Fasting isn’t exactly a new trend — throughout history, people have fasted for political protests, religious reasons, spiritual growth, and annoying blood tests at the doctor’s office.
And intermittent fasting — especially a specific style of fasting called “16/8 fasting” — has been getting a lot of hype lately as a weight-loss strategy. But is it effective? Here’s what you need to know about 16/8 fasting and whether or not it can help you lose weight.
What Is Intermittent Fasting?
Intermittent fasting is an eating pattern that alternates between fasting for a certain period of time and eating for a certain period of time.
There are several different ways to go about intermittent fasting:
- Alternate-day fasting: On this plan, you would alternate between fasting days and days of unrestricted food intake. For instance, on Monday, Wednesday, and Friday, you may eat one large meal that accounts for around 25 percent of your typical daily caloric intake.
- Whole-day fasting: You fast only one or two days a week for the whole day — this can be a complete fast, or up to 25 percent of your daily caloric needs — with no fasting on the other days.
- Time-restricted feeding: You eat and fast during the same set windows every day. For instance, you may decide to eat between noon and 8 p.m. only, and fast during the morning and at night.
What Is 16/8 Fasting?
This is an example of time-restricted feeding. And because it isn’t as restrictive as protocols with full days of fasting — but still offers long periods without eating — 16/8 fasting is one of the most popular fasting protocols.
16/8 intermittent fasting was popularized by Martin Berkhan, a nutritional consultant and personal trainer (and, according to his website, the “high priest of intermittent fasting”). While many trainers swore by a 12/12 intermittent fasting schedule, Berkhan claimed the extra 4 hours of fasting could lead to higher metabolic rate and lower insulin. (We’ll get to the science behind that in a minute.)
However, just because you have an 8-hour window to eat, that doesn’t mean you should stock up on a full arsenal of snacks and meals to devour the whole entire time. “That’s where I see a lot of people go wrong,” says Kellie Davis, personal trainer, founder of Fit Thrive, and co-author of Strong Curves. “You still need to make smart choices with your food and lifestyle.”
What Are the Benefits of 16/8 Fasting?
As far as the rumored health benefits of 16/8 fasting, the evidence is still hit or miss.
In a recent study, the 16/8 approach to fasting was linked to lower systolic blood pressure, lower body weight, and lower daily caloric intake (no surprise there, since you’re only eating for one-third of the day). But researchers didn’t find any significant difference in fat mass, glucose levels, or diastolic blood pressure over a 12-week period.
However, a 2005 study found that intermittent fasting combined with physical activity may improve insulin sensitivity. And a 2016 study linked time-restricted feeding — in conjunction with resistance training — to a significant decrease in fat mass and blood glucose levels. So 16/8 intermittent fasting may have some health benefits — but more research is needed to determine how intermittent fasting might benefit your overall health.
There may be another potential health benefit to foregoing food for a good chunk of time: “It can be good to give the digestive system a break sometimes,” says Mascha Davis, RDN, MPH, and founder of Nomadista Nutrition. (A recent study found a link between intermittent fasting and improved gut health — but, it’s worth noting, the study subjects were fruit flies.)
As with any health or fitness approach, though, fasting has its drawbacks — Mascha Davis notes that it can lead to binge eating, disordered eating, and fatigue. And while 16/8 is considered one of the more accessible and sustainable forms of fasting, it can still get in the way of workouts, social outings, work events, and vacations.
Is Intermittent Fasting Effective for Weight Loss?
Compared to more restrictive forms of intermittent fasting — such as protocols that call for 24-hour fasts — 16/8 fasting is more approachable and sustainable. “It is a relatively easy and socially acceptable way to restrict your energy intake,” Mascha Davis says.
Intermittent fasting may also help people distinguish real hunger from emotional hunger, Kellie Davis says. (Cue the post-breakup Ben & Jerry’s.) “When you go through prolonged fasting windows of 16 hours or more, you get in tune with hunger and can learn to determine the difference between true hunger and emotional hunger,” Kellie Davis says.
Intermittent fasting can be effective for short-term weight loss simply because it can help you cut energy intake in a structured way that doesn’t require calorie counting or food scales. “Many people eat throughout the day, so calories pile up,” says Sonya Angelone MS, RDN, and spokesperson for the Academy of Nutrition and Dietetics. “Intermittent fasting limits all the extra calories consumed, especially in the evening and before bed.” By shrinking your window of eating, you may naturally eat less.
Can Fasting Help Me Lose Body Fat?
It might. In a small, eight-week study on 16/8 fasting in men who regularly did resistance training, researchers found a significant decrease in fat mass, while muscle mass stayed the same.
But there’s a caveat. (Isn’t there always?) During your feeding window, it’s important to eat nutrient-dense, filling foods. If you don’t, you’ll probably ransack your pantry after the next fasting period. “You are likely to overeat at your next meal because you are so hungry,” Angelone says.
Intermittent Fasting Tips
1. Do your research.
“Learn the ins and outs of proper intermittent fasting before you dive in head first,” Kellie Davis says. “Take your time, take ample notes on how you feel, and re-evaluate your decision after a trial period to see if it’s something you can sustain.”
2. Start slowly.
You may want to try an easier fasting schedule for a couple of weeks to get a feel for whether or not it’s something that works for you. “It may be best to start with 12/12 and work up to 16/8 if you’ve never tried fasting,” Kellie Davis says.
3. Don’t forget the H2O.
“Be sure to stay well hydrated,” Angelone says. You can drink as much water as you’d like during your fasting periods.
4. Be mindful of your exercise routine.
If fasting makes you feel sluggish, sticking to your workout schedule can be a challenge. “Eating a larger meal as your last meal will help prevent hitting the wall during training,” Kellie Davis says. If you wake up ravenous and can’t take your mind off food, she suggests eating a little snack before the gym — even if it is outside of your eating window.
5. Remember that not everyone is a good fit for fasting.
Pregnant and breastfeeding women, teenagers, and people who have diabetes or use medications that can’t be taken on an empty stomach should steer clear of intermittent fasting. “Also, anyone prone to an eating disorder, or who has a history of one, is not a good candidate for this,” Mascha Davis says.
Bottom line? There definitely may be some health benefits to 16/8 fasting. And as long as you incorporate plenty of healthy, whole foods and an exercise routine, intermittent fasting may be helpful for weight loss.
That said, fasting may not be the best lifestyle choice for everyone, and we likely need more studies (with longer follow-up periods) to assess the efficacy, safety, and sustainability of intermittent fasting over the long haul.