As science continues to examine the role fasting plays in healing our bodies and balancing our body weight, it seems increasingly likely that temporarily restricting our calorie intake has the potential to lower blood pressure and protect us from the aging process . But with so many online "authorities" touting different eating windows and fasting methods, how long should we really aim to fast and when is the best time of day to eat? Plus, is it safe to fast as we age? We spoke to Steve Hendricks, author of The Oldest Cure in the World: Adventures in the Art and Science of Fasting, to get his thoughts.
Steve Hendricks has studied fasting from both an academic and personal perspective, even settling into various fasting clinics to get a well-rounded perspective. "I'm 52 and I first became interested in fasting in my 30s," he says. "Like many people, I started gaining weight in my 20s and I was interested in how to get it off. Fasting isn't a magic bullet for weight loss, but it can be a useful tool. Before getting into fasting, I had been experimenting with simple calorie restriction, which simply means eating less every day, but CR is notoriously hard to achieve because of the constant hunger gnawing.
“I was pleased to discover that, like so many people, fasting is far more doable than CR because fasting actually suppresses hunger. Better yet, fasting unleashes many of the same healing mechanisms as CR. Our bodies are constantly repairing cellular damage, damage that can eventually become disease, but typically, very little repair occurs because the body is so busy doing other things like processing the nutrients from our meals. But when we give the body a break from processing nutrients, it uses the downtime to speed repairs, prevent disease, and give us an extra opportunity to live longer. It's a wonderful mechanism, refined through at least a billion years of evolution, and we now have some good science to guide us in using it.
How long should we fast?
Studies have shown that even prolonged fasting of four to 21 days is beneficial, providing cardiovascular protection benefits, fat loss, and emotional well-being. "Most fasting doctors recommend that adults do some form of maintenance fasting of 1 week or more under competent medical supervision once a year," says Hendricks, who believes that daily intermittent fasting should always include a timed calorie restriction for at least 12 hours around the time to receive benefits. "t coincidentally, 12 hours is about the point where people start reporting that they feel better and have more energy than if they ate all day," he says. “With every hour you shorten that 12-hour window, the health gains could increase significantly. Scientists aren't exactly sure of the ideal eating window, but most seem to think it's around 6 hours. However, narrowing the time window to less than 6 hours may not be helpful. For example, if you eat in a 4-hour window, some scientists worry that the disadvantages of cramming a full day's food into your gut in such a short amount of time might outweigh the benefits of a longer fasting period."
Is there an optimal time to eat?
"It's a lot healthier to organize your eating window earlier in the day," says Hendricks. “Our circadian rhythm has us hardwired to digest food and process nutrients most efficiently in the morning and early afternoon. Apparently, the longer the day, the worse our bodies perform at such tasks, and it doesn't seem to change that. So when we eat in the late afternoon, let alone in the evening or at night, food and nutrients stay in our gut and blood vessels longer, where they can wreak havoc. Eating later disrupts many of the cleaning and repair processes our bodies perform overnight while we sleep, potentially leading to a higher risk of disease.
"The science on exactly when you should start your eating window isn't out yet, but I think most scientists in the field would say it's likely to go down about an hour or two after you wake up. For many people, that would mean eating in a window of around 8 a.m. to 2 p.m. every day. I know it sounds crazy having dinner at 1:30pm. instead of 6 p.m. I certainly wasn't looking forward to doing it when I first tried it, but people who have made the switch, myself included, report that after the first few days it's proving remarkably easy to make a change. If for some reason you can't eat on this schedule, a compromise might be to eat dinner at the usual time but keep it light and stack most of your calories for breakfast and lunch.
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Is It Safe to Fast at Any Age?
Hendricks believes fasting is something that could be adopted from adolescence by initially eating in a 12-hour window, but there's no reason to give up the habit as you get older. "Many scientists and fasting doctors have concluded that daily fasting of up to about 18 hours is safe and healthy for adults of all ages," says Hendricks. “There are so many health benefits of eating in a narrow feeding window; our body-wide inflammation levels will drop, insulin sensitivity will increase, more antioxidants will be produced, and more worn-out cell debris will be recycled. The ideal age to start is early in life, to just establish daily fasting as a normal way of organizing your eating habits.”
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Tips for getting started with intermittent fasting
"If fasting sounds hard, just do it first," says Hendricks. "If you're now eating 15 hours a day, it might be a challenge for you to cut down to 6 hours straight away. Fasting doctors and researchers recommend simply taking an hour out of your eating window for a week or so, and once you're comfortable with that, skip another hour, then finally another hour. If you can get down to 6 or 7 hours, great. If for some reason that's too hard, congratulate yourself on eating in as tight a window as you can achieve. Every time slot of 12 hours or less gives you some health gain.
"Also, don't let perfectionism get in your way. If you ever want to go out for a late dinner with friends, it won't throw you too much off track, although you'll probably find yourself feeling a bit sluggish the next morning. If you've been training hard in the middle of the day and later find you haven't eaten enough during your eating window, eat a little more so you don't starve all evening and your muscles have the building blocks for recovery."
The World's Oldest Cure: Adventures in the Art and Science of Fasting by Steve Hendricks is available now.