Intermittent fasting is a popular dieting trend. Advocates say it enhances your overall health, increases fat-burning, and leads to effortless weight loss without calorie counting or “dieting.”
Sound too good to be true?
Actually, plenty of research backs up these bold claims about fasting.
In this article, we’ll examine the general health benefits, the science behind intermittent fasting, what happens to your body fat levels during intermittent fasting, and the easiest way to get started fasting–without making beginner mistakes.
But first, a quick overview of what fasting actually is (and isn’t).
First of all, fasting simply refers to the practice of avoiding food and calorie sources, like beverages with calories. (Water is allowed during most types of fasting, as are black coffee and other zero-calorie drinks.)
In fact, aside from the unfortunate few who sleepwalk and raid the fridge, most people already fast 8 or more hours every night while sleeping.
Intermittent fasting (IF) generally means any form of repeated, intentional fasting. IF means going beyond the normal sleep fast and actually delaying or skipping one or more meals on purpose.
The name is slightly confusing, because many people intermittent fast every single day (which isn’t exactly intermittent). Others don’t intermittent fast daily, but still do so regularly.
For now, just keep in mind that IF encompasses a wide variety of fasting practices. We’ll cover them more in-depth in a moment.
On the other hand, IF doesn’t include things like accidentally skipping a meal or forgetting to eat.
Reasons for intermittent fasting include health or weight-loss goals, or both. Spiritual or religious fasting may have similar benefits, but people don’t usually call them “intermittent fasting.”
The Most Popular Types of Intermittent Fasting
The core concept of intermittent fasting is quite simple, but there are many ways to organize your fasting schedule. Here are some of the most popular today.
- Daily intermittent fasting (or “Leangains style” fasting) requires daily fasting, as the name clearly suggests. The most common variant is “16/8”–a full 16 hour fast followed by an 8-hour window of eating. Others include 18/6 and 20/4.
- Time-restricted eating is similar to daily intermittent fasting, but users place more emphasis on limiting the majority of food intake to specific, chosen hours each day. They’re often less strict about avoiding calories outside the eating window.
- Alternate-day fasting, true to its name, involves an every-other-day eating schedule. That means a fast of 24-36 hours between eating windows that last a full day.
- The 5:2 Diet is a weekly eating schedule. It involves 5 full days of normal eating, followed by 2 full days of fasting, or 2 days of eating just 500-600 calories (kcal).
However, the above fasting styles are far from the only ways to fast.
For example, many people choose to include a few fast periods of 12-20 hours or longer each week for weight loss or health purposes. They might follow the same schedule each week, or decide as they go.
And individuals looking to get the most significant health and longevity benefits from fasting may opt for fasts lasting several days in a row or longer, repeating them anywhere from once a month to once a year.
- Intermittent fasting may extend lifespan and allow healthier aging[*].
- Autophagy (the recycling of unhealthy cells during fasting) may reduce the risk of cancer[*].
- Better brain health and mental function[*]
- Less inflammation[*]
- Decreased blood pressure and lower risk factors for heart disease[*]
- Regular fasting lowers blood glucose and insulin levels, improving insulin sensitivity and reducing the risk or severity of type 2 diabetes[*].
- Fasting 3 days or longer resets your immune system[*].
#1: You Eat Zero Calories While Fasting
Eating zero calories while fasting may sound obvious. After all, it’s the definition of fasting.
But think about it. Most weight loss diets guesstimate your daily calorie intake, then have you aim for less.
Not so with fasting, though. You can’t eat fewer than zero calories. Any time you fast, you’re in a guaranteed deficit, so weight loss is more or less inevitable (if you don’t binge during eating windows).
That said, you can also consider fasted cardio to kick your weight loss results up a few notches during fast periods.
#2: There’s Usually No Need for Counting Calories At All
As you may know, to lose significant amounts of weight, you must eat fewer calories than you burn. The technical term for that is a “calorie deficit.”
And if you ever followed a diet in the past, the chances are high that you had to count calories in some form (using a notepad, an app, a food journal, or a system like “points”).
Calorie counting makes logical sense, because the purpose is to help achieve a calorie deficit.
But research shows that in reality, calorie counting usually fails long-term, especially for obese people looking to lose weight and keep it off[*].
There are numerous reasons, but perhaps the biggest one is that it’s complicated and unnatural.
In contrast, fasting makes achieving a deficit without counting calories easy. As long as you eat filling, healthy whole foods during your eating periods, you’ll most likely lose weight.
(Pro-tip: the keto diet also works for weight loss without counting calories.)
#3: Cravings Vanish
One reason dieting is hard is because cravings can rear their ugly heads, derailing you from your meal plan.
When you cut calories and perhaps avoid certain foods, hunger is natural…right?
During eating periods, you get to eat until you’re full. Some research suggests this may make fasting an easier weight loss method than traditional calorie restriction[*].
Essentially, you get to enjoy satisfying meals in between fast periods rather than always being hungry as with dieting.
#4: Your Body Becomes a Fat-Burning Furnace
Fasting works wonders on your metabolism–your fat metabolism, to be exact.
