Ask the Expert: Dietary Fat

The Physicians Committee

Ask the Expert: Dietary Fat

Q: What are the best oils to use in cooking? And what about nuts?

A: The Cancer Project recommends avoiding the use of added oil and minimizing use of nuts. There are many exciting ways to prepare foods without oil, such as using water or vegetable broth for start stir-fries and substituting applesauce, banana, or soy yogurt for baked goods and desserts. If you ever must use oil, use only vegetable oils and only cook with ones that have a high smoke point and are low in saturated fat such as sesame, vegetable, corn, grape seed, peanut, and avocado oil. Safflower, olive, flax, and hempseed oils should not be cooked, but only used very occasionally, if necessary, for flavoring.

Although vegetable oils and nuts generally contain less saturated fatty acids than animal fats (with the exception of coconut and palm oil), when it comes to hormone production and the functioning of your immune system, total fat is what matters—regardless of whether or not it’s a “good” or “bad” fat. For cancer prevention and survival, we recommend avoiding sources of concentrated fat. Use fat-free substitutes for vegetable oils such as vegetable broth or water whenever possible. Nuts and nut butters should be used as a condiment at most. If oils are absolutely necessary, choose ones that are rich in the omega-3 fatty acids such as canola or walnut oil. If you eat nuts, be conscious of your serving size (it’s easy to overdo it—shoot for a serving of no more than 1 tablespoon chopped nuts per day, which contains about 5 grams of fat and 50 calories), and eat ones that are rich in essential nutrients. For example, one Brazil nut supplies you with your daily requirement of the antioxidant selenium. Almonds are good sources of calcium and vitamin E. And walnuts are rich in the omega-3 fatty acids.

Prentice RL et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006;295(6):629-642.

Gregorio DI, Emrich LJ, Graham S, Marshall JR, Nemoto T. Dietary fat consumption and survival among women with breast cancer. J Natl Cancer Inst. 1985;75(1):37-41. 

Chlebowski RT. Dietary fat reduction in postmenopausal women with primary breast cancer: Phase III Women’s Intervention Nutrition Study (WINS). Paper presented at: American Society of Clinical Oncology Annual Meeting; May 16, 2005; Torrance, CA.

Fradet Y, Meyer F, Bairati I, Shadmani R. Dietary fat and prostate cancer progression and survival. Eur Urol. 1999;388:91.

Q: Aren’t there essential oils that you need to get from fish? Can plant sources provide these essential oils?

A: Two essential fatty acids cannot be synthesized in the body and must be taken in the diet from plant foods. Their names—linoleic and linolenic acid—will never show up on a food label and are not important to remember.  What is important is that these basic fats are used to build specialized fats called omega-3 and omega-6 fatty acids.

Omega-3 and omega-6 fatty acids are important in the normal functioning of all tissues of the body. Deficiencies are responsible for a host of symptoms and disorders including abnormalities in the liver and kidneys, changes in the blood, reduced growth rates, decreased immune function, and skin changes including dryness and scaliness. Adequate intake of the essential fatty acids results in numerous health benefits. Prevention of atherosclerosis, reduced incidence of heart disease and stroke, and relief from the symptoms associated with ulcerative colitis, menstrual pain, and joint pain have also been documented.

While supplements and added oils are not typically necessary, good sources of omega-3 fats should be part of a daily diet. Alpha-linoleic acid (ALA), a common omega-3 fatty acid, is found in many vegetables, beans, and fruits. More concentrated sources can be found in oils such as canola, flaxseed, soybean, walnut, and wheat germ. Corn, safflower, sunflower, and cottonseed oils are generally low in ALA. Omega-6 fatty acids, such as gamma-linolenic acid, can be found in more rare oils, including black currant, borage, evening primrose, and hemp oils.

Some people eat fish and use fish oils for their omega-3s. However, plant-derived omegas-3s have none of the potential contaminants nor do they have the fish odor that can be apparent in the perspiration of people using fish oil. They also tend to be more chemically stable and are lower in saturated fats. Fish oils tend to decompose and, in the process, unleash dangerous free radicals. Another downside to fish oil is that it is between 15 to 30 percent saturated fat, which is about double that of plant oils. Fish oils are in no way unique. Fish make their omega-3 oils from ALA in plankton, just as mammals—including humans—synthesize omega-3s from land plants. Research has shown that omega-3s are found in a more stable form in vegetables, fruits, and beans. Adding flaxseed oil to your salad or grinding flax seeds for your breakfast cereal are simple ways to incorporate extra omega-3 fatty acids to your diet.

Hunter JE. n-3 Fatty acids from vegetable oils. Am J Clin Nutr. 1990;51:809-814.

Mantzioris E, James MJ, Gibson RA, Cleland LG. Dietary substitution with an alpha-linolenic acid-rich vegetable oil increases eicosapentaenoic acid concentrations in tissues. Am J Clin Nutr. 1994;59:1304-1309.

Fraser GE, Risk factors for all-cause and coronary heart disease and mortality in the oldest old. The Adventist Health Study. Arch Intern Med. 1999;53(8)585-590.

Q:  Other than the essential fatty acids in flax seeds, isn’t there another reason why breast cancer survivors should eat them?

A:  Flaxseeds are the leading source of plant lignans, a group of phytoestrogen compounds that have been associated with reduced breast cancer risk. A 2005 Canadian study examined the effect of consuming flaxseed oil on tumor growth in postmenopausal women with breast cancer. Twenty-nine women were assigned to either eat a muffin containing 25 grams of flaxseed oil or a muffin with no flaxseed oil. The flaxseed oil muffins offered some clear benefits, as the majority of the women eating them had a significant reduction in breast cell tumor size. This effect is similar to that seen with Tamoxifen, a drug given to some women to prevent breast cancer. The drug acts as a selective estrogen receptor modifier (SERM), and flaxseed, which is rich in plant-based estrogens, appears to act in a similar way.

Want to incorporate more flaxseed into your diet? Try adding ground flaxseed to salads, soups, casseroles, and cereals. You can also top salads with flaxseed oil. Store ground flaxseeds and flaxseed oil in your refrigerator to keep it fresh and avoid rancidity. The best way to use flaxseed is as an addition to a low-fat, vegan diet.

Thompson LU, Chen JM, Li T, Strasser-Weippl K, Goss PE. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res. 2005;11(10):3828-3835.

Saarinen NM, et al. Role of dietary lignans in the reduction of breast cancer risk. Mol Nutr Food Res. 2007;51(7):857-866.