Scientists are working to understand what hormonal and physiological cues in the body lead the brain to respond to food emotionally. iStockphoto.com hide caption

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Bob Karch is the chairman and a professor in the Department of Health and Fitness at American University. Here, he helps cross-country champion Steve Hallinan check his heart rate while cross-training on the bike. Allison Aubrey/NPR hide caption

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Bryce Marcus is a fifth-grader at the KIPP Infinity School in the West Harlem neighborhood of New York City. His curriculum includes emotional development training that teaches him to replace negative thinking with more realistic and flexible thinking. Allison Aubrey/NPR hide caption

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Sam Kass, the assistant White House chef, picks spinach from the garden. Maggie Starbard/NPR hide caption

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A jogger runs near downtown Houston. Recent studies show that running doesn't increase the risk of arthritis, and some runner's actually have healthier joints. David J. Phillip/AP hide caption

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Being in the right place at the right time, like living in the same college dorm, is a strong predictor of friendship. iStockphoto.com hide caption

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