Intermittent Fasting: Pros and Cons of Fasting to Lose Weight

August 28, 2020
Nutrition

It's awesome. Or is it awful? Here's what intermittent fasting is really like.

Food is a huge part of how we structure our days. We have meal routines, snack times, and occasional indulgences that can pop up across the day. It’s rare that these routines are really critically questioned. But a topic has been coming up a lot that may be raising some questions: intermittent fasting, or IF.   

Hollywood has put intermittent fasting in the spotlight. Some of the industry’s fittest actors, including Jennifer Aniston and Terry Crews, have long been singing the praises of skipping meals. Chris Pratt used IF as part of a strategy to transform himself from the goofball on Parks and Recreation to the action hero in Guardians of the Galaxy, and Kumail Nanjiani recently did the same for his role in The Eternals

So what exactly is IF? “In general, intermittent fasting is just patterns of fasting and non-fasting throughout the day,” says Jonathan Valdez, owner of Genki Nutrition and spokesperson for the New York State Academy of Nutrition and Dietetics.

That leaves a lot of flexibility in how you structure your fast to fit it into your routine. In Nanjiani’s case, he followed an 18/6 protocol, which means  for each 24-hour period, he fasted for 18 hours and consumed all his day’s calories in the remaining six. But that’s just one of many strategies, says Valdez.

Other common IF approaches are 16/8 and 14/10. Then there’s the 5:2 method, where you eat normally for five days of the week and limit your calories to 500 for the other two. There’s also alternate-day fasting, where you max out at 500 calories every other day.

To varying degrees, all fasting strategies aim to mimic the periods of hunger that humans experienced naturally throughout history (before each meal was just a Seamless order away). But if you’re considering deploying IF on yourself, it’s worth knowing exactly what you’re in for. So here’s what to expect, both in terms of benefits and potential pitfalls.

Benefit #1: IF will help you lose weight

Weight loss is one of the most well-established benefits of caloric restriction. In a February 2020 review of 27 studies on intermittent fasting among overweight and obese people, every single study found some level of weight loss.

On the low end, the weight loss was 0.8 percent of body weight. But for longer and more substantial studies, it reached 13 percent. For IF interventions lasting more than two weeks, the average participant trimmed 4.3 percent off his or her body mass index. 

Benefit #2: IF can help you control your blood sugar

You might not spend a lot of time thinking about the amount of glucose in your blood, but you should. Too much sugar can be a factor in developing diabetes, which is a rampant issue. In addition to the 34 million Americans who have diabetes, another 88 million have pre-diabetes. And 80 percent of them don’t even know it. If you’re in the pre-diabetic group, you’re more likely to carry extra body weight and develop heart disease. 

Thankfully, fasting offers some degree of protection by keeping your blood-sugar relatively stable. In a 2018 study published in the journal Cell Metabolism, pre-diabetic men who committed to fasting for 18 hours a day experienced substantial improvements in insulin sensitivity, counteracting some of the risks that sugary diets had put on their bodies. The benefits may go even further: According to a study published in the journal Sports Medicine, Muslims who observe the fasting tradition of Ramadan are more resilient against heart disease, stroke, and dementia. Speaking of which….

Benefit #3: IF could boost your brainpower.

By lowering LDL cholesterol and triglycerides, intermittent fasting might offer some protection against neurological diseases, such as Alzheimer’s, says Valdez. And while we don’t have the long-term human studies to prove it, a 2018 study on mice found the effect to bear out. “Preliminary animal studies have associated IF with preventing or slowing cognitive impairments associated with age,” says Valdez. 

Equally impressive, IF could make you feel sharper and more focused right now.

As your body runs out of glucose, it starts burning body fat. This is the hallmark of fasting, and as a byproduct of converting fat into energy, your brain washes itself with cognition-boosting compounds. One is brain-derived neurotrophic factor (BDNF), which stimulates neuron growth. Another is gamma-aminobutyric acid (GABA), which helps keep you calm under stress. This is a similar principle to the mechanism behind the  brain benefits of our Superhuman Supplements product—worth checking out if you want a comparable effect without doing IF. Research from the journal Neurology International shows that IF also increases your serotonin levels, which can make you feel happier.

So it’s no wonder that people who practice IF are so enthusiastic about it. 

Now, what’s the downside?   

Negative #1: IF sucks!

Okay, this one is a matter of perspective. But at some point, almost everyone who fasts ends up watching the clock for their final hour of hunger, or cracking a beer at night only to realize they’re just outside their calorie-consuming window. 

In those situations, will you stick to the plan, or make an exception?  

As proof that IF is challenging, a study published last year found the dropout rates in alternate-day fasting studies—where caloric intake is severely limited every other day—is as high as 40 percent. That’s partly why 18/6, 16/8, and 14/10 fasting protocols have all become so popular. They provide flexibility. Consider starting at 14/10 and working your way up to 18/6.

It really comes back to sticking with the IF habit. We’ve thought a bunch about that here if you need some tips to increase your odds of success: a five-step strategy for building habits that stick.

Negative #2: IF can be risky for certain groups

If you have any history of disordered eating, the risk of fasting probably outweighs the benefits. It can swing dangerously close to anorexia and could result in “malnutrition, moderate damage to organs, or susceptibility to infectious diseases,” says Valdez. 

Furthermore, if you have diabetes, and you’re already taking medication to lower your blood sugar, you should proceed cautiously. A 2019 study found that people in the diabetic-medicine group were at risk for hypoglycemia, or dangerously low blood sugar, when they deployed an intermediate fasting routine. “Certain medications are just not suited for changes in meal timing,” says Valdez. That doesn’t mean you can’t fast, but if you’re taking medication that affects your insulin or glucose levels, consult your doctor first. 

There’s also increasing evidence that IF may not be as beneficial for women as it is for men. A study found that periods of fasting can increase cortisol levels in women, a hormone that can lead to symptoms like acne, irritability, and weight gain if it stays consistently high. Concerns have also been raised about negative impacts on women’s blood sugar levels and the ability of cells to repair themselves.

Negative #3: IF can be hard on your body   

“Fasting causes starvation,” says Valdez. As a result, it could have some weird side effects: People have reported bad breath, constipation, headaches, dizziness, weakness, and sleep disturbances. A 2018 review found intermittent fasting caused a decrease in rapid-eye movement (REM) sleep, which is the slumber phase linked to memory and cognition.

Valdez recommends you avoid fasting if you’re underweight or you have a compromised immune system. It’s also not a great idea if you’re recovering from a surgery or severe illness. 

You’re hearing about IF all the time for a reason – it can be effective to get some pretty remarkable effects. Knowing the benefits can be a big motivator, and if you’re aware of the challenges that are coming you can be way more ready to take them on. So, if intermittent fasting sounds like a fit for you, give it a good try. Just listen to your body, and eat something if things get weird.

Originally published in ASYSTEM's journal.

Emily graduated with a degree in Journalism from Northwestern University and is currently a full-time freelance writer living in Pennsylvania with expertise in health, wellness, nutrition, and lifestyle content.

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