Is fasting safe for weight loss and health?

Everybody wants to be healthy, beautiful and live as long as possible, right? The problem nowadays is that there’s so much information about it and it’s too hard to figure out what really works.

That’s where scientific research comes in because it’s specifically designed to find out the answers to these questions in a controlled environment.

So, is fasting safe for weight loss and health based on scientific research? We’ll find out the answer in this article.

What is intermittent fasting

Intermittent fasting (IF) is an eating pattern during which you periodically switch between periods of time when you consume foods and when you do not consume foods (fast) or when you consume significantly less calories compared to your regular diet (up to 500 kCal). There are different types of fasting which require different periods of time for eating and fasting. Usually fasting periods last 12-48 hours.

Is fasting for weight loss safe and effective

Meta-analysis of 11 studies found that IF was more effective than CCR for weight loss; however, there was no difference in BMI improvement. Although the data are insufficient, our study shows that IF is superior to CCR in metabolism in obese people. [1]

A systematic review of 27 clinical trials says that intermittent fasting shows the potential for the treatment of obesity but the evidence is not strong yet and it’s unknown what impact fasting has on our health in the long-term. [2]

Meta-analysis of 11 randomized controlled trials (RCTs) with duration range of 8–24 weeks shows that in overweight/obese adults, intermittent energy restriction (IER) is as effective as continuous energy restriction (CER) for promoting weight loss and metabolic improvements in the short term. [3]

A Systematic Review of Randomized Clinical Trials says that both intermittent fasting (IF) and short-term calorie-restricted diets produce similar weight loss in people with obesity and people with type 2 diabetes. [4]

One study shows that people may lose more body weight during starvation (fasting) or a keto diet compared to a mixed diet but less body fat. Composition of weight lost (percentage) during the ketogenic diet was water 61.2, fat 35.0, protein 3.8. During the mixed diet, composition of loss was water 37.1, fat 59.5, protein 3.4. During starvation composition (percentage) was water 60.9, fat 32.4, protein 6.7. [5]

Is fasting safe for health

A review of charts from 768 visits of patients who water-only fasted at TNHC from 2007 to 2011 for at least 2 consecutive days followed by a refeeding period equal to half of the fast length suggests that the protocol used in this study can be safely implemented in a medical setting with minimal risk of a serious adverse event (SAE). The median fasting length was 7 days; the shortest fast was 2 days and longest fast was 41 days. [6]

A severe but not life threatening adverse event (grade 3) was the highest grade in 27.6% of visits, and a life threatening AE (grade 4) was the highest grade in 1 visit. There were 2 (0.002%) visits with a serious adverse event (SAE). Adverse events (AEs) that were commonly experienced during visits, including nausea, headache, insomnia, back pain, dyspepsia, and fatigue, were predominately mild, grade 1 events and are reactions that are known to occur during fasting. [6]

A Randomized Clinical Trial showed that alternate-day fasting (25% of energy needs on fast days; 125% of energy needs on alternating “feast days”) did not produce superior adherence, weight loss, weight maintenance, or cardioprotection vs daily calorie restriction. Moreover, mean low-density lipoprotein cholesterol levels were significantly elevated by month 12 among the participants in the alternate-day fasting group compared with those in the daily calorie restriction group. [7]

Considering that other studies show that LDL cholesterol causes cardiovascular disease [8] it’s better to avoid alternate-day fasting or at least consult with your medical advisor before making any changes to your diet including fasting.

Meta-analysis of 18 studies says that the effects of intermittent fasting (IF) on clinical events such as mortality, myocardial infarction and heart failure are uncertain due to lack of data for these outcomes. The individual meta‐analyses show that intermittent fasting may be effective in reducing weight when compared to ad libitum feeding and may be as effective as continuous energy restriction (CER). Despite this, these changes appear to be clinically insignificant at short‐term follow‐up. [9]

Also, it’s mentioned that there was no significant clinical difference between IF and CER in improving cardiometabolic risk factors to reduce the risk of CVD. [9]

A Systematic Review of Randomized Clinical Trials shows that time-restricted feeding (TRF), which is a new form of IF that improves cardiometabolic health, might slow tumor progression, delay aging, and increase life expectancy in rodents. Pilot studies in humans similarly suggest that TRF improves clinical outcomes, such as body weight, blood pressure, and insulin sensitivity. [4]

Is fasting for everybody?

No, fasting is not recommended for the categories of people mentioned below [10]:

  1. Pregnant or breastfeeding women
  2. Elderly people over 75 years old
  3. People who have active infection, risk of repetitive infection, fever, cough, diarrhea, or persistent immune depletion
  4. People who have diabetes.


So, is fasting safe for weight loss and our health based on scientific research?

First, many studies say that there’s lack of data to make certain conclusions.

Second, the majority of studies show that fasting may be effective for weight loss and safe for our health but it may depend on the type of fasting.

For example, one study showed that alternate-day fasting significantly elevated the cholesterol levels while not producing greater weight loss compared to daily calorie restriction. You should take it into consideration because other studies show that cholesterol causes cardiovascular disease.

P.S. If you want to find out how science-based nutrition and diet can prevent the most common diseases, improve your overall health and help you live longer then you can click here to learn more.

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