Intermittent Fasting Glossary

Whether you're brand new to fasting or an old hat, this guide gives you all the terms and major concepts in one place.

For those of you who have friends or family members who are interested in learning more about IF, I thought it would be nice for you to have a definitive post you could direct them to that outlines the key concepts of IF and also defines a lot of the terms they’re likely to come across if they decide to embark on the exciting IF journey.

When you’re brand new to the fasting world, there is so much jargon—and so many acronyms—that can make fasting confusing. But the whole point of fasting is that it’s simpler than other weight loss and health strategies. So I want to take some of the mystery out of it and make it as approachable as possible.

Although many of these concepts will be a review for the seasoned faster, there are likely a few terms below that even a long-term faster might benefit from reviewing. Therefore, you might want to bookmark this page so you can easily refer back to it when reading other posts.

There are three categories below: fasting terms, general diet terms, and fasting strategies. Within each category, I attempted to order the lists with the most common and necessary terms first.

Fasting Terms

IF: abbreviation for intermittent fasting. Most people use the term IF to refer to a fast that is a minimum of 14 hours long. Some people begin their fasting journey with a 12:12 protocol, which means they fast for 12 hours at night and eat all their food within 12 hours.

Although this is a fine place to start for someone who previously ate until 10 pm and then resumed eating at 6 am (only an 8-hour nightly fast), I don’t like to call doing a 12:12 practicing IF. This is because when I tell pregnant and nursing moms and growing teens not to practice IF, I mean for them not to push themselves to a 14 or 16-hour fast. But going for 12 hours without food at night is a healthy practice for anyone and was the norm in human history before chips, breakfast cereal, and Poptarts.

Clean fast: refers to having only water, sparkling water (unflavored), black coffee, and black tea during a fast. No artificial sweeteners, no lemon or flavored water, no cream in coffee, no flavored or herbal tea (lemon ginger tea, mint tea, etc). For why the clean fast is important, see this post.

NSV: abbreviation for Non Scale Victory. NSVs are unexpected benefits that come from fasting that are unrelated to the scale. NSVs include things like walking up the stairs without being winded, seasonal allergies disappearing, a decrease in “food noise,” which is constantly thinking about what you get to eat next.

People sometimes tell me the strangest NSVs. Multiple people have reported that their glasses prescription became less severe even though it had been stable for decades. Many people (including my own husband) had their blood pressure drop 30 points or more. One person came off her Metformin after fasting for one week!

Eating window: refers to the period of time you eat all your food each day.

Fasting window: refers to the period of time that you end eating for the day until you resume eating the next day.

Some people focus on tracking how long the fast is while others only pay attention to how long their eating window is. For example, only person might decide they want to eat all their food within 5 hours. Some days they eat from 1 to 6 and other days they eat from 2 to 7 or even 3 to 8. Another person likes to make sure to fast for exactly 19 hours. So if she closes her eating window at 8, then she doesn’t allow herself to eat until 3. It’s up to you to decide how you want to track but I think that tracking the eating window is easier and allows for a bit more flexibility.

Fat Adapted: this occurs when your body becomes metabolically flexible and can easily switch between burning carbs for fuel and burning fat. The first few weeks of fasting may be difficult as your body learns how to use its own fat for fuel. But keep in mind that the fat was placed there for future use so it’s important that you train your body to burn fat. You’ll know you’re becoming fat-adapted when fasting becomes easy and you no longer overeat in your eating window.

Set weight: this refers to the weight your body will often return to after any diet based on calorie restriction. Fasting resets your body’s thermostat to a lower setting by lowering the fat-storing hormone insulin.

Autophagy: The human body is equipped with an innate recycling system where it takes the damaged parts of cells and reuses them for other uses. This not only provides resources for the body, it also upgrades the inside of cells, keeping them from filling up with damaged parts that could eventually cause the cell to go rogue.

But the catch is that autophagy can only take place when the body has a period of time when it is low on nutrients.

Japanese scientist Yoshinori Ohsumi spent 50 years studying autophagy, resulting in the 2016 Nobel Prize in Physiology or Medicine.

Maintaining autophagy is important as we age. As a person grows older, autophagy slows, which can lead to cells that aren’t functioning at their best due to the build-up of worn-out cellular parts. For more on autophagy, see this post.

Time Restricted Eating (TRE) or Time Restricted Feeding (TRF): these terms are often used interchangeably with IF but Dr. Fung and colleagues use TRE to refer to the practice of eating discreet meals at specific times and not snacking. That’s how I use the term in my Substack to reiterate that you shouldn’t eat continuously in your eating window for best results.

Appetite Correction: after you’ve been fasting for a while, you may find that you now get full more quickly than you used to. When this happens, make a point of listening to your body’s signal to stop. Don’t force yourself to keep eating even if there’s food left on your plate. Appetite correction happens when you begin to cure something called leptin resistance.

Leptin Resistance: Your body releases the hormone leptin when you eat as a signal to the brain of how much energy (aka fat) is available on the system. Leptin is released from the fat stores so the more fat one has, the more leptin is released. This process is supposed to keep heavy people from wanting to eat very much.

