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Is Intermittent Fasting Healthy?

There seems to be an endless number of options when it comes to eating plans and strategies. And one that has become increasingly practiced is intermittent fasting.

But what is intermittent fasting, exactly? Is it a safe and healthy way to lose weight or maintain a stable weight? This blog post will provide an overview of intermittent fasting, including its benefits and drawbacks.

Ultimately, whether or not intermittent fasting is right for you depends on your individual needs and preferences. So read on to learn more about this intriguing eating practice!

What Is Intermittent Fasting?

Intermittent fasting (IF) or time-restricted eating alternates between periods of fasting and eating. This is distinct from typical weight-loss strategies that involve continuous calorie restriction in which the daily caloric intake is reduced while the frequency of meal timing stays the same.

Rather than restricting certain foods and calorie intake, IF is about timing the eating window.

Some people do IF because they believe it can help with weight loss or to experience other health benefits like longevity, while others do it because they find it's a simpler way to eat versus traditional diets.

There is evidence that shows that time-restricted feeding may even positively impact cognitive function and longevity [1].

Different Types Of Intermittent Fasting

There are many different ways to do intermittent fasting, sometimes called time-restricted eating or alternate day fasting but the basic idea is to cycle between periods of eating and fasting.

Many studies conducted on the potential health benefits of fasting will lump three distinct types of fasting under the same umbrella as IF. This can be problematic as these are very different forms of fasting, which can have drastically different physiological effects.

According to Peter Attia, studies on an alternate day fasting (ADF) and 5:2 intermittent fasting allow up to 700 calories per day on the fasting days. In contrast, others don't allow for any calorie consumption.

There's no one right way to fast, and what works for one person may not work for another. But if you're looking to give IF a try, here are three common methods.

Alternate Day Fasting (ADF)

ADT is a subtype of IF that involves eating normally one day and then fasting the next.

Some methods of ADF allow for minimal calorie intake on fasting days (up to 25% of the regular intake) or follow a stricter approach of zero calories.

Both methods have shown promising results in baseline health and weight loss measurements, which means the ADF can be tailored to suit various goals and lifestyles.

5:2 Periodic Fasting

The 5:2 method involves eating normally for five days a week and fasting on two nonconsecutive days, limiting the calorie intake to about 600-700 calories a day.

On eating days, you would eat as if you weren't fasting at all—but it's important to avoid overeating or binge eating junk food, or you're not likely to experience the potential benefits of IF.

On regular eating days, there are two meal patterns most people follow:

  • Three small meals (breakfast, lunch, and dinner)

  • Two slightly larger meals (lunch and dinner)

Daily Time-Restricted Feeding (DTRF)

This method involves a daily fasting period of around 16-hours per day and an eating window of 8 hours.

The 16 hours window of fasting is much simpler than you'd think. Ideally, we'd hit 7–8 hours of sleep at night where we're not eating at all already. In the mornings, we could delay the first food of the day, break the fasting period for lunch and start the fasting window again after an earlier dinner.

DTRF is a relatively new intermittent fasting method and many people find daily time-restricted feeding to be more effective and sustainable long-term for weight loss or weight maintenance.

How Does Intermittent Fasting Work?

The human body hasn't changed significantly since our hunter-gatherer days. It's designed to function without food for extended periods as we never had access to supermarkets or fast food joints.

In many ways, fasting is more "natural" than the conventional idea of eating 3–4 meals a day.

If we consider fasting in the context of evolution, individuals who functioned well during a fasted state were better equipped to find food, enabling survival.

Fasted and fed states are two physiological states that your body can be in. The main difference between the two is that when you're in a fasted state, your body isn't digesting food. Being in a fasted or fed state can have different effects on your body.

In a fed state, the presence of sugar signals the body to produce insulin and store energy. During the fasted state, the body will start to burn stored energy.

Fasting periods and exercise consume glycogen stores, which are essentially stored sugar and carbs from our food. Once our glycogen stores are depleted, a metabolic switch occurs where ketones are formed as cellular fuel.

Research shows that this metabolic switch is often accompanied by adaptations that enhance cellular functionality, making the body more resistant to stress and disease [2].

Health Benefits Of Intermittent Fasting

There are a lot of animal studies on IF, but data on human studies are much less conclusive. Let's have a closer look at some of the reported potential benefits.

Weight Loss

We all know the basics of weight loss: eat less, move more, and move more. But what if there were a more straightforward way to lose weight that didn't involve counting calories or prolonged exercise?

Many people have found success in reaching their weight loss goals with intermittent fasting, as they worry less about calorie counting, which feels much more sustainable long term and doesn't feel like they're restricting calories.

Fewer meals, in general, will lead to consuming fewer calories and gradual weight loss.

Once people acclimatize to the eating and fasting periods, most people find that they don't feel hungry outside of their feeding window, which means they're less likely to over consume calories.

Studies have found successful weight reductions and improvements in cardiovascular health in participants practicing alternate-day fasting [3].

Cognitive Enhancement & Protect Against Neurodegeneration

We all want to stay sharp as we age, and there's no doubt that keeping our cognitive function strong is key to aging well. Some recent research suggests that intermittent fasting may be one thing that helps protect our cognitive function as we get older.

