Questions & Answers

May 25, 2009, 8:04 pm

Reply to: Where's the Rest of the Fat?

User sianna writes:

I have a question regarding fat and the nutrition labels…

Take the "New York Strip Steak Grilled (Home Made)" label for example. It states that there is a total of 8 grams of fat and it shows that there is 3 grams of saturated fat. Where is the other 5 grams of fat?

Surely it's not mono or poly unsaturated fat, or worse yet a trans fat, some labels show all the fats and the grams still don’t always add up to the total fat.

So what's the deal is there some secret fat out there? It doesn't matter what label I read the different types of fat never seem to add up to the total fat. Shouldn't they add up?

Our answer:

As deeishealthy says, "Good question."

In theory the math should work like this:

saturated + monounsaturated + polyunsaturated = total fat

(Trans fats are not included within that calculation, because trans fats are already included within the values for monounsaturated and polyunsaturated fats.)

But as I look into an answer to this question, it gets more and more complicated, requiring an understanding of what constitutes a lipid (fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, phospholipids, etc.) and the varying ways that total lipids and individual fat components are measured when a food is analyzed for nutrition data. We also have to consider basic rounding and Nutrition Labeling and Education Act (NLEA) requirements compared with the USDA data set.

I can see why the standard recommendation is simply to limit your saturated fat, eliminate your trans fat, and keep your total fat within a healthy target range. It would drive the average person crazy trying to keep track of any more than that, for not much added benefit.

Because of these simplified recommendations (and because the hard data just isn't available for most foods) NutriMirror doesn't distinguish between monounsaturated and polyunsaturated fats in our reports.

As for the New York Steak example, that data did not come originally from the USDA database, and we don't have the mono/poly information. So let's look at USDA data for 3 ounces of broiled beef top loin instead:

• Fatty acids, total saturated -- 2.534 g
• Fatty acids, total monounsaturated -- 2.672 g
• Fatty acids, total polyunsaturated -- 0.242 g

The USDA data for the top loin example above has a total fat content of 6.53 grams, so even here the math doesn't seem to add up. The three classes of fat only give us 5.448 grams, leaving about a gram unknown. The difference likely comes from the method used to measure total fat, which includes the weight of all lipid components (as mentioned above) and not just strictly the three classes of fatty acids. And then as far as I can tell, the NLEA requirements for food labels call for a different method of measuring fats ... I'm not sure where the discrepancies would come from there, but I'm not surprised they exist.

But again, the bottom line: simply by limiting your saturated fats, keeping your trans fats as close to zero as possible, and keeping your total fats in the healthy range, you should do fine without having to worry at all about the rest of the math.

Previous | Next Journal Archive