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Pros and Cons to Intermittent Fasting

Intermittent fasting is a popular weight-loss method. But it also comes with some cons. Read on to learn more.
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With intermittent fasting being so popular, you may be wondering what some of the pros and cons are to this type of diet. In this article, we go over some of the key benefits and drawbacks of intermittent fasting.

Written by
Christine Richardson, PhD
Clinical Project Manager at Becton Dickinson

Intermittent fasting is extremely popular, and it seems like just about everyone has either tried it or is thinking of trying it. While this dietary pattern is helping many achieve their physical and health goals, it can also have a few drawbacks worth considering.

Here are a few pros and cons of intermittent fasting to help you decide if this diet is right for you.


1. Easy to Do

The most obvious benefit of intermittent fasting is that it’s pretty easy to do. 

You don’t have to give up your favorite foods, use a calorie tracking application, watch your macronutrients, etc.

You just have to pick a new eating schedule and stick to it. For example, if you decide to try the 16/8 diet, you just pick an eating window (maybe 12pm to 8pm) and eat during those hours only…and that’s it!

2. No Calorie Counting

A calculator and a pen.

That’s right, folks! You do NOT have to count calories while fasting. 

Many people find counting calories time-consuming and tedious and for good reason-it is. Luckily, intermittent fasting doesn’t require you to count or watch your calories, making it a relatively simple diet to adhere to.

This also means that you don’t have to give up your favorite high-calorie foods in order to achieve your daily dietary goals.

We will mention, however, that you may want to try counting your calories for a few days here and there just to make sure you are eating enough food and getting enough vitamins and minerals. 

3. Weight Loss

Person standing on a scale.

Intermittent fasting is as popular as it is probably because of how effective it is at helping people lose weight quickly, easily, and in a healthy way. 

There are many studies that have shown how intermittent fasting helps individuals lose body fat (1,2,3). One of these studies even showed that resistance-trained athletes were able to decrease their fat mass…so if lean individuals can lose fat mass, the average person should be able to as well (3).

The reason why fasting is so great is that it appears to help decrease body fat, not just overall weight. Losing weight doesn’t always translate to a loss of body fat. You lose weight every time you go to the bathroom, when you sweat, etc. The goal of most dieters is fat loss and fasting appears to help individuals lose body fat.

4. Health Benefits

Intermittent fasting has also been shown to have some great health benefits aside from fat loss. 

For example, fasting has been shown to help stabilize blood sugar levels and decrease insulin resistance, increase autophagy, decrease risk for neurodegenerative diseases like Alzheimer’s disease, decrease inflammation, decrease risk factors associated with cardiovascular disease, and improve gut health (4,5,6,7,8,9,10).

This means that fasting can help you both lose weight and reduce your risk of various metabolic conditions.

5. Cognitive Function

Red light bulb in the dark.

We will say right away that more studies are needed on this topic, but it appears that intermittent fasting may help with cognitive function. 

People who practice intermittent fasting often claim that after a week or two, they have feelings of mental clarity and that they can focus better…and there are some studies to back this up. 

One study showed that intermittent fasting improved cognitive ability in older adults with mild cognitive impairment (11). Likewise, an observational study showed that people with a shorter eating window have enhanced cognitive abilities compared to those with longer eating windows (12).

While it isn’t fully understood, a proposed mechanism that explains this effect is that fasting can improve cognitive function by decreasing a specific inflammatory response (13). 

However, like we mentioned, more studies are needed to fully understand if fasting can help with this and how. 

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1. Tired and Hangry

Think about the last time you skipped a meal…how did you feel? Maybe you felt a little tired, grumpy (hangry), or you had trouble focusing. 

These feelings are common side effects for people who skip meals, and this could be how you feel while intermittent fasting until your body adapts. 

People who try intermittent fasting claim that they adapt to the diet after about 1-2 weeks, which means you might not be feeling great for the first couple weeks after starting this diet.

This may be especially true for individuals who like to wake up and workout first thing in the morning. You will have expended a great deal of calories, causing you to feel especially tired and hungry until you are able to eat.

One way to combat this is to ease your way into a fasting regimen. For example, if you decide to try the 16/8 diet, maybe start with fasting for 15 or 14 hours until you get used to that and then progressively prolong your fast until you hit the 16-hour mark.

2. Binge Eating at Night

Burger and fries.

Many people claim that skipping meals throughout the day or eating less throughout the day causes them to feel this insatiable hunger in the evening. This can lead to poor food choices like eating large amounts of highly processed foods or consuming more calories than you need.

Over time, this can lead to you gaining weight.

One way to prevent this is to make sure you are consuming enough food during the day (assuming your fasting regimen of choice permits you to eat during the day). Pay attention to your hunger cues in the evening and if you find yourself overly hungry or craving calorie-dense foods, try eating more during the day.

3. Minimal Research

Another con to intermittent fasting is that there aren’t many human studies that have investigated this diet. The most compelling studies on intermittent fasting have been done in animals, meaning that the findings of those studies may not apply to humans.

Yes, there are some interesting human studies, but they are minimal in number, the sample size (amount of subjects) in each study is often small, and the population used are very specific i.e. the subjects are all overweight and have diabetes or they are well-trained athletes. 

