How do I know which fats are which?

January 4, 2008 4:40 PM

Nutrition label says food has 5 grams of fat, 3 of them are saturated. There is no other information. Would the other fat be trans, polyunsaturated, or monounsaturated?

This seems so simple but I can't find an answer on the net.

I decided to use FitDay to make sure I'm taking in the right amount of calories (and that they're from the right sources) while I try to build muscle. (Nothing seems to be happening and I'm pretty sure its cause of my nutrition)

But it asks for saturated fat, monounsaturated fat, and polyunsaturated fat. The nutrition label for the serving of milk I'm entering says it has 5 grams of fat and 3 of them are saturated...thats it. What about the other 2 grams? Fats have to be either saturated, polyunsaturated, monounsaturated, or trans correct?

posted by Defenestrator to health (7 comments total)

Trans fats represent a subcategory of unsaturated fats (either mono- or poly-), and they occur only rarely in nature. They're basically an industrial food product, and you won't find them in milk.

According to this page, 31% of the fatty acids in cow's milk are unsaturated, 29% monounsaturated and 2% polyunsaturated.
posted by mr_roboto at 4:56 PM on January 4

It's not trans. Those have to be broken out in the list.

(As a meta-comment, I would beware any tracking program that is trying to track at that level of detail.)
posted by smackfu at 4:57 PM on January 4

A clarification on the nomenclature used on that page: fatty acid chains are categorized according to the number of carbon atoms they contain and designated with a pair of numbers in the format Cn:m. The first number, n, represents the number of carbon atoms while the second number, m, represents the number of unsaturated carbon-carbon bonds. So if m is zero, the fat is saturated, if it's one, the fat is monounsaturated, and if it's greater than one, the fat is polyunsaturated.
posted by mr_roboto at 5:01 PM on January 4

Oh ok, I thought there was a way to get this information out of what was presented in the nutrition label. For example, if any fats are left unnacounted for, they are always monounsaturated, or something like that.
posted by Defenestrator at 5:16 PM on January 4

Trans fats ... occur only rarely in nature. They're basically an industrial food product, and you won't find them in milk.

This is false. Trans fatty acids are present naturally in small quantities in nearly all red meat and milk products (except skim milk). 2-8 percent of the fats in most beef, lamb, and full fat milk products are trans fatty acids. The quantities are not large enough for most people to worry about, but if you were truly trying to have a trans fat free diet, you'd have to go vegan.
posted by decathecting at 7:00 PM on January 4

Trans fats do not have to be mentioned on the label if one serving contains less than 0.5 grams.
posted by catseatcheese at 12:08 AM on January 5

The USDA nutrient database has detailed information about the nutrient composition of foods, at a detailed level far beyond what is required on the food label.

If you search for the composition of a cup of milk (sorry, can't figure out how to post the link here), you can see the breakdown by type of fat. It is so detailed that it shows the breakdown by type of fatty acid, indicated by the number of carbons in the chain and the number/location/type of double bonds. (Dietary "fats" are triglycerides, which each contain three fatty acid chains. These chains can differ by length and type; each triglyceride can contain a different mix; and each food contains a mix of different triglycerides.)

--A saturated fatty acid by definition has zero double bonds (ie, the carbons are completely saturated with hydrogens), so they are indicated by something like 16:0 or 14:0. The higher the number, the more the carbons, the longer the chain.

--Monounsaturated fats, which have one double bond, are indicated by 16:1 or 18:1, with the additional information of whether the double bond is cis- (indicated with a c) or trans- (indicated with t). According to this database, a cup of 2% milk has about 0.19 grams of trans fat.

--Polyunsaturated fats have more than one double bond, which can occur at different places, so you will see them labeled with not only the number of bonds, but also their location and their configuration (cis or trans). This is the idea of omega-3 and omega-6 polyunsaturated fatty acids. So if you see "18:3 n-3 c,c,c," it means a fatty acid with 18 carbons, three cis-double bonds, the first of which is at the third carbon.

Post if you have more questions - I just studied this for my qualifying exams and it would be great to share the info with someone other than my committee :)
posted by tiburon at 7:08 AM on January 5