Intermittent Fasting: Will a Long Wait Lead to Weight Loss? -

Kaitlin Little

Chances are you’ve heard of the 5:2 Diet, and maybe even the 16/8 Method. But have you heard of the Warrior Diet?

These are all methods of intermittent fasting. An alternative approach to dieting that has soared in popularity over the last few years.

Intermittent fasting generally involves reducing your eating window to a specific time frame and then eating nothing for the rest of the day. But what’s the point of this? Advocates claim the practice improves body composition, leads to fast fat loss, and enhances your health. Although, is there any real science to support these claims?

What is Intermittent Fasting?

Intermittent fasting is an eating pattern that cycles between short periods of fasting, during which you don’t eat or reduce food intake significantly, and feasting periods of unrestricted eating.

Whereas most diets focus on what you eat, intermittent fasting focuses on when you eat. In this sense, intermittent fasting isn’t exactly a diet, but rather an eating regimen.

It’s not a peculiar thing, either. Fasting simply means to abstain from food. In fact, most of us fast every single night for at least 8 hours. That’s why our first meal of the day is called “break-fast”.

What’s more, the practice is built into our genes. Humans have been fasting since the dawn of time. Our ancient ancestors were forced to fast when food was scarce, but we’ve also chosen to deprive ourselves throughout history for religious reasons.

In recent years, we have rediscovered the benefits of fasting with the introduction of many different mainstream regimens.

Different Types of Intermittent Fasting

There are multiple ways to fast, all of which involve dividing the day or week into “fasting” or “feasting” periods. The most common types of intermittent fasting include:

Time Restricted Fasting: This regimen involves completely restricting energy intake for a specific length of time each day, with meals eaten during the remaining hours of the day.

Example: Fast for 16 hours each day– e.g, from 6pm-10am the following day. All meals must be eaten outside the designated “fasting” period.

Alternate Day Fasting: This regimen involves alternating between fast days, where energy intake is either completely withheld or reduced to 25% of daily energy needs, and feast days, on which food is consumed without restriction. In other words, rather than fasting every day, you fast every other day. Example: Monday-Wednesday-Friday consists of fasting for 24 hours, while alternate days have no food restrictions.

Whole Day Fasting: This regimen involves multiple days per week of complete energy restriction or less than 25% of daily energy needs, with no restriction for the remaining days of the week.

Example: The well-known 5:2 regime consists of five unrestricted eating days with two consecutive or non-consecutive “fast” days.

Is Intermittent Fasting an Effective Weight Loss Tool?

There is an abundance of research to support the role of intermittent fasting in preventing weight gain and promoting weight loss.

According to a recent systematic review, intermittent fasting causes an average weight loss of 0.4 – 1.8 lbs per week. [1] This is considered a healthy rate of weight loss. Research continually shows that people who gradually lose weight (about 1 – 2 lbs per week) are more successful at keeping the weight off.

Another systematic review found that intermittent fasting is just as effective as daily calorie restriction, with both diets causing an average 8% reduction in body weight over the course of 12 weeks. Furthermore, the study found that intermittent fasting preserves three times more lean muscle mass than daily calorie restriction. More specifically, when restricting calories on a daily basis, 25% of the total weight loss came from lean muscle mass loss. Whereas, when intermittently restricting calories, just 10% of the total weight loss came from lean muscle mass. [2]

A common concern when intermittent fasting is that abstaining from food will trigger compensatory overeating on non-fasting days. However, this does not seem to be the case. In fact, studies have shown that overall energy intake typically declines when intermittent fasting. [3]

How does Intermittent Fasting Help Weight Loss?

When eating three square meals a day, our body primarily uses blood glucose (sugar) for fuel. When blood glucose is low, our body converts stored glycogen from our muscles and liver into glucose. During intermittent fasting, blood glucose and stored glycogen levels gradually decline, forcing our body to find an alternative fuel. That alternative fuel is predominantly fat. Stored fat is broken down into fatty acids and released into the bloodstream to be used directly as energy. In fact, clinical trials show that fasting on alternate days increases fat oxidation by 15 grams per day. [4]

In addition, some fatty acids are broken down further in the liver to produce ketones. Ketones are an alternative source of energy that, unlike fatty acids, can be used to fuel the brain. Ketones have also been shown to reduce appetite and inflammation levels. [5]

The following hormonal changes within the body drive weight loss during intermittent fasting:

Increased human growth hormone (HGH): When fasting your pituitary gland produces up to five times more HGH. This hormone encourages the laying down of lean muscle mass, while simultaneously promoting fat loss. [6]

Decreased insulin: As with any diet that restricts calories, intermittent fasting decreases blood glucose levels and insulin levels. When insulin levels and glucose levels are lowered, your body is more likely to burn fat for fuel.

Increased norepinephrine: Intermittent fasting increases levels of norepinephrine, an important stress hormone that keeps your metabolic rate high. Furthermore, norepinephrine encourages the body to burn triglycerides stored in fat tissue rather than glycogen stored in muscles. [7]

Why? Because norepinephrine also works as a neurotransmitter to tell the brain that the body is under stress (e.g. has not been fed lunch!). When the brain recognizes we’re under stress, it encourages the body to preserve its preferred fuel, glycogen and reverts to burning its next preferred fuel–fat.

