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  • Ana Bailoni

Intermittent Fasting: worth the hype?

Intermittent Fasting (IF) has been gaining popularity as a way to lose weight and stay healthy. In this edition of Rio Investigates, we bring you the info to understand what the all the hype is about and let you reach your own conclusion. (We'll tell you what we think, too, of course.)



What is it?

IF is not a diet, it's a style of eating. It doesn't focus on what you eat, it focuses on when you eat. Basically, you limit your eating to a pre-determined time period. Outside of that time period, you consume nothing but water, unsweetened tea, and black coffee.


It's as simple as that.


There are dozens of different ways you can do IF. The most popular are:

  • 16/8 - you eat during an 8-hour window in the day, fast the other 16. For example, you may have your first meal at 8 AM and finish eating for the day at 4 PM. Many people skip breakfast, starting their eating window around noon and ending it around 8 PM.

  • 5:2 - you eat normally for 5 days a week, and the other 2 you either fast entirely, or eat a very restricted calorie meal (400-600 calories).

  • 24 hours (a.k.a Eat-Stop-Eat) - one day a week, you abstain from eating altogether.

  • Alternate day - you alternate days of normal eating with days of fasting.

  • One meal a day - you fast all day, and eat one large meal at night.


Why it Became Popular (The hype)

It became popular because, well... it works! IF actually seems to boost fat loss and muscle building while improving important health markers.


And humans have been doing some form of fasting since the beginning of the species, so we have a lot of experience with it. It's only in the past 100 years or so that eating became the mayhem that it is today.


IF seems to bring a lot of benefits, including:

  • Reduce insulin resistance / improve insulin sensitivity (really important!)

  • Hormone balance (and all this entails!)

  • Stronger immune system

  • Reduced inflammation and oxidative stress

  • Weight loss/management

  • Increased energy

  • Improved focus and concentration


It may even kill cancer cells and improve life span. These are some pretty big claims, and there are a lot of smart people studying these possibilities and they seem to be excited about it, but it's too soon (and, like all things biology, a bit complex) to carve it in stone.


In addition to all this, it's simple to follow. No crazy restrictions (besides the 'not eating for a long time' part), no need to go out and stock your pantry with foods you've never heard of, you don't need to become a vegan chef, and you don't even have to clear out your pantry. It's friendly to your social calendar, and it doesn't require a whole lot planning and preparation. It may even save you money. I mean, you're eating less.


Sounds like a pretty good deal!


Why it works (The science part)


  • Fasting induces important cellular repair: digestion is a pretty complex process and your body does a great job at keeping up with your crazy shenanigans. But at some point, it needs a break. Cells are able to remove waste and rebuild themselves, and the bacteria in the gut become more balanced. This is the true "detox" you should be worrying about.


  • Insulin levels drop: this facilitates fat burning, and improves insulin sensitivity. We want a good degree of insulin sensitivity because this means the calories you consume during your eating window will be used efficiently - for muscle building, for example. The other side of the coin is insulin resistance, which can lead to diabetes, and it happens when your blood glucose rises and falls frequently (like when you eat all the time).


  • Glycogen stores are depleted: this is great news if you want to burn fat because once the body uses all the glucose in the blood, it will go to the glycogen stores in the liver. Once those are gone, it'll have to resort to another energy system that uses fat stored in your cells to produce the energy you need to stay alive and active. It's a little more complex than this, of course, but that's it in a nutshell. This process is called ketogenesis and it produces ketone bodies to be used for energy. I'll never forget when Dr. Dominic D'Agostino called ketones the 4th macronutrient in an interview with Tim Ferris. That's a pretty powerful statement right there with a lot of implications, but I digress. That's a topic for another blog post.


  • Human growth hormone increases: this hormone plays a huge role in muscle building and metabolism. The higher your levels of HGH, the more efficient you build and preserve muscle. This is important if you want to change the shape of your body long term - lose fat, but get strong and build a nice physique.


  • Gene expression changes: did you know that you have genes that simply aren't being expressed? Genetic material is much more complex than a "blueprint" you're born and stuck with. Your genetic makeup is either inhibited or expressed according to your environment and lifestyle choices. Fasting allows certain genes related to longevity and protection against disease to be expressed.


  • It puts you in a calorie deficit: if a diet is effective for weight loss, it is only so because it gets you to eat less calories than what your body expends. That's the only thing that will drive fat burn - not cutting out gluten, or quitting sugar, or eating healthy fats, or eating clean. All that stuff will only yield weight loss if and only if you're at a calorie deficit. That's why sometimes you're eating really healthily but still maintaining weight. You may feel better without the sugar hangover, but if your calories in = your calories out, you'll maintain weight. (If you're strength training with a good progressive overload strength training program you may lose inches over time. We call that body recomposition. Again, I digress). Anyways, if you're eating less meals a day, you're very likely cutting the calories you normally consume in a day, which will put in you fat burning mode. On that note, it's very possible to not experience fat loss when you do IF if you approach it wrongly, and compensate for the fasted time by over eating. It's really important to eat normally - meaning, stop eating when you're full, and eat again when you're hungry during your eating window.


