From Atkins to paleo to Keto and beyond, there has been much chatter over the last few decades about the best way to lose weight and actually keep it off. In the late 2010s intermittent fasting (IF) caught fire, thanks to blockbuster books like "The Obesity Code" and "The Fast Diet."
Intermittent fasting simply means not eating (or drinking anything with calories or artificial sweeteners) for a specific period of time. There are a number of intermittent fasting timetables out there, but the most popular is probably the 16:8 timetable, during which a person fasts for 16 hours (the "fasting window) and then uses the eight-hour window to eat ("the feeding window").
I'm one of the folks who's doing IF. Although challenging in the beginning, I've found it to be a largely sustainable way to lose and maintain weight and avoid common pitfalls like mindlessly snacking in front of the television at night, thanks to the clearly defined parameters. I've lost some weight, but even better, my cholesterol has improved and my blood sugar doesn't dip and spike as much as it used to.
My husband has particularly enjoyed the benefits of an IF-based program. He's down 35 pounds (15 kilograms), with lower cholesterol and now comfortably back in a size 34-waist pant. His only complaint? He had to buy a new belt (an errand he ran smugly and feeling pretty good about himself).
Still, many people are confused about IF, whether it's safe and effective, and how to you make it work. So, let's dig in and explain, starting with the science behind it.
How Does Intermittent Fasting Work?
Why would anyone voluntarily shun food for such a long stretch, when they could just eat reasonably all the livelong day? It all boils down to biology. The carbohydrates we eat are broken down into sugar, which are important because the cells need them for energy. The problem is that any excess sugar is stored in fat cells. These sugars can only be released from the fat cells (to be used as energy) if people allow their insulin levels to dip low enough. Every time we eat or snack, we experience an insulin spike, effectively blocking the sugar from getting burned off. So, intermittent fasting lets insulin levels go down and stay there long enough to burn fat.
"It is thought to be effective for weight loss because it allows the person's body to tap into their fat stores for energy when there is a period of fasting, like overnight," Liz Weinandy, M.P.H., R.D., outpatient dietitian at The Ohio State University Wexner Medical Center in Columbus, Ohio, explains in an email. "It may also be effective for other conditions like reducing the risks of some diseases, which is more hypothetical at this point than confirmed with research, since it sort of allows the body a period of rest and cleanup so to speak."
This period of cleanup is known as autophagy. "During autophagy, the body cleans house and starts regenerating itself — eliminating dysfunctional, damaged cells to make room for new, healthy ones," emails Shelley Salling, a certified FASTer Way to Fat Loss coach (FASTer Way to Fat Loss is a virtual intermittent fasting fitness and nutrition program).
Some research has been done on the effectiveness of IF; however much of it to date involves animal subjects, not humans. Still, many researchers are heartened by their findings, with a 2019 New England Journal of Medicine study noting that fasting for 18 hours and eating in a six-hour period seems to "trigger a metabolic switch from glucose-based to ketone-based energy." This, they report can increase longevity, stress resistance and lower incidence of certain diseases, particularly obesity and cancer.
A 2018 study on 23 obese men and women who were restricted to eating between 10 a.m. and 6 p.m. found that after 12 weeks, they had lost 3 percent of their body weight and had lowered their systolic blood pressure — the top number — by seven points (other health indicators, like cholesterol levels weren't much different from the control group).
Until diverse, long-term studies can fully validate the benefits of IF many people will rely on anecdotal evidence provided by friends and family who've given it a try and found it successful. So, will it work for you?
Challenges of Intermittent Fasting
Let's get to the uncomfortable news first. IF can be difficult in the beginning, as it's not unusual to experience mild headaches, fatigue or other bodily side effects as your body adjusts to a revised feeding window, often coupled with a healthier, less sugar-filled diet. Fortunately, these tend to abate after a few days, and many people report feeling better and healthier overall.
IF is not recommended for people with certain health limitations, such as those with diabetes. People at risk of diabetes, however, are ideally suited to IF complemented with a healthy diet, because at least one study showed it dramatically lowered insulin levels and high blood pressure levels among prediabetic obese men. Anyone with a history of eating disorders, like anorexia or bulimia, as well as women who are pregnant or breastfeeding should not attempt IF unless they are closely monitored by a doctor.
