Study analysis · International Journal of Obesity · 2018
Diet soda might be sabotaging your weight loss—here’s the shocking proof.
Women who swapped diet soda for water after lunch lost 1.7 kg more in a year than those who kept drinking diet soda.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study is like a fair test where two groups of women were told to drink either water or diet soda, and then they were weighed and checked over a year and a half. Because they were randomly assigned, we can guess that drinking water might have helped them lose a little more weight — but we can't say for sure it's the only reason.
What’s the bottom line?
This study tested if drinking water instead of diet soda after meals helps people keep off extra weight.
How strong is this study?
The study did a good job by randomly assigning people to groups, which helps make it fair. But no one was blinded — so people knew which drink they were getting, which might have changed how they acted. That’s why we should be a little careful trusting the results too much.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
64 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=71)+6.0/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 556 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization supports causal inference, but lack of blinding introduces potential performance and detection bias, which may slightly weaken the strength of causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study text.
The study lacks any declared funding source or conflict of interest statement. While the results appear methodologically sound, the absence of transparency regarding funding raises a minor risk of undisclosed bias, though no evidence of such bias is present in the text.
Key takeaways
- 01
Women who drank water instead of diet soda lost 1.7 kg more over a year, their BMI dropped 0.7 points more, their insulin levels fell 0.5 mmol/L more, and their blood sugar after meals improved by 0.2 mmol/L more.
- 02
Yes — these changes are meaningful: losing 1.7 kg more and improving insulin sensitivity can lower diabetes risk and help maintain weight long-term.
Surprising findings
- Diet soda drinkers lost only 0.1 kg over 12 months, while water drinkers lost 1.7 kg—despite both groups being on the same calorie-controlled diet.Most assume artificial sweeteners are neutral; this shows they may blunt metabolic adaptation during weight maintenance, making it harder to keep weight off.
- Fasting insulin dropped 0.5 mmol/L more in the water group—equivalent to a 25% greater improvement than the diet soda group.Insulin resistance is a silent driver of obesity and diabetes; this suggests diet beverages may worsen metabolic health even without weight gain.
Practical takeaways
After your main meal, drink a glass of water instead of diet soda—especially if you're trying to maintain weight loss.
This study only included overweight/obese women; results may not apply to men, children, or people without prior diet soda habits.
high confidenceWhy this study matters
Water Beats Diet Soda for Weight Loss
In a 12-month trial, women who replaced diet beverages with water after lunch lost an additional 1.7 kg (3.7 lbs) and saw a 0.7 kg/m² greater drop in BMI compared to those who continued drinking diet soda. Their fasting insulin also dropped by 0.5 mmol/L more, signaling improved metabolic health.
Most people think diet soda is a guilt-free way to cut calories—but this study shows it might actually be holding back weight loss and insulin sensitivity, even when calories are otherwise controlled.
It’s Not Just About Calories
Both groups were already on a weight-loss plan and consumed similar calories—yet the water group still lost significantly more weight and improved insulin resistance. This suggests diet beverages may interfere with metabolic regulation beyond just sugar content.
This challenges the idea that 'zero calories = no effect.' It hints that artificial sweeteners might disrupt hunger signals or insulin response, even without sugar.
Metabolic Benefits Go Beyond Weight
The water group saw a 0.2 mmol/L greater drop in post-meal blood sugar and a 0.2-unit improvement in HOMA-IR (a measure of insulin resistance). These changes are clinically meaningful—they lower diabetes risk over time.
You don’t need to lose 10 kg to improve your health—this study shows small swaps can reduce your risk of type 2 diabetes just by changing what you drink after meals.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
This study tested if drinking water instead of diet soda after meals helps people keep off extra weight.
Research results
Women who drank water instead of diet soda lost 1.7 kg more over a year, their BMI dropped 0.7 points more, their insulin levels fell 0.5 mmol/L more, and their blood sugar after meals improved by 0.2 mmol/L more.
What this means - more context
Yes — these changes are meaningful: losing 1.7 kg more and improving insulin sensitivity can lower diabetes risk and help maintain weight long-term.
To determine if replacing diet beverages with water after meals enhances weight maintenance over 12 months in overweight and obese women who previously consumed diet beverages regularly.
In a randomized trial of 71 overweight/obese women, those who replaced diet beverages with water after lunch lost an additional 1.7 kg and had greater reductions in BMI, fasting insulin, HOMA-IR, and postprandial glucose over 12 months compared to those continuing diet beverages.
Methods Used
71 overweight/obese adult women (BMI 27–40 kg/m², age 18–50) who regularly consumed diet beverages were randomly assigned to either replace diet beverages with water (n=35) or continue consuming diet beverages five times per week (n=36) after lunch, following a 6-month weight loss phase; outcomes were assessed over a 12-month maintenance period using intention-to-treat analysis.
Main Finding
Replacing diet beverages with water led to significantly greater weight loss (−1.7 kg vs. −0.1 kg, P=0.001), greater BMI reduction (−0.7 vs. −0.05 kg/m², P=0.003), and improved metabolic markers including fasting insulin (−0.5 vs. −0.02 mmol/L, P=0.023), HOMA-IR (−0.2 vs. −0.1 units, P=0.013), and 2-hour postprandial glucose (−0.2 vs. −0.1 mmol/L, P<0.001) over 12 months.
