Intermittent fasting has once again made headlines thanks to the latest work from a research group at the University of Granada. Two studies published in high-impact journals, Nature Medicine and Clinical Nutrition , have analyzed the 16:8 protocol in depth. This protocol involves consuming all meals within an eight-hour window and fasting for the remaining sixteen hours. The results not only confirm that this practice is safe and effective for weight loss, but also demonstrate for the first time that its effects last for up to twelve months after the intervention ends.
The research, conducted with hundreds of overweight or obese adults from Granada and Pamplona, was led by Doctors Manuel Dote Montero and Alba Camacho Cardeñosa. Both agree that the key lies not so much in when one eats, but in reducing the hours available for consuming food , which leads to a natural decrease in calorie intake. However, they caution that fasting is not a magic bullet and should be combined with a balanced diet and professional supervision for individuals with pre-existing health conditions.
Conclusive results from the Granada investigation
The first study, published in Nature Medicine , included 197 participants divided into four groups. While the control group lost around two kilograms following only nutritional education, the three groups that practiced the 16:8 fasting method achieved an average weight loss of nearly five kilograms. This additional three-kilogram difference was maintained regardless of whether the eating window was early (9:00 a.m. to 17:00 p.m.), late (14:00 p.m. to 22:00 p.m.), or freely chosen by the participant . Furthermore, the team observed that early fasting was associated with better blood glucose regulation throughout the 24-hour period and a greater reduction in abdominal subcutaneous fat.
The second study, published in Clinical Nutrition , went further by evaluating weight maintenance one year later. With 99 adults (half women, mean age 49 years, and body mass index of 32 kg/m²), the researchers repeated the same four-group design but added a twelve-month follow-up after the initial twelve-week intervention. The results showed that those who practiced fasting maintained significantly greater weight loss than the control group : an additional 2,6 kg in the case of early fasting and 2,4 kg in the case of late fasting. Overall, the time restriction resulted in a reduction of 2,2 kg of weight, 3 cm of waist circumference, and 1,3 kg of fat mass compared to the control group.
Flexible hours and metabolic benefits
One of the most practical conclusions of both studies is that it's not necessary to impose a single fasting window on everyone . Both early and late fasting proved equally effective for weight loss, allowing each person to adapt their intermittent fasting schedule to their lifestyle, work schedule, or personal preferences. However, the Nature Medicine study found that the early fasting window group experienced a smaller reduction in blood glucose levels overnight and throughout the day, a finding relevant for people at risk of diabetes.
Regarding body composition, both regimens resulted in sustained reductions in fat-free mass (primarily muscle), so the researchers recommend combining intermittent fasting with strength training and adequate protein intake to minimize muscle loss. Dr. Alba Camacho, first author of the Clinical Nutrition study , emphasizes that “until now we didn't know if the effects of fasting were sustained over time; by evaluating the participants twelve months later, we demonstrated that the changes in body weight persist.”
A habit that endures over time
The finding that has most caught the attention of experts is the spontaneous adherence to fasting after the intervention ended. Nearly 26% of participants reported maintaining the time restriction during the year of follow-up , despite not receiving instructions to continue. “One in three people decided to continue practicing intermittent fasting on their own, suggesting that it is a relatively easy habit to integrate into daily life,” the authors point out. Adherence during the twelve weeks of the intervention was very high: over 95% in the early and late fasting groups, and 92,9% in the self-selected group.
The researchers also observed that most of the weight loss occurred in the first six weeks, with a slower and more steady decline thereafter. At twelve months, approximately half of the weight loss achieved in the initial three months was retained. While this figure falls short of the clinical standard of 5% sustained body weight loss, the authors consider it to represent a rare sustained improvement compared to the typical rebound effect of conventional diets . Even modest weight loss can lead to long-term cardiac and metabolic benefits.
Both studies were made possible through the collaboration of the Granada Institute for Biomedical Research (ibs.GRANADA), the Public University of Navarre, the Biomedical Research Networking Center (CIBER), and several Andalusian hospitals. Manuel Dote Montero's work was recently recognized with one of the Pfizer Foundation's Scientific Innovation Awards for Young Researchers. This Spanish research demonstrates once again that intermittent fasting, when properly implemented and supervised, can be an effective and sustainable tool in the fight against obesity, provided it is integrated into a healthy lifestyle that includes physical activity and a varied diet.
