Everything You Want to Know About Intermittent Fasting

Pros, cons, and why you should try it.

By Katherine Fluor

Intermittent fasting is one of those wellness buzzwords that most people (including myself) initially disregard as being just too extreme. In my case, fasting in general sounds like a recipe for a hypoglycemic disaster, and for someone who loves food as much as I do, pretty torturous. That said, too many people have told me all the wonders it’s done for their overall health, so I decided to dig deeper and approach the intermittent fasting research with an open mind.

When I started learning about the fascinating links between intermittent fasting and cellular repair, hormone levels, cognitive function, cancer prevention, metabolism, and inflammation, I realized it was way more than a trendy diet.

One question I kept coming back to was, how can one simple practice possibly have so many benefits? According to researchers, it all comes down to a cellular process called autophagy. Autophagy is what happens when we allow our cells the time and space to clean house, and kill off those that are weak or damaged. This makes room for the regeneration of new, healthier cells and tissues, which affects longevity and helps reverse diseases. In other words: Fasting gives your body much-needed a break from digesting, and allows it to focus on repairing itself from the inside out.

The “intermittent” approach makes it possible for even those who can’t imagine skipping a meal (me) to find a fasting method that works for our schedule, mind, and body. Since there are so many different types of intermittent fasting, I decided to dive into the research and find out about the differences between the methods—their pros and cons, and the health claims that are attached to each one. Scroll on for the intermittent fasting breakdown, and I’d love to hear in the comments about your experience if you’ve given any of these a try.

photo by Kate Zimmerman Turpin

Whole-day Fasting (5:2 diet)

This method of intermittent fasting restricts your calorie intake two days a week. For each fasting day, aim to consume just 500 calories (200 of which are fat, and protein foods)—like eggs, fish and nuts, either eaten consecutively in one meal or spread out over the day. The other five or six days a week, you can eat whatever you want, whenever you want – although it’s encouraged to eat mainly fruits, vegetables, lean protein, whole grains, and minimal carbs on non-fasting days to achieve maximum benefits of intermittent fasting.

Pros: The main benefit of the 5:2 method compared to others is that it’s simple and sustainable for an unpredictable and busy lifestyle. Since most days of the week aren’t locked into a rigid eating schedule, you have more control and can most likely stick to your regular social outings and workout schedule – using the 2 fast days as rest days or non strenuous exercise. Studies show that this type of fasting balances blood sugar levels, lowers inflammation, and improves cognitive function. Also, longer fasts of 24 hours or so are the most beneficial for boosting your metabolic rate and fat burn. Research shows that people who fast from 12 to 24 hours at a time have higher chances of entering enter ketosis—a state when our bodies start to derive more energy from fat, rather from sugar. The more you enter this state, the better your body gets at using fat as fuel. Read more on ketosis and the popular keto diet here.

Cons: Whole-day fasting can be difficult for those who suffer with low blood sugar levels. You can expect to feel hungry and have low energy on fasting days for the first few weeks. You’ll probably be more irritable and experience headaches, because you’re going a full 24 hours without food. “You can jump right into it,” “although it may be easier if you start off with just one day a week for a month or two, says Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging and a professor of neuroscience at the Johns Hopkins School of Medicine.

photo by Molly Winters Culver

Alternate-day Fasting

This method is a step up from the 5:2, in that you fast every other day. With this method, you consume just water plus 500 calories on fasting days, (200 of which are lean protein), either in one meal or spread out over the day. The next day, you’re off the fast and can eat as you normally would. Then you pick up the fast the day after, and so on.

Pros: Alternate-day fasting can help lower your risk of heart disease and type 2 diabetes. It can also be a powerful and manageable weight loss tool for those that like routine, but want the freedom to indulge regularly. This source found that people who didn’t track their food but tried alternate-day fasting for one year lost 6% of their bodyweight—roughly the same amount as people who restricted their calories for the same period of time. Other small studies have shown that the physical changes which can result from this form of intermittent fasting could also lead to reduced cancer risk, particularly for breast cancer.

Cons: With more fasting days than the 5:2 diet, you may experience headaches and difficulty sleeping at night on fast days. If you’re into regular high intensity workouts, you may have to modify your workout schedule due to lack of energy, which could result in loss of muscle mass.

photo by Buff Strickland

Time-restricted Fasting

For those that are more comfortable with the idea of fasting, the time-restricted method is a great intermediate to advanced way of fasting. Essentially, you restrict your eating to a four-to-eight-hour window every day, and for the remaining for 16 hours, you drink nothing but water or zero-calorie beverages. For example, you have dinner at 8 p.m. and don’t eat again until 8 a.m., or you might have a larger meal that ends at 10 p.m., to which you won’t eat again until 2 p.m. the next day. Unlike the other fasts, you can eat whatever you want during your eating window—it’s not restricted to 500 calories.

Pros: Research supports this type of fast for preventing obesity, diabetes, and liver disease, and it is a great way to keep you feeling light and energized throughout the day. Since you’re eating at roughly the same time every day, adherence to the fast is probably a little easier than the others. And if you suffer from low blood sugar levels or are a big snacker throughout the day, this method will keep you happier and more energized than the 24-hour fast options.

Plus, you still lose weight without ever having to count calories. This study found that people who consumed all their calories in an eight-hour window, and fasted for the other 16, lost more fat while maintaining muscle over eight weeks compared to those who ate normally. If you like structure, routine, and predictability, this is the method for you. You’ll also fare well with this method if you hate tracking calories and love snacking.

Cons: If you eat out for dinner or breakfast regularly due to social or business commitments, you’ll probably have to change your schedule around to make lunch outings a regular thing. Also, if your schedule requires you to hit the gym pre-sunrise, that means you’ll probably start your feeding window earlier, which can make post-work socializing a lot harder. You’ll have to give up your wine or Halo Top nightcap too, unless you can hold out until 1 or 2 p.m. for your first meal of the day.

photo by Wynn Myers

In my experience, fasting isn’t for everyone. Experts say pregnant women shouldn’t fast, and neither should women with infertility issues, or anyone who has history of eating disorders. According to Vincent Pedre, a functional medicine physician and author of the Happy Gut, you should also proceed fasting with caution if you have gut issues, diabetes, food sensitivities, sleep problems, anxiety, or chronic stress. Going without food can make your blood sugar dip and trigger your fight-or-flight response, so it’s important to stay in tune with your body at all times.

Of course, anyone should always talk to their doctor before starting a fasting plan. Once you get the all clear from them, give it a try and let us know what you think!