After two weeks of skipping meals intermittently, the body burns fewer calories at rest—which could make you gain weight if you keep eating the same amount.
Scientific Claim
Intermittent fasting for 2 weeks reduces resting energy expenditure in lean healthy adults, which may predispose to weight gain if caloric intake is not reduced.
Original Statement
“IF decreased resting energy expenditure. The decrease in resting energy expenditure after IF indicates the possibility of an increase in weight during IF when caloric intake is not adjusted.”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The abstract states 'IF decreased resting energy expenditure' as a direct effect, but without confirmed randomization or blinding, causation cannot be established. Only association is supported.
More Accurate Statement
“Intermittent fasting for 2 weeks was associated with a reduction in resting energy expenditure in lean healthy adults, which may suggest a potential risk for weight gain if caloric intake is not adjusted.”
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bCausal effect of intermittent fasting on resting energy expenditure in lean adults.
Causal effect of intermittent fasting on resting energy expenditure in lean adults.
What This Would Prove
Causal effect of intermittent fasting on resting energy expenditure in lean adults.
Ideal Study Design
A double-blind, randomized, crossover RCT with 40 lean healthy adults (BMI 18.5–24.9, age 20–40), each undergoing 2 weeks of intermittent fasting (16:8) and 2 weeks of standard diet in random order, with resting energy expenditure measured via whole-room indirect calorimetry under controlled conditions.
Limitation: Short-term design cannot determine if metabolic adaptation persists or reverses after longer exposure.
Systematic Review & Meta-AnalysisLevel 1aConsistency of resting energy expenditure reduction across intermittent fasting protocols and populations.
Consistency of resting energy expenditure reduction across intermittent fasting protocols and populations.
What This Would Prove
Consistency of resting energy expenditure reduction across intermittent fasting protocols and populations.
Ideal Study Design
A meta-analysis of 10+ RCTs comparing resting energy expenditure before and after ≥14 days of intermittent fasting (any protocol) vs. control diets in healthy adults, using standardized calorimetry methods and adjusting for body composition changes.
Limitation: Cannot isolate whether reduction is due to fasting itself or reduced caloric intake or muscle loss.
Prospective CohortLevel 2bLong-term association between intermittent fasting and changes in energy expenditure in free-living adults.
Long-term association between intermittent fasting and changes in energy expenditure in free-living adults.
What This Would Prove
Long-term association between intermittent fasting and changes in energy expenditure in free-living adults.
Ideal Study Design
A 6-month prospective cohort study of 200 healthy adults initiating intermittent fasting, measuring resting energy expenditure monthly via doubly labeled water, alongside dietary intake and body composition changes.
Limitation: Cannot control for confounding behaviors such as reduced physical activity or sleep changes.
Evidence from Studies
Supporting (1)
Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism.
The study found that people who ate only during certain hours for two weeks burned fewer calories at rest, which means they might gain weight if they don’t eat less — just like the claim says.