Study analysis · Europace · 2023
Obese heart failure patients were 22% less likely to die, need a transplant, or need a heart pump — but this 'obesity paradox' may be a mirage.
In a 5-year study of 1,585 people with heart failure getting a special heart device, those with obesity had a lower relative risk of death/transplant/pump than normal-weight patients, but the study can't prove that extra weight caused the benefit.
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 looked back at records of people who got a heart device and compared heavier vs. lighter patients. It can show a link between weight and survival, but it cannot prove that weight itself is the reason for the difference. Other things like age or other illnesses could be responsible.
What’s the bottom line?
This study looked at patients with heart failure who received a special heart device (CRT). It found that patients with higher body weight (overweight or obese) had a lower risk of dying or needing a heart transplant compared to normal-weight patients. This is called the 'obesity paradox'.
How strong is this study?
The study is fairly large and followed people for about 5 years, which is a strength. But it wasn't a randomized experiment, and it was done at one clinic, so the results might not apply everywhere and could be influenced by other differences between the groups.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
37 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=1585)+20.0/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- 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 552 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. Retrospective observational cohort without randomization. Baseline differences between BMI groups, potential unmeasured confounding, and possible reverse causation (lower BMI due to illness/cachexia) prevent causal inference. The study can show associations but cannot prove that obesity causes improved survival.
No Conflicts
No conflicts of interest identified
No conflicts identified; study funded by a public EU grant with no industry involvement.
Funders
Conflict Details
European Union: Public grant funding (EU funding)
All authors are affiliated with Semmelweis University Heart and Vascular Center, an academic institution. No industry funding or author industry employment disclosed. No conflict of interest statement was found in the provided text.
Key takeaways
- 01
Over 5 years, 66% of normal-weight patients had a bad outcome (death, heart transplant, or heart pump) compared to 58% of obese patients.
- 02
That's an 8 percentage point lower absolute risk for obese patients.
- 03
The relative risk was 22% lower for obese patients (HR 0.78).
- 04
Normal-weight patients had a 19% higher relative risk compared to overweight/obese patients (HR 1.19).
- 05
For every 100 normal-weight patients, about 66 had a bad outcome over 5 years.
- 06
For obese patients, about 58 had a bad outcome.
- 07
So about 8 fewer bad outcomes per 100 people.
- 08
The absolute risk difference for the 19% higher risk in normal weight was not reported.
Surprising findings
- Normal-weight patients had higher diabetes and hypertension rates than obese patients.Obesity is typically linked to higher rates of diabetes and hypertension, so this reversal is counterintuitive.
- The study conclusion says obese patients had more comorbidities, but the data show the opposite.The conclusion states: 'Despite having more co-morbidities like diabetes or hypertension, obese patients showed mortality benefit over normal-weighed patients proving, that the obesity paradox was present.' Yet the numbers show normal-weight patients had more diabetes and hypertension.
- No difference in reverse remodeling or peri-procedural complications by BMI.If obesity is protective, one might expect better device response or fewer complications, but neither was observed.
Practical takeaways
Do not intentionally gain weight based on this study.
This is an observational, retrospective, single-center study; it cannot prove that higher BMI causes better outcomes.
low confidenceIf you have heart failure and are considering CRT, obesity should not be a barrier based on this study's complication and remodeling data.
Findings are from one center and may not apply to all populations; discuss with your cardiologist.
medium confidenceFocus on overall health and guideline-directed heart failure therapy rather than BMI alone.
BMI does not capture body composition, fluid retention, or fitness.
medium confidenceWhy this study matters
Obesity linked to lower relative risk in CRT patients
In 1,585 heart failure patients receiving cardiac resynchronization therapy (CRT), obese patients (BMI ≥30) had a 22% lower relative risk of the composite endpoint (all-cause mortality, heart transplant, or LVAD) compared with normal-weight patients (BMI <25): HR 0.78 (95% CI 0.66–0.92; p=0.003). Absolute event rates were 58% vs 66% over a mean 5.1 years — an absolute difference of 8 percentage points. Normal-weight patients had a 19% higher relative risk compared with overweight/obese patients (HR 1.19; 95% CI 1.03–1.38; p=0.02); the absolute risk difference was not reported.
