Intermittent fasting is one of the biggest trends in the diet world right now. Some people love it, some people hate it… and some people are making huge claims about it being a magical key to weight loss and longevity.
Right off the bat, we’re going to say — if anyone says they have the magical key to anything, you should run. So far we haven’t found any magical keys to weight loss. Not fasting, not carbohydrates, not cutting out a certain food group. There is no magic. You have to actually build eating skills.
Learning to eat well is more like learning to drive or learning to play an instrument than it is like finding a secret rule.
Intermittent fasting, interestingly, helps some people build those eating skills, while it hurts others who are trying to build those eating skills. You might fall into either group.
We’re going to take an unbiased look at intermittent fasting; what works, what doesn’t, who it can help, and who it can hurt. Most importantly, we’ll help you decide, for yourself, if it’s a good fit for you.
This article is really going to be for folks who are considering intermittent fasting for either weight loss or a sports performance goal. These aren’t the only two goals a person could have, but they’re what we’re going to talk about here.
What Is Intermittent Fasting (IF)?
There are a few different versions of IF.
They’re basically a ratio of time you don’t eat under any circumstances and a ratio of time that you eat whatever you want and however much you want. Sometimes people will add additional rules for the eating time, like intermittent fasting + a ketogenic diet, or intermittent fasting + Whole 30, or whatever.
At its most basic, though, it looks like this:
So, 16:8 means 16 hours where you can’t eat, no matter what, and 8 hours, where you can.
I tend to look at it in terms of how many meals you’re usually actually eating:
- 16:8 — two meals per day
- 20:4 — one meal per day
- 24:0 — who wants to eat food, anyway?
The two most common forms of IF are 16:8 fasting and 24:0 fasting. 16:8 fasting, people usually do daily.
24:0 fasting is usually done once per week, and people eat normally the other six days per week. Most of the research that we’ll look at on IF has been done on 16:8 fasting.
Can it Work?
Of course it can work! Anything that fits into your life and feels good in your body can work, because you’ll keep doing it. And that’s why it works so well for some people—because they like doing it.
It’s popular and stuff because it worked for someone.
Everyone you see talking about it online, who it really worked for, are the people that it was a great fit for. For some of them, it felt like “the key.” But we have to be careful about that—the fact that it was a good fit for them doesn’t necessarily mean it will be awesome for you.
What we’ll find as we go on, is that it’s a really natural fit for some people and works well for them. On the other hand, it’s a terrible fit for other people, and not only does it not work for them, it can even lead to some disordered eating patterns.
But here’s a reminder: most rigid diet rules are bound to backfire.
What the Gurus Say
The main claims intermittent fasting gurus make around IF revolve around magical weight loss and increased longevity.
It’s sort of like “lose weight now with this one weird trick!” or “You’ve been lied to all along, it’s not how much food you eat, it’s when!”
If someone is making really bold claims about a diet, run. Run, run, run. If they say you can live forever… ruuuuuuuunnnnn.
What Does Research Say?
The weight loss part, they say, comes from changes in metabolic processes and hormones related to fasting. As we’ll later see—in relationship to weight loss—these processes have all been shown to matter at a cellular or hormonal level. Or they have shown promise in rat studies.
Sometimes something works at one level of analysis, and doesn’t work for actual humans in real life. Or, sometimes something works for rats or mice, but doesn’t work for humans.
Look, I think rat studies are cool! But rats don’t care about weight loss.
IF just isn’t something we’ve seen make a big difference with humans, unfortunately. Studies show that it works exactly the same as everything else.
IF: The Good, The Bad, and The Ugly
Whether IF is a good fit for you has a lot to do with your personal temperament and your body’s optimal number of meals. It can also have a lot to do with your goal.
You might have a goal of:
- Weight loss
- Sports performance
- Living forever
- A better relationship with food
IF impacts each of those differently.
Lets take a look at the good, the bad, and the ugly, of IF:
All The Good From Intermittent Fasting
There are a lot of things that can work really well about intermittent fasting. For one, if someone is trying to lose weight, dropping a meal (usually breakfast, in 16:8 fasting) is an easy way to cut out a whole lot of food energy.
