A new study published Monday in the Annals of Internal Medicine has reignited the debate over intermittent fasting versus daily calorie restriction for weight loss, and the results may surprise some.
Researchers found that participants following a 4:3 intermittent fasting plan lost more weight over the course of a year than those who simply reduced their daily caloric intake, even though both groups were intended to have similar calorie deficits.
How the Study Was Conducted
The randomized study involved 125 adults aged 18 to 60 with body mass indexes (BMIs) ranging from 27 (overweight) to 46 (morbidly obese).
Participants were assigned to one of two groups: the first followed a standard daily calorie restriction diet, and the second followed a 4:3 intermittent fasting plan.
That plan included four unrestricted eating days and three nonconsecutive fasting days per week, where calorie intake was cut by about 80%.
Participants in both groups were encouraged to exercise for at least 300 minutes per week and were provided free gym memberships.
They also received behavioral support, including nutrition education, calorie-counting guidance, and help in tracking macronutrients. The goal was to ensure that both groups experienced similar levels of calorie deficit; But the real-world results told a different story.
Fasting Group Lost More Weight
After 12 months, the intermittent fasting group lost significantly more weight. According to the study, those in the fasting group saw an average body weight reduction of 7.6%, compared to 5% in the calorie-restriction group.
Furthermore, 58% of participants in the fasting group achieved at least 5% weight loss, while only 47% in the calorie-counting group did the same.
Interestingly, despite the planned equivalence in calorie deficit, the fasting group ended up eating fewer calories overall.
This unintentional reduction in energy intake may be one reason why intermittent fasting produced better results.
Why Fasting Might Work Better
There are differing theories as to why intermittent fasting can be more effective. Nutritionist and dietitian Carrie Glassman told CBS Mornings that many experts believe the success of fasting is largely due to its simplicity—it makes it easier to restrict calories without counting them daily.
Others argue that fasting triggers biological processes that promote fat burning and other metabolic advantages. These may include improved insulin sensitivity, enhanced fat oxidation, and better hormonal regulation.
However, Glassman emphasized that exercise remains a critical component.
“Not just for weight loss, but actually to help maintain weight loss, exercise is always important,” she noted.
Not a One-Size-Fits-All Solution
Despite its success in the study, intermittent fasting is not for everyone. Glassman cautioned that individuals with Type 1 diabetes, a history of eating disorders, or those taking certain medications should avoid fasting regimens. It is also not appropriate for children or pregnant women.
The study’s authors noted that while intermittent fasting may be attractive for those who prefer not to count calories daily, individual results varied significantly.
They called for future research to help identify biological and behavioral predictors that could guide personalized diet plans.
Implications for Dieters
The results of this study provide compelling evidence that intermittent fasting, specifically the 4:3 method, may offer a more effective and sustainable path to weight loss for some individuals. It may also offer a simpler alternative for those who find daily calorie tracking burdensome.
Still, researchers and nutritionists alike agree: no diet plan is universally effective.
Personal preference, lifestyle, medical history, and long-term sustainability must all be considered when choosing a weight loss strategy.
With information from CBS News