It flips the usual assumption that obesity always worsens heart failure outcomes, but the absolute difference is modest and the study is observational.
No difference in reverse remodeling across BMI groups
Reverse remodeling — a ≥15% relative increase in LVEF within 6 months — occurred in 58% of normal-weight, 61% of overweight, and 57% of obese patients (p=0.75). All groups improved LVEF significantly, but the proportion who achieved reverse remodeling did not differ by BMI.
If obesity were truly protective, you might expect obese patients to have better device response, but that wasn't the case.
Peri-procedural complications similar across BMI groups
Peri-procedural complication rates did not differ significantly between normal-weight, overweight, and obese patients. This suggests that in this cohort, higher BMI did not increase short-term procedural risk.
Many people assume higher BMI makes heart procedures riskier, but this study found no signal of increased complications.
Normal-weight patients were sicker at baseline
Normal-weight patients were older (70 vs 68 years, p<0.0001), had lower baseline LVEF (27% vs 30%, p<0.001), and had higher prevalence of diabetes (48% vs 26%, p<0.0001) and hypertension (82% vs 71%, p<0.001) compared with obese patients. These baseline differences could partly explain the obesity paradox.
The 'normal weight' group may have been sicker from the start, which could make obesity look protective even if it isn't.
Contradictory comorbidity statement in the abstract
The abstract states: 'Diabetes (BMI <25 48% vs. BMI 25-29.9 37% vs. BMI≥30 26%; p<0.0001) and hypertension (BMI <25 82% vs. BMI 25-29.9 74% vs. BMI≥30 71%; p<0.001) occurred more frequently in obese and overweight patients.' But the numbers show the opposite — normal-weight patients had the highest rates. The conclusion also says obese patients had 'more co-morbidities like diabetes or hypertension,' which contradicts the data.
This inconsistency raises questions about the study's reporting and how carefully the conclusions match the results.
Overweight trend was borderline significant
Overweight patients (BMI 25–29.9) showed a trend toward lower risk compared with normal-weight patients: HR 0.86 (95% CI 0.74–1.00; p=0.05). This is borderline and does not meet conventional statistical significance.
It shows the dose-response isn't clean: only obesity reached significance, while overweight was borderline.
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 looked at patients with heart failure who received a special heart device (CRT). It found that patients with higher body weight (overweight or obese) had a lower risk of dying or needing a heart transplant compared to normal-weight patients. This is called the 'obesity paradox'.
Research results
Over 5 years, 66% of normal-weight patients had a bad outcome (death, heart transplant, or heart pump) compared to 58% of obese patients. That's an 8 percentage point lower absolute risk for obese patients. The relative risk was 22% lower for obese patients (HR 0.78). Normal-weight patients had a 19% higher relative risk compared to overweight/obese patients (HR 1.19).
What this means - more context
For every 100 normal-weight patients, about 66 had a bad outcome over 5 years. For obese patients, about 58 had a bad outcome. So about 8 fewer bad outcomes per 100 people. The absolute risk difference for the 19% higher risk in normal weight was not reported.
To investigate the association between body mass index (BMI) and long-term all-cause mortality in heart failure patients undergoing cardiac resynchronization therapy (CRT), and to assess the obesity paradox in this population.
In a retrospective cohort of 1585 CRT patients followed for a mean of 5.1 years, obese patients (BMI≥30) had a 22% lower relative risk of the composite endpoint (all-cause mortality, heart transplantation, or LVAD implantation) compared to normal-weight patients (BMI<25): HR 0.78 (95% CI 0.66-0.92; p=0.003). Absolute event rates were 58% vs 66%, an absolute difference of 8 percentage points. Normal-weight patients had a 19% higher relative risk compared to overweight/obese patients (HR 1.19; 95% CI 1.03-1.38; p=0.02). No significant differences were found in reverse remodeling or peri-procedural complications across BMI groups.
