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!

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Comments (14)
  1. 1
    Bianca October 3, 2018 at 6:05 am

    Great post! I did the 5:2 a little while ago and plan to go back on it again to help loose some baby weight. I found it hard for the first couple of weeks but then actually enjoyed it. My body almost felt grateful (haha sounds silly) for the break from digesting stuff. I would definitely recommend it, and my doctor agreed too.

    • Katherine Fluor October 3, 2018 at 10:17 am

      So glad to hear it, Bianca! Good luck hopping back into it – the first couple weeks of fasting are always the hardest!

  2. 2
    kenneth pastore October 3, 2018 at 2:21 pm

    I must do IF for my arthitis and just yesterday I became fully pain-free from head to toe on a 42-hour water IF fast but then broke it for quite a while till late a night and the pain did return.

    So today again I must fast and I actually think for me in my condition that 42 hours fast is best then eat about 4- 5 hours slowly then stop eating.

    I know that this will take some time to become a habit but what else to do when one has tried everything and nothing works as well as fast, but it must become a lifelong habit for myself as well all those in need to control themselves and become healthy happy and free from many of life’s aches and pains.

  3. 3
    Amanda October 3, 2018 at 5:14 pm

    I do the time restricted and I really like it. For the first time in my life I have easily been able to maintain a healthy weight. I realized when I was eating all day long I was eating too much, and when I splurged even a little it was resulting in added lbs. I don’t eat until noon, which means I skip breakfast-and frankly it’s nice to have one less decision a day!

  4. 4
    Zara October 23, 2018 at 2:59 pm

    Hell no! I cannot go without food for longer than 4 hours or I will literally faint/be completely useless/moan constantly/be extremely ‘hangry’! I know studies show that this has benefits but I really think there can be no substitute for a well-balanced diet with plenty of exercise.

  5. 5
    Jennifer March 24, 2019 at 12:57 pm

    I have been on the OMAD diet (one meal a day) for 3 months and I feel great! I finally lost some weight (about 24 pounds) and I have so much more energy. I usually eat my meal at 11am, (making it a balanced meal with something from each food group) then fast for 24 hours (just iced tea no sugar). I can even exercise and I don’t feel weak! There are two books on this…EAT STOP EAT and THE OMAD DIET. This summer, bikini time!?

  6. 6
    Ann October 28, 2019 at 11:10 am

    The hours seem off in the time restricted fasting paragraph. If you eat at 8 pm, eating again at 8 am would only be a 12 hour fast. If you eat at 8 pm, the next meal would be at 12 pm for a 16 hour fast.

    • Elise Pardue November 4, 2020 at 10:02 am

      Agreed. I noticed that too.

  7. 7
    Molly October 28, 2019 at 3:09 pm

    While I totally get that IF has some scientific backing for various physical conditions, it scares me quite a bit to have it become such a mainstream school of thought. For most people, eating so infrequently can cause irritability, insomnia, etc. More than that though, I worry that this idea of eating one meal a day or “fasting” for large parts of the day creates a disordered way of thinking for women who are already pressured by society to become smaller. It seems much wiser to me to just eat what you want when you’re hungry and to let your body be the size and shape it desires to be. Living in a world of restriction particularly when it comes to food is part of the bigger problem of societal body expectations. It is easy to let something like IF become something that we tell ourselves is for health when really it is disordered eating in disguise.

  8. 8
    Nichelle October 29, 2020 at 12:50 pm

    I do time restrictive fasting. My fitness coach recommended it. I am a stress eater and start work at 7:30am with the busyness already On and moving when I start. So eating from 10am until 7/8pm has helped me with the belly fat decrease as well as weight in general. I am even able to keep that up over the weekend. If it’s a breakfast meeting i just have espresso, tea or water until 10am.

  9. 9
    Sonja October 30, 2020 at 12:37 am

    I have heard some interview where Alisa Vitti mentioned that for women in their reproductive years this might cause bigger problems. I personally do sometimes just stop eating at some point early in the day as I feel better when I get up the next day, however this interview is something I keep in the back of my mind.

    • Annalise October 30, 2020 at 12:36 pm

      Agreed!! Especially if a woman is on hormonal birth control (which creates a fake cycle) it’s difficult to know if fasting is dysregulating her hormones. Fasting can kick off a pattern of your body thinking, ‘she might be starving’ > ‘shouldn’t have a baby while there’s no food available’ > ‘let’s suppress ovulation and hormone production’ … which can mess with mood, sleep, and even erode bone density.

  10. 10
    Cortney C Zieky November 4, 2020 at 2:06 pm

    Most of the research on IMF has been conducted on males. For females in their reproductive years its best to talk to your OBGYN and get a baseline for your hormone levels before you play around with it. If your cycle starts going hay wire–your body is sending you a message.

  11. 11
    Theresa November 4, 2020 at 5:18 pm

    Be careful intermittent fasting has been related to eating disorders especially binge eating disorder. There are articles about this in various publications. Also keep your ears open when speaking g to teens who are using this eating pattern as the risk is higher doe them.



Kristen Kilpatrick