A study published in the April issue of the Journal of the American Dietetic Association found that adolescents with unhealthy weight-control behaviors were three times more likely to be overweight five years later. In addition, adolescents using unhealthy weight-control behaviors were at an increased risk for out-of-control binge eating, self-induced vomiting, and the use of diet pills, laxatives, and diuretics.
"This study shows that a shift from dieting and drastic weight-control behaviors to long-term healthy eating and physical activity is necessary among adolescents," said Dianne Neumark-Sztainer, Ph.D., study author and professor of epidemiology and community health at the University of Minnesota. "A change in lifestyle is needed to prevent obesity and eating disorders in this population."
Researchers conducted a longitudinal study of over 2,000 adolescents to determine risk for gains in BMI, overweight status, binge eating, extreme weight-control behaviors, and eating disorders after five years. Subjects completed two Project E.A.T. surveys in 1999 and 2004 to determine if those who reported dieting and different weight-control behaviors are at an increased risk for obesity and eating disorders.
Project E.A.T. was designed to investigate the factors influencing eating habits of adolescents, to determine if youth are meeting national dietary recommendations, and to explore dieting and physical activity patterns among youth. Through a greater understanding of the socioeconomic, personal, and behavioral factors associated with diet and weight-related behavior during adolescence, more effective nutrition interventions can be developed.
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Because many infants receive soy milk, the impact of genistein in humans should be carefully assessed, he said. Pregnant women are exposed to hundreds of compounds in foods, prenatal vitamins and the environment that could potentially methylate susceptible genes, he said. The effects of each compound could be beneficial or detrimental, depending upon the timing of exposure, the dose and the tissue exposed, said Jirtle.
"Our study demonstrates there are highly sensitive windows early in development when environmental exposures can permanently alter the offspring's adult susceptibility to disease," said Jirtle. "Therefore, we need to examine the effect of environmental exposures during pregnancy, not just in adulthood, if we want to accurately assess their risk or benefit to humans."
His earlier research demonstrated that four common nutritional supplements fed to pregnant mice, including folic acid and vitamin B12, lowered their offspring's susceptibility to obesity, diabetes and cancer by methylating the same agouti gene. Yet how nutrients interact in combination or in extremely high doses remains unclear, he said.
"There could be additive or synergistic effects between folic acid and genistein, or any such compounds, that hypermethylate certain genes," said Dana Dolinoy, MPH, lead author of the study. "What is good in small amounts could be harmful in large amounts. We simply don't know the effects of literally hundreds of compounds that we intentionally or inadvertently ingest or encounter each day."
Of related concern, soy is a staple of almost all laboratory mouse diets. Soy could inadvertently methylate select genes and thus mask the deleterious effects of various chemicals being tested for their risk in humans, she said.
"In the future, we may be able to potentially select compounds to protect a person from being predisposed to developing a variety of conditions," said Jirtle. "There is a vast, unknown potential for studying how our environment interacts with our epigenome to determine how we developed and who we will become."
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