking the total mass of a product and subtracting all the other components (fats, protein, water, ash, etc.). What remains is assumed to be the carbohydrates.
If you do need to know exactly which types of sugars a product consists, it is possible to determine those using a technique called liquid chromatography.
Fat content analysis
Most of the fats in foods are the so-called triglycerides. An important property of fats is that they don’t dissolve in water. As such, they can be extracted from most products. This extraction method can be used to determine the overall content.
If you need to know exactly which tryglycerides are present in a food you will have to use a more advanced technique such as gas chromatography. This is however quite an expensive and complex technique.
2) Used published values from literature
Over time, a wide range of products have been analyzed for their nutritional content. When determining the nutritional value of your product, you might be able to use these existing values for your product.
A lot of countries have their own databases of generally acknowledged nutritional values for food products. The USDA, in the USA, has a very extensive, publicly accessible database. The Netherlands has one as well, as do many other countries.
Let’s start with the 2nd option: the literature route. In this case, no analysis of the actual final product is done. Instead, databases which contain a lot of data on nutritional values of all sorts of products are used.
3) Calculate your nutritional value
If your product is made with your own recipe and has a unique composition, you will not be able to find literature values for it. However, you may find the nutritional value of the ingredients that you used. If so, you can use those to calculate the nutritional value of your product.
You will have to know how much of your recipe is made up by each ingredient. It’s easiest to state this in percentages. Then, you can use these percentages to calculate how much of each nutrient your product contains.
As an example:
- You product is made of 25% ingredient A and 75% ingredient B.
- Ingredient A contains 10% fat and 50% carbohydrates
- Ingredient B contains 7% protein
- The overall composition will be:
- Fat: 10 / 100 * 25 + 0 =2,5%
- Carbohydrates: 50 / 100 * 25 = 12,5%
- Protein: 7 / 100 * 75 = 5,25%
These calculations can be quite simple and reliable if all you’re doing is mixing ingredients. However, if a lot of chemical reactions take place in your product, or if significant amounts of water evaporate, this no longer works well. Some molecules might have reacted and become something different for instance.
Determining energy content is a simple calculation
Once you know the composition of your product, you can easily determine the energy content of your food. The energy content of a food is determined by the amount components that your body can use to make energy. These are the three macronutrients, protein, carbohydrates, and fat, but also alcohol, polyols (strictly a type of carbohydrate) and fibers (also a carbohydrate type).
The energy content of a food is given in kcal (often referred to as Calories) and/or kJ (kilojoule). Converting from kcal to kJ is a simple set calculation
1 kcal = 4,18 kJ
Set conversion values
Research has shown how much energy our body can make from these macronutrients. We know that:
- 1 gram of fats provides 9 kcal of energy
- 1 gram of carbohydrates = 4 kcal
- 1 gram of fibers = 2 kcal
- 1 gram of polyols = 2,4 kcal
- 1 gram protein = 4 kcal
- 1 gram of alcohol = 7 kcal
Using the conversion factors above, you can calculate the energy content of your food by multiplying these values by the amount of each of the macronutrients present.
As an example, let’s look at imaginary product A. In the table below we’ve given how much fat, proteins, and carbohydrates this product contains per 100g of the product. By multiplying these values by the given conversion factors and adding up the result, you can the overall energy content.
|Content in the product (g/100g)||Energy content (kcal/g)||Energy in product (kcal/100g)|
So, if you want to determine the nutritional value of your product, start by deciding whether you will be able to find relevant data in existing literature. If so, you can use those to calculate the nutritional value of your food, sometimes requiring some additional calculations. If not, you will have to send your product to a laboratory for analysis.
If you need to determine the nutritional value because you’re scaling up production, you might want to read our guide to scaling up.
Liliana Krotz, Elena Ciceri and Guido Giazzi, Protein Determination in Cereals and Seeds, August-1, 2008, link ; for more detail on protein determination
RIVM, NEVO online, link ; Dutch database with nutritional values for wide range of products
University of Massachusetts, 6. Analysis of Proteins, link ; for more detail on protein determination
USDA, Food Data Central, link ; very extensive database with nutritional values of a wide range of products