A lot of attention has been given to trans-fats lately, which leaves many wondering about cis-fats. The terms trans and cis are opposites and describe the chemical structure of hydrogen atoms around a double bond. Most naturally occurring unsaturated fats are cis, meaning the hydrogen atoms are on the same side of the double bond. While most foods contain several different types of fat, unsaturated fats are most abundant in plant foods and vegetable oils.
Fat Chemistry and Terminology
Fats are classified as either saturated or unsaturated. Unsaturated fats can have one double bond, called monounsaturated, or multiple double bonds, called polyunsaturated. Cis- and trans- describe whether the hydrogen atoms are on the same or opposite side of the double bond, respectively. Naturally occurring unsaturated fats are cis, except for up to 6 percent of fat from ruminant animals that is naturally trans. Saturated fats have no double bonds because the carbon atoms are saturated with hydrogen, as are fully hydrogenated oils, and are therefore neither cis nor trans. Nonhydrogenated unsaturated fats are the sole source of cis-fats in the diet.
Monounsaturated Fat Food Sources
While trans-fats are harmful to the body, foods containing cis-fats are beneficial. Monounsaturated cis-fats decrease LDL cholesterol and triglycerides, and increase HDL. Foods containing a high percentage of monounsaturated fats include almonds, avocados, bacon, canola oil, cashews, eggs, grapeseed oil, ground beef, hazelnuts, high oleic safflower oil, high oleic sunflower oil, macadamia nuts, olives, olive oil, pecans, peanuts, peanut oil, pistachios, sunflower oil and tea seed oil.
Polyunsaturated Fat Food Sources
Polyunsaturated cis-fats decrease LDL and HDL cholesterol and triglycerides. Foods with mostly polyunsaturated fats include anchovies, Brazil nuts, corn oil, cottonseed oil, flax oil, flaxseed, herring, mackerel, pine nuts, safflower oil, salmon, sardines, sesame seeds, shad, smelt, soybeans, soybean oil, sunflower seeds, trout, tuna and walnuts.
Foods containing cis-fats can decrease the risk of heart disease by improving blood cholesterol levels and lowering blood pressure. They might also reduce the risk of heart attack, abnormal heart rhythms, strokes and death in people with heart disease. Monounsaturated cis-fats can benefit insulin levels and blood sugar control in type 2 diabetics. High doses of cis-fat-containing supplements, such as fish oil, can increase the risk of bleeding and should be taken under medical supervision.
- “Food and Nutrition Research”; "Ruminant and Industrially Produced Trans Fatty Acids: Health Aspects"; Steen Stender et al.; March 2008
- “American Journal of Clinical Nutrition”; "Dietary Cis-monounsaturated Fatty Acids and Metabolic Control in Type 2 Diabetes"; Emilio Ros; September 2003
- Centers for Disease Control and Prevention; "Polyunsaturated Fats and Monounsaturated Fats"; February 2011
- Mayo Clinic; "Dietary Fats: Know Which Types to Choose"; February 2011