Trans Fats and Infertility: Could Cookies and Crackers Hurt Your Ability to Conceive?


A recent study shows that trans fats can dramatically impact a woman’s ability to conceive. What exactly are trans fats, and how can you avoid them?

2007 was a bad year for trans fats—the type of fat that is formed when liquid oils are processed into solid fats like shortening and hard margarine or commercial frying fats that can be used repeatedly without breaking down. First, several states have proposed bills banning all artificial trans fats from restaurants. Then, a Harvard School of Public Health study was published showing that trans fats may prevent women from conceiving.

What’s Wrong with Trans Fats?

Trans fats are no-goodniks in general: They increase levels of “bad” cholesterol (LDL) and decrease relative levels of “good” cholesterol (HDL). They also promote inflammation and the formation of blood clots within blood vessels. The eight-year study measured the impact of a diet high in trans fats on more than 18,000 otherwise healthy women who were trying to get pregnant. Researchers found that, along with other health concerns associated with trans fats (high blood pressure, heart disease, and obesity), decreased fertility appeared to be directly linked to trans fat consumption.

Trans fats can impede fertility in a few ways. First, a diet high in trans fats is a diet likely to lead to obesity. Being significantly overweight is not good for regular ovulation. Second, overweight or not, trans fats interfere with body chemistry such that the body becomes more resistant to insulin. This makes levels of both sugar and insulin in the bloodstream go up, another strike against full fertility. Lastly, the inflammatory effect of trans fats can interfere with ovulation, conception, and even early embryo development.

What Does This Mean for Women Trying to Conceive?

The study shows that for every two percent increase in calories coming from trans fats instead of carbohydrates, women have a 73 percent increased risk for infertility, and the risk rises to 79 percent when trans fats are replacing omega-6 polyunsaturated fats. And, it doesn’t take a lot of trans fats to impact fertility—women consuming just four grams a day are at risk. (See Which Foods Are High in Trans Fats to learn how little that is.)

The effects of trans fats on women with polycystic ovarian syndrome (PCOS) may be even more dramatic, because trans fats seem to amplify the symptoms of PCOS. The Harvard study showed that trans fats can interfere with the cell receptor activity that is involved with inflammation, glucose metabolism, and insulin sensitivity, making it more difficult for women with PCOS to conceive.

Harvard researchers Jorge Chavarro, MD, and Walter Willett, MD, have written a book covering this and other findings from the long-term study, called The Fertility Diet. In short, they write, “Across the board, the more trans fats in the diet, the greater the likelihood of developing ovulatory infertility.” The authors stress that their advice is not to give up fats altogether. Just trans fats.

As Drs. Chavarro and Willett say, “Think of trans fats as the evil cousins of the healthy omega-3 fats in fish, flaxseeds, and walnuts.” (For an excerpt from their book, check out 10 Steps to Increasing Your Fertility.)

Which Foods Are High in Trans Fats?

It’s surprisingly easy to consume a high level of trans fats since they are found in so many of the prepackaged foods that make up a large percentage of modern diets. A small quantity of trans fat is found naturally in foods—usually in animal products—but the vast majority of trans fats are artificial and come from the partially hydrogenated oil found in packaged foods.

The most common culprits are packaged snacks, fried foods, and commercial baked goods like cookies and cakes. According to the Food and Drug Administration (FDA), the following foods are some of the most common sources of trans fats consumed in the United States:

  • Baked goods: cakes, cookies, crackers, pies, bread, etc.
  • Margarine
  • Fried potatoes, or other commercially deep-fried foods
  • Potato chips, corn chips, movie popcorn
  • Household shortening
  • Salad dressing
  • Breakfast cereal
  • Candy
  • Animal products (such as milk products, cheese, beef, and lamb)

Amount of trans fat in commonly eaten foods:

  • French fried potatoes: 8 grams
  • Margarine (stick): 3 grams
  • Margarine (tub): 0.5 grams
  • Shortening: 4 grams
  • Potato chips: 3 grams
  • Doughnuts: 5 grams
  • Cookies: 2 grams
  • Candy bar: 3 grams
  • Pound cake: 4.5 grams

The Good News on Trans Fat

Since January 2006, all food manufacturers are required to list trans fats on their labels, so you no longer have to guess at which foods might pose a risk. Read labels carefully, however; labels can claim “No Trans Fat” if there is less than 0.5 grams. Too many .49-gram servings will add up fast. Look also for the words hydrogenated and shortening, which are likely to mean trans fat. In response to consumer complaints, some manufacturers are eliminating trans fats from their products, and more cities and states are moving toward banning trans fats from restaurants.

Someday trans fats may be eliminated altogether from the foods we eat, but for now your best bet is to choose whole foods as often as possible, read food labels before buying a product, and, at a restaurant or bakery, always ask whether they use trans fats before ordering that pastry.


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