Healthy food doesn't have a long lifespan. With the exception of honey, the wholesome foods that are best for our diet spoil at a relatively quick rate: breads go stale, oils become rancid, and butter turns sour. That costs money at the retail level.

One way the food industry tackles the problem is by adding hydrogen to vegetable oils. The process, called hydrogenation, turns liquid oils into solid fats, lengthening their shelf life and that of products made from them. These fats also have a high melting point, making them popular for deep-frying, and a creamy texture that gives better "mouth feel."

These trans-fatty acids can usually be identified on product labels as "partially-hydrogenated vegetable oils," "hydrogenated oils," or "shortening." Some trans fats are naturally found in meats and dairy products, but not enough to affect the health in a balanced diet.

Hydrogenated fats, on the other hand, may be found in foods that many people consume in quantity: deep-fried foods, stick margarines and some spreadable margarines, ramen noodles, liquid coffee whiteners, pastries, cakes, pie, microwave popcorn, snack foods, crackers, cookies, and French fries. In some cases, food manufacturers have moved away from their use, and some jurisdictions have banned trans fats in prepared foods, but it's important that you read labels and know exactly what you're eating.

A major problem with trans-fatty acid is the effect is has on cholesterol. The body naturally contains two types of cholesterol, manufactured by the liver: low-density lipoproteins, or LDL, commonly called "bad" cholesterol, and high-density lipoproteins, or HDL, known as "good" cholesterol. LDL delivers cholesterol to the body through the bloodstream, while HDL carries it away. The body needs a certain amount of cholesterol to stay healthy, as it's essential to cell health, digestion and hormones, and it helps to route nerve impulses to the brain. But if there's too much, the excess is stored on the arterial walls, where it can impede the flow of blood. If it blocks the artery, the result is heart attack or stroke.

In a healthy body, the LDL levels are low, while HDL levels are high. Trans fats switch this around, raising the levels of bad cholesterol and lowering the levels of good cholesterol.

Many products now trumpet "no trans fat" on their labels, but use caution. In the U.S., a food can be labelled "zero trans fat" if it contains less than 0.5 grams of trans fat per serving. The key is the size of the serving indicated on the label, and you may be getting far more than "zero" trans fat on your plate. It can be common for manufacturers to indicate serving sizes that make their products appear healthier: for example, prepackaged bowls of instant ramen noodle soups, popular as lunches because they just need boiling water added, frequently have nutrition labels that indicate a "serving" is only half a bowl. If you eat the whole thing, as most people do, you'll need to double the numbers, including any trans fat.

Of course, the healthiest diets keep all processed foods to a minimum. Eat fresh fruits and vegetables, lean meats and whole grains, and avoid packaged foods that contain too many ingredients you can't pronounce. Food that spoils is the healthiest food of all.