Homo sapiens pre-20th century alternated between periods of feast and famine: devouring when food was bountiful and enduring an empty stomach when food was scarce.
The human body evolved mechanisms to maintain a constant energy supply, even during these periods of food scarcity. And, these mechanisms are still alive and well in your body today!
Yet, living in the hyper-consumptive age of 21st Century New York City where people eat all day everyday, New Yorkers rarely activate these alternative energy pathways.
The result?
Untapped energy stores.
Persistent fat.
Apple bottoms and muffin tops.
Intermittent fasting mobilizes fat stores.
What It Is
Intermittent fasting.
Intermittent means periodic.
Fasting is choosing not to eat.
Intermittent fasting is alternating periods of eating with periods of abstaining from food.
Sound simple enough? It is.
Intermittent fasting facilitates your ideal body weight through:
hormonal control
Traditional nutritionist thought on weight loss revolved around the calorie equation: calories consumed minus calories burned. This overly simplistic approach ignores the type of calories and the timing of calories, which both influence hormone levels in the body.
One of these hormones in insulin.
So, when the body hasn't encountered food in a number of hours or days, where does energy come from? This depends on the amount of time that has passed since the last meal.
Energy Equilibrium
Despite abstaining from food, your body maintains a constant level of energy mediated by your pancreas, liver, kidney, muscle and fat tissue.
PHASE {Time since last meal}
EATING {0 hours}
Consuming food triggers release of insulin. Insulin helps shuttle glucose from the bloodstream into cells. In the liver, insulin facilitates storage of excess glucose as long chains called glycogen. In fat cells, insulin promotes storage of excess glucose as lipids.
POST-absorption {6-24 hours}
In the 24 hours since the last meal, the body will break down glycogen to release stored glucose.
GLUCONEOGENESIS {24-48 hours}
Once the limited supply of glycogen has been expended, the liver will begin producing glucose from amino acids, the building blocks of proteins. Producing glucose from non-carbohydrate ingredients is called gluco-neo-genesis.
LIPOLYSIS {2-3 days}
At this point, the body chooses to preserve protein and instead prioritizes fat mobilization. Triglycerides are broken down into glycerol and fatty acids. The glycerol is converted into glucose (also a form of gluconeogenesis) and the fatty acids are converted into ketone bodies. In the non-fasted state, the brain uses glucose exclusively; however in the fasted state, the brain also utilizes ketones.
Ketosis
Ketogenic Diet
High fat
Moderate protein
Low carb
Fasting induces a metabolic shift in the body: from burning glucose to burning fat.
Is it possible to switch your body from glucose burning to fat burning without fasting for 48 hours? Yes.
This is the concept behind the ketogenic diet. If very few carbohydrates are consumed, little glycogen can be produced, thereby skipping the glycogenolysis phase because there is minimal glycogen to break down into glucose. Instead, the body will mobilize stored energy in fat in the form of ketones. Ketosis is the state in which ketones provide energy to the body.
Only when the body has been depleted of carbohydrate stores will the body switch to burning fat.
In fact, some proponents of the ketogenic diet argue that humans have no need for carbohydrates whatsoever, as both fat and protein can be converted into glucose by the body (Manninen).
⚠️ Ketosis is not ketoacidosis. Ketoacidosis is a life-threatening condition that typically plagues type 1 diabetics. In type 1 diabetes, the absence of insulin results in glucose-deprivation of cells; in response, the body ramps up production of ketone bodies to dangerously high levels resulting in acidification of the blood. Contrast this with ketosis, a gradual physiologic response to the absence of carbohydrates.
How To Do It
If you're accustomed to eating three or more meals per day, implementing periodic fasting will surely leave you feeling hungry at first. But this is temporary! Eating is just like any other habit. When you are accustomed to doing something your body acts effortlessly. But, when patterns and behaviors change, the effect on the brain and body can be palpable.
Consider this, some people skip breakfast. Simply, it's part of their morning routine to forego calories. Are these people starving in the mornings? Certainly not. Not eating in the morning is effortless because their body isn't habituated to eating upon waking.
The amazing thing about intermittent fasting is that it's flexible! Generally, 12 hours is the shortest duration, while some people fast for 36 hours or longer.
It's simply a matter of finding what eating window works for your schedule and goals.
The longer you fast and the more often you fast, the more dramatic the results.
Do you eat dinner late? No problem. Simply shift your eating window later.
Want to maintain an 18 hour fast everyday? Go for it.
Want to fast for 24 hours every third day? Great.
Want to fast during the week, but not over the weekend? Wonderful.
The most important part is the length of the window, not the timing of the window. The longer the fast, the lower the level of insulin, the greater degree of fat burning.
Of course, if you take prescription medications you should consult with your doctor before undertaking any fasting protocol. Why? Certain medications, especially anti-diabetic medications, lower blood sugar. If these medications are taken while fasting, dangerously low blood sugar and even death can result. Please consult your doctor first!
What about liquids?
Great question! Non-caloric liquids are fine. Drink as much water, tea and black coffee as you like. The caffeine in coffee and tea acts as an appetite suppressant, which will help you through any AM hunger pangs.
Of note, artificial sweeteners are OFF LIMITS because they alter the hormonal system even though they don't add calories. Remember: hormonal control > caloric balance.
Sample Fasting Protocol
Each day, create an eating window of 4-8 hours, during which you will consume all of your calories. This means fasting for 16 to 20 hours at a time.
At 9PM finish eating dinner.
After waking and throughout the morning, consume black coffee and water. Any non-caloric beverages free from artificial sweeteners are fine to consume.
In the afternoon, sometime between 1PM and 5PM, have your first calories.
At 9PM finish eating and repeat the process the next morning.
This is just an example; fasting protocols are flexible to your body, goals and schedule.
Interested in intermittent fasting?
Schedule a consultation:
services@DoctorK.nyc
646.568.6636
Resources
Fung, Jason. "The Complete Guide to Fasting" Las Vegas: 2016.
Manninen, Anssi H (2004). "Metabolic Effects of the Very-Low-Carbohydrate Diets: Misunderstood "Villains" of Human Metabolism". J Int Soc Sports Nutr. 1 (2): 7–11.
http://vitals.lifehacker.com/how-to-free-yourself-from-food-cravings-with-intermitte-1702108722
Yartsev, Alex. "Physiological Adaptation to Prolonged Starvation" 25 June 2015. <http://www.derangedphysiology.com/main/required-reading/endocrinology-metabolism-and-nutrition/Chapter%203.1.8/physiological-adaptation-prolonged-starvation>