It means you stop eating completely, or almost completely, for a certain stretch of time. A fast usually lasts from 12 to 24 hours, but some types continue for days at a time. In some cases, you may be allowed water, tea, and coffee or even a small amount of food during the “fasting period.”
Why People Do It
Besides religious practice, there are a number of health reasons. First, as you might guess, is weight loss. There’s also research showing that certain types of fasting may help improve your cholesterol, blood pressure, glucose levels, insulin sensitivity, and other health issues.
Is It Safe?
Brief fasting isn’t likely to hurt you if you’re a healthy adult, whether your weight is normal or you’re heavier. Still, your body needs good nutrition and fuel to thrive. So make sure to talk to your doctor first, especially if you have health problems or take any kind of medication. If you’re pregnant, breastfeeding, or you have a history of eating disorders, you should avoid fasting of any kind. Kids and teens shouldn’t fast either.
Intermittent Fasting
This is an off-and-on type of fasting. There are three main types that doctors have studied and people have used for weight loss and improved health:
- Time-restricted feeding
- Alternate-day fasting
- Modified fasting
Time-Restricted Feeding
This means you do all your eating in a certain stretch of the day, often around 8-12 hours. One easy way to do this is to skip one meal. If you finish dinner by 8 p.m., you’ve already achieved 12 hours of your fast by 8 a.m. Make it to noon for lunch, and you’ve fasted for 16 hours. You could also stop eating after lunch until breakfast the next morning.
Alternate-Day Fasting
It’s sometimes called “complete” alternate day fasting because the time when you don’t eat lasts a full 24 hours. You follow that with one or more “feast” days when you can eat as much as you want. Even though the studies are very limited, the results suggest that alternate-day fasting can lead to weight loss and improve health. But it may be pretty hard to stick to it over the long term.
Modified Fasting
This type allows you to eat around 20% to 25% of your normal daily energy needs on scheduled fast days — just enough to remind you what you’re missing! One popular version, the 5:2 diet, requires 2 days a week (not in a row) of 24-hour “fasting” except for a very light meal. On the other 5 days of the week, you can eat whatever you want.
Diabetes
Some studies show that fasting might help people with diabetes or prediabetes control blood sugar, improve insulin sensitivity, and lose weight. Other recent research looking at time-restricted fasting disputes some of these claims. If you have either of these conditions, it’s very important to talk to your doctor before you make any changes to your medication, insulin use, or eating habits.