A little more than a year ago, I tried intermittent fasting (IF) to prove my husband wrong. During the last year of my nutrition program, I did all my projects on the topic of fasting but came to conclusion that this might not be just another fad diet. One project included trying a diet for 2 weeks. Of course, I decided to finally attempt a type of IF called time restricted eating by following an 18-hour fast with a 6-hour feeding window.
The beginning was brutal. I was a breakfast person! I loved making overnight oats, eggs and don’t even get me started on pancakes, waffles and cereal. The first 2 days of the time-restricted eating regimen were terrible. I binge ate both nights. I decided to switch my feeding window from 6 hours to 8 hours to make it a little easier on myself. After a few days, my body started getting used to eating at 11am. I wasn’t as ravenously hungry as I used to be in the mornings. I was able to drink my black coffee and plenty of water until my feeding window began. A small confession here; I am usually running late to everything. About a week into IF, I realized that the new regimen was convenient for me! I didn’t have to spend any time in the mornings making breakfast or eating! That saved me 20 minutes each day (and helped with my time management). Not only was I saving time in the morning by not eating breakfast, but I was also more productive! About a month in, I noticed a difference in my mental clarity. I was able to concentrate more in the mornings up until after lunch. I clearly noticed a difference in my ability to process information. It was like night and day! At that time, I did not know that this was the start of a life-long endeavor.
Before I started working as a dietitian, I used to exercise 5-6 days a week which helped maintain my weight at 112-115 lbs. After starting IF, I lost 8 lbs and now my set point weight ranges from 108-110 lbs WITHOUT exercise (I couldn’t find much time for it once I started working full-time plus commuting). Back in the day when I was eating 3 meals and 2 snacks, I would gain weight pretty quickly if I didn’t exercise. Daily fasting became my “metabolic exercise”. I was reaping some of the benefits of exercise through fasting without actually exercising. In Dr. Jason Fung’s book, Obesity Code, he explains that IF drops your set point weight where as other fad diets do not. There's a hormonal change that occurs during fasting that other calorie restriction diets do not do.
Now, let’s fast forward 7 months to when I started working with weight loss patients. The dietitian before me recommended books to read, one being the Ultimate Guide to Fasting (by my favorite MD at the time, Jason Fung). I didn’t know that dietitians could recommend a fasting regimen, but I quickly reminded myself that I am an evidenced-based dietitian. The science and mechanisms were clearly there and I didn’t understand why the Academy of Nutrition and Dietetics (AND) wasn’t making this a standard of care for those with type 2 diabetes, obesity and metabolic syndrome. That’s when the reading started. I was commuting 2-4 hours a day to my work, which left a lot of time-opportunity for audiobooks. At first, it was difficult but after a few months, my brain was able to listen to audiobooks on 1.75 speed and absorb more than 75% of what was being said. I also began reading science literature on fasting to better understand mechanisms.
When I started seeing weight loss patients, I decided quickly that fasting may not be for everyone, but 6 months later, I’d take that back. Seeing my patients follow a time-restricted eating regimen daily and lose weight with ease was very satisfying and only solidified my belief in fasting even more. I started sharing this information with my dietitian friends but not everyone was convinced. I kept reading and bringing more evidence back to them only to receive more doubts and counterarguments. Of course, I am grateful that they were skeptical as it has only made me a more informed dietitian on the subject of fasting.
I concluded that IF was the perfect “diet” for weight loss. I don’t like to call it a “diet” because there are no requirements on what to eat; IF is focused on the timing of meals. Of course, eating a healthful diet in combination with a fasting regimen is ideal but that’s a topic for another blog post.
In my reading, I have come across some people that should not do a prolonged overnight fast (more than 12 hours). This includes children, pregnant/lactating women, type 2 diabetics on insulin, and those with an eating disorder, low BMI (<18) or gallbladder disease. If you are one of the above, I recommend talking with your doctor before starting any fasting regimen.
