Food and Fertility: Good fats for better fertility

Good fats for better fertility

Once upon a time, and not that long ago, fat was a four-letter word. Diet and nutrition gurus told us (and some still tell us) to cut back on fat whenever and wherever possible. Millions of Americans have dutifully followed that advice. Guided by the low-fat mantra, we tossed out salad dressings and mayonnaise made with olive oil or canola oil in favor of fat-free versions made with extra sugar. We replaced other fats in the diet with carbohydrates, usually the rapidly digested ones in white flour, potatoes, white rice, and sugar. This purge didn’t make us any healthier. It had no effect on heart disease, its intended target. And it may have contributed to the epidemic of obesity sweeping the country.

The big problem with the low-fat approach is that not all fats are bad. Let me say that again, because it runs against what we’ve been hearing for years: Not. All. Fats. Are. Bad. In fact, some fats are downright good for you. This good fat–bad fat dichotomy applies to fertility, too. Some types of fat can help you get pregnant, others get in the way:

• Artery-clogging trans fats contribute to infertility.
• Saturated fat has little effect on fertility, but isn’t so hot for your heart.
• Unsaturated fats are good for fertility, and they’re important for pregnancy, a baby’s healthy development, and long-term heart health.

Out with the bad

Trans fat, the “stealth” fat found in many foods, harms the body in a variety of ways. It boosts the amount of artery-clogging low-density lipoprotein (LDL, or bad cholesterol) in circulation, depresses the amount of protective high-density lipoprotein (HDL, or good cholesterol), promotes low-grade inflammation, and increases the tendency of blood to form clots inside blood vessels. Trans fats are so bad for the heart that eliminating them from the food supply could prevent tens of thousands of heart attacks, strokes, and other cardiovascular events each year in the United States alone. Trans fats are just as harmful to reproduction. In the Nurses’ Health Study, the participants who ate the most trans fats were the most likely to have developed ovulatory infertility. An effect was seen at the fairly low level of about four grams a day, an amount you can easily exceed with a small order of fast-food fries.

The Institute of Medicine says there’s no safe level of trans fats, and recommends getting less than two grams a day. Foods that contain trans fats include solid margarines, vegetable shortening, some commercial baked goods, and some fast foods. Until 2006, it was tough to tell if a food contained trans fat because it wasn’t listed on food labels along with saturated fat and cholesterol. Today, food labels must carry information about trans fats (see figure). This change has food makers scrambling to find trans-free fats for their products.

A loophole in the law lets food companies say “no trans fat” on the package and list zero trans fat on the label as long as the food contains less than 0.5 grams of per serving. So if you’re serious about clearing trans fats from your diet, you need to squint at food labels’ fine print, where the ingredients are listed. If “partially hydrogenated vegetable oil” or “vegetable shortening” appears in the list, the food contains some trans fat.

Detecting trans fats in a restaurants isn’t as easy, since they don’t have to provide nutrition information about the food they serve. You’re in luck if you live in New York City or Boston, which have banned restaurants from using oils containing trans fats. California is set to phase out trans fats by 2011. Other cities and states are certain to follow suit. One good strategy is avoiding deep-fried foods when eating out, since many restaurants still use partially hydrogenated vegetable oils in their fryers. A KFC Chicken Pot Pie, for example, has 14 grams of trans fat. A Sausage, Egg, and Cheese Biscuit with a large order of hash browns at Burger King gives you 18 grams, nearly 10 times the daily healthy limit. Other examples are here.

Moderation in the middle

Saturated fats aren’t across-the-board bad for you like trans fats are. A healthy diet can include some saturated fat. Just don’t overdo it.

In the Nurses’ Health Study, women whose diets included a lot of saturated fat were no more likely to have had ovulatory infertility as women whose diets were low in saturated fat. That isn’t a green light to chow down on foods rich in saturated fat. It strongly influences cholesterol levels, and thus heart health. To stay strong for the baby you hope to be carrying—and the grandchildren you may someday have—go easy on saturated fats. For someone who takes in 2,000 calories a day, that means keeping saturated fat intake under 17 grams. That’s the amount in a fast-food cheeseburger, a three-ounce sirloin steak, or a half slice of a Cheesecake Factory Chocolate Mousse cheesecake.

In with the good

Two fat families—the monounsaturated and polyunsaturated fats—are essential for good health. They’re to be embraced, not avoided. That’s doubly true for the group of unsaturated fats known as omega-3 fats. They are especially important for fertility, pregnancy, a baby’s healthy development, and long-term heart health.

Monounsaturated and polyunsaturated fats benefit the body in many ways. They lower levels of harmful LDL and increase protective HDL. Monounsaturated fats improve the body’s sensitivity to insulin and ease inflammation. Omega-3 polyunsaturated fats are an important part of cell membranes, and so help regulate what goes in and out of cells. They provide the body with the raw material for hormones that regulate blood clotting, the contraction and relaxation of artery walls, and inflammation. Babies need omega-3 fats to make connections between nerves, both in the womb and after birth. Later in life, omega-3 fats help the heart beat steadily and not lapse into erratic and potentially deadly rhythms.

Good sources of monounsaturated fats are olive oil, peanut oil, canola oil, avocados, nuts such as cashews and almonds, and seeds such as sesame and pumpkin seeds. Good sources of polyunsaturated fats include vegetable oils, especially corn, soybean, and safflower oils; soybeans and other beans; and walnuts. Make it a point to get some omega-3 fats every day. Good sources of these include fatty fish such as tuna, salmon, herring, and anchovies. (In a separate column I’ll try to clear up the confusion about eating fish.) Plants that are good sources of omega-3s include chia seeds (sold as Salvia), flax seeds and flaxseed oil, walnuts and walnut oil.

More detailed information on the health effects of fats in food are available from the Harvard School of Public Health’s NutritionSource.

Next up: Slow carbs for fertility, not no carbsÂ