Intermittent fasting – health benefits that are more than intermittent

Intermittent fasting is somewhat of a buzzword of late. But it really isn’t anything new. It’s been practiced in many cultures and religions for centuries. And in natural health / wellness circles it’s been recommended for many decades.

I haven’t really paid attention to the trend as it’s something I do for many years already. It wasn’t planned, it just happened. Can’t remember exactly when, but somewhere in the 90’s during my student years I noticed that if, on the occasional Sunday I didn’t eat anything, I felt “lighter”, more energized and more mentally alert on a Monday. So I just continued doing it every now and again.

And then suddenly it becomes a “thing”…

As with many wellness trends, its current rise in popularity may be attributed to celebrities and high performance business figures talking about it and crediting it for benefits they experienced – from weight loss to enhanced mental performance.

Regardless of buzz or hype, it certainly can be of value for optimal health. If you want to lose fat, improve metabolism, and experience other health benefits all without giving up your favourite foods, intermittent fasting might be for you!

It’s an emerging area of research with very promising results. Similar to calorie reduced diets, intermittent fasting has benefits for weight loss and metabolic improvements. It might even improve brain and mental health.

Intermittent fasting (IF) has a few advantages over regular calorie reduced diets though. It is easier for many people to stick with, but more importantly, 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 do IF, and who shouldn’t do it.

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 some churches than in other people. Researchers wanted to know why and discovered 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 explore the health benefits of IF.

Intermittent Fasting for Weight and Fat Loss

For people who have excess weight or obesity, losing weight and fat reduces the risk of diabetes and cardio-vascular disease, 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.

But…

Intermittent fasting has a few key advantages!

Many studies prove what we know already: it’s really difficult to sustain a (continuous) calorie reduced diet for a long time. Often people relapse and start gaining weight again.

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 that may also help with metabolic syndrome, type 2 diabetes, and heart disease.

People who IF sometimes have improved insulin sensitivity and blood sugar levels. They also show improved 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 IF’ed 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 explore more below. This is really important for blood sugar control and diabetes risk because metabolic inflexibility is thought to be the root cause of insulin resistance.

“Metabolic inflexibility is thought to be the root cause of insulin resistance.”
Harvie (2017):

Research suggests that when considering animal studies together with the medical experience with fasting, glucose regulation and diabetes, 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 people claim that they experience improved focus or mental prowess from IF.

Several 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.

It is known that people with lifestyles that include little exercise and frequent eating (three meals every day plus snacks) lead to suboptimal 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 for short periods. 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 fa for energy, which decreases the amount of total fat in the body. This is how IF helps with overweight, obesity, metabolic syndrome, and type 2 diabetes. 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, memory, and mood. BDNF also helps enhance synaptic plasticity (changes in our brain that help with learning and memory) and allows our neurons to better resist stress. These are all improvements in brain function. Some animal studies even show improvements in the structure of the brain too. For example, new neurons are produced in the hippocampus (the part of the brain important for short- and long-term memory) in animals who IF.

According to Anton, 2018:

“In these ways, events triggered by the metabolic switch may play major roles in the optimization of performance of the brain and body by IF.”

Who shouldn’t try intermittent fasting?

PRO TIP:
Before you try any major changes to your diet, check with your healthcare provider.



IF can provide a lot of health benefits, and according to Patterson & Sears (2017):

“Overall, evidence suggests that intermittent fasting regimens are not harmful physically or mentally (i.e. in terms of mood) in healthy, normal weight, overweight, or obese adults.”

There are a few things to keep in mind before considering intermittent fasting, however.

A number of adverse effects have been reported, including: bad temper, low mood, lack of concentration, feeling cold, nausea, vomiting, constipation, swelling, hair loss, muscle weakness, uric acid in the blood and reduced kidney function, menstrual irregularities, abnormal liver function tests, headaches, fainting, weakness, dehydration, mild metabolic acidosis, preoccupation with food, erratic eating patterns, binging, and hunger pangs.