Methods Used
Retrospective examination of 1585 patients undergoing CRT implantation at a single center between 2000-2020 with baseline BMI. Patients were categorized as normal weight (BMI<25), overweight (25-29.9), or obese (≥30). The primary composite endpoint was all-cause mortality, heart transplantation, or LVAD implantation. Time-to-event data were analyzed using log-rank and multivariate Cox regression, adjusting for age, sex, NYHA class, diabetes, hypertension, myocardial infarction, and atrial fibrillation. Peri-procedural complications and reverse remodeling (≥15% relative increase in LVEF at 6 months) were also assessed.
Main Finding
Obese CRT patients had a 22% lower relative risk of the composite endpoint versus normal weight (HR 0.78; 95% CI 0.66-0.92; p=0.003), with absolute event rates of 58% vs 66% (absolute difference 8 percentage points) over 5.1 years. Normal-weight patients had a 19% higher relative risk compared to overweight/obese (HR 1.19; 95% CI 1.03-1.38; p=0.02); the absolute risk difference was not reported. Overweight patients showed a trend toward lower risk (HR 0.86; 95% CI 0.74-1.00; p=0.05). No differences in reverse remodeling or complications were observed.
Confidence Level
Moderate. Large sample size and long follow-up, but retrospective single-center design and potential residual confounding limit causal inference.
Study Flags
Red Flags
- •Retrospective single-center design
- •Potential unmeasured confounders
- •No data on weight changes over time
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
Normal-weight patients had higher diabetes and hypertension rates than obese patients.
Obesity is typically linked to higher rates of diabetes and hypertension, so this reversal is counterintuitive.
Practical Takeaways
Do not intentionally gain weight based on this study.
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 552 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study looked back at records of people who got a heart device and compared heavier vs. lighter patients. It can show a link between weight and survival, but it cannot prove that weight itself is the reason for the difference. Other things like age or other illnesses could be responsible.
The study has a COI section but no disclosure was found. A small penalty has been applied.
Strengths
- Large sample size (n=1585).
- Long mean follow-up of 5.1 years.
- Use of a hard composite endpoint (all-cause mortality, heart transplantation, LVAD implantation).
Weaknesses
- Retrospective observational design without randomization.
- Single-center cohort.
- Baseline differences between BMI groups (age, diabetes, hypertension, LVEF).
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
This study looked at patients with heart failure who received a special heart device (CRT). It found that patients with higher body weight (overweight or obese) had a lower risk of dying or needing a heart transplant compared to normal-weight patients. This is called the 'obesity paradox'.
Research results
Over 5 years, 66% of normal-weight patients had a bad outcome (death, heart transplant, or heart pump) compared to 58% of obese patients. That's an 8 percentage point lower absolute risk for obese patients. The relative risk was 22% lower for obese patients (HR 0.78). Normal-weight patients had a 19% higher relative risk compared to overweight/obese patients (HR 1.19).
What this means - more context
For every 100 normal-weight patients, about 66 had a bad outcome over 5 years. For obese patients, about 58 had a bad outcome. So about 8 fewer bad outcomes per 100 people. The absolute risk difference for the 19% higher risk in normal weight was not reported.
To investigate the association between body mass index (BMI) and long-term all-cause mortality in heart failure patients undergoing cardiac resynchronization therapy (CRT), and to assess the obesity paradox in this population.
