16-Hour Fast FAQ

Short fasts benefit you in a few ways. One is simple calorie reduction: When you don’t eat for an extended period of time, you naturally (and effortlessly) eat less overall. Another is that your digestive system works better when it has a chance to rest and recover—and in fact, your body can repair itself better when it isn’t constantly diverting energy to digestion. Third, fasting causes major changes in several crucial hor mones that impact aging and weight, including insulin and  growth hormone. Fourth, fasting is one of those hormetic “small stresses” that stimulate the longevity gene pathways. Fifth—and this is big—fasting kicks in autophagy, the cellular  detox process critical to strong immunity and aging well.

So here’s the plan: A couple of times a week, have dinner on the early side, and the first meal the next day a little later, leaving a good 16 hours in between. This simple practice is incredibly powerful. And it’s not that difficult. You make it a point to finish dinner by 7 or 8 p.m. You’re sleeping for seven or eight hours, we hope (see page 30). In the morning, you get  up and have a big glass of water. And then you eat a nice nutritious meal at 11 or 12.

Admittedly, fasting can be a challenge at first. You don’t have to go from zero to 16 if this sounds insane to you. Start with 12 hours, then move to 14, building to 16. Once your body adjusts, fasting feels great and is weirdly liberating. Realizing that you don’t need to eat all the time—that your body functions well and doesn’t require constant loading—is freeing, and helps you break that carb addiction. Soon you’ll find your fasting days refreshing: less of a sacrifice and more of a break. And you may find that mornings are especially productive when you’ve taken food out of the equation.

Here are answers to some frequently asked questions about fasting:

What’s the difference between 16-hour fasting,  intermittent fasting, and time-restricted eating?

There isn’t really a difference. They’re just different ways of  saying the same thing, which is that it’s a good idea to have a window during which you eat (we suggest eight hours) and a longer stretch of time when that window is closed (we suggest 16 hours).

Why 16 hours?

Because studies show that it takes about 16 hours of fasting for autophagy to kick in and do its job. Feel free to do 18 or  20 hours if you like.

What if I can’t go 16 hours?

Do what you can. Any short fast is a good fast. Twelve hours is better than 10, and 14 is better than 12. If you increase gradually, it may be easier than you think.

How often should I do this?

Start with two days a week. Generally, newbies find it easier to fast on workdays. The ultimate goal is to do this all the time, with 16 hours between your last meal of the day and your first meal the following day. Folks who do find it very comfortable and report weight loss, increased energy, and better sleep. If  that feels unrealistic to you, don’t sweat it. Get yourself up to  three days a week, and you’ll notice benefits.

But what about my midnight snack?

If you’re a night snacker, you need to find ways to close down the food portion of your day. On fasting nights, clean up and shut down the kitchen right after dinner, so you have no need to step in there. If you’re a morning eater who wakes up starving, the first couple of fasts can be a challenge. When your body adjusts, you won’t wake up craving food. You’re reprogramming yourself. It may take a little while, and improving  your diet as you go will help.

What if I exercise in the morning?

It’s actually great to exercise without eating because there’s no glucose being used for energy, so your body burns fat. It’s a myth that you have to eat something before you exercise.

Can I have water?

Yes, water is great in the morning because it rehydrates you and can get things moving.

Can I have coffee in the morning?

The jury’s still out on whether it’s okay to have coffee while fasting. Strictly speaking, the answer is no. Some folks (includ ing us) go with the theory that a cup of coffee or tea with no  carbs or protein does not end your fast. Others say that as soon  as you have anything but water—including black coffee—the liver is working. We don’t quite know yet. If it’s easy for you to go 16 hours with nothing but water, go for it. That’s ideal, and you’ll probably feel amazing. If you do have coffee or tea, don’t use regular milk or half-and-half (and definitely don’t  use sugary alternatives like sweetened almond or oat milk), because they contain carbs and protein, which will cause your body to secrete insulin. It’s important not to trigger insulin, so if you need something in your coffee, use a pure fat like MCT  (medium-chain triglycerides) oil, which contains no carbs or protein. To review: Best is just water. Second-best is tea or coffee without sugar or milk. Third is tea or coffee with MCT oil.  

What about longer fasts?

There’s not just one way to do this. Intermittent fasting is pretty easy, and there are a few variations you might want to look into. But if you want to explore more intensive fasting— like one whole day per week with no food, or multiple days  of water-fasting—don’t do it without the supervision of your doctor.

What about the fasting-mimicking diet I keep  hearing about?

Researcher Valter Longo’s fasting-mimicking diet shows excellent results. It’s a good option if you prefer it. For five consecutive days once a month, you eat very little—a low-calorie,  low-carb, low-protein diet (no animal protein); it has positive effects on aging biomarkers. This diet lines up completely with the rest of the advice in this book. You can go to ProLonFMD.com to learn more.

What if fasting doesn’t get easier for me?

If your diet contains a lot of sugar and starch, fasting can be harder in the beginning. Take a week to cut way back on sugar,  drop all grains, and even eliminate legumes. Then try again, and see if fasting is a bit easier. It should be.

Is 16-hour fasting safe for everyone?

There are some people who shouldn’t fast. Don’t fast if  you’re on multiple medications, if you’re an athlete training  at a high level, if you’re extremely stressed, or if you have a  history of disordered eating. Although fasting stresses the  system in a good way, it could be too much if your system is  already overloaded from outside stressors. If you’re in a rough place emotionally, fasting may not be the best move for you. Obviously, if you’re pregnant, don’t fast. Kids shouldn’t fast. If  you have any concerns, check with your doctor first.

This is an excerpt taken from my book, The New Rules of Aging Well – Artisan, October 2020.

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