Two studies zero in on DNA-based drivers of weight. Is obesity written in our genes? In two separate papers, published in the journal Science and in the Journal of Clinical Investigation (JCI), researchers describe new genetic factors that could explain weight gain in some people. In the Science study, researchers at Boston Children’s Hospital studying mice found a rare genetic mutation that prevented the animals from burning off fat calories. They also found the same gene was mutated in a group of obese people. And a team based at University College London reported in JCI that a specific form of a gene previously linked to obesity, FTO, can increase craving for high-fat foods. The discoveries add to the growing body of knowledge about the biology behind weight, and the results confirm that while it’s represented by a single number, weight is the complex combination of a multitude of different metabolic processes, from brain systems that regulate appetite to enzymes that control how efficiently calories are turned from food into energy that the body needs. Making matters even more confusing, these factors are also likely influenced by environmental contributors such as diet and lifestyle.