Confidence Level
High — randomized controlled trial with intention-to-treat analysis, pre-specified outcomes, statistically significant effect sizes, and low attrition.
Study Flags
Red Flags
- •Small sample size (n=71)
- •Only included women, limiting generalizability
- •Blinding not specified — participants knew their group assignment
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Diet soda drinkers lost only 0.1 kg over 12 months, while water drinkers lost 1.7 kg—despite both groups being on the same calorie-controlled diet.
Most assume artificial sweeteners are neutral; this shows they may blunt metabolic adaptation during weight maintenance, making it harder to keep weight off.
Practical Takeaways
After your main meal, drink a glass of water instead of diet soda—especially if you're trying to maintain weight loss.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 556 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study is like a fair test where two groups of women were told to drink either water or diet soda, and then they were weighed and checked over a year and a half. Because they were randomly assigned, we can guess that drinking water might have helped them lose a little more weight — but we can't say for sure it's the only reason.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design
- Intention-to-treat analysis used
- Long follow-up period (18 months total)
Weaknesses
- Blinding was not performed and is unknown, risking performance and detection bias
- Small sample size reduces statistical power and precision
- Exclusive focus on women limits generalizability
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
This study tested if drinking water instead of diet soda after meals helps people keep off extra weight.
Research results
Women who drank water instead of diet soda lost 1.7 kg more over a year, their BMI dropped 0.7 points more, their insulin levels fell 0.5 mmol/L more, and their blood sugar after meals improved by 0.2 mmol/L more.
What this means - more context
Yes — these changes are meaningful: losing 1.7 kg more and improving insulin sensitivity can lower diabetes risk and help maintain weight long-term.
To determine if replacing diet beverages with water after meals enhances weight maintenance over 12 months in overweight and obese women who previously consumed diet beverages regularly.
In a randomized trial of 71 overweight/obese women, those who replaced diet beverages with water after lunch lost an additional 1.7 kg and had greater reductions in BMI, fasting insulin, HOMA-IR, and postprandial glucose over 12 months compared to those continuing diet beverages.
Methods Used
71 overweight/obese adult women (BMI 27–40 kg/m², age 18–50) who regularly consumed diet beverages were randomly assigned to either replace diet beverages with water (n=35) or continue consuming diet beverages five times per week (n=36) after lunch, following a 6-month weight loss phase; outcomes were assessed over a 12-month maintenance period using intention-to-treat analysis.
Main Finding
Replacing diet beverages with water led to significantly greater weight loss (−1.7 kg vs. −0.1 kg, P=0.001), greater BMI reduction (−0.7 vs. −0.05 kg/m², P=0.003), and improved metabolic markers including fasting insulin (−0.5 vs. −0.02 mmol/L, P=0.023), HOMA-IR (−0.2 vs. −0.1 units, P=0.013), and 2-hour postprandial glucose (−0.2 vs. −0.1 mmol/L, P<0.001) over 12 months.
Confidence Level
High — randomized controlled trial with intention-to-treat analysis, pre-specified outcomes, statistically significant effect sizes, and low attrition.
Study Flags
Red Flags
- •Small sample size (n=71)
- •Only included women, limiting generalizability
- •Blinding not specified — participants knew their group assignment
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
Surprising Findings
Diet soda drinkers lost only 0.1 kg over 12 months, while water drinkers lost 1.7 kg—despite both groups being on the same calorie-controlled diet.
Most assume artificial sweeteners are neutral; this shows they may blunt metabolic adaptation during weight maintenance, making it harder to keep weight off.
Practical Takeaways
After your main meal, drink a glass of water instead of diet soda—especially if you're trying to maintain weight loss.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 556 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Human RCT
Subject
Moderate probability
on the GRADE evidence scale
This study is like a fair test where two groups of women were told to drink either water or diet soda, and then they were weighed and checked over a year and a half. Because they were randomly assigned, we can guess that drinking water might have helped them lose a little more weight — but we can't say for sure it's the only reason.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design
- Intention-to-treat analysis used
- Long follow-up period (18 months total)
Weaknesses
- Blinding was not performed and is unknown, risking performance and detection bias
- Small sample size reduces statistical power and precision
- Exclusive focus on women limits generalizability
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study did a good job by randomly assigning people to groups, which helps make it fair. But no one was blinded — so people knew which drink they were getting, which might have changed how they acted. That’s why we should be a little careful trusting the results too much.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
64 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=71)+6.0/20
- Follow-up+10/10
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 556 / 100
Probability of being correct
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
This design can establish causation. Randomization supports causal inference, but lack of blinding introduces potential performance and detection bias, which may slightly weaken the strength of causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest or funding disclosures were reported in the study text.
The study lacks any declared funding source or conflict of interest statement. While the results appear methodologically sound, the absence of transparency regarding funding raises a minor risk of undisclosed bias, though no evidence of such bias is present in the text.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
6 researchersIf this is your work, this is how we attribute it on Fit Body Science. Ameneh Madjd is listed as the lead author.
- Hamid R. FarshchiCorresponding