Intermittent fasting does not work for everyone, study finds

Obesity is a global health problem. In 2016, an estimated 650 million people were obese, and that number is increasing. Lifestyle modification through reduced caloric intake and physical activity can help curb obesity.

One of the most popular alternative methods for weight loss today is intermittent fasting (IF), which restricts the time a person can eat to reduce caloric intake. The 5:2 diet is one of the most practiced intermittent fasting methods since it involves reducing the caloric intake for two days each week and unrestricted eating on the other five days.

Though intermittent fasting may be more comfortable than other restrictive diets practiced today, it has not worked for some people.

In a new study by researchers at the  School of Science and Technology at Nottingham Trent University and the National Centre for Sport and Exercise Medicine, School of Sport, Exercise and Health Sciences, Loughborough University, a team of researchers may have the answer to why this is so.

Intermittent fasting has gained immense popularity, particularly the 5:2 diet, because it allows you to eat for a period without restrictions. However, the researchers found that some people cheat on their intermittent fasting diet without knowing it. It explains why some people do not lose weight as well as others when doing IF.

A lifestyle, not a diet

Intermittent fasting is considered a way of life rather than a diet. Fasting has many benefits to health, aging, and illness.  It is not a diet but rather an eating pattern that is committed to the long term to reap the potential benefits.

Initially, people intermittently fasted for weight loss, but various studies have shown other health benefits. These include reducing the risk of diabetes because it lowers the blood sugar, reducing cell damage from inflammation and oxidation, lowering blood pressure, improving memory, and improving endurance when compared to a general calorie-restrictive diet.

The National Institute of Aging also revealed that intermittent fasting might help improve health conditions such as cardiovascular disease, diabetes, obesity, neurological disorders, and cancers.

Does not work for everyone

In the current study, which is published in the journal Appetite, the team wanted to know how eating and physical activity changed around a period of calorie restriction. The team conducted the study in over three days on a group of male participants. They completed two trials, on the first trial, they were asked to consume only about 700 calories the following day.

Throughout the rest of the day, the team monitored how much the participants consumed. Their hunger before and after each meal was also taken into consideration, including their physical activity throughout the day.

The following day, the participants consumed a very low-calorie diet, and their physical activity was noted. The team measured the food intake of the participants as well as their physical activity. The next day, the team measures the food intake of the participants during an unrestrictive breakfast.

Study findings

The team has found that the participants consumed 6 percent more on the first day, and 14 percent more at the unrestricted breakfast during the three-day trial. The findings show that the participants consumed more because they knew food would be restricted the following day, not because they felt hungrier.

Further, physical activity was about 11 percent lower the day before consuming the low-calorie diet and 18 percent lower on the low-calorie day.

The study also shows that spontaneous physical activities, such as household chores, were the most affected component of physical activity. Before, during, and after a low-calorie diet day, there were changes in eating and physical activity behavior among the participants.

For weight loss, calories burned should exceed calories consumed. This way, a calorie deficit will be attained. The team also found that eating a little more and decreasing spontaneous activity may be adequate to recover almost half of the calorie deficit.

“Our study highlights what and when compensatory behaviors occur. This information can be used to improve the effectiveness of intermittent fasting diets. Being more mindful when eating before and after a period of calorie restriction and incorporating exercise into diet plans, could help increase the likelihood of intermittent fasting leading to weight loss,” David Clayton, one of the study researchers said.

Journal reference:
Angela Betsaida B. Laguipo

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.


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  1. jaimie cole jaimie cole United States says:

    This study didn’t use the IF that most people are using where they eat daily normal caloric amounts just in a shorter window of time.  IF is most typically 16:8, 20:4, or 12:12 WITHOUT calorie restriction.  I don’t think
    this research was a good representation of IF.  Most people are going to binge & restrict energy if only given 700kcals...vs. 2000 needed to live & exercise.  Other researchers are finding great results & adherence in the typical daily IF regimen.

  2. JaymiLei JaymiLei United States says:

    This article does not clearly state what the study protocol was. It doesn't say what the hours were, or what type of restrictions were on each day. Also IF, if done properly, does not include binge eating during your eating window. You eat as if you were not fasting at all. Energy can be low for the first few days while the body adjusts, but it doesn't remain that way; therefore activity wouldn't consistently be decreased. There is no way a 3 day study could be an accurate reflection.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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