Dropping one meal per day, every day, can add up to a lot of weight loss, all by itself. It’s not magic, you’re just eating 33% less food.
For some people, IF becomes a way to identify when they ate for non-food issues. For example, if someone is used to snacking every night after dinner when they are bored or tired, then having a “cutoff time” for eating illuminates that.
It can be a catalyst for examining why they were eating at night, and developing alternative ways to cope with boredom or tiredness, like doing something engaging or going to sleep.
In that case, it’s really effective.
It can also help people examine hunger in general. It’s common for folks over-eat because they’re afraid of getting hungry later. IF can be a way to confront their fear of hunger, and find out that a little bit of hunger is not an emergency. Again, it can help them work through their preconceived ideas about hunger, and learn to tolerate a reasonable amount of hunger sometimes.
In those cases, IF is not only effective for people, but it also becomes a framework for working on their relationship with food, both of which are amazing things.
A good indicator that 16:8 fasting is a good choice for you is that you meet all four of the requirements below:
- The 16 hour fast feels good in your body
- The 8 hour eating window feels good in your body
- It makes it easier for you to self-regulate your food intake
- Your relationship to food is getting healthier
The Bad That Comes From Intermittent Fasting
When IF goes bad, it’s because the artificial time restriction doesn’t actually have an impact on anything that would drive their goals forward. Whether their goal is weight loss or sports performance, IF can be a distraction or a detriment.
For weight loss, we sometimes see a cycle that doesn’t work:
- Their body doesn’t tolerate 16 hours of fasting well.
- They’re super hungry and over-eat during the 8 hour eating window.
They don’t actually lose weight because they eat enough in the 8 hour window to make up for the 16 hour fast. The fast becomes an artificial time restriction, but had no impact on their goals.
For sports performance, the 16 hour fast can cause two problems:
- Makes it hard to get enough protein.
- Makes it hard to get fuel for an active day.
If someone is trying to get stronger, protein is always a factor. If it’s harder for you to meet your protein requirements during an 8 hour feeding window, you’re making it harder to meet your performance-related nutritional needs.
Or, if you’re doing anything that requires endurance—going for a hike, going mountain biking, going rock climbing, taking a long martial arts class—it’s usually going to compromise performance to skip breakfast.
For your relationship to food, the 16:8 cycle causes two other problems:
- You don’t eat during the 16 hour fast, even if you are actually hungry.
- You eat extra during the 8 hour feeding window, even if you are full.
You’re getting less and less connected with your body’s actual hunger and fullness cues, because you’re constantly suppressing them. You’re blindly following a completely arbitrary rule, instead.
Good indicators that 16:8 fasting is not great for you, is if any of the four below are true:
- The 16 hour fast feels bad in your body
- The 8 hour eating window feels bad in your body
- It makes it harder for you to self-regulate your food intake
- Your relationship to food is getting worse
When Intermittent Fasting Gets Ugly
There are a lot of things that can work poorly about intermittent fasting. Most people have a long history of dieting. The longer your diet history, the more likely you will start to bring the same diet-world morality and black-and-white thinking into IF. The moralizing of food and the black-and-white thinking are a fast way to destroy your relationship with food.
How to destroy your relationship with food in three easy steps:
- Have rigid rules (like a fasting window).
- Breaking the rules is morally bad, following them is morally good (ie: you’re bad if you break your fast).
- Circumstances never matter, you always follow the rules (it doesn’t matter if your son or daughter made breakfast, you can’t eat it).
Rigid rules, moralizing the rules, and never being able to consider circumstances are how you destroy your relationship with food. They’re also what sets up the diet cycle of failure.
When we moralize food (and weight) we create a downward spiral:
- They get hungry during the 16 hours of fasting, so they start to over-eat during their 8 hour eating window.
- They over-eat and feel gross and bloated.
- The 16 hour fast becomes a way to “fix” their over-eating from the day before.
- They over-eat and feel gross and bloated again.
- The 16 hour fast becomes a form of moral penance for how much they ate.
That cycle continues, with the 16 hour fast feeling more and more like a moral obligation. That it makes you a good person, or fixes your over-eating, regardless of whether they actually feel good fasting or not.
