My role as a dietitian is to guide my clients in determining the best nutrition habits, lifestyle routines, and stress-reduction techniques to help them feel healthy, confident, and comfortable. Over the past 10 years of nutrition counseling, I have learned that what works for one person will not work for everyone. The body is a complicated machine and every individual has a different set of tools. Intermittent fasting is just one of those tools.
Time-restricted eating, most often referred to as intermittent fasting (IM), had been on my list to experiment with for over a year. Despite the emerging research, I didn’t think it would work for me. I get up early and I like to start my day with breakfast right away. If I workout in the evenings, I eat something afterward to help with recovery. Going 14-16 hours without food sounded like hell.
First, what is intermittent fasting?
There are many different types of fasting. I chose to focus on the type I believe can be most sustainable, also known as time-restricted eating. Put simply, it is paying attention to the amount of hours within a 24-hour cycle that you are fasting (not eating). Let’s say you had a snack after dinner or finished a glass of wine around 8:00pm. The next morning you start drinking coffee at 7:00am. Your overnight fast lasted a total of 11 hours. Your fast ends the second you put any food, coffee, or tea in your system (water is the only thing that doesn’t count).
To learn more about the different types of fasting and what would work for you, get our Quick Guide to Intermittent Fasting here.
Every living thing and every cell in the human body follows a circadian rhythm. There are periods of the day when the body is more metabolically active. There are also optimum times for repair and hormone production. For example, we are most insulin sensitive in the morning and least insulin sensitive at night, meaning that eating a high carbohydrate meal at night would be harder for your body to handle. This makes sense biologically because the body uses carbohydrate for fuel and it doesn’t serve you well to overfill your fuel tank when you’re heading to sleep (the optimal time for repair and recovery). To be clear, I’m not saying to stop eating all complex carbohydrates at dinner. I’m saying that your body can’t handle the 2 scoops of ice cream as well at 9:00pm as it could have earlier in the day.
All of our organs also have their own clocks that regulate when they should be working and when they should be resting and repairing. When we eat, we tell our liver genes when to turn on. When we don’t, they turn off. Almost every organ outside of the brain begins to follow and adapt to when we eat. Tapping into those optimal times of work or recovery and allowing our bodies to function on a natural rhythm can have many positive health benefits.
What we already know:
People who work night shift are more likely to have diabetes, heart disease, and obesity.
Late-night eating is associated with a higher risk of obesity, metabolic syndrome, and poor cardiovascular health.
When you eat close to bedtime, blood flow is directed to the stomach to help with digestion which makes core body temperature remain high.
The research:
Mice that are fed only within an 8-12 hour window have reductions in fat mass, increased lean muscle, lowered inflammation, improved heart function, higher levels of ketones, improved repair processes, and improved aerobic endurance.
In 2 groups of identical mice, one group was given unhealthy chow (similar to humans eating cheese, nachos, ice cream, etc.) and had unlimited access to it at any time of the day or night. The other group got the same chow but they had to eat it within 8-12 hours. Time was restricted but calories were not. Surprisingly, the mice eating within the 8-12 hour window did not have diabetes, develop obesity, and had normal cholesterol and liver function. Even eating the same crappy food, their livers were able to metabolize it better.
This does not mean that nutrition doesnt matter (as shown in other many, many, other studies) but it does show that if you are not willing to change anything else, just changing your eating schedule could improve your health.
Another awesome thing is that the mice showed the same benefits eating within the time restricted window for 5 days a week as they did for 7 days a week. That is super helpful for us humans because, hello, weekends! So even if you feel like you can’t eat dinner by 6pm on weekends, you may still be able to do it during the week and see some of the benefits.
As of my review, there are at least 13 more published mice studies demonstrating the health benefits of time-restricted eating including increased insulin sensitivity, decreased cholesterol and triglycerides, and lower blood sugar.
Now how does that translate to humans?
Most people eat naturally within a 15 hour window. Unlike the mice that ate the same amount of calories when researchers reduced their feeding window to 10 hours, humans tend to naturally decrease their caloric intake by an average of 20% when eating within a smaller window. This makes sense because if you are not eating or drinking past 6:00pm, you are much less likely to drink alcohol, go for an ice cream, grab a handful of chips, etc. People also report sleeping better and feeling more energetic in the morning.
Small studies in overweight adults have found that an overnight fasting period of 14 or more hours led to decreased caloric intake, weight loss, satiety at bedtime, and improved sleep.
A comprehensive review of existing literature by the American Heart Association stated that periodic fasting regimens reduced weight and lowered cholesterol and triglycerides.
I could keep listing out more and more research here, but let’s get to the practical stuff.
My experience:
I’ve been eating within a 10- 12 hour window for 5-7 days a week for about 8 weeks, with a 5 day break in between. I’ve found that the 11 hour window works best for my schedule.
