What is your guilty pleasure? Steak? Chocolate? Butter? No problem. You can turn each of these foods into a 99 percent fat-free product.

Here’s the bare-bones recipe: grind the fatty food in a blender. Add a cup or a few cups of water and ta-da, you have transformed the numbers.

Hey, I never said it would be tasty. But I do live up to my word. These things can be called 99 percent fat-free, according to the peculiar rules of nutrition advertising.

While you would never make food this way, or think such food is healthy, big companies do and they boldly advertise their claims. The government has allowed this to happen, and in turn, it has turned the simple, joyful act of eating into a mess of numbers and percentages. My math degree has finally come to use in the most absurd of places: it has allowed me to eat healthy.

We need to be informed as customers to make better choices. I’ll go through an example on milk and then summarize how other foods use misleading labels. I’ll end with some steps you can take to eat healthier.

How much fat is in 2% milk? 2 percent? 7 percent? Try 35 percent.

How much fat is in 2% milk? It should be 2 percent, right? But that’s not what the numbers really say. If you look at a nutrition label, you’ll see that milk has a daily value of 7 percent fat (and a whopping 15 percent of the dreaded saturated fat).

If you look closer, it’s even more confusing. You’ve been told by every health agency that what’s really important is fat as a percentage of calories. This is because calories indicate energy content, and it’s the distribution of how you get calories from fat, protein, and carbohydrates that matter. If you calculate percentage of calories from fat, you find that 2% milk is really 35 percent fat. That bears repeating: 2% milk is really 35 percent fat. Every dietitian and nutritionist knows it, but the label remains.

So where does the 2% milk-fat figure come from? This figure comes from a trick of cooking the numbers. It depends on the observation that milk is mostly water, which weighs a lot but has no fat or calories. To obscure the true fat, milk companies use the convention of calculating fat as a percentage of weight. To verify the figure, you can divide the grams of fat by the grams of the serving size in the nutrition facts. Tricky, isn’t it? The 2% is milk-fat by weight. But who eats by weighing their food?

The trick is particularly useful. Notice that as you add more water (or other non-fat, non-calorie ingredients) to a food product, you will increase the weight while keeping fat constant. This has the effect of reducing the fat by weight, even though the fat content and calories from fat remain the same. This is a tried and true method food companies like Kraft use to make food like salad dressings look healthy (see this video from an insider).

Here is how you can derive all the numbers on milk:

Nutrition facts from nutritiondata.com

Other misleading foods

Here is a sampling of products that claim to be low in fat using the “fat by weight” measure. When you look at them as “fat by calories”—the way nutrition people do—you’ll be surprised by how much fat there really is.

 
Fat by weight (%)
Fat as Percentage of Calories (%)

Creta Farms extra lean bologna (91% fat-free)
9
50

Hebrew National 97% fat-free beef franks
3
33

Albertson’s vegetarian refried beans (98% fat-free)
2
15

Mission 96% fat-free heart healthy whole wheat tortillas
4
14

Progresso 99% fat-free beef barley
1
13

Chef Boyardee 99% fat-free beef ravioli
1
9

Source: calculated from product websites and nutrition labels

This is just the tip of the iceberg! For whatever you eat, look closer.

How much fat should we eat?

The U.S. government suggests less than 65 grams per day, which is based on having less than 30 percent of calories on a 2,000 calorie diet. William P James, head of the International Obesity Task Force, explains the real historical motivation of this figure. It was essentially made up as a compromise. The real figure of 15 percent was more appropriate but felt to be overwhelming, given than Americans ate 40 percent when the guidelines came out.

Fat is controversial so make up your own mind. The point is you have to do a little bit of research beyond the government guidelines to get the scientific recommendations. And don’t blindly trust claims by the food companies!

Steps you can take to reduce fat

Should you start buying things like fat-free half-and-half or fat-free cheese? That’s a question I lack the knowledge to answer, except that I would contend those things are not really food. They are imitation food, designed to achieve a specific nutrition goal and make an advertising claim. That’s how I felt after reading Michael Pollan’s latest book In Defense of Food.

With that in mind, here are two strategies to get you started:

–If you’re big on labels, then ditch the nutrition claims and simply calculate the percentage of calories from fat. Divide the “calories from fat” by the “calories” on the label.

–If you’re like me, and hate going through that kind of work, then consider making better food choices. Avoid the imitation food products which identify themselves with nutrition claims. Eat the natural fat-free foods–fruits and veggies–while limiting or avoiding coconut, avocado, cooking oils and the like. Be careful about lean meats, particularly sliced meat—much of its weight is water so the product will be advertised as lower fat than it is.