They end up in a position where either the 16 hour fast feels good nor does the 8 hour eating window feel good.
Again, it has people disconnect from actual hunger and fullness, and just follow an arbitrary rule instead. The further we get from our actual hunger and fullness cues, the more we’re likely to emotionally eat foods we see, and pound an uncomfortable amount of food when we’re “allowed to.”
Good indicators that 16:8 fasting is horrible and destructive for you, is if any of the five below are true:
- The 16 hour fast feels like a moral obligation.
- The 8 hour eating window feels like your last chance to eat all the food, and you eat until you feel bad.
- It makes it harder for you to self-regulate your food intake.
- You feel like your relationship to food is getting worse.
- You feel a desire to increase your fasting time, or add additional food rules to your eating time (like eliminating a food group).
Optimal Eating Frequency is Different for Different People
The goal with eating skills is to find the optimal number of meals that allows you to self-regulate your food intake.
People fall into a bell-curve of what the optimal number of meals per day is for them (“meals” here includes meals and snacks).
- Most people will find it easiest to self-regulate their food intake at 3-4 meals per day.
- Some people will find it easiest at 2 meals per day.
- A smaller group of people will find it easiest at 5 or 6 meals per day.
2 Meals Per Day
The people who self-regulate their food intake well with 2 meals per day do very well on intermittent fasting.
It’s a plan that’s completely built for them. They’ll often find it life changing, and almost always say things like:
- “It’s the only thing that’s ever worked for me.”
- “I feel so good doing it.”
- “It makes my life so much easier”
Just by trying it, and reflecting on how it went for them, they can tell that it’s a good fit for them.
3-4 Meals Per Day
The people who self-regulate food intake the best on 3-4 meals per day can sometimes suffer through intermittent fasting.
It doesn’t feel great, but people with enough willpower can make it work. It just sucks. They might have low energy in the mornings. Or they find they over-eat at their first meal of the day.
These folks fall into one of three camps with IF:
- “IF sucks, but I make it work because I get some results.”
- “IF sucked, but I got results, until something happened and I fell off the wagon and gave up.”
- “IF sucked, so I over-ate, and didn’t get results.”
Some folks in the first category get results, so it’s “worth it” to them. Even if it’s unnecessary and possibly harder than it would be with 3 meals per day.
People in the other two categories should find a new plan.
5 Meals Per Day
For the rare person who self-regulates their food intake best on 5 meals per day, IF is a total nightmare.
In fact, if someone is in this category, it’s unlikely they’re even reading this post because IF sounds so completely repulsive to them.
Which One Am I?
Well, if you tried IF and it seemed like the magical key for you, you’re almost certainly in the 2-meals-per-day category. Or, if you are someone who has never eaten breakfast before in your life, you already know. If you hit your goals and you feel good eating 2 meals per day, that’s your indicator.
On the flip-side, many folks will have 3-4 meals per day (without snacking in between), find that they lose weight and feel really good. If you hit your goals and you feel good eating 3-4 meals per day, there you go.
The five-meals-per-day option is the hardest one to suss out. Some people do feel much better eating 5 meals day. Most people who are eating that often, though, are eating not from hunger, but from boredom, stress, emotions, tiredness, or procrastination.
It’s often easier to have a snack in the afternoon than it is to stay engaged in your job. So, this category does exist, but to find out if you’re in this category, you need to start investigating why you’re eating. Ask yourself things like, “Do I feel a hollow feeling in my stomach?” and “Am I stressed out or avoiding something?” and “Am I hungry for a balanced meal, or do I just want a specific treat?”
Create Your Own Eating Frequency Experiment
In Eating Skills, we LOVE to have people experiment with meal frequency, and then reflect on their experience. Instead of listening to a guru, you can learn from yourself.
How to run an eating frequency experiment:
- Pick one of the eating frequencies above.
- Do it for two weeks.
- Look back on those two weeks and reflect on your experience.
Here are some reflection questions:
- Was I able to do it for two weeks?
- Did it get easier or harder as the two weeks went on?
- Did it feel natural or like a struggle?
- How did I feel in my body? Energized? Tired? Hungry? Satisfied?
- Do I feel like it’s making my relationship to food better or worse?