The biggest difference that I’ve noticed is sleep. I sleep SO hard and it is glorious. It’s rare that I wake up in the middle of the night now, which has been an issue for me in the past.
I don’t weigh myself on a regular basis. The only time I dust off the scale is when doing this type of experiment in order to report any changes. Right now I’m down about 6 lbs from what I would say is my “normal weight.” Throughout this process, I have continued to do Crossfit 3-4 times a week. I haven’t seen any decrease in strength and I actually saw improvements in several workouts that were cardio-based, which is hard to say whether that’s just because I’m getting better at those movements (rowing and assault bike) or it has something to do with the fasting (perhaps the increased endurance as shown in the mice study).
I’ve found that the need to eat a large meal for dinner is a learned behavior, not necessarily a physiological need. Do I want to eat something when I come home from work late? Yes, especially when I first started this process. But, when I really thought about it, was it because I was actually hungry? No, truthfully, my body was not sending me a signal that I needed more food. Eating late was most times a form of reward for making it to the end of the day. Even if I do a late workout, I’m not eating anything afterward. I’m not experiencing any increase in muscle soreness or as a said above, decrease in strength.
The downside:
There’s no such thing as a family dinner. If I’m not getting done with work before 5pm, I’m packing lunch and something “dinner-ish” to eat at the office then not eating anything when I get home. I get up early and usually do my workouts in the morning and I like to have some fuel in the tank. If you value being able to eat dinner in the evening with loved ones, you may just have to commit to eating dinner a little earlier and eating breakfast a little later.
During the second and third week, I was craving sugar and candy like crazy. Some of that had to be because we had a bunch of Easter candy (which is unusual to have in the house). I ate what I wanted of it, but it had to be before 4 or 5pm. I also noticed I was super moody in the evenings that week. I still like a good dessert, but those crazy cravings did go away.
When I did decide to eat late on a Saturday night, it wasn’t a good experience. My stomach felt hard and bloated and my digestive system was doing nothing to break down that food. It wasn’t unbearable but it was enough to make me not want to “cheat,” even if I could get the same results only doing it 5 days a week.
Will I continue?
Surprisingly, yes. I feel good, I’m seeing the benefits, and there’s nothing about this that I don’t find sustainable. I say surprisingly because usually when I do these experiments (like keto or vegan) I’m excited for them to be over with. This feels more like a new habit, something that I just do naturally. I leave for Italy this week where most restaurants don’t even open for dinner until 7:30pm. It will be interesting to see how my body adjusts to the later schedule.
Summary of the possible benefits:
- Decreased risk of chronic disease such as diabetes and cardiovascular disease
- Weight loss
- Improved endurance
- More restful sleep
- Increased lean muscle mass
- Improved gut microbiome
- Better digestion (with some evidence to suggest improvements in IBS-related symptoms)
How to try time-restricted eating:
Start paying attention to the first time you eat or drink anything other than water in the morning (medications count). Make an initial goal of staying within a 12 hour window. After a week, see if you can cut that down to 11. Keep going (up to 8) until you feel like you’ve reached a sustainable window that works for your schedule. For me on most days, it’s 11 hours. If you are struggling, just know that after 2-3 weeks, hunger levels go way down around bedtime. AKA you get used to it. Your hunger hormones will adjust to your new schedule. You may notice after about 5 weeks if you do eat outside your window, you don’t feel so great. You may feel lethargic and feel like the food is just sitting there. Use that as motivation to continue to stay within your normal window.
Keep a note in your phone of how you feel from day to day. Make a list of the pros or cons that you experience. Give yourself at least a month to adjust. Use your notes to help you decide if eating within a certain time window is sustainable and beneficial for you.
Helpful apps:
Zero: A super simple app with one button to start and stop fasting (basically a stopwatch that stores your data). It counts your fasting hours (not your eating hours). I shoot for at least 13 hours of fasting per night (aka eating within an 11 hour window).
myCircadianClock: This app helps you to understand how your daily patterns affect your health while contributing to research. Dr. Satchin Panda and his group are using the data from real people to shape their future research. You log your meals (via photo), exercise, and sleep. For the first 2 weeks, you share your normal habits. At the end of the 14 days, you’ll be able to see all of the data and set specific goals. The app is a bit old school and clunky, but you’re contributing to real world research!
Resources/Learn more:
Dr. Satchin Panda on Time-Restricted Eating and Its Effects on Obesity, Muscle Mass & Heart Health
Dr. Satchin Panda on Practical Implementation of Time-Restricted Eating & Shift Work Strategies
Fasting Regimens for Weight Loss
Metabolic Effects of Intermittent Fasting
If you have further questions about fasting or time-restricting eating, reach out!