Study analysis · The Journal of Nutrition · 2024
Eating more beef won't make older women stronger—but it might save their knees.
Older women got stronger muscles from lifting weights, no matter how much protein they ate, but eating more protein stopped their knee tendon from getting thinner.
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 gave different diets to older women who did strength training and found that eating more beef protein didn't make their muscles or tendons get any stronger than eating other kinds of protein. It's like testing if adding sprinkles to ice cream makes it tastier — turns out, it didn't.
What’s the bottom line?
Older women did resistance training for 12 weeks and ate either normal or extra protein from beef or other sources. Researchers checked if extra protein made their muscles bigger or tendons stronger.
How strong is this study?
This study was pretty well done because it randomly assigned people to diets and made sure everyone ate exactly what they were supposed to, and used fancy machines to measure muscles and tendons. But it didn't hide who got which diet, and not enough people joined, so we can't be 100% sure the results are perfect.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
62 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=49)+4.3/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
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 569 / 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 allows causal inference, but blinding was unknown and sample size was modest, which may limit precision and increase risk of chance findings. The study found no significant effects, so causation is inferred only in the negative direction (i.e., protein intake did not cause changes).
No Conflicts
No conflicts of interest identified
No conflicts of interest were disclosed, and the study was funded by non-industry sources with no evidence of funder influence on study design, analysis, or publication.
Funders
Conflict Details
National Institutes of Health: Funding provided for the study through NIH grant support
Beef Checkoff Program: Funding provided for the study through beef industry checkoff program
Independent Analysis Safeguards
- Study registered at clinicaltrials.gov (NCT04347447)
- IRB approval obtained from Purdue University
- Dietary and training protocols were standardized and supervised by research team
- Data analysis used validated tools (MATLAB, LabVIEW) and blinded ultrasound tracking
Although the Beef Checkoff Program provided funding, there is no indication that the funder influenced study design, data analysis, or publication. Independent oversight by NIH and university IRB, along with pre-registration and standardized methods, reduce bias risk. The study's neutral findings (no effect of beef protein) further suggest lack of promotional bias.
Key takeaways
- 01
Muscle size and strength went up for everyone, no matter how much protein they ate.
- 02
The tendon at the bottom of the knee got smaller in the low-protein group but stayed the same in the high-protein group.
- 03
Tendon stiffness didn't change at all.
- 04
Extra protein didn't make muscles stronger or tendons stiffer, but it might help keep the bottom part of the knee tendon from shrinking — which could be important for preventing injury.
Surprising findings
- Higher protein intake prevented distal patellar tendon thinning, but didn't improve muscle strength or tendon stiffness.Most studies show protein boosts muscle gains — but here, it only preserved tendon structure without enhancing strength or stiffness, even with identical training.
- Blood urea nitrogen increased with higher protein intake — but showed no adverse effects.Many assume high protein harms kidneys — but this study found elevated urea (a marker of protein metabolism) with no signs of kidney stress or health issues.
Practical takeaways
Older women doing resistance training don't need extra protein to build muscle — but consuming 1.4 g/kg/d (about 95g for a 150lb woman) may help prevent thinning of the lower knee tendon.
This only applies to women aged ~66 with BMI ~28; results may not generalize to men, younger people, or those with tendon injuries.
medium confidenceFocus on consistent resistance training — it improved muscle volume and tendon thickness regardless of protein intake.
Tendon stiffness didn't improve, so adding higher-load exercises or longer training durations may be needed for mechanical gains.
high confidenceWhy this study matters
Protein Doesn't Boost Muscle Growth in Older Women
In a 12-week study of 49 women aged 66, those eating 1.4 g/kg/d of protein (nearly double the recommended 0.8 g/kg/d) saw no greater increase in quadriceps muscle volume or strength than those eating the standard amount. Muscle gains were identical across all groups.
This challenges the widespread belief that more protein = more muscle, especially for older adults trying to fight sarcopenia. It suggests training alone may be enough.
High Protein Prevents Knee Tendon Thinning
While the low-protein group (0.8 g/kg/d) saw a significant decrease in distal patellar tendon CSA (P < 0.05), the high-protein groups (1.4 g/kg/d) maintained their tendon thickness — suggesting protein may protect this specific knee region.
Tendons are often ignored in fitness, but this finding hints that protein could prevent age-related tendon degeneration — a silent cause of mobility loss and injury.
Tendon Stiffness Didn't Change — Even With Training
Despite 12 weeks of supervised resistance training at 70% 1RM, patellar tendon stiffness and modulus remained unchanged in all groups — meaning tendons got thicker but not stronger at the material level.
