QUESTION: A seminar at a local natural-food store said that when you open a bottle of cooking oil, such as corn, safflower, canola or peanut oil, it allows air to enter, and the oxygen begins spoiling the oil. It is not like we are going to die from this, but it is one of the hidden causes of disease. They advise that we refrigerate all cooking oils after opening. I read the label on bottles of vegetable oil, and it makes no mention of any need to refrigerate after opening.
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– A.I., Sun City, Ariz.
ANSWER: It is true that air gets in when you open the bottle, and that the oxygen in the air can participate in oxidation reactions associated with spoilage. However, under normal circ*mstances, this is a slow process, and there is no evidence that your oil (or your body) is at risk.
You can keep oils at room temperature, but you should follow some simple guidelines: Stored oils should be kept out of the sunlight and away from heat. And always keep the container sealed when it is not in use. If you buy more than you tend to use in about four months, split the large size into smaller portions, refrigerating the unused bottles until needed.
There’s no problem storing oil in the refrigerator, but if you decide to go that route, be sure to have a tight seal on the container to keep the oil from picking up undesirable refrigerator odors. Some oils may become cloudy when refrigerated, but this disappears when they return to room temperature, and this is no reflection on the oil’s wholesomeness.
Oils will go rancid if they are mistreated or stored in the wrong way. Rancidity occurs when the oil reacts with oxygen, and aside from giving foods an off-taste, oxidized oil does represent a health risk if you consume it.
The greater the degree of an oil’s unsaturation (double bonds), the greater the tendency to oxidize. Omega-3 oils, such as fish oil, have four or five double bonds, so they are very susceptible to spoilage. That helps explain why discarded fish lends a special nasty aroma to the trash.
Our bodies have to deal with unwanted oxidation on a regular basis. We have a series of systems designed to neutralize these events before they cause any problems. The antioxidants in whole foods empower this first-alert system. Eating well makes it so that we don’t have to sweat the small stuff.
Can you explain to me why food labels can say nonfat but then sometimes have upward of 20 grams of sugar? How can I be sure I’m being healthy when, say, my Red Vines say that 1 serving is 140 calories, no fat, and yet has 16 grams of sugar? Sugar just becomes fat anyway, right?
– A.S., Davis
The body has a constant need for energy, but we eat only a few times a day. Most of the time, we eat quite a bit more than we need at a given moment. The human machine has a finely tuned ability to put excess calories away until needed.
We store energy as fat, the most concentrated form of storage we have. (If we stored excess energy as carbohydrate or protein, it would take up more than twice the space.)
This efficient mechanism turns all sources of excess energy into fat, but there is another system designed to get the fat out into the bloodstream to fuel bodily processes as needed. Food labels deal with what is in the food, not what happens once it is in the body.
Besides, much depends on the context. If you had your Red Vines during a 15-minute bike ride, hardly any of it would end up as fat.
Ed Blonz, Ph.D., is a nutritional scientist based in Northern California. General-interest questions about nutrition can be mailed to: Ed Blonz, Focus on Nutrition, P.O. Box 120191, San Diego, CA 92112-0191, or sent via e-mail to UTFood@blonz.com
