The longer you go without eating at night, the less weight you tend to carry — not because fasting burns fat magically, but because it naturally reduces total food intake.
Scientific Claim
Prolonged overnight fasting (>18 hours) is associated with lower body mass index due to reduced total daily caloric intake.
Original Statement
“They also found, believe it or not, that the longer the overnight fast, the less the BMI. doesn't mean that fasting is magic, but it does mean that maybe if they like fasted a little bit longer overnight, they ended up eating less or they had a longer fast, so they only ended up eating one or two meals because, hey, that's crazy. Maybe that's all they had time for, right?”
Context Details
Domain
nutrition
Population
human
Subject
prolonged overnight fasting (>18 hours)
Action
is associated with
Target
lower BMI
Intervention Details
Evidence from Studies
Supporting (3)
People who went without eating for 18+ hours overnight tended to lose weight or gain less weight over time, likely because they ate fewer calories overall.
People who went longer without eating at night were less likely to be overweight, even when researchers accounted for what they ate during the day — meaning long overnight fasts might help people stay lean.
Technical explanation
This paper directly links longer overnight fasting duration with reduced likelihood of overweight/obesity in older adults, and importantly, the association persisted even after adjusting for morning and evening food intake — suggesting the effect is not just due to reduced total calories, but the fasting itself may drive lower BMI, supporting the assertion.
This study found that people who fasted overnight for a long time (more than 18 hours) tended to have lower body weight, which supports the idea that long fasting helps people lose weight.
Technical explanation
This study directly examines prolonged overnight fasting (>18 hours) in a human population and reports a potential improvement in BMI, aligning with the assertion that such fasting reduces BMI via reduced caloric intake, even though caloric intake isn't directly measured, the BMI outcome and fasting duration match the assertion.
Contradicting (2)
Fasting during Ramadan didn’t make teens lose weight unless they also learned how to eat better — so fasting alone doesn’t seem to be enough to lose weight.
Technical explanation
While Ramadan fasting involves prolonged overnight fasting, the study shows weight loss only occurred when combined with nutrition education — suggesting fasting alone is insufficient to reduce BMI, contradicting the assertion that prolonged fasting alone lowers BMI via reduced intake.
People who ate more often and had shorter fasts at night actually had better diets and didn’t weigh more — so long overnight fasts don’t seem to help people lose weight.
Technical explanation
This study directly finds that shorter overnight fasting is associated with higher nutrient density and more regular eating patterns, and crucially, longer fasting was NOT associated with lower BMI — directly contradicting the assertion that prolonged overnight fasting reduces BMI via reduced caloric intake.