Although many people are fine with IF on the 16:8 scale, it's not for everyone. "There is some concern that fasting long periods of time might cause some hormonal shifts in women that are unwanted," Weinandy says. "It probably depends on the individual since we are talking about humans and there is a lot of variation amongst us! I usually recommend people start with a 12 hour fast then go up an hour at a time and see how they feel. Most people will know what works for them based on how they feel."
How to Make Intermittment Fasting Easier
As a FASTER Way to Fat Loss Coach, Salling has guided dozens of men and women through the process, myself and my husband included. IF isn't necessarily easy in the beginning, but she says there are some hacks to make the transition process less difficult.
- Choose the best window for you: Everyone in the world on the 16:8 schedule doesn't have to abide by the same timetable. So, if you are the early to bed, early to rise type, consider starting your fast at 6:30 or 7 p.m., and ending it 16 hours later. "The exact time you choose to have as your feeding window doesn't matter as much as the length of the fasting window, as cellular changes occur when the system is at digestive rest," Salling says.
- Start small: If the idea of a 16-hour fast is daunting, start smaller at 12 or 13 hours. Then, every day try to go a little longer.
- Drink lots of water: This is especially important when you wake up in the morning, as most of us rise dehydrated. "Your thirst signal is the same as your hunger signal so if you drink lots of water when you wake up your body will not think you need to eat," Salling explains. Take steps to get and stay hydrated all morning by drinking water, carbonated water, black coffee and tea. Aim for half your body weight in ounces per day (example: if you weigh 100 pounds (45 kilograms), shoot for 50 ounces (1.4 liters) of water per day). Drinking plenty of water will help keep headaches and other detox effects at bay.
- Stay busy: Most of us snack when we're bored. Avoid the urge to break your fast too early by getting active, whether by exercising, working extra hard or enjoying a hobby. And beware of watching TV at night, if that is a prime snacktime for you! You might have to do something else during those hours to keep busy, like working on the computer or pursuing that hobby you didn't get around to in the morning.
- Don't overthink it: Because many people are immediately intimidated by going without food for 16 hours, it can be helpful to think about it a different way. "Intermittent fasting is an eating schedule, not a diet," explains Salling, noting that a lot of the challenge is mental because people assume they can't go that long without eating. "I believe the 16:8 protocol is the best because it isn't as extreme as some of the other forms, so most people can maintain the fasting lifestyle long term."
- Stay positive: "Don't fast so long that you dread it because then it becomes a negative and is no longer very helpful and not sustainable," Weinandy says. "Food should be enjoyed and provide us with many needed nutrients. The moment it becomes the enemy is when we need to rethink what we are doing and why we feel that way."
- There's an app for that: If technology helps keep you focused and honest, download a fasting tracker app. I like the LIFE Fasting Tracker, which also allows friends to join circles so you know who is fasting, and when. Also, using an app to track what you eat is a good way to ensure you're eating enough of the right things. MyFitnessPal is a particularly helpful tool to make the nutrient tracking process easier.
- Join a group: Some of us need the cheerleading that comes along with doing the group thing. You can informally gather like-minded friends via a Facebook group, or you can look into using a certified coach, like Salling. Groups are an effective way to lose weight, as they provide much-needed support and encouragement during the getting healthy process, plus they're a great place to swap recipes and ideas and do troubleshooting, if needed.
- Plan ahead: As with most "diets," planning ahead is the key to success with IF. After all, you only have so many hours to get your nutrients in. "It is very important to still eat enough calories during your feeding window, as under-eating can be detrimental to your hormone health," Salling says noting that planning out meals and snacks in advance will help you to get enough whole foods during the feeding window. "A good way to do this is to add in snacks and eat every two to three hours. Some find success by eating three meals spaced apart while others eat two and snack in between."
- Keep the meals healthy: Eating lots of junk food during your eight-hour window won't help you to lose weight. "There will be some results one could see just from fasting because it usually reduces the total number of food and calories eaten," says Weinandy. "However, if during the eating period the foods are very high calorie and not very healthy, it can defeat the purpose. There might be some health benefits still just from fasting but we don't know for sure yet based on the current research we have."