Genes can also increase the risk of diabetes by increasing a person’s tendency to become overweight or obese. One theory, known as the “thrifty gene” hypothesis, suggests certain genes increase the efficiency of metabolism to extract energy from food and store the energy for later use. This survival trait was advantageous for populations whose food supplies were scarce or unpredictable and could help keep people alive during famine. In modern times, however, when high-calorie foods are plentiful, such a trait can promote obesity and type 2 diabetes.