The method is not appropriate for everyone, however, particularly pregnant women and those with medical conditions such as diabetes or eating disorders. And though studies are promising, it remains to be seen if this type of eating can become a sustainable lifestyle habit instead of a drop-a-dress-size-in-a-week fad.
"The jury is still out, especially on how healthy, sustainable and realistic this approach is," said Samantha Heller, a registered dietitian and senior clinical nutritionist at NYU Langone Health in New York. "Eating very low calories, or none, on alternate days feels punitive to many and may exacerbate an already difficult and complex relationship someone has with food."
If you are still hoping to give intermittent fasting a try, there are some things to consider that can increase your chances of reaching your goals. Also, be sure to check with your doctor before starting a fasting regimen.
The appeal of intermittent fasting may be related to its simplicity, as it seems to require less effort than restricting calories every day. But there are different approaches to the eating pattern that vary in intensity.
One regimen known as time-restricted feeding advises consuming all of your calories within a range of three to 12 hours a day, whereas an approach known as the "5:2" diet advises eating 500 to 600 calories for two days of the week and eating whatever you want on the other five days. A third, much more stringent type of regimen involves alternating 24-hour fasting periods (in which no foods or calorie-containing beverages are consumed) with non-fasting days, during which anything can be eaten in any amount.
Though time-restricted feeding might not seem that different from a typical eating day, especially if you tend to skip breakfast, alternate-day fasting may cause intense hunger on fasting days and can be much more challenging to sustain.
"People who are accustomed to eating regularly scheduled meals or suffer from 'head hunger' may find alternate-day fasting extremely difficult," said Kristen Smith, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics. Head hunger is the desire to eat when you are not physically hungry but are triggered to eat by emotions and social factors.
For the greatest success, Smith recommends choosing a fasting regimen that best suits your lifestyle, your health history and your ability to sustain fasting. For example, alternate-day fasting may not be appropriate for someone with an active job that requires manual labor or a job that centers around food, such as a chef.
Focus on protein and fiber-rich foods on semi-fasting days
Protein and fiber-rich