Janet Bond Brill - Intermittent Fasting For Dummies

Intermittent fasts cycle between periods of fasting with periods of eating. Whether or not you’re fasting, the body still requires energy to run efficiently. The body’s main source of energy is a sugar called glucose, which typically comes from carbohydrates such as grains, fruits, vegetables, and even sweets. Both your liver and muscles store the sugar and release it into the bloodstream whenever the body needs it.

To understand how intermittent fasting works, you need a quick adaptive physiology refresher. Because food wasn’t always abundant, and sometimes wasn’t available at all, the human body was forced to adapt to fasting involuntarily — and then, when Stone Age humans found food, they would feast. Because of those evolutionary conditions, human bodies evolved to permit their bodies to thrive by adapting to those cycles of feasting and fasting. In order to survive in such environments where food was scarce, humans had to possess the ability to quickly shift their metabolism from fat storage to fat breakdown for energy. This metabolic flexibility became built into human’s genetic code, producing a system where energy was stored in the form of body fat when food was available and then easily accessed for energy to enable humans to perform at a high level, physically, during extended periods when food wasn’t available. This pattern enabled human brains and bodies to function optimally in a food deprived/fasted state, giving the human race a survival advantage.

Scientists have hypothesized that the human body’s adaptive benefits of intermittent fasting led to the superior cognitive capabilities (brain power) of humans compared to other mammals. These brain adaptations facilitated human’s ability to invent tools, novel hunting methods, animal domestication, agriculture and food storage, and processing.

Because intermittent fasting patterns can replicate the feast-or-famine diet of human ancestors, many researchers have now recognized the advantages of periodically fasting (such as increased brain power, physical enhancements, and disease prevention) for the multitude of health benefits this lifestyle gives rise to.

What is the physiology of fasting? Although everybody responds to fasting a little differently (genetics, health, and age all play a role), there is a general timeline of events — a predictable set of metabolic responses as your fast stretches from hours into a day or longer. (For a much more detailed discussion of the different metabolic states your body goes through when practicing intermittent fasting, refer to Chapter 5.)

After fasting for a mere eight hours, here is the timeline of what happens in your body:

1 You have no food coming in, so you exhaust your supplies.Your body has tapped into your liver reserves of blood sugar to continue to keep your blood sugar level in the normal range. You’re now in what’s termed a catabolic or breakdown state.

2 You enter the fasted state; your liver has run out of its sugar reserves.This triggers the liver to manufacture new sugar from noncarbohydrate sources (scientifically termed gluconeogenesis ) to continue to supply energy to the cells. With no carbohydrates consumed, the body creates its own sugar by using mainly fat. This marks the body’s transition into the fasting mode. Studies have shown that gluconeogenesis increases the number of calories the body burns, meaning when your metabolism starts to increase.

3 You flip your metabolic switch.One key mechanism responsible for many of the beneficial health effects of short-term, intermittent fasting is flipping of the metabolic switch. The metabolic switch is the body’s preferential shift from utilization of blood sugar to fat and fat-derived ketones for energy. In this step, your body breaks down fat, shuttling it to the liver, which creates ketones from fat to use for energy. The metabolic switch typically occurs between 12 to 36 hours after cessation of eating.

4 Extended fasts (longer than 36 hours) begin to slow metabolism down.That’s why you shouldn’t practice extended fasting with intermittent plans. After about 36 hours, the body stops using these energy sources (sugar and fat). The fasting mode then transitions to the more serious starvation mode.

5 You enter starvation mode.At this point, your metabolism has slowed dramatically, and your body begins to burn your own muscle protein for energy. The lack of essential nutrient intake plus using muscle for energy sets off an alarming cascade of dangerous complications.

During your recommended intermittent fasting periods, your fasting periods shouldn’t extend beyond 36 hours. Although some people choose to fast for up to 48 hours, I recommend your intermittent fasting periods don’t extend 36 hours because of the physiological reasons I mention here. Chapter 5probes much deeper into the science of intermittent fasting.

The most effective dietary plan is the one you can adhere to for the long term while still living your best life. If you want to lose weight and are sick and tired of counting calories, then this eating pattern may be the right fit for you. The popularity of intermittent fasting lies in its simplicity and the fact that the fasting periods are time-limited, which people find easier to maintain than traditional diets.

Intermittent fasting is not only for people who want to lose weight, but it’s also a phenomenal lifestyle plan for individuals who want to improve their health, fight aging, and simplify their lifestyle. The scientific data shows intermittent fasting has powerful effects on your body and brain and may even extend your life. Chapter 6discusses the miraculous health benefits linked to intermittent fasting.

Part 3discusses the five most common ways of practicing intermittent fasting in detail. These different alternative protocols are as follows:

Time-restricted intermittent fasting: The time-restricted intermittent fasting , also called the eating window plan, is by far the most popular plan, because many rave about it being the easiest to follow. This plan consists of fasting for a daily 16-, 18-, or 20-hour consecutive period and setting your daily eating window for the remaining 8, 6, or 4 hours (albeit, you can use other time windows). Check out Chapter 9for more details.

Warrior intermittent fasting plan: The warrior intermittent fasting plan is based on the eating patterns of ancient warriors who ate very little during the day and then feasted at night. Flip to Chapter 10for the details on this method of intermittent fasting.

Alternate day intermittent fasting: Alternate day fasting (ADF), another form of intermittent fasting, involves fasting one day, eating the next, and repeating. Chapter 11gives you the lowdown on this method.

5:2 intermittent fasting plan: The 5:2 plan, also known as the fast diet, entails eating 500 to 600 calories on two nonconsecutive days of the week. Chapter 12explains the ins and outs of this plan.

Eat-stop-eat intermittent fasting: This plan requires fasting for a full 24 hours, once or twice a week. Head to Chapter 13for how to incorporate eat-stop-eat intermittent fasting into your life.