In murine studies, restricted energy intake—specifically alternate day fasting—increased the brain-derived neurotrophic factor (BDNF), which plays a role in neuronal growth, learning, and memory [4, 5].

Longevity/ Anti-Aging

Could fasting be the answer to anti-aging? Many people seem to think so, but most of the research in this space is conducted on animals in small, short-term trials.

Calorie restriction in rodents has been linked to slowing the rate of aging and increasing the average lifespans of the subjects. Short-term intermittent energy restriction is believed to affect the metabolic processes and may increase levels of anti-oxidants, reducing cellular aging in mammals [6].

Cardiovascular Health

Many people think of cardiovascular disease (CVD) as a problem that only older adults have to worry about. However, the fact remains that CVD is the leading cause of death for Americans of all ages.

One of the most significant risk factors for developing heart disease or a stroke is high cholesterol levels. Intermittent fasting may help to reduce "bad" LDL cholesterol levels and combat insulin resistance.

Alternate day fasting, consuming 25% of calories on the fasting days, has been shown to facilitate weight loss and lower the risk of cardiovascular disease in a short-term study of a sample of 12 women and four men [7].

Is Intermittent Fasting Safe?

The human body is equipped to handle short periods of fasting. Many religious groups today integrate periods of fasting as part of rituals. Studies on the effects of religious fasts found many favorable outcomes, such as reducing body weight, blood sugar regulation, and reduced oxidative stress [8].

Intermittent fasting isn't dangerous when done correctly, but it may not be a good choice for certain groups of people.

People with a history of eating disorders, a body max index below 19, pregnant or breastfeeding, or over the age of 70 should avoid intermittent fasting due to increased muscle wasting and other health concerns.

The Takeaway & Tips To Getting Started

Contrary to the name, intermittent fasting is not a diet. Instead, it's an eating pattern where you cycle between periods of eating and fasting.

It's not difficult to get started, but it may take some preparation and patience to train the body to eat within the designated feeding windows.

For most people, the biggest challenge is the mental barrier to fasting. The most friendly way to get into intermittent fasting is the daily-timed restricted eating, as many people instinctively eat this way.

It could be as easy as stop eating at 8 pm, and if your first meal is breakfast at 8 am, that is a fasting period of 12 hrs.

From there, if you so desire, you can delay your first meal of the day until later and later in the day, 9 am, 10 am, 11 am or 12 pm. Thereby extending your fasting window to 13 hrs, 14 hrs, 15 hrs and then 16 hrs.

Again, there is no right or wrong way to do it. It just depends what your goals and intentions are. Simply giving your body a digestive rest from 8pm to 8am is already beneficial to your long term health even without intentions of weight loss.

To sustain yourself during the fasting period, ensure you eat enough fiber, healthy fats and protein during your feeding window to avoid feeling starved and exhausted.

It would help if you also drank plenty of water. The hunger signals in our brain can also be triggered by thirst—staying hydrated can help fight off false alarm hunger signals that can give you the urge to snack.

Most importantly, listen to your body and give it what it needs.


  1. Piper, M. D. W., & Partridge, L. (2007). Dietary restriction in Drosophila: delayed aging or experimental artefact?. PLoS genetics, 3(4), e57.

  2. Jensen, N. J., Wodschow, H. Z., Nilsson, M., & Rungby, J. (2020). Effects of ketone bodies on brain metabolism and function in neurodegenerative diseases. International journal of molecular sciences, 21(22), 8767.Chicago

  3. Tripolt, N. J., Stekovic, S., Aberer, F., Url, J., Pferschy, P. N., Schröder, S., ... & Sourij, H. (2018). Intermittent fasting (alternate day fasting) in healthy, non-obese adults: protocol for a cohort trial with an embedded randomized controlled pilot trial. Advances in therapy, 35(8), 1265-1283.

  4. Tripolt, N. J., Stekovic, S., Aberer, F., Url, J., Pferschy, P. N., Schröder, S., ... & Sourij, H. (2018). Intermittent fasting (alternate day fasting) in healthy, non-obese adults: protocol for a cohort trial with an embedded randomized controlled pilot trial. Advances in therapy, 35(8), 1265-1283.

  5. Kashiwaya, Y., Bergman, C., Lee, J. H., Wan, R., King, M. T., Mughal, M. R., ... & Veech, R. L. (2013). A ketone ester diet exhibits anxiolytic and cognition-sparing properties, and lessens amyloid and tau pathologies in a mouse model of Alzheimer's disease. Neurobiology of aging, 34(6), 1530-1539.

  6. Sogawa, H., & Kubo, C. (2000). Influence of short-term repeated fasting on the longevity of female (NZB× NZW) F1 mice. Mechanisms of ageing and development, 115(1-2), 61-71.

  7. Varady, K. A., Bhutani, S., Church, E. C., & Klempel, M. C. (2009). Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. The American journal of clinical nutrition, 90(5), 1138-1143.

  8. Trepanowski, J. F., & Bloomer, R. J. (2010). The impact of religious fasting on human health. Nutrition journal, 9(1), 1-9.

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