This means that the ability for the findings and conclusions of the study to be applicable to the general public is questionable. 

4. Not for Everyone

Intermittent fasting is a unique eating pattern that isn’t for everyone. 

Some people who probably shouldn’t try fasting include:

  • People who have to take medications multiple times per day that need to be taken with food
  • Individuals with certain metabolic disorders (talk to your doctor about fasting!)
  • Ultra-runners – you may not be able to eat enough calories
  • People with a history of eating disorders
  • People that tends to have headache, although there are solutions about that.

While fasting has been shown to decrease your risk for various metabolic disorders, if you’re unsure if fasting is a good choice for you, consult your physician first. Then if you decide to try fasting and you don’t like it or it doesn’t suit your lifestyle, this may not be the best diet for you…and that’s ok!

5. Intermittent Fasting is Hard

Man holding two dumbbells.

There, we said it. Voluntarily choosing to not eat is a hard thing to do. Most people enjoy eating and look forward to it so choosing to eat less is not easy.

What can make intermittent fasting particularly challenging is that you should try to be consistent with your eating/fasting schedule. This can become challenging if you enjoy late night meals and drinks with friends or family. 


Intermittent fasting presents with some pros and cons. While it can be an effective dietary strategy for weight loss and improving overall health, this doesn’t mean that it’s the best decision for you.

Consult your physician before making any dietary decisions and if you’re told you are safe to try fasting, then give it a shot! But if you decide it isn’t the best diet for you, that’s fine! What’s right for someone else may not be right for you.

If you want to learn more about the pros and cons of intermittent fasting, we invite you to join our intermittent fasting community for women only.


1. Ganesan K, Habboush Y, Sultan S. Intermittent Fasting: The Choice for a Healthier Lifestyle. Cureus [Internet]. Cureus, Inc.; 2018 [cited 2021 Jun 19];10. Available from:

2. Welton S, Minty R, O’Driscoll T, Willms H, Poirier D, Madden S, Kelly L. Intermittent fasting and weight loss Systematic review [Internet]. Canadian Family Physician. College of Family Physicians of Canada; 2020 [cited 2021 Jun 19]. p. 117–25. Available from: /pmc/articles/PMC7021351/

3. Moro T, Tinsley G, Bianco A, Marcolin G, Pacelli QF, Battaglia G, Palma A, Gentil P, Neri M, Paoli A. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med [Internet]. BioMed Central; 2016 [cited 2018 Mar 6];14:290. Available from:

4. Furmli S, Elmasry R, Ramos M, Fung J. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Rep [Internet]. BMJ Publishing Group; 2018 [cited 2021 May 18];2018. Available from: /pmc/articles/PMC6194375/

5. Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. Cell Press; 2018;27:1212-1221.e3. 

6. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Research Reviews. Elsevier Ireland Ltd; 2017. p. 46–58. 

7. Fujikake N, Shin M, Shimizu S. Association between autophagy and neurodegenerative diseases [Internet]. Frontiers in Neuroscience. Frontiers Media S.A.; 2018 [cited 2021 Jun 9]. p. 255. Available from: /pmc/articles/PMC5972210/

8. Longo VD, Mattson MP. Fasting: Molecular mechanisms and clinical applications. Cell Metabolism. NIH Public Access; 2014. p. 181–92. 

9. Eshghinia S, Mohammadzadeh F. The effects of modified alternate-day fasting diet on weight loss and CAD risk factors in overweight and obese women. J Diabetes Metab Disord. J Diabetes Metab Disord; 2013;12. 

10. Maifeld A, Bartolomaeus H, Löber U, Avery EG, Steckhan N, Markó L, Wilck N, Hamad I, Šušnjar U, Mähler A, et al. Fasting alters the gut microbiome reducing blood pressure and body weight in metabolic syndrome patients. Nat Commun [Internet]. Nature Research; 2021 [cited 2021 May 24];12:1–20. Available from:

11. Ooi TC, Meramat A, Rajab NF, Shahar S, Ismail IS, Azam AA, Sharif R. Intermittent fasting enhanced the cognitive function in older adults with mild cognitive impairment by inducing biochemical and metabolic changes: A 3-year progressive study. Nutrients [Internet]. MDPI AG; 2020 [cited 2021 Jun 19];12:1–20. Available from: /pmc/articles/PMC7551340/

12. Currenti W, Godos J, Castellano S, Caruso G, Ferri R, Caraci F, Grosso G, Galvano F. Association between time restricted feeding and cognitive status in older italian adults. Nutrients [Internet]. MDPI AG; 2021 [cited 2021 Jun 20];13:1–11. Available from: /pmc/articles/PMC7827225/

13. Shojaie M, Ghanbari F, Shojaie N. Intermittent fasting could ameliorate cognitive function against distress by regulation of inflammatory response pathway Intermittent fasting could ameliorate cognitive function against distress. J Adv Res [Internet]. Elsevier B.V.; 2017 [cited 2021 Jun 19];8:697–701. Available from: /pmc/articles/PMC5608558/

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