Randomised controlled trialindependent cross-checkabstract checked I-FAST-120 standard review
Protein amount versus timing in older adults
Quantity of dietary protein intake, but not pattern of intake, affects net protein balance primarily through differences in protein synthesis in older adults.
Overview
Kim IY et al.. Am J Physiol Endocrinol Metab 2015 · PMID 25352437 · DOI 10.1152/ajpendo.00382.2014
In older adults, eating more protein improved protein balance, while how it was spread across meals made no difference.
Does the study support the specific claim? Partly · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Compare protein dose and distribution.
- How was the study done?
20 older adults randomised to 4 diets; tracer measurements.
- How many people, animals or samples were studied?
20 healthy adults aged 52-75.
- What was actually found?
Higher dose better; pattern no effect.
- How large was the observed effect?
Net balance 94.8 vs 58.9 g/750 min.
- What do the results mean in everyday life?
Getting enough protein each day matters more than exact timing.
- What are the study's limitations?
Tiny, 4 days.
- What does it say about Elawady's specific claim?
Does not support protein-free days; emphasises daily adequacy.
- Do the results apply to Germany and Europe?
Applies; same physiology.
- What can explicitly not be concluded from this study?
Effects of whole protein-free days.
Scientific in-depth review
1. Full reference
- Authors
- Kim IY et al.
- Journal
- Am J Physiol Endocrinol Metab
- Year
- 2015
- Identifier
- PMID 25352437 DOI 10.1152/ajpendo.00382.2014
- Verification
- verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
NIH funded (record).
2. Research question
Do protein quantity and within-day distribution affect protein balance in older adults?
3. Study design and population
- Study design
- Randomised controlled trial – Randomised trial, 4 groups (2 protein doses x 2 distribution patterns), tracer study
- Population
Healthy older adults aged 52-75
- Country
USA
- Period
not stated in abstract
- Sample size
20
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
1.5 g/kg/day (~2x RDA) vs 0.8 g/kg/day; even vs uneven distribution over 3 meals
- Comparator
Other dose/pattern
- Endpoints
Whole-body protein synthesis, breakdown, net balance; muscle FSR
- Statistical methods
Group comparisons
5. Actual results
- Results
Positive net balance at both doses, greater with 2RDA (94.8 +/- 6.0 vs 58.9 +/- 4.9 g protein/750 min; P=0.0001), without effect of distribution; greater synthesis with 2RDA; MPS greater with 2RDA regardless of pattern.
- Absolute risks
not reported
- Authors' conclusion
Net protein balance greater with protein above the RDA in mixed meals, without demonstrated effects of intake pattern.
6. Strengths
- Stable-isotope methods
- Factorial design
7. Weaknesses
- Very small
- Only 4 days; within-day distribution, not alternate days
8. Risk of bias
- Orienting tool
- RoB 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Small, short; randomisation details not in abstract.
9. Assessment of the statistical interpretation
Quantity matters; within-day pattern did not, over 1 day of measurement.
10. Relevance to the specific claim
Fairness: how protein is distributed within a day matters less than total amount; but it tested daily intake and does not support skipping protein on whole days.
11. Independent contrary findings
12. Transferability to Germany and Europe
Universal biology; applies in Europe and Egypt.
13. Overall methodological judgement
Indirect; supports flexibility in timing but emphasises adequate daily amount.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | indirect |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Protein should not be eaten every day: give the digestive system a rest day between protein meals (rotate protein through the week). – Studies with mixed or unclear results