The Brain and Health Benefits of Intermittent FastingApr 10, 2022
The Brain and Health Benefits of Intermittent Fasting
If you want to sharpen your mind, improve metabolism, and experience other health benefits (like fat loss!) even without giving up your favourite foods, intermittent fasting (IF) might be for you!
And while it may simply seem like IF is just the latest “trend” 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 great advantages 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 reducing the time period in a day where you are eating–your feeding window–and increasing your fasting window when you consume nothing (water is OK!). In other words, it’s about controlling when you eat and drink, as opposed to what you eat and drink. (Of course you still want to be eating, healthy, nutrient-dense, Real Food as much as possible!)
There are lots of ways to intermittently fast. It can be done daily, weekly, or monthly. After I go over the health benefits, I’ll look at some of the most popular ways of practicing intermittent fasting.
Background: History and animal studies
In the early 2000s, researchers started looking at what happened for people who fasted. They found that people who reported routine fasting (some for religious reasons, others believing there were health benefits) 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. They show a lot of health benefits 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.
Health Benefits of Intermittent Fasting (IF)
IF 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 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.
IF for Metabolic and Heart Health
IF also has metabolic benefits and may help not just with brain health, 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 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 I’ll talk about more 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.
IF 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 consistently reduces the amount of food ingested by anywhere from 15-60%. 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 is not a continuous reduction, but rather an intermittent one. It allows you to eat what you want (well, within reason), but only during certain times. It’s an alternative to calorie reduced diets. Both continuous calorie reduction and IF have similar weight loss results.
But … 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 can be easier for many people to stick with.
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.
How IF helps our bodies and brains
How do we explain the health benefits that IF has on our bodies and brains?
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 stored 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 is 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 on to fuel the 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, and some animal studies also 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.”
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.”
Plus, Intermittent Fasting gives your body and your digestive system time to rest and reset. It’s not wise, or something experienced by our Palaeolithic ancestors, to eat continuously all day and evening long. When you take a break between meals, your glucose levels remain stable, your insulin levels drop and your body has a chance to clean up shop—all of which can support major benefits like weight management and longevity.
How to Practise Intermittent Fasting
There are lots of ways to practise intermittent fasting, and we don’t yet know how these different methods have different health effects for different people with different health goals.
Here are some of the different ways to IF:
- Alternate-day fasting (ADF) - One day of fasting, one day of “feasting.” Continue fasting on alternate days.
- Periodic fasting (PF) or “Two day” fasting - Each week has 1 or 2 days to eat very few calories per 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. For example, wait until 11:00 am to eat your first meal of the day, and finish your last by 7:00 pm. This type of fasting schedule is great for those who don’t usually find themselves hungry in the morning when they wake up.
My personal experience is with Time-Restricted Eating - shortening the eating window to 7 to 8 hours. I’m not usually feeling hungry in the morning, so I often wait until at least 10:30 am to eat my first meal. I usually have a light snack mid-afternoon, and then finish dinner by 6 or 7 pm. Plenty of time to digest everything before heading off to bed! And because I know that I won’t be eating 3 meals plus snacks in the day, the first meal especially can be a bit bigger than what many women seem to eat for lunch these days!
But you don’t need to dive right into a 16-hour fast. Begin by just noticing what time you finish eating at night (try not to have after dinner snacks!) and what time you eat breakfast. Then whatever that is, simply delay “breaking your fast” by increments of ½ hour to an hour every few days until you’ve arrived at the Fasting to Eating ratio that works for your body.
So yes, listen to your body. On days where you know you can’t wait to eat or your schedule won’t allow for it, it’s OK to shorten the fasting window. In fact a “day off” from your IF routine periodically is a good thing. And make sure you are eating satiating meals that contain quality fats and protein, plus plenty of fibre.
I also recommend that you not try IF yet if you know you tend to eat a lot of processed food products and starchy carbs – instead start with simply eating more Real Food, including lots of veggies, plus healthy proteins and fats to help build up the health of your body and tame that sugar monster! Once your body is healthier, give it a go!
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 non-restricted days, some people naturally reduce their energy intake by up to 20-30%.
Is intermittent fasting healthy for everyone? The short answer is no. Anyone pregnant, breastfeeding, with a history of disordered eating, with a medical condition or on medication, should speak to their healthcare practitioner about whether to engage in intermittent fasting.
REMEMBER: Keep in mind that reducing your food intake could also reduce your nutrient intake. It’s important to ensure you get enough essential nutrients for long-term health, so this is an incentive to eat nutrient-dense Real Food, and cut back on any processed food products you may be used to consuming.
Intermittent fasting is a way to get the benefits of a regular calorie reduced diet without having to go on a “diet.” 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.”
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.
DISCLAIMER: Before you try any major changes to your diet, check with your healthcare professional.
Recipe: Asparagus and Tomato Salad with Lemon-Basil Dressing
Break your fast with this lovely salad for springtime! Add the protein of your choice for a complete meal.
- 1 lb asparagus, woody ends trimmed
- 1 cup heirloom cherry tomatoes, halved
- 1/2 cup sliced radishes
- 4 cups mixed salad greens
- 2 tablespoons fresh basil leaves, minced
- 2 tablespoons fresh parsley, minced
- 1 clove garlic, minced
- 2 teaspoons lemon juice
- 4 tablespoons olive oil
- salt and ground black pepper (to taste)
- 1/4 cup cheese (your choice, optional)
- Trim and steam asparagus for 3-4 minutes.
- While asparagus is steaming, make the dressing by combining the basil, parsley, garlic, lemon Juice and olive oil in a small bowl. Set aside.
- Drain asparagus and rinse with cold water to stop the cooking process. Pat dry with a paper towel.
- Plate salad: lettuce topped with asparagus, tomatoes and radishes.
- Drizzle dressing on top of salad and toss.
- Sprinkle a little salt and black pepper to taste. Add cheese or vegan cheese of your choice (optional).
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