April 13, 2024

Intermittent Fasting: Does It Really Work?

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Manisha B K

MPH (James Lind), MBA, CTAA, 200 RYT Yoga

Intermittent Fasting: Does It Really Work?
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The cycle of weight loss and weight gain can be perplexing, especially when you are not aware of the reasons for your weight gain. This game of losing weight and regaining it over and over is called ‘weight cycling.’ 

We are all aware of yo-yo dieting patterns, in which people starve themselves to weight loss and then regain the lost weight quickly. This cycle repeats, which is not a great way to maintain a healthy metabolism

Quite frankly, I deal with many cases of yo-yo dieting (especially with youngsters) where I have to interfere and ascertain their reasons for this behavior and try to establish a better eating routine for them. 

What is Intermittent Fasting?

Intermittent fasting is a metabolic switch. Different approaches to intermittent fasting allow the meal gaps to vary according to the person’s choice of specific meal timings. 

The person might eat only one meal a day, two days a week, or maintain a 16-hour fasting routine by managing an 8-hour eating window in a day. The approach to fasting depends on the person's weight, considering their health condition and the risks associated with fasting methods. 

tray of chocolate pancakes served with banana slices between plates of cookies and sandwiches
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The science behind long hours of fasting is to use the body's fat reserves that help burn calories, ultimately leading to weight loss and increased insulin sensitivity

In my experience, people are unaware of the best fasting approaches that suit their metabolic conditions. 

As we know, one size does not fit all! 

Considering a family of four, you might observe that everyone will have a different appetite, and they adjust their eating patterns according to their lifestyle and stressors. 

Similarly, intermittent fasting also has different approaches ranging from the fasting periods to the eating windows. (Always seek professional help for dietary advice)

Types of Fasting

Let us understand the different types of intermittent fasting approaches.

Complete alternate-day fasting: In this approach, the person maintains complete fasting on alternate days. This model is used to achieve weight loss, especially in cases related to obesity and adipose dysfunctions. 

Modified fasting regimen: This model generally allows for 20-25% of energy needs on regularly scheduled ‘fasting’ days. In this approach, fasting describes periods of severely limited energy intake rather than no energy intake.

Time-restricted feeding: This is quite a regular model that most people follow, where the person fasts for a specific period and keeps an open eating window for a couple of hours, consuming a regular diet. The best examples of this model are 16:8 fasting (fasting for 16 hours with an eating window of 8 hours), 5:2 fasting (fasting for two days a week while consuming a regular diet for the rest of five days), 20:4 fasting (fasting for 20 hours with an eating window of 4 hours). 

Religious fasting: Religious fasting is seen in certain Asian communities (especially during Ramadan). Religious fasting is quite popular in Indian communities during festivals and rituals. 

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Overnight fasting: Overnight fasting is considered the safest model of fasting and is also pretty easy to follow. In this fasting regimen, the body is in the resting (sleeping) phase during the fasting window. This model does not need any distraction from food because the person spends all of their fasting window in sleep. 

Spontaneous meal skipping: To follow this approach, one must be very observant about their body, appetite, and satiety. Not all people would feel the need to have 3-4 meals a day. As we grow, especially from the mid-40s, we might find a decrease in our appetite. Changes in nutrient absorption, bowel movements, dental health, and decreased activity might lead to spontaneous meal skipping. 

OMAD (one meal a day) fasting: As the name speaks for itself, this model involves having only one meal (can be any time in a day), making peace with the appetite for the rest of the day. 

24-hour or 36-hour fasting: Some people also maintain a huge fasting time gap of 24 hours and, in some cases, 36 hours. This is a very difficult regimen and must be practiced only under supervised care. (Always seek professional help for dietary advice)

(A Comprehensive Guide To Fasting: Timeline, Stages & Benefits, n.d.)

How Effective is Intermittent Fasting for Weight Loss?

The primary goal of intermittent fasting is weight loss, which people understand on the surface. But intermittent fasting is also known for its benefits in metabolic syndrome (A cluster of conditions that increase the risk of heart disease, stroke, and diabetes). 

Dr Jason Fung, a nephrologist, invented intermittent fasting. And the 5:2 fasting model was popularized by Michael Mosley in 2012.

In his book The Cancer Code, Dr. Jason explains how intermittent fasting can reduce one's risk of cancer and other diseases. 

The entire idea of intermittent fasting is to allow insulin levels to go down far enough and for long enough that we burn off our fat. If we let our insulin levels go down, we lose weight. (Intermittent Fasting: The Positive News Continues - Harvard Health, n.d.)

Intermittent fasting works by prolonging the period when your body has burned through the calories consumed during your last meal and begins burning fat. Research shows that the intermittent fasting periods do more than burn fat. Changes in your metabolism with this metabolic switch affect both the body and brain. (Intermittent Fasting: What Is It, and How Does It Work? | Johns Hopkins Medicine, n.d.)

What do Researchers Say About Intermittent Fasting? 

The gold standard in health outcomes research is a randomized controlled trial. A randomized control trial was conducted for ‘time-restricted eating’ (one of the approaches to intermittent fasting) among overweight and obese young adults. 

Overweight and obese young adults were randomized into three categories. In the first group, 21 people were randomized for a 6-hour early time-restricted eating (eTRE) (eating from 7 a.m. to 1 p.m.). In the second group, 20 people were randomized for 6-hour late restricted eating (lTRE) (eating from 12 p.m. to 6 p.m.). In the third group, 19 people were randomized as the control group (ad libitum intake in a day or a non-restrictive diet). 

