Is Intermittent Fasting Healthy? The Science Behind It All!

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Is intermittent fasting healthy? Is it safe? There are so many different diet trends and weight loss plans. And anytime you encounter someone who believes in a particular diet, whether you encounter them on social media, on infomercials, at the gym, or at work, each person seems totally convinced that their plan is the best. And when it comes to intermittent fasting, I find that people who have been successful with losing weight with it are no less enthusiastic.

Indeed, you can lose weight with intermittent fasting. There's no question. And there are even some studies to suggest that there are other health benefits, even beyond weight loss. The question is, is intermittent fasting safe? And that's what I'll be answering today. Is intermittent fasting a health risk? The science behind it all. Keep reading.

What Is Intermittent Fasting?

Intermittent fasting is when you have a certain span of hours in a day or days during your week when you do not eat when you fast. And there are several different categories or schedules for intermittent fasting.


Is intermittent fasting healthy


Time-Restricted Eating

You can do daily, time-restricted eating. That is when, for each day, there are a certain number of hours where you fast and a certain number of hours where you restrict yourself to eating only within that time. And there are different schedules for that.

  • 16/8 Fasting Schedule

You can choose a 16/8 schedule, where you fast for 16 hours, no food at all, and for eight hours you eat. So for example, on each day, you may choose to fast for 16 hours, but then from 10:00 AM to 6:00 PM, during that eight-hour span, you will allow yourself to eat during that time, and that time only.

  • 18/6 Fasting Schedule

If you choose an 18/6 schedule, you may fast for 18 hours. And then for just six hours a day, within that time only you will eat, say from noon until 6:00 PM. This is the daily time-restricted eating.

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Alternate Day Fasting

You can also have an intermittent fasting schedule where you choose alternate days to fast for the entire day. There's a 5/2 schedule, where you have five days when you eat regular meals, but then you fast for two of those days. You might choose Monday and Thursday, for example. You know, Mondays and Thursdays, if those are your fasting days, you will not eat, but you may limit yourself to only one meal that's less than 500 calories.

There are many more schedules than this, but these are just some of the different schedules with intermittent fasting.


How To Lose Weight With Intermittent Fasting

So how does intermittent fasting help you to lose weight? What's the physiology behind it? Well, when you fast, when you go without food, initially, your body will burn the sugar. It will convert those easily accessible glucose stores into energy. So you'll burn off the sugar first, then your body will start to burn fat.

It will convert fat into energy. Specifically, the liver will convert fatty acids into ketones. And so this is how you end up losing weight when you go into fasting intermittently. Scientific studies have revealed that intermittent fasting can help one to lose weight.


intermittent fasting vs calorie counting


Intermittent Fasting vs Calorie Restriction

Is intermittent fasting better than calorie restriction when it comes to losing weight? Well, according to a New England Journal of Medicine study that was published, the answer is no. In fact, you had two groups of patients. There are 139 patients randomized into two different groups.

You had one group that had time-restricted eating, or intermittent fasting and calorie restriction, while the other group only had calorie restriction. Both groups were eating the same amount of calories, the difference is that one did it with intermittent fasting.

For the other group, there was no specific time interval for eating, but they both had the same amount of calories. These patients were studied for one year. So this is one of the long-term studies for intermittent fasting. And what was found was that there was no significant difference between the group that did intermittent fasting and the group that just did the calorie restriction.

And beyond that, they found that there was no difference in waist circumference and no difference in belly fat. Now, there have been other short-term studies prior to this study, which have revealed potential differences. But for this long-term study, it was found that there was no difference in the amount of weight loss with calorie restriction versus intermittent fasting. Still, more studies need to be done.