This flips the script: bigger doesn't mean better. Tendons may need different stimuli (like higher loads or longer durations) to improve mechanical function.
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
Older women did resistance training for 12 weeks and ate either normal or extra protein from beef or other sources. Researchers checked if extra protein made their muscles bigger or tendons stronger.
Research results
Muscle size and strength went up for everyone, no matter how much protein they ate. The tendon at the bottom of the knee got smaller in the low-protein group but stayed the same in the high-protein group. Tendon stiffness didn't change at all.
What this means - more context
Extra protein didn't make muscles stronger or tendons stiffer, but it might help keep the bottom part of the knee tendon from shrinking — which could be important for preventing injury.
This study tested whether higher protein intake (1.4 g/kg/d) from lean beef or mixed sources enhances resistance training-induced gains in muscle and tendon outcomes in older women, compared to the recommended 0.8 g/kg/d.
In older women (age 66, BMI 28), 12 weeks of supervised resistance training increased quadriceps muscle volume and proximal/mid tendon CSA, but higher protein intake (1.4 g/kg/d) did not significantly enhance these gains. However, higher protein intake prevented a decline in distal patellar tendon CSA seen in the 0.8 g/kg/d group. Muscle strength and tendon biomechanical properties (stiffness, modulus) were unchanged by protein intake. Blood urea nitrogen increased with higher protein intake, indicating greater metabolism without adverse effects.
Methods Used
Randomized controlled feeding trial with 49 older women assigned to three dietary groups: 0.8 g/kg/d (control), 1.4 g/kg/d mixed protein, or 1.4 g/kg/d lean beef. All participants performed supervised resistance training (3x/week, 70% 1RM) for 12 weeks. Muscle volume was measured via MRI; tendon cross-sectional area and biomechanics via ultrasound and MRI. Dietary intake was strictly controlled and monitored.
Main Finding
Higher protein intake (1.4 g/kg/d) did not significantly enhance resistance training-induced increases in quadriceps muscle volume or strength, nor did it improve patellar tendon stiffness or modulus. However, it prevented a significant decrease in distal patellar tendon cross-sectional area observed in the 0.8 g/kg/d group.
Confidence Level
Moderate. The study is a well-conducted RCT with controlled diet and training, but sample size (n=49 total) and attrition in tendon biomechanics subgroups limit power. Primary outcomes (muscle volume, strength) were robustly measured and showed no effect of protein; tendon findings are region-specific and trend-based.
Study Flags
Red Flags
- •Modest sample size (n=49) with attrition in tendon biomechanics subgroup
- •Multiple statistical comparisons without Bonferroni correction
- •Timing of protein intake was spread throughout day, not post-exercise, potentially limiting anabolic response
Surprising Findings
Higher protein intake prevented distal patellar tendon thinning, but didn't improve muscle strength or tendon stiffness.
Most studies show protein boosts muscle gains — but here, it only preserved tendon structure without enhancing strength or stiffness, even with identical training.
Practical Takeaways
Older women doing resistance training don't need extra protein to build muscle — but consuming 1.4 g/kg/d (about 95g for a 150lb woman) may help prevent thinning of the lower knee tendon.
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 569 / 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 gave different diets to older women who did strength training and found that eating more beef protein didn't make their muscles or tendons get any stronger than eating other kinds of protein. It's like testing if adding sprinkles to ice cream makes it tastier — turns out, it didn't.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design with three dietary arms
- Strict dietary control with all food provided
- Supervised resistance training protocol
Weaknesses
- Blinding status unknown — participants and possibly assessors may not have been blinded
- Modest sample size, especially for tendon biomechanical testing (attrition up to 20%)
- Multiple statistical comparisons without adjustment for family-wise error rate
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Older women did resistance training for 12 weeks and ate either normal or extra protein from beef or other sources. Researchers checked if extra protein made their muscles bigger or tendons stronger.
Research results
Muscle size and strength went up for everyone, no matter how much protein they ate. The tendon at the bottom of the knee got smaller in the low-protein group but stayed the same in the high-protein group. Tendon stiffness didn't change at all.
What this means - more context
Extra protein didn't make muscles stronger or tendons stiffer, but it might help keep the bottom part of the knee tendon from shrinking — which could be important for preventing injury.
This study tested whether higher protein intake (1.4 g/kg/d) from lean beef or mixed sources enhances resistance training-induced gains in muscle and tendon outcomes in older women, compared to the recommended 0.8 g/kg/d.