When scientists first discovered leptin, they thought they could package it into a pill and give it to heavy people so they’d never be hungry. The pill didn’t work because the scientists discovered that the heavy people had plenty of leptin, their brains were just resistant to the signal so giving them more leptin did nothing.

When you fast, your brain gets a break from leptin’s signal and regains its sensitivity to leptin. Now you can feel satisfied after eating instead of feeling like you could eat forever. It really is one of the best NSVs.

Insulin Resistance or IR: Most hormones have only 2-3 jobs in the body. However, insulin, our fat-storing hormone, can signal over 200 different processes. As a master hormone, insulin affects every cell and tissue in the body. Therefore, if there is too much of it flowing through our veins, it can cause a host of health problems.

The fat cells’ immediate response to a small amount of insulin is called being insulin sensitive. When fat cells are very responsive, only a little insulin is needed to accomplish the job of getting the excess glucose out of the blood and into the fat cell.

As our metabolic health declines, this delicate fuel storage process begins to go awry. Now when the taste buds sense food and the pancreas releases a small amount of insulin, the fat cells no longer respond. This makes the pancreas release much more insulin to pry open those fat cells to get the glucose out of the blood.

When our fat cells become somewhat deaf to insulin’s signal we call this being insulin resistant.

In a person who is insulin resistant, it takes higher and higher insulin levels to get a response out of the fat cells to take glucose from the blood. This is also why a fasting insulin test is the most important test you can take to determine your metabolic state and overall health.

For more on IR see this post: Understanding Insulin is the Key to Fasting Success

General Diet Terms

SAD: standard American diet. It’s a great acronym because eating the SAD also makes you sad, maybe not in the short term but in the long term.

CICO: abbreviation for calories in, calories out. This is the old diet paradigm of the 80s that failed to take insulin, leptin, set weight, and appetite correction into account. Unfortunately, it still lives on today in the mainstream media and many universities.

Bulletproof Coffee: this was developed by Dave Asprey and means that you add fat (like grass-fed butter, coconut oil, or MCT oil) to your coffee during a fast. I’m not a fan of having anything other than water, black coffee, or black tea during a fast. Otherwise, you’re robbing your body of important digestive rest.

Ketones: Ketone bodies are an alternate fuel source naturally generated by the liver when you keep carbs low putting you in a fat-burning, ketogenic state. There are three kinds of ketones: acetoacetate, β-hydroxybutyrate, and acetone.

Ketones are signaling molecules that are among the most anti-inflammatory substances known to man. They have an amazing ability to directly enter the mitochondria in the cell to be used for fuel, unlike glucose from carbohydrates which must be converted to be used as fuel. Ketones also generate 27% more energy than glucose and give off fewer toxic by-products like reactive oxygen species and free radicals.

Ketosis: A metabolic state in which the body is low on carbs and so begins running primarily on fats, either from the diet or from body fat. For an overview of ketogenic therapies and who they can help, see this post and this post. I recently completed my certificate in ketogenic therapies through Dr. Timothy Noakes's ketogenic coach training program called The Nutrition Network.

If you know someone who needs a coach for ketogenic therapies, they can make an appointment with me through this link. I currently have experience with helping cancer patients, Parkinson's cases, type 2 diabetics, and those with chronic migraines. (Note: they all see medical doctors as well. This is strictly nutritional therapy coaching.)

Keto: Refers to the keto diet where one reduces carb intake to under 20 grams of net carbs per day to enter the metabolic state of ketosis.

LCHF: Low carb high fat. This term is somewhat interchangeable with keto and Atkins. If you are a person who doesn’t feel well while fasting or are at a weight loss stall, LCHF may benefit you. Just make sure the fat includes zero seed oils. Butter, beef tallow, egg yolks, and dairy fat from full-fat raw milk, yogurt, cheese, etc is best for the human body. Coconut oil, avocado oil, and olive oil are all good too but not as nutritious as animal fat.

See my post on seed oils for a discussion as to why you should never consume soy, canola, corn, sunflower, or grapeseed oils, and no margarine, or Crisco, and please no I Can’t Believe They Try To Call It Butter.

MCTs: Medium Chain Triglycerides are a type of fatty acid that is quickly converted by the liver into ketones when glucose is low. People use it to boost their ketone levels because of the brain-boosting power of ketones.

I don’t believe you need MCTs unless you are using ketogenic therapy to solve a severe health problem such as cancer, severe migraines, concussions, epilepsy, Alzheimer’s, or Parkinson’s. Even then, your own liver needs to be making most of the ketones to obtain the therapeutic effect. MCT can only slightly boost what your body is already doing but doesn’t work as a substitute for being in ketosis through eating low carb.

PUFA: polyunsaturated fatty acids found in high amounts of industrial seed oils. Small amounts naturally occur in most fatty foods but high amounts are associated with weight gain and many modern diseases.

UPF: Ultra-processed foods. Keep to a minimum for health and weight loss.

MSM: mainstream medicine, corrupted by John D. Rockefeller, should be referred to as the sickcare system instead of the healthcare system.

An Overview of Fasting Strategies