That leaves everyone else! If you are wondering if you could do it, even though you aren’t trying to lose weight, I highly suggest starting with an overnight 12 hour fast daily. Most people think they already do this; however, an ongoing research study suggests that the average “feeding” window is 15 hours. This exhausts our digestive system. Every time we eat, our bodies have to produce hormones and digestive enzymes. Towards the end of the day, especially as it gets dark outside, our metabolism does not work as efficiently. It slows down in preparation for sleep. Humans are not meant to be eating all day and all night, just like we aren’t meant to be awake all day and all night. This is where I bring in a concept called circadian rhythm. This is usually associated with our sleep and wake cycle. We are diurnal creatures! What most people don’t realize is that our digestive system is also on a biological clock. If we eat at 8am every day, our body will eventually get used to receiving food at 8am. That is why it may be difficult initiating a time-restricted eating regimen initially. When you change the time of your meals, your body will be confused so it’s best to eat your meals at the same times every day. This is why it was difficult for me and many others to start IF. Our circadian clock gives us cues (hunger/ghrelin) that it's time to eat; However, your body can get used to eating at 11am or even once a day with minimal hunger after some time and consistency.
IF is not just for weight loss, though. The main reason why I continue doing it is for longevity. The science of aging and increasing health span is picking up speed. I’ve recently gotten into the research on fasting and increased longevity. Caloric restriction increases longevity in many animals. Even the Japanese people in Okinawa (one of the blue zones) believe that one should eat until they are 80% full. This is caloric restriction. Obviously, when we restrict calories, we need to ensure we get enough nutrients to avoid malnutrition. There are no benefits to being malnourished. A slight reduction in calories DOES, though. I’ll explain the mechanisms.
1. Insulin – keeping insulin levels low and insulin-like growth factor low has been shown to increase life span not only animals, but also humans. Loran Dwarfs lack IGF-1 (there is a defect in the receptor). Despite eating the same diet as their relatives, those that did not have the syndrome, had 20% rate of cancer. Remember, cancer is a leading cause of death in the USA.
2. mTOR – dietary protein activates this guy. Decreased intake of protein increases life span. Increased mTOR turns off autophagy, a very important recycling process in the body. As we age, autophagy decreases. Autophagy is a very important component in increasing health span and preventing diseases such as cancer.
3. AMPK – increases when we have low ATP (energy). AMPK increases glucose uptake into the cell, increases autophagy and increases lipid metabolism.
I could go on and on about mechanisms, but I want to keep this article simple.
How to start IF:
1. Start with a 12 hour fast daily. For example, abstain from eating between 7pm to 7am. Follow this strictly for a couple weeks.
2. Start shortening your “feeding” window by an hour each week. Bring breakfast up to 8am or finish dinner by 6pm.
3. If you find this easy after a couple weeks, you can attempt a 16 hour daily fasting regimen. Most people follow a 11-7pm feeding window regimen while other follow 12-8pm. Some even have breakfast and follow a 9-5pm feeding window. Customize to your lifestyle and schedule.
4. Continue this for as long as you’d like. Most people adopt IF as a lifestyle. I, for example, rarely eat breakfast and feel great without eating until 12pm.
5. If you still have difficulty, make an appointment with a registered dietitian to help. I see patients in Irvine, Ca.
I predict that fasting will become standard of care within the next couple decades. Whether it’s a 12 hour overnight fast, a 24 hour fast once a week, or a Fasting Mimicking Diet, I say with confidence, this is the solution to our obesity epidemic. Fasting increases insulin sensitivity so it can be used as a treatment method for those with type 2 diabetes. Fasting helps reduce caloric intake (in a much easier way) which can be used to treat obese people. Fasting even lowers triglycerides and inflammation which lowers cardiovascular disease risk! There needs to be more research published, I know, to officially become standard of care. It’s coming, though.
Disclaimer: This article was written off the top of my head but there is evidence for every single claim I make in this article. I've been wanting to write an article for months now but I have limited time. I will eventually be adding references to this article but I would be more than happy to send you specific articles if you need me to do so.
Who I follow for new evidenced-based fasting information:
1. Dr. Rhonda Patrick
2. Dr. Satchin Panda
3. Dr. Valter Longo
4. Dr. Peter Attia
If you feel at all skeptical, please go to the "Research" tab in the upper left side of the page. Feel free to leave questions below.
Tatiana Keay, MS, RD
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