Try it: fasting-mimicking

How to do it:

On day one, your macro totals should be about 11 percent protein, 46 percent fat, and 43 percent carbs (that’d be about 30 grams of protein, 56 grams of fat, and 117 grams of carbs if you eat 1,100 calories).

For the next four days, they’d drop to 9 percent protein, 44 percent fat, and 47 percent carbs—or 16, 35, and 85 grams, respectively, on a 725-calorie diet.

On all five days, it’s important to stay well-hydrated; aim for two to three liters of water a day, Foroutan says. While you can take part in low- or moderate-intensity workouts (like yoga or a steady-state, five-mile run), you should avoid vigorous exercise like HIIT and heavy lifting so your body has energy to create stem cells, Foroutan says. You can, however, stick to your regular fitness routine before and after those five days, so you can even try it during high-volume training blocks.

Try it: 

As long as you're fit, healthy, and you don't meet any of the three criteria noted below, you're cleared to try fasting-mimicking, says Foroutan. The experts agree everyone should do so with guidance from a registered dietitian or other health professional. That person can help make sure you’re still getting all the nutrients and vitamins you need for complete nutrition, Foroutan adds.

You could also try a ready-to-go plan, which includes things like vegetable- and grain-based soups, teas, flax bars, and high-fat snacks such as olives.

You should feel pretty normal on day one. On days two and three, you might feel hungry or unsatisfied (but not dizzy or on the verge of passing out) at mealtimes, Foroutan says. On day four you should feel good, and on day five when stem cell production kicks in, great.

“Everybody is after anything that helps slow down aging,” she adds, and fasting-mimicking may be an answer.