I think I am one of the few people who actually reads those nutritional facts on the back of food labels. And sometimes when I do, I notice something rather odd (the following being just a hypothetical example, of course):
Basically, there seems to be a fat that is neither Saturated, Monounsaturated, Polyunsaturated or “Trans”. I know the FDA recently added trans, so the nutrition information would be complete. So what is left?
This could have been caused by rounding error. Say, for example, that there are 1.35 grams of each of the four types of fat. This amount would be rounded down to 1 gram each for the label. The total amount of fat would be 5.4 grams, which would be rounded down to 5 grams.
Cis. Double bonds between carbon atoms can be cis or trans, if each carbon is connected to a radical ® and a hydrogen (H). In a cis bond, both radicals are on the same side of the double bond; in a trans bond, they’re on opposite sides (H not drawn):
(each ==== represents a single bond, but using only one = looked horrible)
The majority of natural fats are cis; trans fats are much more prone to producing clogs, i.e., bad for your health, simply because the body isn’t anywhere near as efficient at using them, moving them, etc. - it doesn’t have the specialized tools it does have for cis fats.
Note that the example label is wrong: any fat will be cis or trans at any of its bonds which fulfill the condition in my first paragraph: a biunsaturated fat could be trans, trans, or trans, cis, or cis, trans, or cis, cis. Or, if one of the double bonds is in the terminal carbon, it would have a double bond that’s neither trans nor cis. Any difference between the total of saturated, mono- and poly- and the total fat would be due to method errors, but trans/cis measures something else.
Having worked in the food industry, including dealing with label information, I’m pretty sure that it is a rounding issue, as Jeff Lichtman noted. If I recall correctly, most numbers including fat, are rounded down. So 1.9 g of trans is rounded down to 1 g.
My understanding is that “saturated” and “unsaturated” cover the whole range of fats. “Saturated” means that the fatty acid chains have no double bonds, and “unsaturated” means they have at least one.
“Monounsaturared” and “polyunsaturated” are sub-types of “unsaturated”. “Monounsaturated” means that the chains have exactly one double bond, and “polyunsaturated” means they each have more than one. The two types comprise all unsaturated fat.
Trans-fats, as Nava discusses, relates to the particular arrangement around the double bonds in the fatty acid chains. Any trans-fat is by necessity also an unsaturated fat, because only unsaturated fats have double-bonds to be in a cis-or-trans isomer.
Cholesterol is not a fat – it’s a sterol. Its serum levels, however, seem to be affected by dietary fat levels.
I suspect, seemingly like most, that the OP’s label inconsistencies are due to rounding allowances.
Again, as Jeff Lichtman pointed out, cholesterol is not a fat. Cholesterols, which are sterols (a type of steorid with a hydroxyl functional group attached) are found in varying degrees in all animal fats, where they play a role in soluability of vitamins and minerals stored in the fats. Cholesterols are compounds which contain both lipids and proteins, but are of such small quantities even in very fatty foods that their overall contibution to the caloric content is negligible.
It looks like the label in the OP was breaking down unsaturated into 3 subcategories: mono, poly, and trans.
But if I were to see trans, saturated, and unsaturated as the lables, I would assume that the label was calling out trans and therefore not including it in the count for the more generic categoy, unsaturated (unless it was listed as a subitem, indented, and the sum made sense). In general, the lawyer in me will always assume that the specific overrides the general.
I am rather shocked to have to say that this is mostly false.
Cholesterol is a specific compound and, besides being a sterol, is also a lipid, and “contains” no protein at all. “Fat” is not really a scientific term, and is sometimes used to refer just to the commonest type of lipid, the triglycerides, however it is also commonly used to refer to lipids in general, which includes cholesterol and several other types of compound. It is true that there is very little actual cholesterol in foods (as opposed to other lipids which tend to produce cholesterol in the body), but there are other lipids that are not saturated, unsaturated, trans, or cis triglycerides.
And yes, trans and cis fats are both subtypes of (mono or poly) unsaturated fats. All unsaturated triglycerides will be either cis or trans. (Strictly speaking it is the fatty acids in them, of which there are 3 per molecule, that are saturated or unsaturated, and, if the latter, trans, or cis.)
My WAG is that the anomaly noticed by the OP is simply because the nature of some of the fat in the item is unknown.