If you spend any time reading wellness blogs (aside from this one, of course!) or scrolling through your fave health gurus’ accounts on social media, you’ve probably caught wind of today’s topic—intermittent fasting.
This eating schedule (I’m not calling it a diet—you’ll find out why soon!) has gotten more attention in the wellness community lately, and I’ve noticed a lot of confusion about what it is, who it’s good for, and its potential benefits and risks.
You know what that means… time to put on my crazy sexy detective hat and investigate!
So I partnered up with our super smart Crazy Sexy Nutrition Director, Jen, and we’re gonna answer questions you didn’t even know you had. This post will equip you with the info you need to determine if intermittent fasting is something you want to try (or at least learn more about).
Because ya know what? Your well-being is precious. It’s not something to take lightly or play guessing games with—and to avoid that, you need the facts. Yes, trial and error are part of figuring out what works for you, but empowering yourself with knowledge is the safest way to experiment.
That’s why I love what my team and I get to do every day. We’re here to help you figure this all out, because vibrant health doesn’t have to be a solo effort.
OK, let’s do this… Take it away, Jen!
What You Need to Know Before You Try Intermittent Fasting
by Crazy Sexy Nutrition Director Jen Reilly, RD
Intermittent fasting is a trend that’s gained quite a bit of steam in the wellness community over the past decade. And because of its increasing popularity, researchers are more motivated than ever before to study its possible benefits and negative effects.
The main difference between intermittent fasting and other diets? It’s about when you eat, not what you eat. That’s why you’ll typically hear intermittent fasting advocates call it a schedule or plan rather than a diet.
People who practice intermittent fasting say it has helped them boost their energy and metabolism, fight off illness and reduce brain fog. There’s even some initial human research pointing to intermittent fasting’s ability to help people lose weight, reduce body fat, better manage type 2 diabetes, lower blood lipids to reduce heart disease risk, increase muscle mass and decrease inflammation.
Today we’re going to cover the three different types of intermittent fasting, what the research says so far about its possible health benefits, and what to keep in mind if you’re considering intermittent fasting for yourself.
Ready to dive in? Let’s do this!
What is Intermittent Fasting?
Fasting is defined as eating or drinking a minimal amount over a period of time ranging from 12 hours to 1 month or more. People often choose to fast for health, religious or cultural reasons. In fact, fasting has a long history! When humans were hunter-gatherers, they’d have no food for days at a time followed by several days of feasting when sustenance was available. And while that kind of fasting was a necessity, it’s also been used for healing and religious reasons for thousands of years!
Intermittent fasting as it’s known today includes both a planned “fasting window” and an “eating window” every day, or for a few days throughout the week depending on your regimen. Different methods follow different schedules—let’s cover some of the most common types!
Types of Intermittent Fasting:
- The 16/8 Method: People who practice this form of intermittent fasting choose an 8-hour window to eat and a 16-hour window to fast every day. The most common schedule involves eating from 12-8 p.m. or 1-9 p.m. then fasting from 8 or 9 p.m. until 12 or 1 p.m. the next day. Within that 8-hour eating window, people typically have meals at 12/1 p.m. (whenever they break the fast), 4 p.m. and 8 p.m. This method has been nicknamed the “just skip breakfast” plan. Many folks who aren’t breakfast people do it without even realizing it!
- Alternate Day Fasting (ADF): This type of intermittent fasting is characterized by continuously alternating a “feed day” with a “fast day.” The “fast day” includes calorie restriction to 25% of what you need, so about 500 calories total on those days (the equivalent of a green smoothie and a piece of avo toast).
- Eat Stop Eat: This concept was coined by nutritionist and intermittent fasting guru, Brad Pilon (he wrote a book about it if you’re curious). It involves fasting (eating just 400-600 calories) for 24 hours once or twice a week, typically from dinner one day until dinner the next day.
- Calorie Restriction 1-3 days per week: This is a variation of the “Eat Stop Eat” method in which people consume only 500–600 calories 1-3 non-consecutive days a week. The most popular form of this regimen has been called the “5:2 Plan” where you eat normally for 5 days and restrict calories for 2 days every week. Most people make the fasting days non-consecutive, but there are a few folks who prefer do both fasting days in a row.
