Rhonda: What sort of time-restricted eating pattern do you follow, Satchin?

Satchin: So I try to do around 10 hours' time restricted eating. So that means if I start my breakfast around 8:00, then I try to finish dinner by 6:00, 6:30. And what is interesting is if I occasionally eat at 8:00 or 9:00, even if it's a small snack or something, then that night my sleep is bound to become really fragmented. So I have a negative feedback loop that if I eat less then I don't sleep well, and then the next day will be really crappy, I need more caffeine and other stuff to stay awake. So that's my eating habit these days.

Rhonda: Do you personally count caffeinated beverages that don't have any calories like black coffee resetting your clock in the morning?

Satchin: Yes. There are actually studies showing that a cup of coffee is equivalent to an hour or two hours of bright light. That's the impact on circadian clock. So it does impact our sleep. And definitely, no coffee after 2:00 in the afternoon because if I drink coffee after 2:00, then my sleep will be totally impaired. The other day I had coffee, a big cup of coffee actually around noon and that completely disturbed my sleep that night. So we do consider that coffee might disrupt your circadian rhythm. But at the same time, we understand that a lot of people cannot function without coffee, particularly night owls who are getting less sleep. It's much better to be caffeinated than be sleepy when you're driving to work. Also, some people though, the work requires them to be completely alert. For example, people who work in the entertainment industry who have to go in front of the camera at 4:00 in the morning, if they don't have enough sleep, it's better to be caffeinated to do your job, otherwise, you'll lose your job. So we make those exceptions. And in our studies, we ask all of our participants to log everything so that we can go back and redo the calculation to see whether caffeine intake, even without cream and sugar or with cream and sugar, had any impact on time-restricted eating, which led to some changes and health consequences. But I must say that since all of our studies are relatively small in number, and also the number of people who drink black coffee outside the eating window in our study is maybe even smaller, we're yet to see strong statistical power to dissect this effect.

Rhonda: Great. Have you seen any data, are you aware of any data suggesting any time-restricted eating differences between men and women? Perhaps, there's obviously a fasting component to time-restricted eating when you're not eating. Other than pregnancy and breastfeeding, do you know of any concerns for women, for example, regarding time-restricted eating?

Satchin: No, time-restricted eating is a very loose and broad term. So that means even if somebody...as I said, only 10% of adults eat for 12 hours or less. So that means if somebody was eating for 16, 17 hours, and even if they're pregnant or breastfeeding, they can come down to, say, 14 hours or 12 hours of eating, 13 hours of eating. And if they continue with that routine, they may still see some benefit. But for medical risk reason, we don't suggest that people who are pregnant or breastfeeding sort of even try to think of time-restricted eating. But it's a common sense that if you adopt a good habit, even when you're expecting or when you're breastfeeding, even if it's 13 hours of eating and 11 hours of constant downtime, that will have an impact on the family because when your baby is growing up on that 3 to 5 years of age, they'll slowly pick up that habit of eating so within 14 hours or 11 hours and then slowly they can sync. So now, coming back to the adverse effects, so that's why I say that anyone from 5-year-old to 100-year-old year old can do 12 hours' time-restricted eating without much concern about adverse side effects unless the person has type 1 diabetes, which is equivalent to brushing your teeth once a day. And if you are trying to do 10 hours' time-restricted eating, then it may be better that if you're breastfeeding or if you're pregnant, then it may not be the ideal time-restricted eating window. Ten hours might be too restrictive. But for the rest of them, again, without type 1 diabetes, it might be brushing your teeth twice to take care of your health. And if you are doing eight hours' time-restricted eating, it's almost like brushing your teeth twice, flossing your teeth, taking too much care of your health. So if you can do it for lifelong, then it may be better. But at the same time, be careful about not reducing your calories too much because occasionally we do see some people try to do 8 hours' time-restricted eating, at the same time reducing calories to almost 1000 kilocal per day and increasing their activity level, running half a marathon once a week or a 5K 3 times a week. And that can adversely affect your body weight, can affect even your bile acid metabolism and might increase risk for kidney stones. So we don't try to combine too many things at the same time. And 12 hours' time-restricted eating, as I said, maybe safe for most of us, except a type 1 diabetic, unless they have a continuous glucose monitor and they have some calories handy if they become hypoglycemic.

Rhonda: And you mentioned children five and over, do you think that, kind of much like your anecdote, if you eat a snack or something later in the evening, you have more fragmented sleep? Is that something that you think maybe hold true for younger children like preschool age as well, or is there any evidence of that?

Satchin: No. I don't think there is any evidence because it's very difficult to do studies on children. We don't want to intervene too much. But if you think about...the general recommendation is children of that age should sleep for 9 to 10 hours every night. So if you're a good parent and you're putting your child to sleep for 8 to 10 hours, then hopefully, you are not waking up your kid in the middle of the night to feed something... so they're fasting for 10 hours when they're sleeping. And then after waking up, it's not that they wake up and immediately eat something, they have to brush their teeth, and then maybe get cleaned up. And let's add one hour there. So that's almost 11 hours. And similarly, just before going to bed, they might have half an hour to one hour before bedtime when they had their last calorie. So in that way, you can see how a 5 to 10-year-old can easily fall into eating within 12 hours or, say, 13 hours window, which is not that bad. It means if you put together the sleep hygiene, and the common sense bedtime ritual, and wake-up time ritual, then you can easily see how we can maintain a 12 to 13 hours eating window for a 5 to 10-year-old.