Two European geriatricians argue that insulin resistance in older people has been badly misfiled. In the young and obese it is a disease of excess fat. In the old it is something else: a readout of how much spare capacity the body has left across muscle, fat tissue, and brain. The paper assembles existing evidence that ageing muscle loses metabolic competence before it loses bulk, that ageing fat tissue turns into an inflammatory organ regardless of how much of it there is, and that the brain becomes insulin resistant in ways that track with memory loss and late-life depression. The authors conclude that chasing blood glucose in older patients treats the dashboard light rather than the engine, and propose measuring muscle strength, body composition and physical performance alongside metabolic markers. The argument is coherent and clinically sensible.
The standard story about insulin resistance goes like this: you eat too much, you store too much fat, your cells stop listening to insulin, and eventually you get type 2 diabetes. It is a good story for a 45-year-old with a large waist. Boccardi and Sinclair argue it is close to useless for a 70-year-old.
Their evidence is the mismatch. In older populations insulin resistance shows up routinely in people who are not obese, appears years or decades before any diabetes diagnosis, and arrives in company that has nothing to do with glucose: weakness, slow walking, falls, memory complaints, low mood. Two people of the same age and the same body mass index can sit at opposite ends of the insulin sensitivity range.
The paper’s answer is physiological reserve, a formal way of saying spare capacity. Skeletal muscle is the body’s largest glucose sink, absorbing most of what you eat after a meal. Ageing muscle does not simply shrink. It changes character first: fast-twitch fibres are lost preferentially, fat infiltrates between and inside the fibres, mitochondria become less efficient, and the tissue stops responding to protein the way it used to. Clamp studies find older adults with normal muscle bulk still handling glucose poorly. The buffer degrades before the volume does.
Fat tissue undergoes a parallel conversion. It migrates inward toward the viscera even in people whose weight never changes, fills with inflammatory immune cells, and accumulates senescent cells that leak inflammatory signals into the circulation. Once fat loses its capacity to store lipid safely, the overflow lands in liver and muscle, where it directly interferes with insulin signalling.
Then the brain. Insulin crosses into the brain less readily with age and neuronal insulin signalling degrades, which the authors link to reduced cerebral glucose uptake, impaired synaptic function, and the well-documented associations between insulin resistance, cognitive decline and late-life depression.
The practical consequence is the interesting part. If insulin resistance in older adults is a symptom of eroding reserve rather than a disease of sugar, then a drug that normalises glucose while stripping muscle mass has made the underlying problem worse. The authors are pointed about GLP-1 agonists and SGLT2 inhibitors in frail patients for exactly this reason. Their proposed alternative is to judge treatments by whether they preserve muscle function, dampen inflammation and protect cognition, with glucose control retained as one component rather than the target.
Actionable Insights
Take-home messages with real magnitudes. Cohen’s d below measures how far a treated group shifts relative to an untreated one. Roughly: 0.2 is small, 0.5 moderate, 0.8 large.
Lift weights. In adults over 60, resistance training improved insulin resistance with d of -0.25 (95% CI -0.43 to -0.06) and HbA1c with d of -0.51 (95% CI -0.84 to -0.18), pooled across 12 trials. In plain terms, the average trainee ends up better than about 60% of non-trainees on insulin resistance and about 70% on blood sugar control. Real, modest, and requiring no weight loss.
Intensive lifestyle change is the strongest effect on this list. In the Diabetes Prevention Program, diabetes incidence fell from 11.0 to 4.8 cases per 100 person-years, a 58% reduction (95% CI 48 to 66). About seven people needed treating for three years to prevent one case.
Structured exercise plus nutrition in frail older diabetics improved physical performance by 0.85 points on a 12-point scale (95% CI 0.44 to 1.26), roughly d of 0.4. Note what it did not do: no reduction in death, hospitalisation, or improvement in quality of life.
Distribute protein across meals rather than loading dinner.
Context and Source
- Open Access Paper: Rethinking insulin resistance in aging: A reserve-oriented clinical framework
- Authors: Virginia Boccardi (corresponding), Alan J. Sinclair
- Institutions: Division of Gerontology and Geriatrics, Department of Medicine and Surgery, University of Perugia, Italy; Foundation for Diabetes Research in Older People (fDROP) and King’s College London, UK
- Countries: Italy and United Kingdom
- Journal: Ageing Research Reviews (Elsevier), Volume 119, article 103180, 2026
- Article type: Review Article, narrative. online 17 May 2026.
- Impact evaluation: The impact score of this journal is 15.5, evaluated against a typical high-end range of 0 to 60 plus for top general science, therefore this is a High impact journal.