(Originally published as a newsletter for The Dragontree Holistic Day Spa)
Most of the fats we eat are subject to a constant process of breakdown called oxidation. When fats become oxidized we call them “rancid.” A 2007 Israeli study stated that oxidation of fats is “one of the major degradative processes responsible for losses in food quality.” (1) It leads to the formation of free radicals and “advanced lipid oxidation endproducts” (ALEs) – chemicals that are toxic and damaging to our cells. Consumption of rancid fats appears to increase our risk of cancer and atherosclerosis (hardening of blood vessels). ALEs cause inflammation in the circulatory system, gut, liver, kidneys, and lungs.
I’ve found that many people don’t really know what rancid oil smells like. To me, rancid oils smell sort of musty or cardboardy. Sometimes they have a slightly sour “high note.” Here’s a good way to get a sense of it: The next time you buy some fresh cooking oil, make sure it was bottled fairly recently, since occasionally oil is already rancid when you open the bottle. Also make sure it has no added antioxidants, such as vitamin E, BHA, or BHT (since these help prevent rancidity and the experiment won’t work). Open it and take a whiff. There should be a clean, light smell – no mustiness. Put an ounce or two into a glass and leave it uncovered near a window. Unless your house is very cold, within two weeks (but probably sooner) it should be rancid. Smell it every couple days and you may detect the progression. The rancid smell is not necessarily glaringly unpleasant, which is probably why many folks aren’t aware of it. We have learned to accept a certain degree of rancidity as normal.
Another good place to learn the smell of rancid oil is at your local day spa or massage therapist’s office, where the sheets will inevitably have been saturated repeatedly with oil, perhaps over several years. Don’t worry, they’re clean and harmless, but the rancid smell is often persistent (especially at our spa, since we always use natural and scentless detergents).
The reason I had you leave the oil exposed to air and light is that these are the two main factors in rancidification. Heat, salt, water, bacteria, and molds in oils also contribute to rancidity. Besides cooking oils, other fat-containing foods are also susceptible to rancidity. These include seeds and nuts, as well as oily and starchy snacks such as crackers and potato chips. Rancid crackers are very common. Among nuts and seeds, all can go rancid, but I seem to smell oxidation most often in walnuts, sunflower seeds, pecans, pine nuts, and brazil nuts.
When nuts, seeds, and grains are intact in their shells or husks, they have some natural protection from oxidation. Once they’re shelled/hulled, their oils turn rancid more quickly. When they’re chopped or cracked, the oxidation process happens even faster. I have thrown away several jars of rancid almond butter that didn’t get eaten quickly enough. Early in my medical training, I studied the biology of cancer with a great professor at UMass Amherst named Dr. Albey Reiner. I’ll never forget how adamant he was about avoiding rancid oils. He once said, “If you ever put a bad nut in your mouth, I don’t care if the Queen herself gave it to you, spit it out.”
Some foods resist rancidity better than others. Flax seed goes rancid quite fast after being ground, so I always tell patients who like ground flax to buy it whole, grind just what they need each day, and throw out (or at least refrigerate) any extra. Saturated fats – those that stay solid at room temperature (such as coconut oil, butter, and lard) – are less susceptible to rancidity. Polyunsaturated fats – the ones that stay liquid even when cold (most vegetable oils) – are more susceptible to rancidity. Monounsaturated fats, such as olive oil, fall somewhere in between.
Although grains are less oily than nuts, they still have a tendency to oxidize after being ground. Thus, flour is a commonly overlooked source of rancid fat. Learn to smell rancid flour. I once put an old Saltine cracker in my mouth and immediately realized it was revoltingly rancid. Many people who don’t know what rancidity is might have thought it was merely stale. In this case, the cracker was offered to me by a relative in a social situation where it would have been difficult to tactfully get it out of my mouth, so I managed to swallow it. But my daughter had a handful of them and I was determined to not let her eat them, so I distracted her (she was three years old – it wasn’t hard) and switched the crackers out for an orange. Besides the rancidity factor, any food that is ground to a fine powder – such as flour and ground spices – has so much surface area that it will quickly degrade and lose its nutritional value. This is why powdered spices lose their flavor much faster than whole spices. So, if you consume flour, try to use fresh flour. You can even get a small grain mill and make your own if you don’t bake very often.
While rancid oils in food have gotten some press, I haven’t heard anything about the issue of rancid oils in skin products. These, too, are worth avoiding – especially if you use large amounts of them (such as body oil). Our skin is highly absorbent, especially of oils. If you’ve ever put some oil on your skin and noticed that after a little while your skin isn’t oily anymore, it’s because your skin drank most of it up. I have purchased sticks of natural lip balm that were already rancid when I first opened them – and these are meant to be applied to the thin, super-absorbent skin of the lips! Free-radicals are a major contributor to the aging process. Why speed up this process by administering them directly to your skin in the form of rancid oils? Start sniffing your lotions and cosmetics and toss them if they’re rancid. Unfortunately, if they’re strongly scented, this may mask the smell of their rancidity.
What to do: Throw away rancid oils. Buy oils, nuts, grains, and flour in small enough quantities that you’ll use them up within a few months at most. Keep them in dark, cool places. You can break open a few vitamin E capsules and add the contents to your oils; because it’s a antioxidant, it will delay rancidity (but won’t prevent it altogether). Wrap oily foods well and store them in airtight containers. It’s a good idea to treat skin products similarly, though they usually contain stronger preservatives that protect against rancidity. Consider taking a few thousand milligrams of vitamin C daily – it’s one of the best and safest antioxidants. Antioxidants, as the name implies, protect against oxidation and sometimes reverse oxidative cell damage. (Some other powerful antioxidant nutrients include beta carotene, manganese, lycopene, lutein, selenium, and coenzyme Q10). Finally, eat lots fresh fruits, vegetables, and spices (rosemary, sage, garlic, etc.) since they are the most abundant food sources of antioxidants, and of course, they’re just plain good for you.
(1) Kanner J. (2007, Sept.). Dietary advanced lipid oxidation endproducts are risk factors to human health. Molecular Nutrition & Food Research. 51(9), 1094-101.