Largest Intermittent Fasting Study to Date Shows Fasting Works For Weight Loss

Illustrations by Kayla O’neal

LifeOmic conducted the largest intermittent fasting study to date, reporting higher weight loss in users of their mobile apps who were overweight or obese and in those who fasted longer or more frequently.

The study, published in JMIR mHealth and uHealth, examined the fasting behaviors of almost 800,000 users of LIFE Fasting Tracker and LIFE Extend, collectively known as LIFE Apps, including over 160,000 people who tracked their weight for up to a year. The work was a collaboration between scientists at Indiana University School of Medicine and LifeOmic. 

“Studies of intermittent fasting to date have been done in small populations and following strict protocols that don’t reflect the many fasting schedules that people normally follow,” said Dr. Benjamin Salisbury, scientific director at LifeOmic in a press release. “We’re proud of our research with renowned scientists at Indiana University School of Medicine, which looks at intermittent fasting behavior in the real world. Our results solidify the positive therapeutic effects intermittent fasting can have on metabolic diseases such as obesity.” 

Intermittent fasting is avoiding calories for a period of time, but fasting periods and methods can vary. The study focused on determining how many hours users were fasting, when the fasting was taking place, the weight loss experienced and how well LIFE Apps users were sticking to the apps to record their fasts.“We are excited that our two-year study found that intermittent fasting with a dedicated mobile app can be an effective and sustainable approach to weight loss and maintenance for some adults,” said Dr. Joy Lee, assistant professor of medicine at Indiana University School of Medicine, in the press release. All data included in the study was self-reported by app users. 

User characteristics 

About 81% of users identified as female, and most were located in the United States. However, 200 countries were represented in the study. Users ranged in age from 18 to 100 years old.

When users were voluntarily surveyed upon downloading the app, 77.3% indicated that they wanted to lose weight. In fact, ~50% of total users were obese and ~30% were overweight based on their body mass index calculated from their starting weight and height. 

Fasting patterns in LIFE Apps users

The most common fasting length was 16 hours, although there was considerable variation. About 25% of users fasted 6 to 7 times per week. About 8% of users typically practiced multi-day fasting. 

The most common days to start a fast were Sunday, Monday and Tuesday. Friday and Saturday were the least popular days for users to fast. The most common time to start a fast was 7pm, and noon was the most common time to end a fast. 

Those most likely to stick with fasting long-term were older, exercised regularly, did not smoke and had low stress

Older users and those who reported daily exercise in the initial survey were likely to use LIFE Apps to record their fasts for more weeks and months compared to younger users and those who led a sedentary lifestyle. 

Those who reported more stress or daily smoking were less likely to adhere to fasting within the apps compared with those who had no stress and never smoked. 

Overweight and obese users lost the most weight and kept it off

“We found that users who had the highest BMI at the beginning of the study lost the most weight, both in pounds and as a percentage of their starting weight, ” said Dr. Luisa Torres, science communications manager at LifeOmic and one of the study authors. Of the users who were categorized as overweight or obese at the start of the study, 67% lost at least 5% of their starting weight in the first 6 months. In the same period, 39% lost at least 10% of their starting weight. 

Studies in people with obesity demonstrate that losing 10% of your body weight is enough to improve blood pressure and normalize cholesterol blood levels, while losing just 5% is enough to improve glycemic control. This is central to prevention and management of chronic diseases such as diabetes.

Overweight users sustained most of their weight loss for at least a year, and obese users trended toward even more weight loss 12 months into the study. 

The weight loss observed is likely due in large part to the reduced calorie intake that spontaneously occurs with intermittent fasting. Studies show that fasting reduces calorie intake by 10-30%, leading to 3-9% weight loss in 12 months. Intermittent fasting can also induce a metabolic switch— the ~12-hour point into a fast during which the body switches from burning sugar to burning fat. This metabolic switch is associated with low insulin, weight loss and improvements in body composition..

Users who fasted longer or more frequently lost the most weight

Daily 16-hour fasts for 6 months yielded 6% weight loss on average. But fasting longer helped people lose even more. For every hour of fasting per day beyond 12 hours, users lost over 1% more of their weight by 6 months.

The effect of higher weight loss with longer fasting hours was more pronounced in users whose BMI classified them as overweight or obese. In 6 months, users classified as obese lost an average of 18 lbs with 16 hour fasts, while those fasting daily for 18 hours lost an average of 25 lbs. Fasting longer led to more weight loss, particularly in obese users. Those who did 20-hour fasts lost an average of 31 lbs in 6 months, while those restricting their eating to 2 hours (i.e. OMAD – one meal a day) lost an average of 45 lbs.

Users who started off as underweight gained weight over time 

This study included users who were underweight or at a healthy weight, unlike most other studies. Users who started at a healthy weight did not lose much weight. Underweight users did not see a weight change at 3 months of the study, and actually gained weight by month 6. These results indicate that intermittent fasting is safe even for underweight users because even those who fasted extensively tended to lose little weight.

Future research

Future studies could attempt to determine whether intermittent fasting is associated with improvements in diet or in the amount of physical activity.

Additionally, future studies could capture data on calorie intake and the energy expenditure of users. Although reduced calorie intake has been shown to spontaneously occur with intermittent fasting, more closely tracking diet and exercise habits of users could offer more insight into the connection between intermittent fasting, energy balance and weight loss. 

“These real-world studies are important for understanding the effects of practices like IF on a large population,” said Dr. Lee in the press release. “We look forward to uncovering other impactful data in future collaborative research with LifeOmic.”

Most people can benefit from practicing moderate fasting. However, pregnant or lactating women, children, individuals with type-1 diabetes, individuals who are malnourished, and those who have struggled with eating disorders should not fast for weight loss. Our apps are intended for those 16 and older.