Intermittent Fasting

Intermittent fasting is a diet trend that has garnered a great deal of popular attention over the past few years. Followers of intermittent fasting incorporate fasting methods traditionally reserved for religious, medical, or sociopolitical purposes into their daily diet patterns by alternating intervals of extreme calorie reduction with intervals of normal eating during certain days of the week or specific hours of the day. The amount of time spent fasting and eating differs between the three main intermittent fasting methods.

The Different Types of Intermittent Fasting

Alternate-day fasting consists of alternating days of complete fasting and unrestricted, normal eating. On fasting days, no food or beverages are consumed with the exception of water and other zero-calorie drinks like black coffee or unsweetened tea. Alternate-day fasting is considered to be the most restrictive type of intermittent fasting.

Modified fasting incorporates several days of fasting into each week. Food is not completely avoided during fasting days in modified fasting, but calories are restricted to about 20-25% of an individual’s total daily need. This is usually about 500 calories for women and 600 calories for men. Modified fasting plans tend to include fewer fasting days per week than alternate-day fasting plans do.

Time-restricted feeding is characterized by practicing fasting during certain hours of each day instead of over entire days. The goal behind time-restricted feeding is to extend the time you spend already fasting overnight while you are asleep into the day-time hours. Time-restricted feeding is often seen as a less restrictive approach to intermittent fasting.

Taking a Closer Look at the Science

Much research done on this type of fasting has, to date, been done on mice and rats. Some benefits seen in animals include weight loss, longer lifespans, and protection against many chronic diseases like type 2 diabetes, heart disease, and some cancers.

Can intermittent fasting also help people lose weight, improve their health, and reduce their risk of chronic disease? According to the current human research, maybe. Human studies have shown that each of the three types of intermittent fasting diets may lead to weight loss, but the impact of intermittent fasting on disease risks has been much less consistent. There is still a need for more research to determine the true impacts of intermittent fasting on humans and if there are any long-term health risks to following these types of diets.   


  • Intermittent fasting doesn’t appear to be dangerous for normal-weight, overweight, or obese adults without underlying health conditions. Anybody considering intermittent fasting should always talk with his or her doctor first to make sure that this kind of diet is safe for them and with a registered dietitian to assure they are meeting their nutrition needs.
  • Anyone with a history of disordered eating behaviors, women who are pregnant or breastfeeding, children, adolescents, the elderly, athletes, those with type 1 diabetes, and those with type 2 diabetes that is poorly controlled or must be controlled with medication should avoid fasting.  This list is not inclusive, so check with your doctor to see if these diets are safe for you!