I have been speaking to more and more people who are dabbling in intermittent fasting, and a majority have overwhelmingly positive things to say about their fasting experiences. However, there are many questions regarding the safety, efficacy, and longevity, of the “alternative” eating pattern. You may have read about it or heard friends talking about it and wonder: does intermittent fasting work?
What is Intermittent Fasting?
Simply put, intermittent fasting is the period of not eating in between meals. Most people naturally fast between meals, but intermittent fasting is a set schedule that you follow of when to eat. These are the most popular methods:
- 16/8: Eat for 8 hours and then fast for 16 hours.
- Eat-Stop-Eat: Fasting for 24 hours once or twice a week.
- 5:2 Diet: Consume 500-600 calories for two days a week and then eat normally the other five days.
Let’s first start by saying that intermittent fasting is not a new concept. In fact, it is the oldest dietary pattern of humankind! Our ancestors had to hunt and gather, and eventually grow their food, making times of feast and famine a regular occurrence. Additionally, many religions have also incorporated fasting into their religious practices (ex. Ramadan).
It was not until the advent of mass produced food and easy refrigeration that humans had an endless supply of food at their fingertips 24/7. This relatively new accessibility, along with mass marketing with juicy, mouth-watering food commercials, toy-shaped processed treats that memorize children, and phone apps that deliver anything your heart desires within minutes to your doorstep, it is no wonder obesity has become the new norm! Why wait for season to scavenge the garden for squash when you can tap your phone and have a gyro delivered in under 30 minutes?
With that said, we really cannot blame people for eating nonstop. But what so-called experts (including healthcare providers) unfortunately do is, they blame people for not losing the weight and keeping it off. Weight loss is hard! It’s incredibly hard! And it’s harder to achieve the longer you have been overweight. What so-called experts and guidelines have been telling the public for ages is that if you eat less calories and exercise more, and you will lose weight. Calories in vs calories out. And what is even harder, if not darn impossible, is maintaining the weight loss after cutting calories and increasing exercise.
Why is that? Why can we decrease our caloric intake to 1600 calories a day by cutting out condiments and soda and drop 5 pounds fairly quickly, only to eventually gain it all back and then some? The science behind it is resetting of the resting metabolic rate. Our bodies want to maintain a steady weight. So whenever we cut back calories for a sufficient amount of time, the body will reset its resting metabolic rate (RMR) at a lower level. Before you know it, the 1600 calorie/day diet just decreased your RMR to 1500 calories and you are officially gaining weight (sans soda and all guilty pleasures you used to enjoy!).
Another problem with the calories in vs calories out concept is that does not address the hormones that help regulate energy storage and expenditure. This is where intermittent fasting really shines! For example, when you eat, your body releases insulin to help bring glucose into the cells for energy, store excess energy in the form of glycogen, and prevent the breakdown of fat. So, regardless how few calories you may be eating, each time you eat or drink something with insulin stimulating abilities (pretty much everything except pure fat), you are inhibiting the breakdown of fat.
Does Intermittent Fasting Work?
So how is intermittent fasting different from a reduced calorie diet? As insulin decreases during a fast, your body will switch fuel sources from food to stored fat, and lipolysis (fat breakdown) will occur. Additionally, when insulin decreases, there is an increase in counter-regulatory hormones, with an increase in adrenaline, cortisol, and growth hormone. The adrenaline surge helps to keep RMR up, and the increase in growth hormone helps rebuild proteins to maintain lean muscle mass.
Speaking of hormones, you may have heard the term “leptin resistance”. When fat cells increase in size, they can stimulate a hormone called leptin to be released. Leptin turns down appetite, which should decrease food intake, which ultimately decrease insulin. It is the body’s way of trying to maintain homeostasis. However, if you eat constantly throughout the day and continuously stimulate insulin, you will also continuously stimulate leptin, which eventually leads to leptin resistance.
So how long should you fast for? Fasting schedules vary widely. Most people will have substantially depleted their glycogen stores by 12 hours after the last meal. Thus, if you do even a 12 hour overnight fast (ex. 8pm-8am) that is a good start! If you want to take it a step further, a very popular schedule is a 16 hour fast with an 8 hour window for eating. Others do well with 24 hour fasts 1-3 times/week. When you personalize the fasting schedule to your work and social schedule, it can be very sustainable. Additionally, you can take a break from intermittent fasting for vacations, illness, etc, and pick it back up later without weight gain since you preserved your RMR.
Is It Safe?
However, when deciding whether or not to try intermittent fasting, you need to take into consideration your individual health. I would not recommend intermittent fasting for those with a current or recent history of eating disorders, pregnant, underweight, or those who are on medications that increase insulin or on insulin injections (the latter should work with their healthcare team).
If you have tried or are currently doing intermittent fasting, I would love to hear about your experience!