A 2014 review[16] described that intermittent fasting has not been studied in children, the elderly, or the underweight, and could be harmful in these populations. It also suggested that people choosing to fast for periods of time greater than 24 hours should be monitored by a physician, as changes to the gastrointestinal system or circadian rhythm can occur.[16] The review concluded that fasting is unlikely to have much effect on conditions other than obesity, such as aging or other chronic condition, unless combined with moderate calorie restriction and a plant-based diet such as the Mediterranean diet.[16]