Jennifer Aniston Says She’s on the 16:8 Intermittent Fasting Diet—But What Is That?

Is the 16:8 diet good for you?

Some advocates of the 16:8 diet claim it helps control blood sugar levels and boost brain function, but there’s little scientific evidence to back these up. And if you don’t stick to nutritious food during the eight-hour window, any positive effects are quickly negated. In other words, 16 hours of fasting doesn’t compensate for eight hours of stuffing your face with junk food.

For the best results, you should be careful about your choice of eating window. According to Freirich, it should start early in the day, preferably no later than about 10 a.m., and finish early in the evening. “This allows for the energy you consume during your eating window to serve your activities throughout the day, plus it’s in line with our natural circadian rhythms, presuming you wake up around 6 a.m. to 9 a.m.,” she explains. If you choose a much later eating window, say 4 p.m. to 12 a.m, you could actually see weight gain, she warns.

Wait… is celery allowed during fasting? Doesn’t it have some calories?

Aniston also told Radio Times that she likes to start her day with a celery juice around 9 a.m., which some fasting purists might not agree with. (Typically, intermittent fasting permits nothing but water, tea, or coffee for the entire 16-hour fasting period). “There are no super specific rules to intermittent fasting, however, having anything with calories like celery juice is technically not fasting,” confirms Harris-Pincus.

But hey, it’s not as if Aniston’s having soda for breakfast. And she’s not the only one to extol the virtues of celery juice—it seems like every social media influencer is celebrating the green stuff right now.

Any magical health benefits of celery juice are exaggerated “beyond the fact [that] it’s a vegetable,” says Harris-Pincus. Yet if it works for you, go for it. “I always tell clients that if they like celery juice, then have some,” she adds. “Make half of your food volume fruits and veggies, and you’re good to go.”

Is there anyone who shouldn’t do intermittent fasting?

The 16:8 diet isn’t suitable for everyone. Freirich doesn’t advise it for people with diabetes or problems with low blood pressure or low blood sugar, as well as children, athletes, and pregnant women. “These groups of people need food more consistently throughout the day or have high energy needs that are difficult to meet with time constraints,” she explains.

Are there any side effects to be aware of?

Intermittent fasting shouldn’t come with any nasty side effects, but—like all restrictive eating plans—it’s important to not let it take over your life. “Sometimes people shy away from social events because they interfere with the timing of the fast,” Harris-Pincus says. “I never recommend letting an eating behavior determine your interaction with friends, family, or coworkers.”

It’s also important to pay attention to exercise in relation to fasting. Harris-Pincus warns against exercising while fasting or waiting several hours after exercising to eat your first meal. “You want to feed those muscles and replenish carbohydrate stores after an intense workout,” she says.