Research shows that intermittent fasting is safe and effective  

Krista Varady
Krista Varady, professor of kinesiology and Nutrition. Photo: Roberta Dupuis-Devlin

Intermittent fasting, an increasingly popular weight loss regime, is an effective and safe way to lose weight, according to a body of research from UIC’s Krista Varady

Varady, a professor of kinesiology and nutrition, has studied different versions of intermittent fasting, such as alternate-day fasting, where people alternate between eating up to 500 calories one day and then whatever they want the next, and time-restricted eating, where people only eat during a fixed window of time each day.  

Overall, her research has found that intermittent fasting is as good as calorie counting when it comes to weight loss, with people losing, on average, 3% to 8% of baseline weight, depending on the type of fast they’re doing. And fasting can provide other health benefits, such as decreasing blood pressure and insulin resistance.  

“People love intermittent fasting because it’s easy,” Varady said. “People need to find diets that they can stick to long term. It’s definitely effective for weight loss, and it’s gained popularity because there are no special foods or apps necessary.” 

Here are some highlights from the dozens of research papers she has published on the topic: 

A six-hour window of time-restricted eating cuts calories and leads to weight loss: The researchers followed people who restricted their eating to only four hours a day or to only six hours a day. After 10 weeks, participants in both groups cut daily calorie intake by about 550 calories and lost about 3% of their body weight. Compared with a control group that did not fast, both groups of fasters showed reduced insulin resistance and oxidative stress levels. There was no effect on blood pressure, cholesterol or triglycerides. There also was no significant difference in weight loss or cardiometabolic risk factors between the four-hour and six-hour diet groups. The study is published in Cell Metabolism

Time-restricted eating works as well as calorie-counting for weight loss: Study participants were asked to either eat only between noon and 8 p.m. each day or to reduce their calorie input by 25%. After 12 months, both groups lost, on average, roughly the same amount of weight, suggesting that the two weight-loss regimes are equally effective. The study is published in Annals of Internal Medicine.  

Time-restricted eating works for weight loss in obese individuals: A study of 23 obese volunteers examined what happened after 12 weeks when participants only ate between 10 a.m. and 6 p.m., though they could eat whatever they wanted during those hours. On average, participants consumed about 350 fewer calories, lost about 3% of their body weight and saw their systolic blood pressure decrease. The study is published in Nutrition and Healthy Aging

Intermittent fasting is safe, effective for those with Type 2 diabetes: Participants with Type 2 diabetes who ate only during an eight-hour window each day lost more weight over six months than participants who were instructed to reduce their calorie intake by 25%. Both groups had similar reductions in long-term blood sugar levels, as measured by a test of hemoglobin A1C, which shows blood sugar levels over the past three months. Additionally, participants in the time-restricted eating group had an easier time following the regime than those in the calorie-reducing group. The research is published in JAMA Network Open.

Insights into the impact of intermittent fasting on female reproductive hormones: Researchers followed a group of pre- and post-menopausal obese women on the “warrior diet,” which allows for a four-hour window of eating each day. They found that levels of several reproductive hormones were unchanged at the end of the eight-week study. However, dehydroepiandrosterone, a hormone that improves ovarian function and egg quality, was lower at the end of the eight weeks, though it was still within a normal range. The research is published in Obesity

Alternate-day fasting is a good option for those with fatty liver disease: A three-month study of 80 people with nonalcoholic fatty liver disease found that those who followed an alternate-day fasting diet and exercised improved their health. Participants saw increased insulin sensitivity and decreased liver fat, weight and alanine transaminase enzymes, which are markers for liver disease. Approximately 65% of obese adults have fatty liver disease, and the condition is strongly related to the development of insulin resistance and Type 2 diabetes. The study is published in Cell Metabolism

To stay up-to-date on the latest research on intermittent fasting, you can follow Varady on Instagram, where she posts regularly on the topic. 

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