Fasting Three Days a Week Boosts Weight Loss Success | Image Source: news.cuanschutz.edu
DENVER, Colorado, March 31, 2025 – In a new, innovative clinical trial, researchers at the University of Colorado have found that a simple intermittent fasting program – usually by eating four days a week and cutting calories the other three – can produce more lasting weight loss and health benefits than the long-standing daily method of reducing calories. The study, published in the Annals of Internal Medicine, draws attention in medical and fitness communities in order to reveal long-term weight management and behavioural adhesion.
To understand the meaning of this research, he helps to briefly explain what intermittent fasting is and why it has become such a hot topic. At its heart, the IMF is planning further periods of consumption and fasting to limit calorie intake and rapid metabolic changes. But unlike extreme diets, IMF protocols often focus on sustainable windows and strategic restrictions on calories. Over the years, many forms have emerged, including the popular 16:8 food model restricted by time and the 5:2 heat restriction plan. However, this latter test illuminates a less spoken but potentially more effective model: the fasting approach 4: 3.
What is the intermittent fasting plan 4: 3?
In short, IMF Plan 4 provides for three non-consecutive days per week of a significant calorie restriction – usually 400-700 calories depending on the size of the body – while allowing for unrestricted eating, but with health awareness within the other four days. Unlike the daily restriction of calories (DCR), which requires a constant reduction of 30-35% of daily intake, model 4: 3 offers a psychological and practical respirator of chronic restriction. According to Dr. Victoria Catenacci, Principal Investigator and Endocrinologist at the University of Colorado, this approach could be easier to follow in the long term.
“It was amazing and exciting for me to make it better,” Catenacci said. “It’s just another strategy to consider for people. »
In the 12-month study, 165 adults aged 18 to 60 years with overweight or obesity were assigned to 4.3 MFIs or a RCN regimen. Both groups received behavioural support, exercise advice and nutrition education. Both approaches created the same projected weekly calorie deficit (about 34%), but their actual results varied considerably.
What does the study on weight loss reveal?
The data speak of volumes. Intermittent fasting participants lost an average of 7.6% of their initial weight, or approximately 17 pounds, compared to 5% (approximately 11 pounds) in the DCR group. In addition, 58% of the IMF group reached a clinically significant 5% weight loss reference point, compared to 47% in the CRD cohort. These figures are particularly important because a 5% reduction in body weight is often linked to a marked improvement in blood pressure, blood glucose and cholesterol levels.
“This style of intermittent fasting seems easier to respect over time,” Dr. Catenacci told ABC News. “It is very difficult to limit calories every day.”
Beyond the weight scale, the fasting group also exceeded cardiometabolic markers. According to Dr. Danielle Ostendorf, co-author and assistant professor at the University of Tennessee, participants following Appendix 4: 3 saw more favourable changes in systolic blood pressure, total cholesterol, fasting glucose and haemoglobin A1C.
Why is membership so crucial in weight loss?
Membership – simply clinging to a plan - is probably the most critical factor in the success of long-term weight loss. According to Ostendorf, the flexibility and simplicity of the IMF 4: 3 routine can explain why it has been more effective in real world configuration. Using the dual label water method (DLW) to objectively measure energy metabolism, researchers confirmed that the IMF group is more closely respecting the prescribed calorie limits than the RCD group.
The drop-out rates reinforced this trend: only 19% of IMF Group 4 participants declined during the year, compared with 30% in the DCR group. In a saturated world with overly ambitious diet plans, this is a significant difference. The doctor. Amy Rothberg, Director of Weight Management at the University of Michigan, echoed this sentiment:
“If you do not want to count calories, intermittent fasting can be beneficial for some people. This really is what someone can do in a coherent way. “
How have calorie limits been customized?
To determine calorie targets, researchers measured the rest energy expenditures of each participant to estimate their daily calorie needs for weight maintenance. As a result, RCD participants usually consume between 1,300 and 1,800 calories per day for women and between 1,500 and 2,000 calories for men. In contrast, at the time of fasting, 4 : 3 IMF participants were limited to 400-600 calories (women) and 500-700 calories (men).
Participants also received tools and education to help track their consumption, as well as detailed macroutrient guidelines: 55% carbohydrates, 15% protein, 30% fat. This level of customization was essential to ensure safety and effectiveness, particularly in an annual study of this scale.
What behavioural support was offered?
Weight loss does not occur in the vacuum, requires responsibility, education and support. Therefore, the study incorporated a behavioural intervention model aligned with the national guidelines for the treatment of obesity. Participants met weekly with registered dietitians during the first three months and then fifteen days for the rest of the year. They also had access to gymnastics facilities and were encouraged to exercise 300 minutes a week, further improving the holistic design of the program.
According to Ostendorf, this structure played an important role in the success of the participants:
“This program really provided social responsibility and support. They could have learned from each other
What are the consequences of 4: 3 fasting health?
Although the study was not prompted to make conclusive statements on secondary outcomes such as blood glucose regulation or microbial changes, early evidence suggests that the IMF can offer benefits beyond weight control. Researchers collected stool and blood samples to examine possible changes in hunger hormones and intestinal bacteria, from which they could shed light on the physiological mechanisms behind the IMF’s success.
In addition, Catenacci and Ostendorf are considering exploring how approach 4: 3 could be integrated into clinical and community programs. Currently, there is no specific structured program adapted to Model 4: 3, but the results of this test could catalyze new models of intervention based on both evidence and evolutionary evidence.
What should people consider before starting?
Although the results are promising, experts warn that intermittent fasting is not for all. Individuals with underlying medical conditions, such as diabetes, or those requiring regular meals, should consult with medical care providers before making dietary changes. As the doctor pointed out, Alice Gao of Temple Northwest Community Family Medicine, a personalized topic approaches:
“There is no higher food approach. So you need to find one that fits your lifestyle and health needs
However, for individuals who struggle daily against the detection of calories or feel overwhelmed by complex diets, IMF strategy 4: 3 can offer a liberating alternative. By minimizing daily restrictions and providing normal feeding days, it addresses physiological and psychological barriers to sustainable food.
And that’s the problem. Diets should not be perceived as punishment. They should feel feasible. As Catenacci said, the best diet is always the one you can hold. And for many, it could be three days a week.
