Side Effects of Fasting for Three Days

Fasting has been a dietary practice for millennia, featured in many age-old religious writings and even spoken of by the Greek philosophers Socrates and Plato. In contemporary times, it is used to support weight loss and weight management, but beyond that, not eating for three days can also be used to benefit the health of the body as a whole.

Water fasting has some benefits. (Image: diane39/iStock/GettyImages)

However, there are many things to consider before fasting, and not eating for three days can be quite a dramatic alteration to a usual diet if proper thought is not applied.

The Water Fasting Diet

As its name may suggest, the water fasting diet consists of no food for three days where only water is consumed instead. Though this may sound initially alarming, and that it may pose damage to the body as opposed to anything productive or positive, clinical trials have actually found that there are benefits associated with water fasting when executed with the proper process in mind.

In a June 2014 interview with Alan Goldhamer, DC, published in the Journal of Integrative Medicine, he describes his own research into water-based fasting. Based at the True North Health Center in Santa Rosa, he has personally overseen thousands of patients engaging in therapeutic fasting in a controlled, comfortable environment.


The environment is a key factor in the safe application of water fasting. The body cannot continue as normal when it is consuming nothing but water, as energy levels are not the same. It's important when water fasting to be comfortable and relaxed and never overexert the body.

Is Water Fasting Safe?

Despite living on a diet of solely water for a few days sounding similar to a form of punishment, in actuality, it has been demonstrated to provide health benefits not only relating to weight loss and management but also to overall physiological well-being.

A February 2018 study published in the Journal of Complementary and Alternative Medicine consolidates this safety but also highlights the numerous ways it can be positive from a physiological perspective, citing that it helps to induce:

  • Ketogenesis
  • Hormone modulation
  • Reduced oxidative stress
  • Reduced inflammation
  • Increased stress resistance

All of which greatly benefit the body and can even help the amount of protein the body absorbs and prevent cardiovascular illnesses that can emerge from undue stress.

Out of the 652 patients who partook in the February 2018 study, only two patients experienced adverse side-effects that resulted in hospitalization, and both of these cases featured 70-plus-year-old men who suffered dehydration.

From this data, providing due care is taken, water fasting is demonstrably safe when applied in a comfortable environment.

Not Eating for 24 Hours

A common implementation of fasting in contemporary times is the practice of not eating for 24 hours. One day per week, ordinarily, an individual will fast in the hopes of weight loss or body detoxification. Unfortunately, clinical evidence has demonstrated that 24-hour fasts are not actually the most productive action to proceed with.

Alan Goldhamer, DC, advises that the most beneficial aspects of fasting occur in the body progressively, so in the instance of not eating for three days, the most productive elements of the fasting period will occur on the third day.

This is why, in Goldhamer's words, "The idea of fasting one day a week, arbitrarily, is a bit of a misnomer because the main biological and therapeutic benefits of fasting actually take place progressively over time," he continues, "It is not the first day or two that are the most efficient at detoxification: It is the last day or two."

Weight Loss in a Day

While not eating for 24 hours can be beneficial in the pursuit of substantial weight loss, as Goldhamer informs, it is not the most productive way to utilize fasting where the overall benefit of the body is concerned.

A July 2018 study published in the Cureus Journal indicates that alternate day fasting, which is when fasting only takes place on one or two days in a week non-consecutively, is highly effective in weight loss. However, it is not clear what other effects this has on the body and how detrimental it may be in the long run.

A July 2017 study published in the JAMA Internal Medicine Journal following the diets of 100 obese individuals found no significant benefit or detriment in weight loss through fasting compared to a daily calorie restrictive diet. Lifestyle changes are thought to be the best way to lose weight and maintain the loss, so it may be worth looking into more conventional calorie restriction diets before deciding to commit to fasting.

Who Shouldn't Fast?

Though fasting definitely has its benefits, it still consists of depriving the body of food that it would ordinarily expect. Therefore, it's important to consider all of the details of an individual's biological makeup and requirements before embarking on what could potentially become not eating for three days.

According to the Harvard T.H. Chan School of Public Health, the following groups should not commit to fasting:

  • Those with diabetes: This is because diabetes requires a careful maintaining of sugar levels in the body, and depriving the body of food can severely impinge an individual's ability to keep their sugar levels optimal.
  • Individuals suffering from an eating disorder: If the body is already under stress from conditions such as anorexia or bulimia nervosa, then fasting is not applicable. Consistent and balanced food intake should be maintained in regard to eating disorders.
  • Those taking medication that requires food intake.
  • Individuals going through growth such as children and adolescents.
  • Individuals who are pregnant or breastfeeding.

Effects of Not Eating Enough

There are many side-effects that can arise when the body is not receiving enough food. When completing a fast, there are inevitably going to be sensations the body is not used to, but some may be symptomatic of something more serious.

  • Fatigue: If the number of calories the body is receiving is reduced, the amount of energy it produces will decline too.
  • Hair loss: A lack of food can mean a lack of necessary vitamins and nutrients, which can lead to the breakdown of proteins necessary for hair growth.
  • Recurring illness: Diet has a direct effect on the strength of the immune system, so frequent illness can be a sign of insufficient intake of food.


If any of these symptoms relate to your condition, fasting is not recommended. Should you have any concerns regarding your diet, contact your usual health care professional.

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