Skipping food two days a week (but not starving) for 3 months helps overweight people lose a bit of fat and weight, on average about 3.5% body fat and 2.8 kg.
Scientific Claim
In overweight or obese adults, intermittent fasting (two non-consecutive days of light fasting per week) for 12 weeks is associated with a mean reduction in body fat percentage of approximately 3.5% and body weight of 2.8 kg, indicating it may contribute to fat loss.
Original Statement
“Both the ketogenic diet group and the intermittent fasting group can effectively reduce the weight and body fat percentage of the subjects... the combined group showed a more significant decrease, reaching -4.7 ± 1.4kg and -6.3 ± 1.8%, respectively.”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The abstract and text imply causation ('effectively reduce'), but without blinding, causal inference is compromised. Only association can be claimed.
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.
Systematic Review & Meta-AnalysisLevel 1aWhether intermittent fasting (e.g., 5:2 or alternate-day) consistently reduces body fat compared to daily calorie restriction across diverse populations.
Whether intermittent fasting (e.g., 5:2 or alternate-day) consistently reduces body fat compared to daily calorie restriction across diverse populations.
What This Would Prove
Whether intermittent fasting (e.g., 5:2 or alternate-day) consistently reduces body fat compared to daily calorie restriction across diverse populations.
Ideal Study Design
A meta-analysis of 15+ RCTs (n≥1000 total) comparing 5:2 intermittent fasting (2 days ≤500 kcal) to daily 20–25% calorie restriction in overweight/obese adults (BMI 27–40), measuring body fat via DXA, weight, and metabolic health over 12–24 weeks.
Limitation: Cannot determine optimal fasting window or long-term adherence effects.
Randomized Controlled TrialLevel 1bCausal effect of 5:2 intermittent fasting on body fat reduction when compared to an isocaloric control diet.
Causal effect of 5:2 intermittent fasting on body fat reduction when compared to an isocaloric control diet.
What This Would Prove
Causal effect of 5:2 intermittent fasting on body fat reduction when compared to an isocaloric control diet.
Ideal Study Design
A double-blind, parallel-group RCT of 120 overweight/obese adults randomized to 5:2 intermittent fasting (two days ≤500 kcal, five days ad libitum) vs. daily 15% calorie restriction, with matched protein intake, DXA body composition measured at baseline and 12 weeks, and adherence tracked via app logs and biomarkers.
Limitation: Blinding participants to dietary intervention is inherently difficult, limiting internal validity.
Prospective Cohort StudyLevel 2bLong-term association between habitual intermittent fasting and body fat changes in free-living populations.
Long-term association between habitual intermittent fasting and body fat changes in free-living populations.
What This Would Prove
Long-term association between habitual intermittent fasting and body fat changes in free-living populations.
Ideal Study Design
A 3-year prospective cohort of 800 adults tracking fasting patterns (frequency, duration), body composition via bioimpedance, and lifestyle confounders via annual surveys.
Limitation: Cannot establish causation due to self-selection bias and unmeasured confounders.
Evidence from Studies
Supporting (1)
Study on the influence of ketogenic diet and intermittent fasting on the change of body fat rate
The study found that people who ate normally five days a week and ate very little on two other days lost about 5% body fat and 3.5 kg of weight — which is even more than the claim said. So yes, this kind of fasting helps overweight people lose fat.