Fasting for fat loss

While many regard fasting as a difficult challenge, it has been a normal part of the human experience for millennia and is a time-honored tradition among virtually all major religions of the world.

Part of the normal human experience

Historically, our distant and not-so-distant ancestors certainly endured many periods of fasting, thanks to many factors such as environmental conditions, socioeconomic factors, and simple bad luck.  Today, we take for granted the remarkable availability of food at all times, a stark contrast to the food environment in generations past.

While our ancestors were faced with many adversities related to food supply (poverty, famine, war, etc.), we are now surrounded by an unprecedented availability of food.  Imagine living through the Great Depression and now seeing someone order pizza from their couch at midnight via a smart phone . . .

Do we eat too often?

Archaeologic records indicate that humans generally ate only 2 meals per day.  The convention of 3 meals per day appears to be a result of the push to make breakfast the “most important meal of the day” by cereal manufacturers.  Creatures of habit as we are, our days are often now [disappointingly] structured around meal times.

Most people are consuming food on a regular basis throughout the day, which provides a steady supply of energy to fuel the body.  The downside of this way of eating is that your body rarely has any chance to burn fat.  When fasting, however, your body uses up the available glucose (and glycogen) over time, which forces your body to tap into your fat stores for a fuel source.

Rate of fat loss

When fasting, the average person burns about ½ pound of fat per day.  Obviously, there are many contributing factors to this rate of fat loss.  This observation makes sense when considering that the average person has a basal metabolic rate of 1,500 – 1,700 calories per day, along with the widely accepted notion that a pound of fat contains 3,500 calories.

 

How does fasting work for fat loss?

There are a few mechanisms at play with fasting when it comes to fat loss.

• First is the simple energy equation – calories in, calories out. Obviously, when fasting, there are no calories entering the body, thus there is a clear negative energy balance that favors weight loss.  This overly simplistic framework is satisfying to those who adhere strongly to the law of conservation of energy.  I say it’s overly simplistic because it falls far short of capturing the complexity of the human body.
• Second, there is a significant drop in the hormone insulin when fasting that facilitates fat-burning. Insulin regulates how energy is utilized in the body, and one of its primary functions is to turn OFF fat-burning.  Given that carbohydrates (glucose, etc.) are the primary driver of insulin release by the pancreas, a period of fasting allows the insulin level to decrease.

You can fast as long as you prefer

There are many variations of fasting, and there’s no clear “best method”.  Intermittent Fasting refers to compressing one’s eating window into a narrower time period, often a 6-hour window during which the daily meals are consumed, leaving 18 hours of fasting – referred to as 18:6 intermittent fasting.  Other strategies include one-meal-a-day (OMAD), skipping one whole day of eating (roughly a 36-hr fast), 5 days of normal eating followed by 2 days of very low calorie intake (5:2), or multi-day fasting.

Many people question how it is possible to fast for multiple days and still carry on with work, play, life, etc.  There are two important adaptations that our bodies utilize to allow us to perform normally in the absence of food intake.

Fat adaptation

In general, the average person is running on carbohydrates nearly all the time, thanks to regular intake of carbohydrate-containing foods which results in a continuous supply of energy in the form of glucose.  If your carbohydrate intake is abruptly cut off, your body must switch gears to utilizing a different fuel, i.e. fat.  Burning fat, however, requires different machinery than burning carbohydrates.  In this average person, the fat-burning machinery is “untrained” and sluggish.  Cutting carbohydrate intake often causes people to feel fatigued and lightheaded, because their bodies are not “fat-adapted”.

Fat adaptation is a condition in which one’s body can efficiently run on fat as a primary energy source.  Because our bodies carry exponentially more fat calories than glucose calories, being fat-adapted makes considerably more energy available.  One good indicator of being fat-adapted is the ability to skip meals or go several hours at a time without hunger pangs.

Ketosis

When our bodies break down fat, the resultant fatty acids can generate ketone bodies (i.e. ketones) that are themselves an efficient energy source.  Ketones have a striking appetite-suppression effect.  Thus, as you generate more ketones by fasting, it actually gets easier to continue fasting.
Many people experience a sensation described as “mental clarity” when fasting for multiple days.  This observation may reflect improved brain functioning, as the brain is remarkably adept at using ketones as a fuel and, in fact, prefers ketones over glucose.

Summary

Fasting is the simplest intervention possible – do nothing!  It is effective for fat loss and has been proven to be safe for extended periods of time.  Critics abound, but fasting has been a part of the human experience for millennia.  In fact, our survival as a species would not have been possible if humans hadn’t endured periods of fasting.