Friday, February 25, 2011

Intermittent Fasting 101

Many people have heard of caloric restriction, and it's implications on human health and longevity.  Time and time again, lab-testing of CR has been shown to produce a whole range of physiologic benefits, as well as extend lifespan in all animals- be it silkworms or apes.  There is however, a more practical way to reap these benefits, via intermittent fasting.

Intermittent fasting (IF) has been a very useful tool for me in my health and fitness journey. It is beneficial both to the body and the mind, in so many ways.

This was the first article I ever read about IF, from Dr. Michael Eades, author of Protein Power (an awesome book I recommend everyone reads).

"Like caloric restriction, intermittent fasting reduces oxidative stress, makes the animals more resistant to acute stress in general, reduces blood pressure, reduces blood sugar, improves insulin sensitivity, reduces the incidence of cancer, diabetes, and heart disease, and improves cognitive ability."

An interesting thing he mentions is that while both caloric restriction (CR) and IF provide numerous health benefits and potentially increase lifespan, CR animals in lab settings exhibit depression and irritability, even hostility and violence. IFing shows no such behavior.

Another excellent article from Mark's Daily Apple: The Myriad Benefits of Intermittent Fasting

Beyond the tangible physiologic benefits of IF, there is the idea that IF sort of re-primes your innate hunger mechanisms, can resensitize appetite hormones such as leptin and ghrelin, and just generally change/improve/reset your relationship to food. Which is obviously important in this culture of binge eating, food cravings and the like.

There are several different approaches or strategies to IF; likewise there are a few already established plans or "diets" that various people advocate commercially.

1. Alternate-Day Fasting - You basically eat for 24 hours, then fast for 24 hours, repeated indefinitely. For this to be successful, you need to be eating a lot of calories on your eating days (so not necessarily running a large weekly caloric deficit)*. A variation of this is Brad Pilon's "Eat Stop Eat" where you skip meals to create 24 hour fasting periods, but don't necessarily go an entire day without eating.

2. Condensed Feeding Windows- In any given 24 hour period, you only eat during 4-8 hours. For example you would fast til noon, and then eat anywhere from 1-4 meals between noon and 8pm, then fast til noon again the next day. The Warrior Diet is an extreme version of this, where you consume the bulk of your calories in 4 hours at the end of every day.

3. One Day/Week Fasting - Pretty simple, you just don't eat for one day per week. You could expand this to say, 3 times per month or whatever.

I like to use a more combined, instinctual approach; you just kind of make it up as you go along- "I'm not so hungry tonight, I'll skip dinner". Or you might plan to skip breakfast the next morning, hit the gym hard and have an awesome lunch.

Another fascinating viewpoint from Dr. Kurt Harris from PaNu.

"We are told to eat frequent snacks because the standard american diet with 55% carbs has you metabolically and emotionally tethered to frequent boluses of glucose."

Advantages of Infrequent Meals:
1. Enhanced metabolic training in the direction of fat metabolism
2. Lower insulin levels and fewer insulin related diseases (Metabolic syndrome, degenerative diseases, Alzheimer's, common cancers)
3. Greater tolerance for fasting makes it easier to tolerate not eating - this give you "metabolic headroom" -it makes you more functional and resilient - You are a Porsche with a 40 gallon gas tank instead of a truck running on lead acid batteries.
4. If you exercise while fasting, the lack of insulin in the fasting state improves the fat-mobilizing and insulin-sensitizing benefits of the exercise.

And for the encore:  
"Let's say involuntary periods of hunger were something that we are so adapted to that we metabolically depend on them to avoid some diseases. Maybe we are less likely to get cancer if these periods happen to us with some regularity not found in a modern food-abundant environment. Because intermittent fasting might enhance our modern health, do we then say this was a "good" part of paleolithic life, even though the experience might have been uncomfortable and terrifying for paleo man or may have killed weaker members of his kin when it happened?"

*Very important!! You must consider weekly caloric intakes as well as daily. This is a huge factor in binge behavior. If you don't eat enough 1-2 days, then by the third day, even though you ate good, substantial meals, you are still ravenously hungry.

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