The Controversy

Well, you're not eating. That can't be good, right? Don't they call that an eating disorder? What about the starvation mode that down-regulates your metabolism? Let's tackle some of these issues:


Isn't breakfast was the most important meal of the day? It may be for some people, but it's not a biological fact of the human race. What we have seen is that insulin sensitivity is much higher after a period of fasting (like after you wake up, that's why that first meal of the day is called break-fast. Get it?), so your body uses those calories more efficiently for energy and it will be less likely to store excess as fat, but it doesn't seem to matter what time that first meal is taken - whether it's within an hour of waking up or 4 hours later.


Doesn't eating every 3 hours keep your metabolism working? Not at all. This myth became popular in the 90s, but we've learned a lot since then. Your metabolism is always working, even when you're sleeping. The truth is, there are hundreds of factors that affect your metabolism, and meal frequency is not necessarily one of them. What really counts in terms of weight loss/maintanance is calories in vs. calories out. Whether you spread those calories across 2 meals or 6 is a matter of preference, convenience, and individual metabolic factors.


Is it true that IF may not be good for women from a hormonal perspective? Jury is still out on that one. Most studies have been done on men, and generally (as with all things physical fitness and weight loss) men tend to respond more efficiently to IF. There have been some questions of whether IF is dangerous for women over 40ish, and I personally am hesitant to impose it on my own clients that fit this profile because we simply don't know. Generally, some women report fantastic results from IF, others don't, and still others have some scary experiences, like irregular periods, for example.


Will it eat away at my hard earned muscles? This one depends on your overall calorie intake. If you're a skinny guy and you want to put on muscle, IF probably won't help you. You need to eat at a calorie surplus, and that is harder to do in a small eating window. It will depend on calories in vs. calories out, whether or not your strength training, and your body type (whether you're naturally skinny or you pack on muscles easily). Science doesn't help us much with this one. Some studies showed an increase in muscle mass with IF, regardless of all other factors, and others showed the exact opposite. We really don't know what's going on there.


Isn't it bad to ignore my hunger and just not eat? Humans can go up to 7 days without food. Twelve to 16 hours won't get you anywhere close to the danger zone. At about 10-12 hours after your last meal, your body goes into ketosis, and that's generally a very efficient system of energy production. Your fat stores are there to be used, you'll be all right.


Is it going to slow down my metabolism? Again, depends on calories in vs. calories out. If you eat normally, meaning you eat a balanced, normal sized meal without overeating and wait until you're hungry to eat again, it's very unlikely that you'll be at such an aggressive calorie deficit as to slow down your metabolism. Especially, if you're strength training!


Doesn't this seem like an eating disorder to you? Chronic dieting and the constant pursuit of thin has done a number on our view of food, eating, and our bodies. Whether IF is problematic will depend on the individual and how the person approaches it. If it leads to a restriction/binge pattern, then it absolutely should not be done. That's no way to live, and seems to me like an eating disorder waiting to happen. However, it is not inherently dangerous and will not "cause" an eating disorder.


Doesn't it suck to feel hungry all the time? It can, and this is probably the biggest hurdle for people because of what we've been conditioned to - hungry hurts, end the discomfort with food... all the time, every single time, immediately. The truth is, hunger signals are conditioned to your habits. Once you change your habits, your hunger signals will change too. And at about day 3 or 4 of IF, these feelings and sensations change. You also learn to view hunger in a different way, and you'll realize that after about 20 minutes, the discomfort subsides and you still have a lot of energy because of ketosis.


What We Think

Overall, IF can bring great benefits for a low-maintaince lifestyle. As a matter of fact, I believe it's how nature intended it - you eat while it's light out. When it's dark, stay put and sleep while your body does its thing. But the discovery of energy changed, the industrial revolution, globalization, technology, and booming economies really changed that.


I believe most everyone will benefit from a naturally, daily 12 hour fast - don't eat your first meal of the day until a full 12 hours after your dinner, no matter what time that was.


This is an eating style I'm pretty confident will bring great benefits to most people, and it's a fun little challenge. But like anything of the sort, you need to decide if it's really for you. The information I've presented here, though sound, is like anything else in the nutrition field - tentative educated guesses.


Although IF is awesome, keep your feet on the ground. Like everything in this field, it's not for everybody, and it's not the end all, be all. There is no such thing.


WARNING: If a friend can't stop telling you about their newfound miracle for weight loss or fitness, and they're convinced that everyone, including you, needs dot it, they've probably just paid an enormous amount of money for some nutrition program they've been on for a month. Every new program is exciting. Every healthy eating regimen will make you feel great. But that doesn't mean it's without flaws, and it definitely doesn't mean it's for everybody.


DOUBLE WARNING, just because I like you: if a fitness or nutrition professional approaches you like that. Run. They just want your money, or they've been at the profession for all of 6 months.


IF is a fantastic tool for you if:

  • You're stuck in a weight loss plateau

  • You're healthy overall

  • You have a busy lifestyle and hate diets

  • You have a pretty sedentary job

  • You're strength training


It may not be great for you if:

  • You're a naturally skinny guy who wants to build muscle

  • You're a woman and you've experienced hormonal imbalances or hormone disorders

  • You have a history of eating disorder or disordered eating patterns

  • You're hypoglycemic or diabetic

  • You're pregnant or breast feeding


What now?

My suggestion about IF? Try it out!


Unless you have any medical reason why you shouldn't, fasting is a really interesting experiment, and it's not as hard as you think. Who knows, you might even like it!



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