Here are some of the many ways fasters are changing up their eating patterns in the hopes of losing weight and living longer. As with any weight loss program, participants are advised to consult with a doctor first.

Forms of Intermittent Fasting (IF):

• The "5:2 diet." The fasting person eats normally for five days and significantly cuts calories for the other two days of the week. On fasting days, calories are restricted to about 500 calories for women and 600 calories for men. (The average adult needs between 1,600 and 2,400 calories a day, according to USDA estimates.) Some IFers fast for two days in a row, while others prefer to split up their fasting days, e.g. Mondays and Thursdays.

• "Alternate-day fasting." Fasters alternate between eating nothing or very little one day and eating normally the next day. The cycle is repeated throughout the week.

• Other IFers eat just one meal a day, with no restrictions on how many calories the one meal contains.

Who does it and why:

Most people who try intermittent fasting do it to lose weight and burn more fat. Some IFers also believe the fasting cycles can increase mental focus and improve longevity.

What IFers eat, drink:

• Followers of the 5:2 fasting diet strive for foods that are rich in fiber and protein, such as fish and vegetables.

• They avoid refined carbs on fasting days. No cookies!

• They may consume water, coffee and tea without cream or sugar throughout the fasting day.

Side effects:

It can take anywhere from a few days to weeks for the body to adjust to a new eating schedule. Mild headaches and feeling cranky (aka "hangry") are common side effects in the beginning.

Allie Shah