Trans Fat - Presence in Food

Presence in Food

A type of trans fat occurs naturally in the milk and body fat of ruminants (such as cattle and sheep) at a level of 2–5% of total fat. Natural trans fats, which include conjugated linoleic acid (CLA) and vaccenic acid, originate in the rumen of these animals. CLA has two double bonds, one in the cis configuration and one in trans, which makes it simultaneously a cis- and a trans-fatty acid.

Animal-based fats were once the only trans fats consumed, but by far the largest amount of trans fat consumed today is created by the processed food industry as a side effect of partially hydrogenating unsaturated plant fats (generally vegetable oils). These partially hydrogenated fats have displaced natural solid fats and liquid oils in many areas, the most notable ones being in the fast food, snack food, fried food, and baked goods industries. They can only be made by cooking with a very high heat, at temperatures impossible in a household kitchen.

Partially hydrogenated oils have been used in food for many reasons. Partial hydrogenation increases product shelf life and decreases refrigeration requirements. Many baked foods require semi-solid fats to suspend solids at room temperature; partially hydrogenated oils have the right consistency to replace animal fats such as butter and lard at lower cost. They are also an inexpensive alternative to other semi-solid oils such as palm oil.

Partially hydrogenated plant oils, and also non-hydrogenated plant shortenings made from naturally saturated palm oil, coconut oil and palm kernel oil, can be used to replace animal fats in foodstuffs for adherents to the dietary rules of Kashrut (kosher) and Halal, and for vegetarians and vegans.

Up to 45% of the total fat in those foods containing artificial trans fats formed by partially hydrogenating plant fats may be trans fat. Baking shortenings, in general, contain 30% trans fats compared to their total fats, whereas animal fats from ruminants such as butter contain up to 4%. Margarines not reformulated to reduce trans fats may contain up to 15% trans fat by weight.

It has been established that trans fats in human milk fluctuate with maternal consumption of trans fat, and that the amount of trans fats in the bloodstream of breastfed infants fluctuates with the amounts found in their milk. Reported percentages of trans fats (compared to total fats) in human milk range from 1% in Spain, 2% in France, 4% in Germany, and 7% in Canada and the United States.

Trans fats are used in shortenings for deep-frying in restaurants, as they can be used for longer than most conventional oils before becoming rancid. In the early 21st century, non-hydrogenated vegetable oils that have lifespans exceeding that of the frying shortenings became available. As fast-food chains routinely use different fats in different locations, trans fat levels in fast food can have large variations. For example, an analysis of samples of McDonald's French fries collected in 2004 and 2005 found that fries served in New York City contained twice as much trans fat as in Hungary, and 28 times as much as in Denmark (where trans fats are restricted). At KFC, the pattern was reversed with Hungary's product containing twice the trans fat of the New York product. Even within the US there was variation, with fries in New York containing 30% more trans fat than those from Atlanta.