Pros and Cons of Intermittent Fasting

Health Benefits Of Intermittent Fasting

So what are some of the other health benefits beyond weight loss of intermittent fasting? Well, the New England Journal Of Medicine also published a review of multiple studies on intermittent fasting. And according to these studies, many of them were small studies, and some of these studies actually were with animal models, like rats, but some of the potential benefits of intermittent fasting that were found include:

  • An improvement in inflammation in the body
  • An improvement in blood pressure
  • Improvement in blood sugar regulation
  • Decrease in cholesterol or lipid levels
  • Improved memory

Some of these small intermittent fasting studies even suggest that there could be an improvement in asthma, in multiple sclerosis, diabetes, and other diseases associated with inflammation. Mind you, these studies tended to be small. And again, some of them are in animal models, which makes it difficult to translate the success in animals to the success in humans. All in all, it is inconclusive and we need more studies.

Nevertheless, there are still potential benefits outside of weight loss with intermittent fasting. There is science that supports it, but it's not conclusive. Larger studies and longer-term data are needed.


pros and cons of intermittent fasting


Dangers of Intermittent Fasting

So now, I've talked about some of the benefits of intermittent fasting, and some of the pros. Now let's talk about some of the cons.

Hunger, Headaches and Irritability

I'm sure you can probably guess, hunger. Yes, you might be hungry in the period when you're fasting, especially when you're just getting used to it. You may develop headaches and irritability. You may be hangry, basically, when you're doing the fasting.

Bad Breath

You may also get bad breath during the fasting periods. That's a reality that can happen.


Another con of intermittent fasting can be cravings. You might just be sitting there, starving and craving different things, and you can even get malnutrition. If you're not careful to get all the proper calories, proteins, fruits, and vegetables during the eating phases, you could develop malnutrition.

Low Energy

And another con is that you could have low energy while you're fasting. The good thing about forming habits is that most people develop a habit after two to four weeks of the same repetitive behavior. And so after the habit is formed, some of these initial cons will likely get better.


Is Intermittent Fasting Healthy? Is It Safe?

So now, for the question of the hour, is intermittent fasting healthy and safe? Well, the answer is that it depends. Intermittent fasting may be safe for a certain portion of the population. You certainly want to consult with your physician before starting an intermittent fasting plan.

The truth of the matter is there are certain people who will be able to do intermittent fasting safely. It depends on how long the interval is of the fasting and how well you do with making sure you get the proper nutrition and the proper hydration. Again, consult with your physician.

People Who Should Not Do Intermittent Fasting

Conversely, there are definitely people who should not do intermittent fasting. In these people, the risks will very likely outweigh the benefits.

People Who Have An Eating Disorder

One group, if you have an eating disorder, or if you have a predisposition to getting an eating disorder. When you have the intermittent fasting, this time-restricted eating, you have a very specific parameter of when you're allowed to eat.  If you make a mistake, if you're not perfect, and of course, last I checked, no one is perfect, and so you are likely to have some mishaps where you eat a little early, or you eat a little late.

If you are a person with an eating disorder or a predisposition to developing an eating disorder, then if you make a mistake and you don't eat exactly when you're supposed to eat, the eating may be associated with anxiety and shame, and this could potentially trigger an eating disorder.

Again, when you think about being restricted and fasting for so many hours, or even days, if you're someone who is predisposed to binging, then these intense restrictions could potentially trigger a binge. And then when you think about recovery. Say you're someone who speaks about having an eating disorder in the past tense.


dangers of intermittent fasting


If you say that you used to have anorexia nervosa, or you used to have bulimia. Part of the recovery, as you know, is associating eating with your body getting used to listening to its cues. You want to learn how to follow your body's natural cues for hunger and the cues for when you're actually satisfied. Well, intermittent fasting is the exact opposite. You are being taught to ignore your body's cues for when you're hungry.

And so again, if you have an eating disorder, or if you are predisposed to having an eating disorder, then intermittent fasting may be a health risk for you. Even for people who choose to do intermittent fasting, during the eating period, when you're supposed to have regular foods, you want to focus on a heart-healthy diet. Please be sure to watch my YouTube video on a heart-healthy diet after you finish reading this article.

