"Feeling better isn't just this selfish, hedonic thing — it actually is fuel. I consider energy from taking care of yourself as essential fuel for the things that matter most in our lives," says Michelle Segar, a psychologist at the University of Michigan who studies how we sustain healthy behaviors like exercise. Saviour Giyorges / EyeEm/Getty Images/EyeEm Premium hide caption
What seems like an obvious choice to lose weight doesn't look so obvious based on available data. Sharon Pruitt/Getty Images hide caption
It turns out it's difficult to get people to adhere to the various dietary restrictions that come with participating in a fasting study. Xsandra/Getty Images hide caption
Kate (Chrissy Metz), left, and Kevin (Justin Hartley) are sibling comrades in NBC's This Is Us. Paul Drinkwater/NBC hide caption
All that holiday grubbing really does pack on the pounds. How much? Researchers tracked the weights of 3,000 people in Germany, Japan and the U.S. and found a weight spike after every major holiday. Peter Dazeley/Getty Images hide caption
Every bit of steel in the car you drive has been measured as to its capability to withstand certain forces — pushing and pulling. Machines like this do the measuring. Jennifer Lauren Lee/NIST PML hide caption
Sylvester Williams, a Denver Broncos nose guard, nabs Isaiah Crowell of the Cleveland Browns last October. If measured by BMI, Williams is obese. AAron Ontiveroz/Denver Post via Getty Images hide caption
The problem of dangerously thin standards for fashion models has been debated for years. Marcin Kilarski/EyeEm/Getty Images hide caption
Fun hikes offer health benefits for kids of every shape and size. Annette Birkenfeld/annedde/iStockphoto hide caption
Oh, these look good! But how much the fries hurt your waistline depends not only on how many you eat but also your DNA. angela n./Flickr hide caption
Government workers exercise at their office in Mexico City, August 2013. To counter the obesity epidemic, the city requires all government employees to do at least 20 minutes of exercise each day. Tomas Bravo/Reuters /Landov hide caption
Posting a picture like this on the fridge might seem like good motivation for weight loss. But scientists say it might instead inspire weight gain. iStockphoto.com hide caption
Pictures like these helped British researchers gauge people's attitudes about weight. Courtesy of Martin Tovee hide caption
Skip the chips to help keep weight gain at bay. iStockphoto.com hide caption