If you want to lose fat, improve metabolism, and experience other health benefits all without giving up your favorite foods, intermittent fasting might be for you!
It’s an emerging area of research and the results are very promising. Similar to calorie reduced diets, intermittent fasting has benefits for weight loss and metabolic improvements, and might even improve brain and mental health.
Intermittent fasting (IF) has a few advantages over regular calorie reduced diets. Not only is it easier for many people to stick with, but it also seems to have a metabolic advantage. These are really good things when it comes to long-term health.
Intermittent fasting is just that - fasting intermittently (periodically). It’s an “eating pattern,” rather than a “diet.” That means regularly reducing your eating and drinking during pre-set times. It’s controlling when you eat and drink, as opposed to what you eat and drink.
There are lots of ways to intermittently fast. It can be done daily, weekly, or monthly. After we go over the health benefits, we’ll look at some of the most popular methods on how to, and who shouldn’t, IF.
Background: History and animal studies
Back in the 1980s and 1990s U.S. studies looked at effects that reducing smoking had on heart disease risk. Interestingly, the risks seemed to reduce more in members of the churches of Latter Day Saints and Mormons than in other people. Researchers wanted to know why, and that’s when they found a possible connection with fasting.
Beyond smoking, researchers started looking specifically at people who fasted. In the early 2000s, they found that people who reported routine fasting (for religious reasons or not) had lower risk of heart disease. People who reported fasting had lower blood sugar levels, body-mass indices (BMIs), and risks of diabetes.
When it comes to animal studies, it’s easy to restrict when an animal eats, so there are a lot of studies on the health effects of IF in animals.
Animal studies show a lot of health benefits of IF including longer lives and reduced risk of atherosclerosis (narrowing of the blood vessels due to buildup of plaque), metabolic dysregulation (includes type 2 diabetes), and cognitive dysfunction (ability to learn, remember, solve problems). They also have lower levels of inflammation and generally live longer.
So, let’s dive into the health benefits of IF.
Intermittent Fasting for Weight and Fat Loss
For people who have excess weight, losing weight and fat reduces the risk of diabetes, improves healthy lifespan, and increases function of both the body and mind.
After about 5-6% of a person’s body weight is lost, even more health benefits are seen - lower blood lipids (LDL cholesterol and triglycerides), better blood sugar management (lower glucose and insulin), lower blood pressure, and lower levels of inflammation (C-reactive protein).
These benefits are seen with both calorie reduced diets and with IF.
When it comes to weight and fat loss, a typical calorie reduced diet works. By consistently reducing the amount ingested by 15-60%, people with overweight and obesity lose weight and fat. This is called “continuous” calorie reduction because one is continuously reducing what is ingested - at every meal and snack, every day. Calorie reduced diets can include eating smaller servings, low calorie substitutions, and/or cutting out some snacks/desserts every day.
Intermittent fasting isn’t a continuous reduction, but rather an intermittent one. It allows you to eat what you want, but only during certain times. It’s an alternative to calorie reduced diets. IF is a way to “diet” without “dieting,” so to speak.
Both continuous calorie reduction and IF have similar weight loss results.
Intermittent fasting has a few key benefits!
Many studies prove what we know already: it’s really difficult to sustain a (continuous) calorie reduced diet for a long time.
This is the reason why many people prefer intermittent fasting - it gets similar weight and fat loss results, plus it’s easier for many people to stick with.
This makes IF a great alternative for anyone who wants to lose weight and fat, but has difficulty sticking with a reduced calorie diet.
Other advantages to IF over calorie reduced diets are that it can help people eat more intentionally (and less mindlessly). Also, some studies show that IF makes our metabolism more flexible so it can preferentially burn fat, while preserving the muscles. This is a great benefit because that can help improve body composition in people with excess weight.
Intermittent Fasting for Metabolic and Heart health
Over and above the weight and fat loss benefits, IF has metabolic benefits and may help not just with overweight and obesity, but with metabolic syndrome, type 2 diabetes, and heart disease as well.
