Most people can benefit from practicing moderate fasting (shorter than 24 hours). However, there are safety concerns for pregnant women, children, individuals with type 1 diabetes and individuals who are malnourished or not getting proper nutrition. These individuals are advised not to practice intermittent fasting and should talk to their doctor before contemplating doing so in the future.
There are also concerns for young children, although not eating after dinner and fasting overnight for 8-12 hours is probably not a concern for young adolescents. Preliminary data suggest that alternate day fasting (with 500 calories or less on fast days) may be safe and effective for obese young adolescents. However, Dr. Krista Varady recommends against IF for children under 12 years of age.