Take ten minutes at the end of those two weeks, and write out your answer to those questions.
Clients in the GMB Eating Skills program have learned more from writing out their answers to reflection questions than from any diet book they’ve ever read before. You can do the same thing. Stop listening to gurus and their rules, and start reflecting on your own experiments.
Andy, Ryan, and Jarlo have all done IF
Hopefully you can tell that, here at GMB, we aren’t against IF. We just want you to find the optimal amount of meals for you to be able to self-regulate food intake.
To really drive the point home, the three founders of GMB have all done intermittent fasting for long periods of time, and it worked really well for them.
- Andy has been doing intermittent fasting, on and off, since 2004. He’s just too lazy to put anything in his mouth before noon. Essentially, IF is a good fit for him because breakfast is a bad fit for him.
- Ryan did IF from 2010 to the beginning of 2020. He’s the kind of person who never gets hangry, and didn’t miss having breakfast at all. He really liked to not have anything in his stomach before doing one-arm-handstand training. He also thought it was easier when traveling. Now that he isn’t traveling, he likes including breakfast into his schedule.
- Jarlo has never cared if he missed a meal, so skipping breakfast didn’t matter. He isn’t someone who stresses about food. Plus, he liked getting to have bigger meals for lunch and dinner. He’s added breakfast back in, just because he likes the routine of having breakfast, lunch, and dinner
For all three of them, it totally worked. It fit their schedule and it made their lives easier.
It’s also worth noting that they all have really healthy relationships with food. None of them really stress about food, and can actually have multiple things “work” for them. Case in point, Jarlo and and Ryan have both switched to three meals per day now and it works great. For them, 2 or 3 meals per day worked the same. It’s just about which one fits better, or which one they like better at any given time.
What’s the Alternative to Timed Eating or Diet Rules?
The GMB Eating Skills program ditches all of the rules. Literally, there are no rules.
But that doesn’t mean it’s a free-for-all, either.
There are guidelines, like fasting 4-6 hours between meals. So, people have a structure where they can start to eat healthy meals, and then not stress-eat between meals.
But that’s a guideline, not a rule. Inside of that guideline, we put skills. Skills where people learn to differentiate between hunger and stress. If it turns out that they are actually hungry, they can eat. If it’s stress, they don’t eat.
Let me repeat: If it’s actual hunger, they totally eat some food.
The guideline is a structure for them to check in with themselves. Instead of their default being “I always have a snack at 3pm,” their default becomes, “I don’t have a snack between meals. If I want a snack, I have to check in with my body first.”
Essentially, they end up doing experiments all of the time. And learning what works for them in their bodies.
They might have a guideline for eating a balanced meal, but there’s no magic to it. Eating a balanced meal just works really well for noticing when you are full, and staying full between meals. You aren’t a bad person if you eat a balanced meal, you aren’t a good person if you eat a balanced meal… you’re just usually going to stay full longer. That’s it.
So, we give you structures that allow most people to succeed, most of the time. Then, we use those structures as training wheels to teach you exactly how, step-by-step, to check in with your body.
The irony is, if you learn to check in with your body, and trust it, it doesn’t matter which eating frequency you end up at. You’ll do really well self-regulating your food intake. You’ll hit your goals. And you’ll have a better relationship with your body.
Intermittent Fasting and Eating Skills
Most people in GMB Eating Skills end up eating 3-4 meals per day. The program is built around that, and they do really well.
Some people in GMB Eating Skills, though the guidelines and checking in with their bodies, find that they do best on 2 meals per day. And that’s awesome!
The big difference between normal IF and how it shows up with eating skills is that they’re usually much more loose about the feeding window and the fasting restriction. They just eat 2 meals when it makes sense in their day or when they’re hungry.
How to win with nutrition, with or without intermittent fasting:
- Plate balanced meals most of the time.
- Eat slowly, stop when full.
- Notice the difference between hunger and stress/emotions/tiredness.
- Have the skills to manage stress/emotions/tiredness without food.
So, people can actually do awesome with intermittent fasting and eating skills, if both of those are a really good fit for them. If you’re doing the four things above, you’ll sort out your own best eating frequency.
