July 31, 2026

expert reaction to review paper looking at protein intake and health and lifespan in humans, rodents and insects

A review paper published in Cell Press Blue looks at protein intake, ageing and longevity in humans, rodents and insects. 

Prof Paul Greenhaff, Professor of Muscle Metabolism, University of Nottingham, said:

“Firstly, the article is a review (so not original research).  Secondly, it is primarily based on evidence from rodent and insect research and the central question of whether protein restriction positively impacts of healthy ageing and longevity has not been addressed in humans.  Of course, such human volunteer studies are very difficult to deliver however it is essential that is achieved because rodents and insects are not representative models of human ageing.  The trajectory of body composition change over the lifespan is different to humans, and insects and rodents have greater metabolic rates relative to the human alongside poorer metabolic stability.

“Here are two good papers^1,2that highlight these differences.

“So in short, the associations identified in the review article are thought provoking and bring mechanistic insight, but whether they translate to the human condition is debatable.”

1 Demetrius L. Of mice and men. When it comes to studying ageing and the means to slow it down, mice are not just small humans. EMBO Rep. 2005 Jul;6 Spec No (Suppl 1):S39-44. DOI: 10.1038/sj.embor.7400422

2 Rennie, M.J., Selby, A., Atherton, P., Smith, K., Kumar, V., Glover, E.L. and Philips, S.M. (2010), Facts, noise and wishful thinking: muscle protein turnover in aging and human disuse atrophy. Scandinavian Journal of Medicine & Science in Sports, 20: 5-9.https://doi.org/10.1111/j.1600-0838.2009.00967.x

Prof Kevin McConway, Emeritus Professor of Applied Statistics, Open University, said:

“As a statistician it’s beyond my competence to comment on the physiology in this paper, or its conclusions about the effects of reducing protein intake on human health.

“However, I do know about how different types of research paper are produced, and I therefore want to comment on the labels at the top of the press release describing some key attributes of the study.

“The first one says the paper was peer-reviewed, which it doubtless was.

“The second one says it is a systematic review.  It simply isn’t.  In a systematic review, the researchers make efforts to find all the papers and research reports that are relevant to the question of interest.  There are accepted standards for how to carry out a systematic review, and how to report it.

“This paper doesn’t claim to be a systematic review.  Instead it is a narrative review of the literature.  The authors have clearly based their findings on a large number of research papers, and it’s beyond my expertise to comment on whether they missed any important ones.  But they don’t explain how they chose the papers to review, and they don’t use statistical methods to combine the findings.

“I’m absolutely not criticising the authors of the paper for using this approach.  It’s a common way of reviewing a field of study.  But I wanted to mention that it’s not a systematic review, in case anyone thinks that it will have the characteristics that a systematic review should have.

“The final label says that the paper is about people.  Well, it does draw conclusions about the effects on human health of restricting protein intake.  But to label a paper as being about people typically means that the research reported in the paper was carried out using human subjects.  That’s not the case here.  Many of the studies that are reviewed did use human subjects, but the review also covers a lot of studies that were carried out using experimental animals.  That raises another question that I’m not competent to answer – can the findings from these animal studies really be carried over to humans?

“To examine the subject that this new study covers, in such a broad-ranging review, it is often necessary to include findings from animal studies.  So again I’m not making any criticism of the paper authors for doing just that.  Unlike me, they are experienced in understanding which findings from animal studies also apply in humans.  It’s only the labelling in the press release that I’m criticising.”

‘The hallmarks of protein and amino acid restriction in aging and longevity’ by Bailey A. Knopf and Dudley W. Lamming was published in Cell Press Blue at 16:00 UK time on Friday 31 July 2026. 

DOI: 10.1016/j.cpblue.2026.100079

Declared interests

Prof Paul Greenhaff: “I have no conflict of interest that I am aware of.”

Prof Kevin McConway: “I have no conflicts of interest.”