For years, daily calorie restriction has served as the standard method for achieving weight loss. But a recent study conducted at the CU Anschutz Health and Wellness Center (AHWC) suggests that intermittent fasting, specifically the 4:3 approach, in which participants restrict calories by 80% on three non-consecutive weekdays and eat normally on the other four days each week, may offer a sustainable alternative for some individuals.
A year-long trial, recently published in Annals of Internal Medicine and led by Dr. Vicki Catenacci, found that participants following a 4:3 intermittent fasting (4:3 IMF) regimen lost more weight than those following traditional daily caloric restriction (DCR). The study randomized participants into a structured 12-month behavioral weight loss program, directly comparing traditional DCR with 4:3 IMF. Importantly, both groups were prescribed the same weekly calorie deficit (-34.3%). A subsequent secondary analysis, led by an AHWC doctoral student, Matthew Breit, and published in Nutrients, examined how the two approached affected eating behaviors and appetite hormones.
The findings showed that intermittent fasting can be equally or even more effective than daily restriction for some individuals. Participants following the 4:3 IMF plan also reported meaningful psychological benefits, including reductions in binge and uncontrolled eating behaviors. In contrast, those in the DCR group experienced increases in these behaviors, underscoring the difference between flexible and rigid approaches to dieting.
“These behavioral differences point to the benefits of flexibility in eating patterns,” Breit explains. “Reductions in uncontrolled and binge eating behaviors, paired with increases in cognitive restraint in 4:3 IMF, suggest a more flexible style of eating control—less strict and more adaptable—which is associated with lower energy intake, greater weight loss, and improved long-term weight maintenance.”
Breit notes that these outcomes reflect an important principle: flexibility matters. “No single diet works for everyone; rather, the degree to which someone can adhere to a dietary approach is the key determinant of long-term success,” he says. He explains that while daily restriction remains the standard of care for obesity, “its effectiveness is limited by metabolic adaptation and compensatory mechanisms, such as decreased energy expenditure and increased appetite, which favor weight regain.”
The study also highlighted the critical role of behavioral and environmental support. Fasting appetite hormones did not differ between groups, suggesting that behavioral and psychological factors played a major role. “While we cannot draw strong conclusions about acute hormonal responses, the behavioral data suggest that improvements in eating patterns and mindset, particularly more flexible control of eating, likely played an important role in the effectiveness of 4:3 IMF,” Breit says.
The group-based behavioral program was another key to success. Participants benefited from structure, accountability, and strategies for navigating daily life challenges, support that is difficult to replicate when attempting fasting alone. “The behavioral support likely helped participants sustain the 4:3 IMF eating pattern, apply it flexibly in daily life, and avoid some of the pitfalls of rigid dieting,” Breit explains.
Although the study included exercise targets, prior research suggests that pairing intermittent fasting with physical activity may enhance benefits, including improved eating behaviors and reduced appetite. Breit also notes that the flexibility of 4:3 IMF can be particularly appealing for people with busy or unpredictable schedules. “For people with unpredictable schedules or busy lifestyles, 4:3 IMF may provide a structured, yet adaptable, approach to managing eating while in a calorie deficit,” he says.
The CU Anschutz Health and Wellness Center provides a uniquely integrated environment for this type of research, combining clinical care, fitness, nutrition, behavioral support, and academic expertise under one roof. With NIH- and industry-funded trials underway, Breit is optimistic about the role AHWC will continue to play in advancing the science of weight management.
Looking ahead, Breit hopes this research will expand the strategies available for sustainable weight management. By studying how intermittent fasting interacts with behavioral and psychological factors, the team aims to identify factors that support adherence, flexibility, and long-term success. Breit adds, “Ultimately, we aim to provide evidence-based tools that help individuals manage their weight more effectively, reduce the burden of obesity, and inform personalized approaches in nutrition and behavioral weight management.”