It’s About Autonomy
The name of the game is you being able to eat in line with your personal values. If a certain eating frequency helps you self-regulate, that’s awesome. You should find out that frequency for yourself.
We don’t want to give you more rules.
We can give you guidelines to do your own experiments within. We can give you progressive structure to build your own eating skills within. But ultimately it’s about you being able to make those decisions for yourself.
When you can figure this stuff out for yourself, and you don’t need gurus and rules, a whole new world opens up for you. On one hand, you can hit your goals. On the other hand, you can attend social events, fuel up for hikes, and eat your favorite dessert.
Rules make your life smaller. Rules put someone else in control of how you eat. Skills make your life bigger, you can make different choices at different times. You’re actually in the driver’s seat with your eating, because you can eat in ways that both match your goals, your own body’s needs, and all of the other things in your life that matter even more.
Build Eating Skills that Last
Eating Skills is a coaching experience that will help you build sustainable skills around how you eat, giving you a healthy, non-dogmatic approach to food.
Hey wait! You never answered the question about if IF will help me live forever!!!
It’s true, I didn’t. I have no idea man, that’s so not my department.
Intermittent Fasting and Weight Loss
Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, 164(4), 302-311.
Review of research in humans: No difference in weight loss between intermittent fasting, alternate day fasting, and caloric restriction.
Freire, R. (2020). Scientific evidence of diets for weight loss: different macronutrient composition, intermittent fasting, and popular diets. Nutrition, 69, 110549.
Review of multiple diet strategies. Shows no difference between intermittent fasting and caloric restriction. Also, no difference between high fat and low fat diets. Recommends anything that has high adherence.
Headland, M. L., Clifton, P. M., & Keogh, J. B. (2019). Effect of intermittent compared to continuous energy restriction on weight loss and weight maintenance after 12 months in healthy overweight or obese adults. International Journal of Obesity, 43(10), 2028-2036.
One year randomized controlled trial. Compared two different kinds of intermittent fasting to caloric restriction. There was no difference in weight loss between either form of intermittent fasting, or continuous caloric restriction.
Jospe, M. R., Roy, M., Brown, R. C., Haszard, J. J., Meredith-Jones, K., Fangupo, L. J., … & Taylor, R. W. (2020). Intermittent fasting, Paleolithic, or Mediterranean diets in the real world: exploratory secondary analyses of a weight-loss trial that included choice of diet and exercise. The American journal of clinical nutrition, 111(3), 503-514.
Non-randomized trial — people self-selected either intermittent fasting, paleo, or Mediterranean diet. No difference between groups.
Klempel, M. C., Kroeger, C. M., & Varady, K. A. (2013). Alternate day fasting (ADF) with a high-fat diet produces similar weight loss and cardio-protection as ADF with a low-fat diet. Metabolism, 62(1), 137-143.
Adding keto to intermittent fasting made no difference. High-fat and low-fat alternate day fasting groups got the same results.
Lowe, D. A., Wu, N., Rohdin-Bibby, L., Moore, A. H., Kelly, N., Liu, Y. E., … & Shepherd, J. A. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Internal Medicine.
Randomized controlled trial showed no difference in weight loss between intermittent fasting and caloric restriction.
Obert, J., Pearlman, M., Obert, L., & Chapin, S. (2017). Popular weight loss strategies: a review of four weight loss techniques. Current gastroenterology reports, 19(12), 61.
Intermittent fasting and paleo both produce similar weight loss, if they reduce calories. They also looked at juicing fasts, and said it was stupid, and looked at HIT and said it was cool.
Pinto, A. M., Bordoli, C., Buckner, L. P., Kim, C., Kaplan, P. C., Del Arenal, I. M., … & Hall, W. L. (2020). Intermittent energy restriction is comparable to continuous energy restriction for cardiometabolic health in adults with central obesity: A randomized controlled trial; the Met-IER study. Clinical Nutrition, 39(6), 1753-1763.
Randomized controlled trial. No difference in weight loss between intermittent fasting and caloric restriction.
Schübel, R., Nattenmüller, J., Sookthai, D., Nonnenmacher, T., Graf, M. E., Riedl, L., … & Kirsten, R. (2018). Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 wk: A randomized controlled trial. The American journal of clinical nutrition, 108(5), 933-945.