In older women (age 66, BMI 28), 12 weeks of supervised resistance training increased quadriceps muscle volume and proximal/mid tendon CSA, but higher protein intake (1.4 g/kg/d) did not significantly enhance these gains. However, higher protein intake prevented a decline in distal patellar tendon CSA seen in the 0.8 g/kg/d group. Muscle strength and tendon biomechanical properties (stiffness, modulus) were unchanged by protein intake. Blood urea nitrogen increased with higher protein intake, indicating greater metabolism without adverse effects.
Methods Used
Randomized controlled feeding trial with 49 older women assigned to three dietary groups: 0.8 g/kg/d (control), 1.4 g/kg/d mixed protein, or 1.4 g/kg/d lean beef. All participants performed supervised resistance training (3x/week, 70% 1RM) for 12 weeks. Muscle volume was measured via MRI; tendon cross-sectional area and biomechanics via ultrasound and MRI. Dietary intake was strictly controlled and monitored.
Main Finding
Higher protein intake (1.4 g/kg/d) did not significantly enhance resistance training-induced increases in quadriceps muscle volume or strength, nor did it improve patellar tendon stiffness or modulus. However, it prevented a significant decrease in distal patellar tendon cross-sectional area observed in the 0.8 g/kg/d group.
Confidence Level
Moderate. The study is a well-conducted RCT with controlled diet and training, but sample size (n=49 total) and attrition in tendon biomechanics subgroups limit power. Primary outcomes (muscle volume, strength) were robustly measured and showed no effect of protein; tendon findings are region-specific and trend-based.
Study Flags
Red Flags
- •Modest sample size (n=49) with attrition in tendon biomechanics subgroup
- •Multiple statistical comparisons without Bonferroni correction
- •Timing of protein intake was spread throughout day, not post-exercise, potentially limiting anabolic response
Surprising Findings
Higher protein intake prevented distal patellar tendon thinning, but didn't improve muscle strength or tendon stiffness.
Most studies show protein boosts muscle gains — but here, it only preserved tendon structure without enhancing strength or stiffness, even with identical training.
Practical Takeaways
Older women doing resistance training don't need extra protein to build muscle — but consuming 1.4 g/kg/d (about 95g for a 150lb woman) may help prevent thinning of the lower knee tendon.
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 569 / 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 gave different diets to older women who did strength training and found that eating more beef protein didn't make their muscles or tendons get any stronger than eating other kinds of protein. It's like testing if adding sprinkles to ice cream makes it tastier — turns out, it didn't.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Randomized controlled trial design with three dietary arms
- Strict dietary control with all food provided
- Supervised resistance training protocol
Weaknesses
- Blinding status unknown — participants and possibly assessors may not have been blinded
- Modest sample size, especially for tendon biomechanical testing (attrition up to 20%)
- Multiple statistical comparisons without adjustment for family-wise error rate
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
This study was pretty well done because it randomly assigned people to diets and made sure everyone ate exactly what they were supposed to, and used fancy machines to measure muscles and tendons. But it didn't hide who got which diet, and not enough people joined, so we can't be 100% sure the results are perfect.
40 / 100
- COI disclosure+40/40
- Data availabilitydata not shared
- Code availabilitycode not shared
62 / 100
- Randomization+20/20
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=49)+4.3/20
- Follow-up+10/10
100 / 100
77 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registration+15/15
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 569 / 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 allows causal inference, but blinding was unknown and sample size was modest, which may limit precision and increase risk of chance findings. The study found no significant effects, so causation is inferred only in the negative direction (i.e., protein intake did not cause changes).
No Conflicts
No conflicts of interest identified
No conflicts of interest were disclosed, and the study was funded by non-industry sources with no evidence of funder influence on study design, analysis, or publication.
Funders
Conflict Details
National Institutes of Health: Funding provided for the study through NIH grant support
Beef Checkoff Program: Funding provided for the study through beef industry checkoff program
Independent Analysis Safeguards
- Study registered at clinicaltrials.gov (NCT04347447)
- IRB approval obtained from Purdue University
- Dietary and training protocols were standardized and supervised by research team
- Data analysis used validated tools (MATLAB, LabVIEW) and blinded ultrasound tracking
Although the Beef Checkoff Program provided funding, there is no indication that the funder influenced study design, data analysis, or publication. Independent oversight by NIH and university IRB, along with pre-registration and standardized methods, reduce bias risk. The study's neutral findings (no effect of beef protein) further suggest lack of promotional bias.
Standing
Who’s using this study?
The videos and claims on this site that lean on this study, and the researchers who wrote it.
2 videos from 2 different creators cite this study, drawing 2 claims from it.
- Very strong evidence
Randomized or controlled trials support this claim, alongside consistent supporting evidence.
Evidence