Why "0 g Trans Fat" on a Label May Not Mean None

"0 g" next to Trans Fat on a Nutrition Facts label looks like a guarantee, but it is really the result of a rounding rule. Under FDA labeling requirements, a food can contain a small amount of trans fat per serving and still be labeled 0 g. Here is how that works, and why it matters less today than it once did.

1. How trans fat must be listed

The FDA's compliance guide for trans fat labeling, which restates the requirements of 21 CFR 101.9 in plain language, sets out the format:

• Trans fat is listed as "Trans fat" or "Trans" on its own line under saturated fat.
• It is shown in grams per serving.
• Below 5 grams, it is rounded to the nearest 0.5 gram. Above 5 grams, it is rounded to the nearest gram.
• If a serving contains less than 0.5 gram, the amount, when declared, must be expressed as "0 g."

The FDA required trans fat on the label through a final rule published on July 11, 2003, effective January 1, 2006.

2. What "0 g" can hide

Because anything under 0.5 g rounds to zero, "0 g" means less than half a gram per serving, not necessarily none. That is accurate for a single serving, but it can add up when you eat more than one.

Here is a worked example for a snack with 0.4 g of trans fat per serving:

At three servings, the actual amount is more than double the 0.5 g threshold, even though every serving's label reads 0 g. If the manufacturer had labeled a larger serving that contained 1.2 g, the rounding rule would have required it to be shown as 1 g.

This is one more reason to look at the serving size and count how many servings you actually eat.

3. When "0 g" is not shown at all

The guide describes one exception. For conventional foods with less than 0.5 g of total fat per serving, the "0 g" trans fat line is not required, as long as no claims are made about fat, fatty acids, or cholesterol. In that case, the label may instead carry the statement "Not a significant source of trans fat" at the bottom of the nutrient table.

Dietary supplements follow different rules. The guide says that when a supplement contains less than 0.5 g of trans fat per serving, trans fat must not be listed on the Supplement Facts panel at all.

4. Trans fat is part of total fat

The guide also notes that adding the trans fat line did not change the Total Fat line, because trans fat is already included in the Total Fat amount. So the trans fat figure is a breakdown of total fat, not something added on top of it.

5. Why the FDA wanted it on the label

The FDA explains that eating trans fat raises LDL ("bad") cholesterol in the blood, and that elevated LDL cholesterol increases the risk of heart disease. That is why trans fat must be declared on the Nutrition Facts label.

6. Where trans fat comes from now

The bigger change since then has been in the food supply. According to the FDA:

• Most trans fat in foods used to come from partially hydrogenated oils (PHOs), made by a process that turns vegetable oil into a solid fat.
• In 2015, the FDA determined that PHOs are no longer "Generally Recognized as Safe."
• For most uses, June 18, 2018 was the date after which manufacturers could not add PHOs to foods, and the FDA extended the final compliance date to January 1, 2021 to let products move through distribution.
• In 2023, the FDA removed outdated references to PHOs from its regulations.

The FDA also notes that trans fat occurs naturally in foods from ruminant animals, such as milk, butter, cheese, and meat, and that its PHO actions did not affect these natural sources. So a "0 g" label on a dairy or meat product may still reflect small natural amounts below the rounding threshold.

7. A quick way to read the trans fat line

1. Check the serving size and how many you will eat.
2. Treat "0 g" as "under 0.5 g per serving," and multiply if you eat several servings.
3. Remember natural sources. Dairy and meat products can contain small natural amounts.

8. Key takeaways

• FDA rules require trans fat under 0.5 g per serving to be shown as "0 g."
• Below 5 g, trans fat is rounded to the nearest 0.5 g; above 5 g, to the nearest gram.
• Several servings of a "0 g" food can add up to more than a gram.
• Trans fat is included in the Total Fat figure, not added to it.
• The FDA ended most use of partially hydrogenated oils by 2021, but natural trans fat remains in dairy and meat.

This article explains how to read labels and is not medical or dietary advice. Talk to a doctor or registered dietitian about fats in your diet, especially if you have high cholesterol or heart disease.