50-week long randomized controlled trial. There was no difference between caloric restriction and 5 days on / 2 days off fasting.
Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent fasting: is the wait worth the weight?. Current obesity reports, 7(2), 172-185.
A review of current research shows that there’s no difference in weight loss between intermittent fasting and caloric restriction.
Welton, S., Minty, R., O’Driscoll, T., Willms, H., Poirier, D., Madden, S., & Kelly, L. (2020). Intermittent fasting and weight loss: Systematic review. Canadian Family Physician, 66(2), 117-125.
Systematic review of intermittent fasting. 27 randomized controlled trials showed no difference in weight loss between intermittent fasting and caloric restriction.
Intermittent Fasting and Meal Frequency
Duval, K., Strychar, I., Cyr, M. J., Prud’homme, D., Rabasa-Lhoret, R., & Doucet, E. (2008). Physical activity is a confounding factor of the relation between eating frequency and body composition. The American journal of clinical nutrition, 88(5), 1200-1205.
Eating more often increases the number of calories eaten. When someone has a high frequency of eating meals, but is also lean, the difference is usually physical activity.
Leidy, H. J., & Campbell, W. W. (2011). The effect of eating frequency on appetite control and food intake: brief synopsis of controlled feeding studies. The Journal of nutrition, 141(1), 154-157.
Eating 3x per day was the baseline.
Eating 1 or 2 meals per day made people more hungry than 3 meals per day.
Eating 4 or 5 times per day had no impact on hunger at all.
This review of the evidence indicated that 3 meals per day might be ideal for most people.
Ma, Y., Bertone, E. R., Stanek III, E. J., Reed, G. W., Hebert, J. R., Cohen, N. L., … & Ockene, I. S. (2003). Association between eating patterns and obesity in a free-living US adult population. American journal of epidemiology, 158(1), 85-92.
Skipping breakfast is associated with obesity. People who skipped breakfast still ate 4 meals per day, on average.
Mattes, R. (2014). Energy intake and obesity: ingestive frequency outweighs portion size. Physiology & behavior, 134, 110-118.
Frequency of eating (meals + snacks) is a more important determinant of obesity than portion size. Part of how they looked at frequency was time between meals. The average time between meals/snacks keeps getting shorter. For Americans, it’s now down to 3 hours.
McCrory, M. A., & Campbell, W. W. (2011). Effects of eating frequency, snacking, and breakfast skipping on energy regulation: symposium overview. The Journal of nutrition, 141(1), 144-147.
3 meals (meals + snacks) per day is the easiest meal frequency to self-regulate intake.
1 or 2 meals (meals + snacks) per day has a moderate risk of over-eating
4 or 5 meals (meals + snacks) per day has a moderate risk of over-eating
6+ meals (meals + snacks) per day has a high risk of over-eating
Mills, J. P., Perry, C. D., & Reicks, M. (2011). Eating frequency is associated with energy intake but not obesity in midlife women. Obesity, 19(3), 552-559.
Increased eating frequency is associated with higher energy intake. Higher energy intake is associated with higher BMI.
Women who ate 1-3 times per day had the lowest energy intake. It increased at 4, 5, 6, and 7 times per day.
Murakami, K., & Livingstone, M. B. E. (2015). Eating frequency is positively associated with overweight and central obesity in US adults. The Journal of nutrition, 145(12), 2715-2724.
Eating 3.5 meals per day (combined meals + snacks) leads to lower energy intake, BMI, and waist circumference than eating 4 or 4.5 meals per day.
Smeets, A. J., & Westerterp-Plantenga, M. S. (2008). Acute effects on metabolism and appetite profile of one meal difference in the lower range of meal frequency. British journal of nutrition, 99(6), 1316-1321.
2 meals per day vs 3 meals per day, with the amount of total calories matched in both groups. Crossover design where both groups did both meal patterns over the course of the study. Their metabolic rate was tested both times, and neither meal pattern had any impact on metabolism. Similarly, no difference in body weight between groups. The 3 meal per day group felt more satisfied than the 2 meal group.