Here are some of the best and worst food choices for women who want to become pregnant, according to The Fertility Diet (McGraw-Hill, $24.95) by Harvard researchers Jorge E. Chavarro and Walter C. Willett.

Peanuts NOT potatoes: The type of carbs you consume makes a big difference. "Slow carbs" (low-glycemic index foods such as peanuts, nuts, dried beans, whole grains) promote ovulation. "Fast carbs" that spike blood sugar (like cold cereal, white rice, white potatoes and sugary drinks) decrease fertility.

Beans NOT beef: Participants in a study who ate the most animal protein were 39% more apt to have ovulatory infertility than women who ate the least. Even adding one daily serving of red meat or poultry could raise infertility risk by a third. Replacing 25 grams of animal protein with 25 grams of plant protein, such as dried beans, could cut risk of ovulatory infertility by half.

Avocados NOT doughnuts: Trans fats are huge villains in infertility; the more eaten, the higher the chances of ovulatory infertility. Even the 4 grams of trans fat in a daily doughnut, compared with the monounsaturated fat in a serving of avocado, can more than double the infertility risk. Substitute unsaturated fats for trans fats, for a pregnancy boost.

Whole milk not fat-free yogurt: Heretical as it sounds, women troubled by infertility are advised to eat high-fat, rather than low-fat, dairy foods. Recommended to improve fertility: a glass of whole milk daily. Threats to fertility: frozen yogurt, sherbet and low-fat yogurt.

Coffee not soda: Surprisingly, research finds that caffeine in moderation—several cups of coffee or tea—does not seem to interfere with becoming pregnant. But sugary soda (caffeinated and decaf) can seriously diminish fertility. Best beverage: lots of water. New studies suggest no caffeine after conception.