How do nutritionalists measure the amount of vitamins, fats, proteins, and sugars in a food.


Forgot the question mark, “?*”

In: Chemistry


Let’s start with protein. We know protein to be ~16% nitrogen; thus, if we are able to obtain the amount of nitrogen, we can calculate the protein content. This is often done using the [Kjeldahl Method.]( Basically, sulfuric acid is used to digest the food. This helps to convert the nitrogen to ammonium ions. Next, NaOH is added to the mixture to convert the ammonium to ammonia gas, which can be separated and distilled to determine the mass. This information is used to calcualate protein content.

Now, fats. Most fats are insoluble in water (meaning they don’t dissolve). However, they DO dissolve in organic solvents like chloroform. Therefore, we can weigh a sample of food, put it in the chloroform, then take out the remaining food and weigh it. Because the fat should have dissolved, the difference in mass is most likely all fat.

Vitamins can be done through chromatography. Basically, it takes advantage of the fact that the chemical components of a food react differently with absorbent materials. You’ve seen a similar effect if you get paper wet that has ink on it; if the ink was purple, you’ll often see red and blue stains. This reflects the fact that the red and blue ink used to create that purple flow at different rates through a piece of paper. This can be done with food in a more complex process to obtain the quantities of each type of vitamin. The actual process for vitamins is called High Pressure Liquid Chromatography if you want to read more.

Sugar can be done using enzymes that digest sugars. You can use this rate of breakdown to determine if there are sugars and how many there are. This can be done through a photometer. Basically, you put a small sample in a tube. You mix it up and measure how much light it absorbs using this photometer that can tell light absorbance. Then, you put in the enzyme. You mix it up again, to let the enzyme break down the sugars. You then put it back into the photometer. Based on the amount of residue left behind after breaking the sugar down, the absorbance of that tube will have changed. You can use this increase in absorbance to deduce how much sugar originally existed. A sample protocol can be found [here](

Carbs are easiest. It’s assumed that after accounting for fat, protein, alcohol, etc. that the remainder must be carbs. If you take the original weight and subtract all these other masses, what’s left over is carbohydrates.

The title “Nutritionist” has no legal meaning. Any one call themselves that and then start preaching the benefits of drinking your own urine or getting all your energy from staring at the sun etc.

If you are looking for dietary advice avoid anyone and everyone who calls themselves a Nutritionist. What you are looking for is a Dietitian. Dietitian IS a protected title that requires a higher education and to be board certified to get.

So to directly answer your question of “How do nutritionalists measure the amount of vitamins, fats, proteins, and sugars in a food”, they don’t.

Mass Spectrometry, is not always useable… Just like theyre not officially forced to put an ingredient on a product label, food or other product, if its less than 5%, which is why you sometimes see 5+ different names on sugar on a product, in reality, it can be way more, sadly :*(