Millions of people who fast to lose weight believe that the timing of meals plays a crucial role. However, a new clinical trial involving participants over a 12-week period suggests otherwise. Restricting food intake to a 10-hour window offered no clear advantage over spreading meals across a 16-hour period when total caloric intake was matched between the two groups. Both groups lost roughly the same amount of weight—about 2.7%—and by the end of the study, levels of hunger hormones and inflammatory markers were virtually identical.
The study, published in the journal Obesity, monitored adults with obesity and either prediabetes or diet-controlled type 2 diabetes over 12 weeks. Meals were specially prepared for the participants, allowing researchers to compare the two eating regimens while strictly controlling total calorie intake and overall diet. Such a tightly controlled setting is rare in nutrition research, where most studies rely on self-reported dietary habits, which can be unreliable.
Time-restricted eating—often referred to as intermittent fasting—has gained a reputation as being more than just a weight-loss method. Proponents and some earlier studies suggested it could reduce inflammation and suppress hunger hormones, offering benefits beyond those achieved by simple calorie reduction. This study—one of the few to directly test this hypothesis while controlling for calorie intake—found insufficient evidence to support those claims.
Researchers from Johns Hopkins University recruited adults with obesity who also had prediabetes or diabetes managed solely through diet. Thirty-nine individuals, with an average age of 60, participated in the portion of the study analyzed here. The majority of the group (92%) were women, and 92% were Black—a demographic often overlooked in previous studies on this type of eating pattern.
Participants were randomly assigned to one of two groups. One group consumed all their food within a 10-hour window early in the day, starting breakfast between 8:00 and 10:00 a.m. and finishing dinner by early evening. The other group followed a more traditional 16-hour eating schedule, with dinner permitted up until 8:00 p.m. Both groups consumed the same number of calories and the same mix of protein, carbohydrates, and fats. All meals were prepared by research dietitians in a research kitchen, eliminating any guesswork regarding portion sizes or ingredients. Participants in both groups adhered to their assigned eating windows on the vast majority of days.
Each participant completed a standard questionnaire measuring three parameters: conscious control over eating, susceptibility to loss of control over eating, and general feelings of hunger. Blood samples were collected before and after the 12-week period to assess levels of hormones related to appetite and satiety, as well as markers associated with inflammation and metabolic stress.
Both groups lost a similar, moderate amount of weight—approximately 2.5–2.7% of their body weight—with no significant difference between them. Restricting the eating window did not result in additional weight loss once calorie intake was controlled.
From a psychological perspective, eating behaviors improved across the entire group. Participants reported exercising greater conscious control over their eating and losing control less frequently after they began eating. Hunger levels also decreased, though the reduction was so slight that it could have been due to chance. Researchers had expected that eating earlier in the day might specifically dampen hunger signals, given that appetite hormones naturally rise and fall in sync with the body’s internal biological clock. Instead, neither eating schedule proved more effective than the other.
There was one notable feature. While the general improvements appeared similar across the groups, individual results varied widely—particularly in the early-eating group. Some individuals in this group experienced a significant reduction in episodes of seemingly uncontrollable overeating, whereas others saw negligible changes or even slight worsening. This variability was greater than in the group following a standard eating schedule, suggesting that some people may respond much better than others to a restricted eating window, although the study could not pinpoint exactly who or why.
Regarding the biological mechanisms of hunger …the overall picture remained stable. Fasting levels of the appetite-stimulating hormone did not change significantly in either group, nor did the hormonal response to the sugary drink used for blood glucose testing. Levels of the hormone associated with satiety decreased in both groups, but this decline correlated with weight loss rather than the specific dietary regimen followed. Markers of inflammation remained virtually unchanged in both groups.
One detail stands out in the discussion: the food provided to both groups during the experiment was likely healthier than what the participants typically ate at home, as it was prepared according to a tailored meal plan rather than left to individual choice. This shift alone—moving from typical eating habits to a structured menu designed by a nutritionist—could explain why both groups developed a healthier relationship with food, regardless of when they ate.
This distinction is worth noting for anyone considering time-restricted eating as a health strategy. The takeaway from this study is not that meal timing is irrelevant, but rather that when food quality and caloric intake are already optimized, narrowing the eating window does not appear to offer additional benefits for appetite control or inflammation—at least not in this group of older adults with prediabetes and obesity. Enthusiasm for intermittent fasting has often been based on the assumption that the timing of meals itself confers a unique metabolic advantage. In this strictly controlled study, however, timing yielded no clear additional benefit when caloric intake and diet composition remained essentially the same.
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