People who IF sometimes have improved insulin sensitivity and blood sugar levels. They also show improve blood lipids and even reduced inflammatory markers. All of these are related to improved metabolism and reduced risks for many chronic diseases.
One study found that people who IFed for 6-24 weeks and lost weight also benefited from reduced blood pressure.
One unique way IF works is by making our metabolism more flexible, which we’ll talk about below. This is really important for blood sugar control and diabetes risk because, according to Harvie (2017):
“Metabolic inflexibility is thought to be the root cause of insulin resistance.”
Another researcher, Anton (2015) says:
“When taken together with animal studies, the medical experience with fasting, glucose regulation and diabetes strongly suggests IF can be effective in preventing type 2 diabetes.”
Most researchers find these results promising, and recommend more high-quality longer-term trials.
Intermittent Fasting for Brain and Mental Health
Many animal studies show that intermittent fasting can help improve their cognition (ability to think). When mice fasted on alternate days for 6-8 months, they performed better in several learning and memory tests, compared to mice that were fed daily. This improvement even happened in mice who started IF later in life.
Studies also show that alternate day fasting protects brain neurons in animal models of Alzheimer’s, Parkinson’s, and stroke, and reduces oxidative stress in the brain.
We know that people with lifestyles that include little exercise and frequent eating (three meals every day plus snacks) lead to sub-optimal brain function and increases the risk of major neurodegenerative and psychiatric disorders.
Researchers are still learning about the brain and mental health benefits of IF in people. Short-term studies show some people report improvement in tension, anger, and confusion from IF; while others report bad temper and lack of concentration as side effects from it.
More longer-term human studies of different calorie reduction diets, including IF, will shed light on effects on cognitive performance and mental health.
How intermittent fasting helps our bodies and brains
How do we explain the health benefits that IF has on our bodies and brains? One way is the “metabolic switch” that is flipped during fasting.
While continuous calorie reduction and IF have many of the same health benefits, IF might have a different biological mechanism at play. Some research suggests that IF might “flip” a metabolic switch.
Here’s how it works.
After we eat our bodies use carbohydrates (e.g. glucose) from our food for fuel. If there is extra left over, then it’s stored as fat for future use.
With fasting, just as during extended exercise, our bodies flip from using glucose (and storing fat), to using that stored fat and ketones (made from fats) for fuel. Sometimes called the “G-to-K switch,” (glucose-to-ketone) the ability to flip what our bodies use as fuel (between glucose and ketones) is called “metabolic flexibility.”
It’s thought that we, and many animals, evolved to have this ability to survive short periods of fasting from when we were hunter-gatherers. There were times when people didn’t have a lot to eat, but they still needed to survive and think clearly enough to successfully hunt and gather food. This can explain why our bodies and brains don’t necessarily become sluggish when we’re fasting. It makes a lot of sense, although it has yet to be tested in current-day hunter-gatherers.
This metabolic switch can explain some of the health benefits of fasting. When our bodies prefer using fats for fuel, the body starts burning our stored fat. This is how IF helps with overweight, obesity, metabolic syndrome, and type 2 diabetes. When the body uses fat for energy this decreases the amount of fat in the body. Reduced fat reduces weight, and health benefits from weight loss (like lower blood pressure and insulin resistance) are felt.
This “flipping” of the metabolic “switch” happens after the available glucose, and the stored glucose are depleted. This is anywhere from 12-36 hours from the last meal, depending on the person. At this point the fats in our cells start getting released into the blood and are metabolized into ketones. These ketones then go to fuel cells with “high metabolic activity” - muscle cells and neurons.
Since the body is burning fat and using ketones to fuel the muscles, IF can preserve muscle mass. Some studies of IF show that it preserves more muscle mass than regular calorie reduced diets do.
The other high metabolic activity cells fueled by ketones are neurons (in the brain and nervous system). IF helps our brains because when our neurons start using ketones for fuel, it preserves brain function and increases brain-derived neurotrophic factor (BDNF) which is very important for learning, me