Thin people may be able to summon more mental defenses to resist tempting, high-calorie foods than obese people.  Yale University School of Medicine researchers have found that brain scans of thin people who looked at pictures of high-calorie foods showed increased activity in a region of the brain used for impulse control, but obese people showed little activity in this region.  Larger studies are needed to confirm the findings, but the study does suggest that obese people may be less able to shut off parts of the brain that drive food cravings.