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Posted 12.12.05
 
 
   

Saturated Fats Alter Ratio of Male to Female Offspring, Researcher Finds

COLUMBIA, Mo. -- A striking variation in the numbers of male and female mice babies can be attributed to the amount of saturated fats fed to their mothers, University of Missouri researchers have found.

"It is now clear that the male-to-female sex ratio can be strikingly skewed," said Cheryl Rosenfeld, assistant professor of veterinary biomedical sciences. "In particular, a diet high in saturated fats but low in carbohydrates leads to the birth of significantly more male than female offspring."

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An additional important variable was the age of the mothers. Laboratory mice first bred at 10 weeks of age delivered similar numbers of sons and daughters. Virgin mice bred later than 20 weeks of age produced litters skewed toward males or females according to their diets.

"When calories are provided mainly by carbohydrates rather than fat, female offspring predominate," she said. "The skewing of sex ratio was related to diets fed and not to body mass of the mothers."

Two diets were used in the study: The first was very low in saturated fat with most of the calories provided by sugars and complex carbohydrates; the second was very high in saturated fat with most of the energy provided by lard.

Four litters of mice pups were bred, totaling more than 1,000 pups. The ratio of male pups born to mothers on the high fat diet was unusually high at 67 percent, while the ratio of male pups born to mothers on the low fat diet was 39 percent.

Normal expected sex ratio in birth rates of mice would call for 52 male and 48 percent female, Rosenfeld said. Gestation length and litter size did not differ.

MU research continues to study how the high fat diets affect the females' serum concentrations of steroids including estrogen, progesterone and testosterone.

The prediction that females in better body condition would produce more males than female progeny has been observed in several species including deer, reindeer, sheep and domestic pigs, she said.

That high-fat diets favor sons and low-fat diets favor daughters is consistent with the generally accepted hypothesis that females with access to the greatest food resources produce more sons than daughters, Rosenfeld said.

Skewing of offspring ratio may have important implications for food producers, she said. For example, females are preferred in the dairy industry, while males are preferred in the beef industry.

"Altering the animals' diet content prior to breeding might provide a means of manipulating the desired sex ratio," she said.

Funding for this research is provided by the National Institute of Health.

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