In a retrospective cohort of 1585 CRT patients followed for a mean of 5.1 years, obese patients (BMI≥30) had a 22% lower relative risk of the composite endpoint (all-cause mortality, heart transplantation, or LVAD implantation) compared to normal-weight patients (BMI<25): HR 0.78 (95% CI 0.66-0.92; p=0.003). Absolute event rates were 58% vs 66%, an absolute difference of 8 percentage points. Normal-weight patients had a 19% higher relative risk compared to overweight/obese patients (HR 1.19; 95% CI 1.03-1.38; p=0.02). No significant differences were found in reverse remodeling or peri-procedural complications across BMI groups.
Methods Used
Retrospective examination of 1585 patients undergoing CRT implantation at a single center between 2000-2020 with baseline BMI. Patients were categorized as normal weight (BMI<25), overweight (25-29.9), or obese (≥30). The primary composite endpoint was all-cause mortality, heart transplantation, or LVAD implantation. Time-to-event data were analyzed using log-rank and multivariate Cox regression, adjusting for age, sex, NYHA class, diabetes, hypertension, myocardial infarction, and atrial fibrillation. Peri-procedural complications and reverse remodeling (≥15% relative increase in LVEF at 6 months) were also assessed.
Main Finding
Obese CRT patients had a 22% lower relative risk of the composite endpoint versus normal weight (HR 0.78; 95% CI 0.66-0.92; p=0.003), with absolute event rates of 58% vs 66% (absolute difference 8 percentage points) over 5.1 years. Normal-weight patients had a 19% higher relative risk compared to overweight/obese (HR 1.19; 95% CI 1.03-1.38; p=0.02); the absolute risk difference was not reported. Overweight patients showed a trend toward lower risk (HR 0.86; 95% CI 0.74-1.00; p=0.05). No differences in reverse remodeling or complications were observed.
Confidence Level
Moderate. Large sample size and long follow-up, but retrospective single-center design and potential residual confounding limit causal inference.
Study Flags
Red Flags
- •Retrospective single-center design
- •Potential unmeasured confounders
- •No data on weight changes over time
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
Normal-weight patients had higher diabetes and hypertension rates than obese patients.
Obesity is typically linked to higher rates of diabetes and hypertension, so this reversal is counterintuitive.
Practical Takeaways
Do not intentionally gain weight based on this study.
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 552 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Human Cohort Study
Subject
Moderate probability
on the GRADE evidence scale
This study looked back at records of people who got a heart device and compared heavier vs. lighter patients. It can show a link between weight and survival, but it cannot prove that weight itself is the reason for the difference. Other things like age or other illnesses could be responsible.
The study has a COI section but no disclosure was found. A small penalty has been applied.
Strengths
- Large sample size (n=1585).
- Long mean follow-up of 5.1 years.
- Use of a hard composite endpoint (all-cause mortality, heart transplantation, LVAD implantation).
Weaknesses
- Retrospective observational design without randomization.
- Single-center cohort.
- Baseline differences between BMI groups (age, diabetes, hypertension, LVEF).
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study is fairly large and followed people for about 5 years, which is a strength. But it wasn't a randomized experiment, and it was done at one clinic, so the results might not apply everywhere and could be influenced by other differences between the groups.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
37 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control groupno control group
- Sample size (n=1585)+20.0/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervals+15/15
- 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 552 / 100
Probability of being correct
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
This design cannot establish causation — the findings describe an association, not a cause. Retrospective observational cohort without randomization. Baseline differences between BMI groups, potential unmeasured confounding, and possible reverse causation (lower BMI due to illness/cachexia) prevent causal inference. The study can show associations but cannot prove that obesity causes improved survival.
No Conflicts
No conflicts of interest identified
No conflicts identified; study funded by a public EU grant with no industry involvement.
Funders
Conflict Details
European Union: Public grant funding (EU funding)
All authors are affiliated with Semmelweis University Heart and Vascular Center, an academic institution. No industry funding or author industry employment disclosed. No conflict of interest statement was found in the provided text.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
13 researchersIf this is your work, this is how we attribute it on Fit Body Science. Eperke Dóra Merkel is listed as the lead author.