Laura B. Enyedi, MD, is a pediatric ophthalmologist at the Duke Eye Center in Durham, North Carolina. She is a professor of ophthalmology and pediatrics at Duke and is the university’s principal investigator for the Pediatric Eye Disease Investigator Group. She is the editor for the pediatrics section of the Academy’s ONE Network and a clinical spokesperson for the Academy. The Academy asked her to share her experience with intermittent fasting.
Please note: “I am sharing my personal experience, not medical advice,” said Dr. Enyedi. “What worked for me might not be applicable to everyone—we all have unique bodies, preferences, and needs.”
How Have Your Food Habits Evolved?
I have eaten my way through several types of diet:
- childhood: meat and potatoes
- teens and early twenties: low calorie
- residency and fellowship: low fat (high in sugar and other carbs)
- late 20s and 30s: I was almost continuously pregnant or nursing and didn’t have time to think about my diet
- 40s: portion control and sometimes low carbohydrate (difficult because I love carbs)
- most recently: intermittent fasting.
I have always been a fan of fruit and vegetables. Although I eat meat, it hasn’t been a large part of my diet since childhood.
Why Intermittent Fasting?
Until recently, it was always easy for me to control my weight with exercise and portion control. That recently stopped working, and I found myself gaining weight, especially in my midsection, despite eating very little and exercising almost daily. This is when I discovered intermittent fasting (IF), which is the simplest and most effective way I have found to control my weight (especially belly-fat accumulation), while maintaining muscle and feeling less hungry.
IF burns fat and preserves muscle, provides mental clarity, and has lots of health benefits.1 For me, it is a much easier and more appealing way to get into ketosis than eating a ketogenic diet.
Ketosis is a fat-burning, rather than glucose-burning, mode of metabolism. When you get there, you will have more energy and mental clarity, and less hunger. Everyone gets into ketosis at different rates. I get into ketosis quite easily, which make IF ideal for me. Others may need longer periods of fasting to get into ketosis, and may find it more challenging, especially at first.
What Does IF Involve?
There are many ways to approach IF. You can find the way that works best for you and change it up as your needs and activities change. If you simply skip breakfast and don’t snack between dinner and lunch, you have done a 16-hour fast and can then eat between noon and 8:00 p.m. (Note: Fasting means no sugar in your morning coffee.)
I do 20-hour fasts (allowing four hours for eating) four days each week (on clinic/OR days) and about 14- to 16-hour fasts on weekends. When I travel, I sometimes do 20 hour fasts, sometimes shorter fasts, and sometimes I don’t fast at all.
I have found that exercise during fasting has been fine for me, and it helps me to get into (or stay in) ketosis.
Tips for Getting Started With IF
# Make sure it is safe for you. IF may not be for everyone. For example, it might not be appropriate if you are medically fragile, elderly, or pregnant, etc. Ideally, you should consult your physician before you start IF.
# Start small. Start by fasting for a small period of time, and then extend that by an hour a week (e.g., fast for 12-hours periods during your first week, 13-hour periods during your second, etc.). I initially felt more comfortable skipping IF on OR days, but now have no problem doing surgery while fasting.
# In lieu of breakfast. On the days that I do IF, I add whipping cream (pure fat) to my morning black coffee. It is a treat that keeps me fueled until I enter ketosis. If you don’t do dairy, you can add another pure fat, but no sugar or carbs (they would break your fast). Some people feel that anything that is less than 50 calories is okay during the fast (which would allow a tiny bit of protein or carbs, such as almond milk).
# Hydrate, and watch for dizziness. Drink lots of water and have some salt if you feel weak or dizzy. (Some people advocate a pinch of pink Himalayan sea salt under the tongue. This also provides magnesium and other trace elements.)
When I first started IF, I would drink bone broth (high in protein) or chicken broth. Both also have salt which can help you feel better when you start IF. I no longer feel any need to do this.
Early on, there were times when I felt weak and dizzy. In my case, I am convinced that a lot of that was due to dehydration and/or was “in my head.” I have zero problems with that now, even when exercising during fasting or doing extended fasting.
# Breaking your fast. Eat what you want (within reason!) when you are not fasting. It is ideal to break your fast with something healthy. I usually eat a handful of almonds when I get home. Don’t forget to also drink a big glass of water!
# Weekdays versus weekends. I find IF easy when I am working and distracted, but it is almost impossible when I am home on the weekends. I do much shorter fasts during the weekend. It is fine to skip fasting if there is a social event or some really delicious food that you want. You can always fast another day.
How Do You Overcome Hunger While Fasting?
Embrace the feeling of hunger—it usually means you are having a temporary spike in ghrelin (the hunger hormone). It often spikes around mealtimes and will naturally ebb, so the feeling of hunger will go away before you chew your arm off.
Also, when you are hungry you are usually burning fat. Notice your feeling of hunger, reassure yourself that all is okay, and move on.
Food Fact You Wish You’d Known When You Were Younger?
When you eat may be just as important as what you eat (this is the principle of IF). Breakfast is not the most important meal of the day!
Biggest Nutrition Mistake(s) that Ophthalmologists Make During Residency?
This depends on when you did residency and what nutrition fad was popular at that time. I trained during the days of the low-fat craze, so I fueled up on sugar and other carbohydrates—which wasn’t ideal. On the other hand, because there is little or no time to eat during training, I was also practicing IF, and this may have been helping me all along without me realizing it!
Food Tip(s) When You Have Limited Breaks During the Day
Tip #1. IF is perfect for busy physicians.
Tip #2. Drink lots of water throughout the day. My challenge is that I can’t have water in the clinic, and I don’t have time to go to the office to drink water. So I drink a big glass of water first thing in the morning, I try to drink another 16-oz glass all at once at some point during the day, and I drink another big glass of water when I get home. I also try to remember to drink big glass of water before any caffeine or alcohol intake. I find water easiest to guzzle down when it is at room temperature, but hot water can be nice to sip on when it is cold. Always feel free to add lemon or drink herbal tea (not caffeinated and no added sugar or milk) during IF.
How to Get Into Better Feeding Habits
Start with a small, measurable goal. Writing it down can help you to be accountable to yourself. For example:
- I will fast for 16 hours three days/week.
- I will drink 16 oz of water every morning.
- I will drink one less serving of alcohol (or soda, or whatever your vice is) this week.
If successful, you can build on your initial goal. If not, try again or set a slightly different goal. For example, you can link a habit that you want to gain with another that you already have:
- I will drink a big glass of water immediately before filling my coffee cup in the morning.
What Resources Would You Recommend?
Three resources that might be helpful:
- “Effects of Intermittent Fasting on Health, Aging, and Disease” is an article from the New England Journal of Medicine that explains a lot of IF’s health benefits.1
- Why We Get Fat and What to Do About It (Anchor Books, 2011) argues that much of the medical doctrine on weight loss may be wrong and may have contributed to the obesity epidemic in the United States. This is a fascinating read and full of information backed by science.
- “Fasting vs. Eating Less: What's the Difference? (Science of Fasting)” is a 12-minute YouTube video that helped me to understand some of the differences between simply restricting calories, which can lead to starvation, and IF.
1 de Cabo R, Mattson MP. New Eng J Med. 2019;381(26):2541-2551.