KNOWLEDGE YOU CAN USE

KNOWLEDGE YOU CAN USE
Yams: nature’s fertility food?

Do you know any twins? Have you ever wondered how common twins are? In the United States and Europe, about 12 in every 1,000 births are twin births. In Asia, the number is slightly lower, at 8 sets of twins per 1,000 births. Elsewhere, the rates are similar—except for southwest Africa, particularly in Nigeria, which has been called “The Land of Twins.” There, the rate of twin births among the Yoruba people is more than four times that in the United States, with about 50 pairs of twins per 1,000 births. (Triplet births are unusually common, too, occurring 16 times more frequently in Nigeria than in the United States.)

Question 12.9

Q: Why are so many twins born in Nigeria? Is it something in the water? Nope. But that’s not too far off. It’s the diet of the Yoruba people. A staple in their diet is the white yam, a starchy vegetable that looks a bit like a potato; many people eat yams several times a day.

Question 12.10

Q: What’s in the yams? Some preliminary studies suggest that an estrogen-related compound in yams is responsible for stimulating the ovaries, increasing the likelihood, in any given month, that more than one egg will be released.

Question 12.11

Q: How can we be sure it’s the yams? At this point, the relevant data are still being collected. In one intriguing laboratory study, rats fed a diet rich in yams doubled their litter size. In another, the circulating levels of the follicle-stimulating hormone (which stimulates growth and maturity of follicles in the ovaries) and estradiol were both 32% higher in rats fed diets rich in yams than in rats fed a standard diet, while the levels of luteinizing hormone (which triggers ovulation) were 158% higher in the yam-fed rats.

Question 12.12

Q: So, will it work for you? It’s unclear. Anecdotes abound about women having twins after purposely increasing their yam consumption. But a randomized, controlled, double-blind study has yet to be conducted. How would you set up and analyze a study like that? (It is important to note that the yams consumed in Nigeria are not the same as American yams, which are sweet potatoes and do not contain the steroid levels of yams grown in Nigeria.)

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