Hungry?
A recent reader question regarding the topic in my previous blog post has prompted me to delve a little deeper into intermittent fasting and how it differs from caloric restriction. To some, it may seem like the two concepts are the same thing but they are not. So, let me lay out the differences.
Intermittent fasting is an eating pattern where one attempts to increase the time elapsed between meals on a semi-regular basis.
Whereas the typical meal frequency might be three per day spaced out with four or five hours between them, a fasting person might skip breakfast (of course, since we’re not breaking the fast yet) and not eat their first meal until the normal midday lunch hour.
Combined with the overnight fast which occurred during sleep, we could estimate a total fasting period of around 12-14 hours, depending on how much sleep was obtained.
There are other ways to accomplish this, like skipping dinner instead or even fasting an entire day. However, the fast is typically ended with some sort of feast or large meal. (This kind of thing is pretty common in old religions and cultures – ancient wisdom?)
This does not necessarily imply that you eat less total calories), merely that your food intake will be compressed to a smaller window of time during the day. You might eat the same amount of food as with a typical meal pattern, yet will spend more time overall in the fasted state.
And simply put, the fasted state is just the state of being unfed, where your body seeks to provide energy to it’s tissues from stored fat, protein, or glycogen.
Caloric restriction on the other hand has an explicit purpose geared towards reducing the amount of calories consumed. The mechanism is not so much about meal timing or frequency as it is about just eating less. One could accomplish caloric restriction by fasting and skipping a meal every day.
Intermittent fasting and caloric restriction diverge in this case because in caloric restriction one would avoid replacing the missed calories through a bigger fast breaking meal (which might have occurred either consciously or subconsciously). The calorie restrictionist would continue to keep their caloric intake below the generally accepted baseline.
The body’s normal reaction to a missed meal will likely be to eat more at the next feeding, whether you intended to gorge yourself or not.
Your body fat stores which are continuously being utilized during the day to keep energy levels stable, produce a protein called leptin that is a key component of appetite. Leptin signals to the brain that the body has had enough to eat, producing a feeling of satiety.
Your body is smart enough to figure out how to manage it’s energy reserves, despite the suggestion by modern medicine that people must count calories to lose weight.
Purposefully restricting calories, basically like dieting, will inevitably place you in a position where you’re fighting the hormonal triggers for hunger and to eat that your body produces. This is probably why weight loss diets which are based on caloric restriction almost always fail.
Besides trying to lose weight, one reason that people try to do caloric restriction (I say try because being starved all the time is incredibly difficult [1]) is to increase longevity. There isn’t much debate about whether or not caloric restriction helps you live longer. There is lots of evidence to support this claim.
However, your long life might be spent being extremely depressed and asexual.
One theory behind how this works is that higher metabolic rates, and specifically chronically elevated insulin levels [2], have an inhibitory effect on physiological pathways which promote longevity.
Fortunately, you can achieve comparable benefits [3] just by doing intermittent fasting instead. In the previous post I mentioned how this type of fasting can improve blood sugar and insulin markers, so you can extrapolate how this applies to the theory on longevity and disease as well.
The great thing about intermittent fasting is that you don’t have to deal with the negative side-effects of forcing your body to be in a negative energy state every day. Sure, initially it will be difficult to go 12 hours without eating, but your body will adapt.
Humans have been doing this kind of thing for thousands of years, I’m sure yours will figure out how to do it also. Give it a try, you might come to find that you actually enjoy not being tethered to the meal table three to four times a day!
“Eat Stop Eat” is a method of using flexible, intermittent fasting as a style of fasting for weight loss and body fat burning. This program will help you lose weight and naturally stimulate growth hormone – all while having a fast metabolism and building lean muscle.
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8 Responses to Intermittent Fasting Versus Caloric Restriction
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Great post, David! I actually do both IF and caloric restriction (on top of Paleo) and after months of tinkering with both I’ve found the combination that works for my body and my goals. I started on January 1 with a 14 hr fast but within weeks I found myself going longer and longer simply because I wasn’t hungry. I currently fast intentionally Monday through Friday a minimum of 16 hours (up to 24 hours) with an eating window generally from 12pm-8pm. (This window narrows if I choose to fast longer.) I eat two meals a day, one at noon and one around 7pm. I average around 1500 cals a day with a macro ratio of 60% fat 20% carb 20% protein. The key to avoiding hunger on caloric restriction is lots of fat and low carb. And the IF actually helps tremendously with any cravings.
I recommend IF to anyone, but because everyone is different they will have to experiment for themselves to see the benefits and the best way it works for their own body and goals. And don’t give up! It’s taken me nearly 5 months to find the perfect combination!
But it’s definitely worth the time. I love that feeling of “clean” that I get during a fast. 
I’d also like to point out that in my experience when you’re recovering from injury or disease IF is also incredibly beneficial. It takes a lot of energy for your body to digest food – energy that would better benefit your body by being used to heal itself. When I started Paleo it was due to severe auto-immune symptoms. Going Paleo eliminated all of my symptoms, but adding the IF really jump-started the healing process. Food for thought!
Cheryl,
I’ve actually been reading lately about how high dietary fat intake upregulates the body’s ability to utilize fatty acids for energy in a glycogen depleted state – which could occur in fasting. So yeah, your high fat diet is probably helping quite a bit.
Ha! Nice to know the science is backing my observations!
I’ve only been tracking this religiously for two weeks, but I’ve stayed in a steady state of ketosis and my energy has remained at the same level. I started tracking because I was experiencing periodic lethargy and wanted to see if I could ascertain the problem. I was afraid it might be the IF, so about a month or so ago I stopped IF for a couple of weeks. I gained 5 lbs and the lethargy didn’t go away. Needless to say, I went back IFing immediately!
Cheryl, do you do carb refeeds, and such every now and then?
I’m not sure if you’d call it refeeding, but I do up the carb count prior to any intense workout. For me this usually means a Yukon Gold potato. I know it’s very un-paleo of me, but I don’t like sweet potatoes. LOL But as I only do a max of maybe two intense workouts a week it isn’t that often. My other workouts (like hiking, heavy weights, yoga) are not intense so they don’t require those extra carbs.
I think the idea that you shouldn’t eat potatoes while paleo is kind of fading. I feel like white potatoes are far more benign than wheat at least.
I’ve been doing Intermittent Fasting for years and love it.
I actually do all my workouts in a fasted state and find it has improved my fitness.
Although some people say that you cannibalize muscle (you do), the rate of post exercise protein synthesis is elevated for up to 48 hours which I believe offsets the negative effects.
It has also been show to increase VO2 Max and up-regulate the enzymes responsible for beta oxidation (fat burning).
Another study showed that even though people training in a fasted state were glycogen depleted, they still had the same blood sugar levels as those in a fed state.
As for the high fat intake: Your body will become more efficient at burning whatever you give it most. I think you could likely get many of the same benefits by just intermittent fasting, but a high fat diet is awesome anyway (I’m eating bacon right now;).
Great work man:D
-Armi
Armi Legge´s last [type] ..The Lady Gaga Approach To Triathlon Training
“Although some people say that you cannibalize muscle (you do), the rate of post exercise protein synthesis is elevated for up to 48 hours which I believe offsets the negative effects.”
That’s the key, I think.