What the Research Says About Intermittent Fasting
Intermittent fasting’s rising popularity has gotten the attention of health gurus and nutrition researchers, which has led to a handful of clinical human trials testing its long-term sustainability and the potential benefits found in animal studies. Human research is still in its infancy, but there are some interesting insights emerging that we’ll want to keep our eyes on.
One thing to keep in mind: I’m not covering all potential benefits of intermittent fasting below—people also say that intermittent fasting helps with mental clarity and immune function, may increase longevity, and much more. I’m simply highlighting some of the most interesting research I’ve come across so far!
Intermittent Fasting for Weight Loss
When evaluating intermittent fasting for its role in weight loss, it’s important to consider whether weight changes can be attributed to the meal timing and fasting periods OR the calorie restriction itself. When comparing an intermittent fasting plan to a typical weight loss plan that limits calories, weight loss results have been similar when total calories for the two plans were comparable (study). However, in one study where weight loss was similar, the intermittent fasting group experienced fat mass loss—3 ½ lbs (1.6 kg) over an 8-week period compared to insignificant fat loss in the regular diet group (study). Athletes looking to build muscle and lose fat might find this particularly appealing.
Researchers have explored what happens when individuals can eat whatever they want (no calorie or food type restrictions) on some days as long as they fast on other days. In a comparison study of overweight and normal weight individuals, Alternate Day Fasting (ADF) resulted in an average of 11.5 lbs (5.2 kg) of weight loss over 12 weeks (study). This demonstrated that individuals weren’t consuming so much on non-fast days that it hindered their weight loss. This study also showed an increase in leptin (a hormone that regulates appetite) among the ADF group—a sign that ADF may help suppress appetite, potentially making weight loss easier.
Intermittent Fasting for Managing Type 2 Diabetes
Weight loss and exercise have been shown to decrease the need for type 2 diabetes medications and in some cases, allow people to eliminate the medications completely (article). So it makes sense that intermittent fasting that leads to weight loss in individuals who need to lose weight may also help with type 2 diabetes management. One case report showed that three men following 24-hour fasting schedules were able to eliminate insulin within just 18 days (study). This finding has led researchers to further explore intermittent fasting as a better or comparable way to manage or cure type 2 diabetes.
One study looked at how intermittent fasting compared to a low-calorie diet for weight loss and glycemic control in people with type 2 diabetes—the results were similar (study). Another study purposely prevented weight loss (to rule it out as a factor in results) among people with pre-diabetes and found that those on an intermittent fasting regimen had significantly improved insulin sensitivity and blood pressure, and better appetite control (study).
When meals aren’t consistent, people with diabetes may experience hypoglycemia (low blood sugar). One trial found that this was in fact an issue for participants with type 2 diabetes on fast days (study). Because of this, the risks may outweigh the benefits for people with type 2 diabetes—at least when it comes to the types of intermittent fasting that involve full fasting days. But because people have reported better satiety and more energy with intermittent fasting (compared to low-calorie diets), it may be a useful strategy—if medically supervised—to help people better manage their type 2 diabetes.
Intermittent Fasting for Reducing Inflammation
Chronic inflammation is at the root of many chronic diseases, making it high on the priority list among health researchers. Some studies indicate that fasting may help reduce inflammation. For example, studies among Muslims who practice Ramadan by fasting from dawn until sunset (about 12 hours) for one month have had their markers of inflammation tested before, during and after Ramadan. Their markers of inflammation (proinflammatory cytokines, tumor necrosis factor and C-reactive protein) as well as body weight, blood pressure and body fat showed significant reduction during Ramadan when compared with the same markers before and after the fasting period (study and study). These results suggest that regular 12-hour periods of fasting may indeed help reduce inflammation, thereby potentially contributing to disease prevention.