What are the Health Benefits of Intermittent Fasting?

In addition to weight loss, intermittent fasting may have a positive effect on the following:

Cardiovascular Disease: Intermittent fasting is associated with lower blood pressure and increased loss of abdominal visceral fat, two big risk factors for cardiovascular disease. [8]

Inflammation: Several studies also have shown that intermittent fasting decreases inflammation, a major factor in most chronic diseases. [9]

Type II Diabetes: Intermittent fasting has been shown to significantly decrease markers for type II diabetes thru improved blood glucose regulation and reduced insulin resistance. However, most studies have been undertaken in animals. [10]

Alzheimer’s Disease: Studies show that intermittent fasting can slow the progression of brain aging and preserve cognitive function, presenting a potential protective mechanism against Alzheimer’s disease. [11] [12]

DNA Repair: When our body is fasting we go into DNA repair mode and autophagy, two processes that play important roles in maintaining healthy cells and protecting against the development of disease. Autophagy is a recently discovered process during which the body degrades damaged or dysfunctional proteins, that could otherwise harm healthy cells. [13]

Increased life expectancy: Intermittent dietary restriction has shown to significantly increase the lifespan in rats. [14]

Common Myths about Intermittent Fasting

Several myths have been perpetuated about intermittent fasting including:.

Myth #1 You will Develop Hypoglycemia and Lose Consciousness

It’s a commonly held misconception that by refraining from eating, you will immediately develop hypoglycemia, or extremely low blood glucose. This is not true. As explained above, our body stores glucose as glycogen in our muscles and liver. Glycogen is a chain of glucose molecules. When our blood glucose gets low, our body simply converts stored glycogen back into glucose for energy. In fact, our muscles and liver can store up to 24-36 hours worth of glycogen.

If you were to fast for longer than this, your body will switch to predominantly burning its next preferred fuel—fat. Triglycerides stored in adipose tissue (fat cells) are broken down into fatty acids, which are then metabolized, just like glucose, within the mitochondria and used to produce energy. Except, fat produces even more energy than glucose.

One thing that’s important to understand is that we’re never (except, maybe in the most extreme cases) burning just one fuel. We are always burning carbohydrates, fats and protein. It’s simply the percentages that change.

Myth #2 You will Lose Large Amounts of Muscle

Another common misconception is that intermittent fasting will lead to muscle loss through a process known as gluconeogenesis. Gluconeogenesis is the formation of glucose from stored protein. But, the belief that intermittent fasting will automatically increase gluconeogenesis is not true.

With that said, whenever you lose weight, you will lose some lean mass, whether you’re intermittent fasting or restricting calories. For instance, an obese person will burn about 90% of the calories as fat when fasting, whereas a lean person will burn closer to 78% with the remaining coming from stored glycogen and protein. One study compared the effects of traditional calorie restriction vs intermittent fasting on lean muscle mass loss and found intermittent fasting was almost 4 times better at preserving lean muscle mass. [2] In other words, restricting calories is more likely to lead to muscle loss.

Are there any adverse effects of Intermittent Fasting?

As you might imagine, intermittent fasting makes you hungry and increases your appetite. This can make intermittent fasting difficult for many people to sustain long-term.

You may also experience low energy levels and have poor concentration initially. However, most of these side effects are only temporary and will subside as your body adjusts to burning fat for energy.

Who Shouldn’t Try Intermittent Fasting?

Intermittent fasting is not for everyone. If you have a medical condition, it’s highly recommended that you consult with your doctor before beginning any diet, but especially intermittent fasting.

Intermittent fasting may be unsafe for:

Diabetics
Pregnant or breastfeeding women
Women with infertility issues
Underweight individuals

As well as anyone with:

Low blood pressure
A history of eating disorders
A history of amenorrhea

Should You Try Intermittent Fasting?

Your decision to try intermittent fasting is an individual one. There is a great deal of evidence to suggest you can indeed lose weight by waiting that little bit longer for your food. But that doesn’t mean intermittent fasting is the right option for you. At the end of the day, when it comes to nutrition, there is no one-size-fits-all solution.

References

[1] https://www.nature.com/articles/ejcn2015195

[2] https://onlinelibrary.wiley.com/doi/full/10.1111/j.1467-789X.2011.00873.x

[3] https://watermark.silverchair.com/ajcn109553.pdf

[4] https://www.ncbi.nlm.nih.gov/pubmed/15640462

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3753545/

[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC329619/

[7] https://www.ncbi.nlm.nih.gov/pubmed/8023917

[8] https://www.sciencedirect.com/science/article/pii/S095528630400261X

[9] https://www.sciencedirect.com/science/article/pii/S0271531712001820

[10] https://www.sciencedirect.com/science/article/pii/S193152441400200X

[11] https://jneuroinflammation.biomedcentral.com/articles/10.1186/1742-2094-11-85

[12] https://www.sciencedirect.com/science/article/pii/S1568163706000523

[13] https://www.sciencedirect.com/science/article/pii/S1568163716302513

[14] https://www.karger.com/Article/Abstract/212538

[15] https://onlinelibrary.wiley.com/doi/full/10.1111/j.1467-789X.2011.00873.x

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