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A small portioned lunch plate with an over easy egg, broccoli, cucumber, tomato, cheese and a sausage.

It seems like every few years we hear of a new “revolutionary” diet with extraordinary claims of quick and easy weight loss. Of course, most of these fad diets have little research behind them and can often do more harm than good. 

Today we’re taking a look at intermittent fasting, a diet plan that has exploded in popularity over the last 9 years. The purpose of this blog is to break down the science, the benefits, and the risks of Intermittent fasting so that you can make an informed decision on whether or not it may be right for you.

Where did Intermittent fasting (IF) originate?

Fasting has been practiced for centuries by many cultures and religions. Ramanda, for example, is observed by Muslims worldwide as a month of fasting, prayer, and reflection. The fast begins at dawn and ends at sunset. The act of fasting is said to redirect the heart away from worldly activities, with the purpose of cleansing the soul by freeing it of harmful impurities.

Intermittent fasting as we know it today piqued the public’s interest in 2012 by BBC broadcast journalist Dr. Michael Mosley’s TV documentary Eat, Fast, Live Longer and book The Fast Diet. Following this, books such as The 5:2 Diet by Kate Harrison and The Obesity Code by Dr. Jason Fung contributed to its steady rise in popularity. Intermittent fasting was one of the 5 most googled diets of 2019.

What is Intermittent Fasting

Intermittent fasting is an eating plan that has specific hours of eating and fasting. There are three common fasting plans:

  • 16/8 fasting, which means restricting your eating to an 8 hour period and then fasting for 16 hours each day.
  • 5:2 fasting, which involves eating regularly for 5 days of the week and for the other two days, limiting yourself to one 500-600 calorie meal
  • Longer periods of fast such as 24, 36, 48, and 72 hour periods. (Important note: fasting for long periods of time has not been shown to be beneficial and can be very dangerous)

Intermittent fasting is unique from other diet plans, as it does not restrict the type of food you eat but rather the time in which you consume it. 

What does Intermittent Fasting do to the body? 

The idea of intermittent fasting is that when the body goes without food for a short time, it produces ketosis- a process that occurs when the body doesn’t have enough sugar for energy so it instead breaks down stored fat instead, triggering an increase in substances called ketones. 

Ketones are produced by the liver from fatty acids during periods of low food intake. These ketone bodies are readily transported into tissues outside of the liver and converted into acetyl-CoA which then enters the citric acid cycle and is oxidized in the mitochondria for energy. 

Intermittent Fasting in scientific studies

There have been a sizeable number of studies done on intermittent fasting. However, a majority of these studies we conducted on animals. A review of 40 studies found that the diet was effective for weight loss, with the typical loss of 7-11 pounds over ten weeks. These studies ranged in size from 4 to 334 subjects and followed from 2-14 weeks. Each study also used different study designs and had a wide range of participant characteristics. Half of the studies were controlled trials which compared the fasting group to a comparison group/control group, with the other half examining an intermittent fasting group alone.

An article published by the Harvard T.H. Chan School of Public Health highlighted the following findings:

  • Dropout rates ranged from 0-65%. The review did not find that intermittent fasting did not have a low dropout rate, meaning it was not necessarily easier to follow than other weight loss approaches
  • When examining the 12 clinical trials that compared the fasting group with the continuous calorie restriction group, there was no significant difference in weight loss amounts or body composition changes.
  • Ten trials that investigated changes in appetite did not show an overall increase in appetite in the intermittent fasting groups despite significant weight loss and decreases in leptin hormone  levels (A hormone that suppresses appetite 

Essentially, this analysis of research did not consistently show that intermittent fasting was superior to calorie-restrictive diets for weight loss.

However, in 2018, new research  suggested that certain IF approaches are more effective than others. Nighttime eating has been associated with a higher risk of obesity and diabetes, this prompted researchers at the University of Alabama to conduct a study with a small group of obese men with pre-diabetes. One group ate their meals between 7 am and 3 pm (an 8-hour window) while the other group’s window went from 7 am-7 pm (12-hour window). 

After 5 weeks the 8-hour group had dramatically lower insulin levels and significantly improved insulin sensitivity, as well as significantly lower blood pressure and a significant decrease in appetite. Even individuals in this group who did not lose weight experienced significant metabolic benefits from eating earlier and fasting overnight.

Reported Benefits of Intermittent Fasting

  • Improved metabolism
    • Decreased inflammation
    • Lowers blood sugar
    • Weight loss

    Possible risks of Intermittent Fasting

    • As with any restrictive diet, IF can lead to disordered eating and unhealthy relationships with food. 
    • Intermittent fasting can cause some to go into a calorie deficit, which can result in hair loss and irregular/missed periods. 
    • Ignoring your body’s natural cues to eat can make you “hangry” and irritable.
    • Feelings of shame and guilt if you break your fast early.
    • Binge eating due to prolonged calorie restriction.
    • Disrupted sleep due to hunger
    • Those with advanced diabetes or who take medication for diabetes, people with a history of eating disorders, and pregnant or breastfeeding women should not attempt intermittent fasting unless they are under the close supervision of a physician. 

    The bottom line

    Though the potential benefits of Intermittent Fasting have been promising, more research is needed to determine its long-term benefits and risks to humans. The allure of intermittent fasting is undeniable, especially when insanely fit celebrities like Terry Crews tout its benefits. It’s important to remember that celebrities and fitness influencers have access to the best personal trainers, private chefs, and other resources that make IF much easier to maintain. Sustainability is key. Before you consider IF, you should assess whether it is something you can incorporate safely and sustainably into your lifestyle. Finally, always talk to your doctor before starting a new diet.