Similar to how the keto diet boosts fat-burning, fasting for 6 hours or longer increases your ability to burn fat[*]. As with keto, the primary reason appears to be that you aren’t eating carbohydrates[*][*].
And when you regularly fast for extended periods, the effects become even more pronounced[*].
In other words, the longer and more often you fast, within reason, the better your body’s ability to burn fat becomes!
#5: Greater Loss of Belly Fat
Fasting may be more effective for reducing belly fat compared to other weight loss practices[*].
Aside from physical appearance reasons, here’s why that’s a big deal.
The presence of visceral fat, the scientific name for belly fat that’s inside your abdomen, may indicate higher inflammation levels in your body. And it’s associated with a higher risk of heart attack and heart disease, too[*].
Fortunately, by fasting, you can reduce your belly fat, which may also reduce the risk of heart problems.
#6: Short Fasts May Speed Up Your Metabolism
You may have heard that skipping meals will slow down your metabolism. But what about intermittent fasting?
Although starvation mode is a real thing, it’s not going to happen due to skipping a few meals.
In fact, one study found that during a 3 day extended fast, the study participants’ metabolism increased by a full 14% due to hormonal changes[*].
#7: You Can Preserve More Lean Muscle
Losing lean muscle mass is a considerable problem during weight loss.
If you’ve never tried fasting before, getting started is easy.
Just follow these tips as you make intermittent fasting a part of your lifestyle:
- Choose a reasonable plan: pick a beginner-friendly plan like daily IF or time-restricted eating, or several short fast periods each week. Save more advanced methods like alternate-day fasting for later, if at all.
- Ease in and be consistent: if you’ve never fasted before, start slow. Less is more–commit to what you feel you can handle. You’ll get better results compared to overdoing it and crashing.
- Eat a healthy diet: fasting is excellent for fat loss, but you still need to eat healthy foods to be healthy.
- Exercise regularly: cardio and weight training help up your calorie burn and make preserving muscle easier as you lose weight by fasting.
- Track your results: although you don’t need to obsess over calories, you should track body weight and other results from time to time. If you aren’t getting the progress you want, you need to know ASAP so you can fix any problems.
Lastly, you can try pairing fasting with the keto diet–the best weight loss strategy of all. To learn more about the super-potent combo of keto and fasting, check out The Benefits of Fasting on Keto.
But Don’t Make These Mistakes
Fasting is pretty simple, but for best results, you’ll want to avoid these beginner mistakes:
- Don’t rush in: take the time to educate yourself as much as needed, and most of all, prepare and set worthy goals. Don’t start skipping meals tomorrow without a solid plan.
- Don’t eat unhealthy foods: fasting doesn’t grant you the ability to stay healthy while eating junk food, so avoid unhealthy foods. You can enjoy the occasional indulgence during eating periods, but healthy, whole foods should be your regular staples.
- Don’t overeat or binge eat: although most people don’t need to count calories to lose weight while fasting, you should still be mindful of overeating. Just because you had a successful fast doesn’t mean you can binge eat and shed fat. If you’re new to fasting, be especially mindful of food intake as you break your fasts.
- If you want to pair up keto and intermittent fasting, add them in one at a time. If you’ve never done either, start with either keto or IF, not both at once.
- Don’t fast overly long: for fat loss purposes, methods like 5:2, 18/6, or alternate-day fasting all work exceptionally well. You probably won’t lose more fat by lengthening your fasts. Fasting 3+ days for health purposes is one thing, but it doesn’t fit into a balanced approach to fat loss or a weekly fasting schedule.
Fortunately, as long as you avoid the most common fasting mistakes, fasting is far easier and more effective than most conventional forms of dieting.
Nearly everyone can safely benefit from intermittent fasting, but the best type of fasting depends on your goals.
For instance, longer fasts are most conducive to health and longevity, while shorter fasts are more manageable for beginners and generally the best option for fat loss purposes.
Athletes or people who are looking to add lean muscle mass should be careful with fasting, as it may affect recovery or muscle-building. If you fit in these categories, you can still fast, but ease in extra-slowly.
And some individuals should consult their doctor before attempting intermittent fasting to ensure it’s safe.
If you are a senior citizen, pregnant or nursing, take medication, or have a medical condition–especially a metabolic condition like type 2 diabetes–be sure to talk to a qualified healthcare professional before doing any intermittent fasting.
Or if you’ve never tried an extended fast of 2-3 days or longer, you may also choose to speak to your doctor before doing so to stay on the safe side.
Lastly, people who have eating disorders or body image issues may want to avoid fasting, or approach it with extreme caution. There’s a chance fasting could be triggering.
If you aren’t sure whether or not fasting would be a healthy decision for those reasons, please speak to a counselor or therapist you trust to help you decide.
Fasting is simple, costs nothing, and is highly effective for losing weight while also enhancing your health.
If you haven’t tried it yet, don’t be intimidated. You can start off slow, and you don’t have to take a hardcore approach to reap the benefits.
For beginners, less is more. Daily 16/8 fasting is a popular option, or you can begin by doing shorter fasts a few times a week.
And if you’re an experienced faster, don’t miss out on combining fasting with keto. Read Keto Fasting for Beginners: Why It’s a Good Idea to learn more.