People Who Have Diabetes

Another group where intermittent fasting may pose a potential health risk is diabetics, especially Type 1 diabetics. If you are a diabetic, then you are likely taking a medication that will lower your blood sugar. You may be on insulin, which lowers the blood sugar, or you may be taking certain oral pills that will lower the blood sugar.

When you're taking medicines like this, especially when it's long-acting medication, your body is dependent upon your eating. If not, you can develop low blood sugar or hypoglycemia. So intermittent fasting can pose a health risk to diabetics. Again, you definitely want to consult with your physician.

People Are Pregnant, Breastfeeding and Athletes

Intermittent fasting can also pose a health risk to pregnant ladies and to ladies who are breastfeeding, and athletes, athletes who are training. Especially if you are in an intense training program, intermittent fasting can pose a health risk for you. When you are training hard, you need to be well hydrated, and you need to have plenty of protein, but if you are on a day where you're fasting, you're only having 500 calories while you're out doing "two-a-days", then the intermittent fasting can certainly pose a health risk.

Patients With Kidney Stones

If you are a patient with kidney stones. And, yes, remember, I am a board-certified nephrologist, a kidney doctor. If you have kidney stones, then intermittent fasting can pose a risk, because oftentimes, especially if you're a person who associates drinking with eating, there are times when you're fasting where you could get dehydrated. Dehydration can definitely exacerbate kidney stone formation.

People Who Have Gastroesophageal Reflux Disease (GERD)

And if you have GERD, Gastroesophageal Reflux Disease, then intermittent fasting could also pose a health risk to you, and it could exacerbate that condition.


Intermittent fasting can also pose a health risk to children. When you are a growing child dependent upon calories as you're going through your development, if you are being restricted, that could pose a health risk.

Elderly People

Lastly, elderly patients. If you are an elderly patient, or if you are frail, then intermittent fasting can certainly pose a health risk for you.


is intermittent fasting safe



So now that we've answered the question is intermittent fasting healthy?  I've given you the science behind intermittent fasting and we've discussed when intermittent fasting may actually be beneficial, and when intermittent fasting may pose a health risk. If you found this information to be helpful and informative, please be sure to share this article with the people you care about.

Also, if you have not done so already, please be sure to subscribe to my YouTube channel. And don't stop there, please make sure that you also follow me on Instagram @dr.frita I also have a podcast, Healthy Happy Life Podcast With Dr. Frita. Make sure you check out those episodes.

And of course, don't forget to purchase my book, "Under pressure: A Guide to Controlling High Blood Pressure."

Have you tried intermittent fasting? If so, let me know about your experience in the comments below.


Dr. Frita - Frita McRae Fisher, M.D.
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  1. Jane Njeha on April 10, 2023 at 4:35 am

    Mine is really not a comment but it is a question, yes, when you are fasting are you allowed to drink plain water?

  2. jane njeha on April 10, 2023 at 4:41 am

    I thank you very much for the education concerning intermittent fasting

  3. jane njeha on April 10, 2023 at 4:42 am

    Thank you very much

  4. Jessica Gibbs on April 23, 2023 at 3:33 am

    I am 63. I train everyday alternating powerwalking, gym weights and ballroom dancing and enjoy gardening. I have always been on the slim side. No HBP or sugar. My BMI is 20.5 is was 18.6. I am not sure what my issue is as I urinate very frequently re in an hour about 3 times with a slight odour. In the bladder area it is unforgettable but not painful. My uric acid levels is 35. My daily smoothie is a carrot frozen pineapple celery beetroot and frozen blueberries very yummy. My snack is 25g dried cranberries. Only chicken breast and fish grilled. I also have daily in a litre of water juice of 2 lemons a tbsp of of sugar and iodated sea salt. The frequent urination is crazy as I also don’t get enough sleep.
    Can you please assist.

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