A 10-week randomized controlled trial was conducted to compare the three groups. The first two weeks are the baseline period (for the subjects to meet the criteria for this study). The next eight weeks are the TRE (time-restricted eating) intervention period for the subjects.

During this intervention period, the subjects in eTRE were allowed to eat ad libitum from 7 a.m. to 1 p.m., lTRE subjects were allowed to eat ad libitum from 12 p.m. to 6 p.m., and the controlled group had no time restrictions. 

It was observed that the primary outcome was weight loss, and the secondary outcome was changes in cardiometabolic parameters, metabolic hormones, markers of inflammatory cytokines, and oxidative stress

The 6-hour eTRE has more reductions in carbohydrates and protein than the control group, whereas the 6-hour lTRE has more reductions in fat compared to the control group. 

What are the observations and the benefits of intermittent fasting in these three groups:

  • The 6-hour eTRE and lTRE resulted in a greater reduction in fat mass and visceral fat area by week 8 compared with the control group. (Zhang et al., 2022)
  • Lean mass loss in the eTRE group was greater than that in lTRE group at week 8.
  • 6-hour eTRE, but not 6-hour lTRE, reduced mean glucose, fasting insulin, and insulin resistance compared with the control group (as the study was conducted in healthy adults). 
  • To sum up, 6-hour eTRE may improve glucose regulation compared with 6-hour lTRE by shifting the feasting window to earlier when the circadian system may promote better glucose tolerance.
  • 6-hour eTRE reduced systolic blood pressure, mean glucose, fasting insulin, insulin resistance, leptin, and thyroid axis activity, whereas lTRE only reduced leptin regulation. (Horne et al., 2015)

Is Intermittent Fasting Associated With Cardiovascular Death?

The current debate on intermittent fasting has become a hot topic in the health industry.  

A recent news roll-out about intermittent fasting and its ill effects on cardiovascular health is rampaging among the public. 

So, is intermittent fasting bad for the health? We cannot infer this hypothesis for now because:

  • The recent statement that made headlines about the ill effects of intermittent fasting associated with cardiovascular death was only an abstract based on an observational (recall) study. 
  • The study has not yet been published in a peer-reviewed journal. 
  • Certain detailed aspects must be considered when conducting a research study. Long-run studies and short-term studies show differences in their outcomes. 
  • Before concluding the hypothesis, one must always consider the confounders (external variables that may or may not influence the study) and other lifestyle and demographic factors.
  • Appropriate statistical analysis is required to derive the data for a cohort study, which was lacking in this current observational study. 

(Cardiologists Tell Us What You Really Need to Know About Intermittent Fasting and Heart Health | GQ, n.d.)

The Bottomline

It is important to note that not all people respond similarly to the same fasting approaches. Each person has a different appetite and metabolism, so there is no one-size-fits-all approach to diet. 

There are always two sides to a coin, and intermittent fasting is no less than a flipping coin. How a person responds to fasting depends on multiple factors. Numerous fasting models allow people to adjust according to their lifestyle and weight loss goals. 

Studies have shown both benefits and disadvantages of intermittent fasting. Intermittent fasting benefits weight reduction by lowering blood pressure, improving insulin sensitivity, and reducing oxidative stress and inflammation markers. 

Although intermittent fasting may be a good choice for some, it’s not appropriate or safe for everyone (Always seek professional help for dietary advice). The following are the side effects found in people who cannot adjust to the fasting models:

  • Hunger and cravings 
  • Fatigue
  • Light-headedness and headaches
  • Bloating or diarrhoea
  • Nutrient deficiencies due to caloric insufficiency
  • Bad breath
  • Dehydration 
  • Sleep deprivation

You may want to contact your healthcare team before starting intermittent fasting to perfect your health. 


  • A Comprehensive Guide To Fasting: Timeline, Stages & Benefits. (n.d.). Retrieved March 25, 2024, from https://dralexisshields.com/guide-to-fasting
  • Cardiologists Tell Us What You Really Need to Know About Intermittent Fasting and Heart Health | GQ. (n.d.). Retrieved March 26, 2024, from https://www.gq.com/story/intermittent-fasting-heart-health
  • Horne, B. D., Muhlestein, J. B., & Anderson, J. L. (2015). Health effects of intermittent fasting: hormesis or harm? A systematic review. The American Journal of Clinical Nutrition, 102(2), 464–470. https://doi.org/10.3945/AJCN.115.109553
  • https://www.medicalnewstoday.com/articles/323605#brain-health
  • Intermittent fasting: The positive news continues - Harvard Health. (n.d.). Retrieved March 25, 2024, from https://www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156
  • Intermittent Fasting: What is it, and how does it work? | Johns Hopkins Medicine. (n.d.). Retrieved March 25, 2024, from https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-workZhang, L. min, Liu, Z., Wang, J. qi, Li, R. qiang, Ren, J. yi, Gao, X., Lv, S. shuai, Liang, L. yao, Zhang, F., Yin, B. wen, Sun, Y., Tian, H., Zhu, H. chen, Zhou, Y. tian, & Ma, Y. xia. (2022). Randomized controlled trial for time-restricted eating in overweight and obese young adults. IScience, 25(9), 104870. https://doi.org/10.1016/J.ISCI.2022.104870
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