Q. What's the difference between the cooking oils that you buy at the regular grocery store and the higher-quality oils you find in specialty or health food stores? Is there really any difference when it comes to my health? Are they processed differently?

A. This is an excellent question, because the way oils are processed can determine how healthy they are for you. Most people don't even think about how seeds, nuts, olives, coconuts and other foods are turned into the oils they use for cooking. The mechanical process can be complex, and depending on the method used, can yield either a flavorless, nutritionally dubious oil with added chemical preservatives or a tasty, high-quality, nutritionally rich oil.

Let's compare the typical mass-marketed conventional cooking oils you purchase at your local grocery store with the higher-quality oils often found in health food stores.

Oil expert Udo Erasmus, author of "Fats That Heal, Fats That Kill," explains that conventional cooking oils "are highly processed, using manufacturing methods that are destructive to oil molecules. After oils are pressed or solvent-extracted from seeds and nuts, they are degummed, refined, bleached and deodorized. What many people don't know is that valuable "minor ingredients, including antioxidants, phytosterols ... and other oil-soluble beneficial molecules are removed, too. In addition, 0.5 to 1 percent of the oil molecules themselves are damaged during the processing." He points out that these damaged molecules can be far more toxic than the infamous transfats that, according to the Harvard School of Public Health, can double the risk of heart attacks. In addition, mass-marketed oils are often processed with harsh chemical solvents, and preservatives are added to prolong shelf life up to 48 months.

In contrast, healthier oils found at your health food store are often expeller- or cold-pressed. This means (in the case of seed oils, for example) that the seeds go through a chemical-free extraction process and no external heat is applied; the only heat produced in the process is naturally generated by extraction. The cold-pressing process is used to extract especially delicate oils, like flax oil, and temperatures are kept below 120 degrees F. These oils are sometimes refined with natural agents like citric acid — instead of the potentially problematic chemicals, like phosphoric acid, used in many conventional oils, and they have shorter shelf lives.