Calculating the nutrients loss in food processing
July 25, 2021
The purpose of this article is to describe the method we have used to calculate the nutrient loss after food processing from the nutritional composition of raw and processed foods.
We analyzed the foods available in the public databases that we use on this site and we offer the results of our calculations in our website, as part of the nutritional information of each food.
The direct comparison between the nutritional composition of a raw food and that of the processed food itself does not provide us with explicit information on the loss of nutrients of this food after processing.
We know that water, energy, carbohydrates, proteins, lipids and ashes can be reduced after food processing, and that only water, lipids - and therefore energy - can increase; For example, when a dry food is rehydrated or some grain is cooked in water, or cooking oil is added when roasting or frying). But in any case, the nutritional composition of raw foods, as well as that of the processed foods, is referred to 100 gr. of food.
Thus, when we compare a raw food with the same processed food, we can see that it increases the percentage of many micronutrients, which can be perceived as a contradictory fact or at least can be a little frustrating if for certain nutrients we do not know how much has really been lost.
If we take the next nutrients that are expressed in GR units: water, carbohydrates, proteins and lipids, which add up to 100gr ± 2 gr, for each food, we observe that:
a/ when the percentage of each of them decreases, the percentage of the others increase proportionally.
b/ when the percentage of water increases, the percentage of the others decrease proportionally.
If we want to know which is the nutrients loss after food processing and we only have the nutrients proportions in 100 gr of raw food and in 100 gr of the processed food, firstly we need to find the coeficient M that must be applied to the processed food mass, so we could get the mass gain/loss of the food after processing.
To do this we establish that:
case a / (water loss) the nutrient that has increased the most, which is really the one that decreases the least, after food processing, has the same mass that it had in raw foods.
case b / (water gain), the nutrient that has decreased the least, after food processing, has the same mass as it had in raw food.
We do not include in our statement the nutrients that can be added during food processing: water and lipids and therefore also energy.
We also do not include micronutrients whose mass gain or loss is not significant for being the reference for calculating the gain or loss of mass of other nutrients.
To do so we filter the results by selecting the minor S coeficient:
S = (Ar - Ap) / (Ar + Ap )
* Ar: raw food nutrient average
* Ap: processed food nutrient average
and the M coeficient maximum, for mass gain or loss (depending on if it exists water loss or gain).
Therefore, we will make an approximation to the actual values of nutrient loss, as our results will show a minimum value of the loss of each nutrient, but will not show the maximum value; therefore, the loss could be greater. For our purpose, this information is sufficient for us.
After finding the M coeficient, we can apply it to each micronutrient of the processed foods to obtain the amount of each nutrient after food processing (after mass loss or gain), according to the nutritional composition of the compared foods.
Food database: > sections
Data Type:SR Legacy Foods (April 2018), Food Data Central (US), fdc.nal.usda.gov
SR-Legacy contains data on 7,793 food items.
At DietNutrientsCalc site we have discarted almost all branded foods, so that there are 6761 foods left.
Groupping Foods: > sections
The first step was identifying all foods that were related to the same food but differently processed, and group them into a single food which had different processing methods.
To do this we selected firstly all foods that included 'raw' keyword in their food name. We found 1411 foods like this.
Secondly, we identifyied 36 food processing methods found in the whole database:
Food processing methods > sections
After groupping foods by processing method, foods list decreased because all food names which didn't contain the required processing method keywords where discarted.
The list of foods has also been reduced because we have discarded some of the selected foods that did not have a positive value for water, carbohydrates, proteins and fats; These are the nutrients expressed in GR that we use to check that we start from approximately 100 gr of raw food.
So, finally, food processing transitions and foods were left to include into our calculations.
Results (all food categories): > sections
The following table shows the average nutrient loss of each food processing method, including foods from all food categories.
Results (for each food category): > sections
We observed that nutrients loss average could be really different between food categories, causing information loss.
So we decided include in this article the results for each food category, with the purpose to get the results as accurate as possible, considering the limitations of our aproximation method.
Calculation method applied to a single food : > sections
So far, we have shown the results when we apply this calculation method to a set of foods and we calculate the average food loss for each processing method. Nutrients loss average calculate for each food category is more accurate thant that obtained from all foods, because of difference between the nature if foods is smaller. But the most accurate result only can be obtained from a single food; if for a given food we search all foods that are the same food but processed in a different way, result is much better.
We have added to our website a page that does exactly this. You can find it at: Nutritional Charts.
In this page, select a single food and submit; Page will search for all foods that are the same food but differently processed and will let you compare each processing method of that food between each other, and with the 'raw' one.
The comparison is displayed as a set of bar charts.
If you want the graphs to show this information, when comparing two or more processed foods, check option 2 under "Food Comparison Options" and submit the form.