Limit fasting to avoid these effects.

If you do experience any side-effects, the first thing to do is to ensure your food intake is adequate on the non-fasting days. Second is to ty fasting less often (see the section on How to Intermittent Fast below). If side effects continue, it may be wise to go for a checkup with your healthcare professional to rule out underlying conditions.

If done too often or for too many days IF can actually have more serious effects.

Excessive fasting can lead to malnutrition, micronutrient deficiencies, decreased bone density, eating disorders, low immunity (susceptibility to infectious diseases), or moderate damage to organs.

Fasting for several weeks (about 5-7 weeks) becomes starvation, even in healthy adults. At this point your body breaks down and consumes muscles and vital organs for energy. It leads to excessive weight loss, anemia, chronic diarrhea, delirium, lactic acidosis, small bowel obstruction, kidney failure, heart arrhythmias and eventually death.

IF is not for everyone. If you have a history of eating disorders or are underweight, it may be outright harmful to you and should not be attempted without first consulting a health professional.

Al that said, IF can be considered to have an outstanding safety profile. Not eating for a while is safe if you are generally healthy and well-nourished.

How to Intermittently Fast

There are lots of ways to intermittently fast. It isn’t totally clear yet how these different methods have different health effects for different people with different health goals.

Here are some different ways to IF:

  • Alternate-day fasting (ADF) – One day of fasting, one day of “feasting.” Continue fasting on alternate days.
  • Alternate-day modified fasting (ADMF) – Eat 25-40% of your daily needs one day, then eat normally the next. Continue alternating days.
  • Periodic fasting (PF) or “Two day” fasting – Each week has 1 or 2 days to eat very few calories per day (e.g. 0-880 cal/day). The other 5 days you eat normally. Example: 5:2 diet, where you eat no more than 500 calories/day for two non-consecutive days each week.
  • Time-restricted fasting (TRF) – Fast for 12-16 hours every day and eat normally during the other 8-12 hours.
  • One 24-hour period of fasting each month.

Several researchers suggest that the alternate-day modified fasting is preferable because it is likely the easiest to follow and may cause the least amount of stress on the body and mind.

You may be wondering if fasting intermittently increases what you eat during those times when you do eat. And that’s a great question.

The interesting thing is, it seems not to!

Studies show that alternate-day fasting reduces overall calorie intake. Plus, on the non-restricted days, some people naturally reduce their energy intake by up to 20-30%.

This means another side benefit of IF is that it can help reduce food costs too!

PRO TIP:
Keep in mind that reducing your food intake also reduces your nutrient intake. It’s important to ensure you get enough essential nutrients for long-term health.



When it comes to preserving muscle mass, the jury is still out on IF, but there are a few tips:

  • Eat enough protein (1.2 g protein/kg weight), and
  • Exercise, preferably with resistance training.

Conclusion

Intermittent fasting is not something that anyone must or need to do. It is just one lifestyle strategy amongst many others, that can help control weight and improve your health. Intermittent fasting is a way to get the benefits of a regular calorie reduced diet without restricting what you eat, just when you eat it. Intermittent fasting reduces both weight and fat, and can improve blood sugar and blood lipids. It has been shown to reduce blood pressure and some markers of inflammation. Many animal studies show improvements in brain health too.

While these benefits of IF are similar to those with calorie reduced diets, IF has some key advantages including being easier for some people to stick with and it might help people eat more intentionally. There is also evidence that IF preferentially reduces fat while preserving muscle and may help our bodies become more “metabolically flexible.”

Regardless of the potential health benefits, two things are certain about IF:

  1. It cannot make up for and should not replace other health supportive behaviors like exercise, a healthy diet of “real” food, sufficient rest and sleep.
  2. It is not a license to binge on unhealthy foods on non-fasting days.

More research is needed to really understand long-term benefits of IF on the body and brain, as well as which IF approach is optimal for different people and different health goals.

It’s not for everyone. The only way to find out if it’s for you is to give it a try.

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