Intermittent Fasting for Heart Health
Maintaining a healthy weight, limiting intake of refined sugars and saturated animal fats, eating more plant foods, and exercising regularly help reduce bad cholesterol and blood pressure, which in turn improves overall cardiac health. Because intermittent fasting can help with weight loss and lowering blood pressure as long as overeating doesn’t occur during the “feeding” period, it can be credited with the same resulting cardiac benefits. But keep in mind that eating an overall heart-healthy diet also helps your immune system, mental health and your ability to fight off cancer.
High blood pressure is even more common than you might think (one in three Americans have it). It’s often called the “silent killer” because most people with high blood pressure don’t even realize they have it. Increased pressure weakens your heart and makes blood vessels narrower, potentially leading to heart attacks, strokes and damage to other vital organs. That’s why finding natural ways to lower blood pressure is so important. Intermittent fasting often leads to weight loss, which in turn usually promotes lower blood pressure. Also, one 2018 study found improved blood pressure during intermittent fasting even when no weight loss occurred (study).
As for overall cardiac health, though, a recent study found that ADF increased “bad” LDL cholesterol levels among participants (study). So if you’re considering intermittent fasting and have a family history of heart disease or high cholesterol, I suggest checking in with your doctor first.
Intermittent Fasting: What to Watch Out For and Who Should be Careful
- People with hypoglycemia or diabetes—especially those on insulin—should be extra careful and work with their doctors before trying any of the intermittent fasting regimens. Low blood sugars may result from fasting or calorie restriction and should be closely monitored.
- Those who experience hanger (hunger + anger), beware! Some folks report mild headaches during the first week of intermittent fasting. Chances are, if you get cranky when you skip meals, intermittent fasting isn’t for you.
- People with a history of disordered eating may be more likely to binge during eating periods than others. Binging can exacerbate an eating disorder, not to mention put a strain on several organs when too much food enters the body over a short period of time. Check with your doc if you have a history of anorexia nervosa, bulimia nervosa or binge eating disorder.
- Pregnant or breastfeeding women should only try intermittent fasting under close supervision of a doctor. Eating this way could make it challenging for pregnant women to meet their high nutrient demands and could lead to unwanted weight loss.
- Do your research and check with your doc if you deal with chronic constipation. Fasting can exacerbate constipation, especially if it goes beyond 16 hours on a regular basis.
- People with elevated cholesterol or a family history of heart disease should proceed with caution. Studies have shown both positive and negative effects on blood lipids with intermittent fasting. Check with your doc before considering a diet change like this.
- Be sure to hydrate! Remember that dehydration happens a whole lot faster than starvation, so you need adequate fluids on fast and non-fast days. Aim to drink half of your body weight in ounces of fluids per day (or 2 liters for women and 3 liters for men). And if you do choose to include caffeine, increase those fluid amounts by 8-12 oz (240-360 ml) per day.
The Bottom Line on Intermittent Fasting
Now that we’ve covered some of the possible benefits and risks of intermittent fasting, the big question remains: Is intermittent fasting really better than any other healthy eating plan?
Intermittent fasting may help people lose body fat and maintain muscle mass during weight loss, improve insulin sensitivity, lower blood pressure, boost energy, and regulate appetite. But at this point, there isn’t enough evidence to prove that it’s any better than eating a whole foods, plant-based diet on a standard schedule. Plus, most of the human studies we came across noted that more research is needed to confirm the results.
I’m sure there’s more to come on this topic, so stay tuned! If you want to give intermittent fasting a try, get the blessing from your doc and let us know your story.
Intermittent fasting the crazy sexy way!
If you’re thinking about trying intermittent fasting and want to ease into it, consider giving our crazy sexy version a shot! Give your digestive system a break by fasting from 6 or 7 p.m. until 6 or 7 a.m. the next day. That way, your body gets 12 hours of rest and you still have plenty of time to fit in three healthy, whole foods, plant-based meals each day. Plus, your stomach will have time to settle before you sleep, which should help prevent tummy troubles that can arise from eating too close to bedtime. And for those of us who need some sustenance to get energized in the morning (hello, green smoothie!), this take on intermittent fasting doesn’t require you to wait for several hours after you wake up to eat.