Weekly Issue — 2025-07-20

The starting point is familiar. Liraglutide, the first GLP-1 receptor agonist approved for weight management, produced roughly 6–8% weight loss. Once-weekly semaglutide pushed that to around 12–15%. Tirzepatide, which engages both the GIP and GLP-1 receptors, has reported about 20% in adults with obesity but without diabetes. Each step has been a genuine clinical advance, and each has reset expectations for what an injectable metabolic drug can do. A 2025 review in Expert Opinion on Investigational Drugs lays out the trajectory in plain terms and surveys what is moving through phase 2 and phase 3 development.

What that pipeline shows is a field branching in several directions at once. There are multi-receptor agonists, including GLP-1/glucagon co-agonists and the triple agonist retatrutide, which targets GIP, GLP-1, and glucagon receptors simultaneously. There are combinations, such as semaglutide paired with the long-acting amylin analogue cagrilintide, now in phase III. And there are oral formulations — both peptide-based oral semaglutide and a generation of small-molecule, non-peptide GLP-1 agonists designed to be swallowed rather than injected.

Retatrutide is the molecule attracting the most attention, and for understandable reasons. By adding glucagon-receptor activity to the GIP/GLP-1 mechanism of tirzepatide, it appears to lean harder on energy expenditure as well as appetite. Reported phase 2 weight-loss figures sit above the tirzepatide benchmark, with the 2025 review describing weight reductions in the region of 20%-plus across the multi-agonist class and noting parallel benefits on steatotic liver disease.

The appropriate posture here is measured optimism. Phase 2 data are encouraging, not definitive; larger phase 3 trials are still needed to confirm durability, cardiovascular safety, and how the drug behaves outside tightly controlled study populations. The class as a whole also shares a familiar adverse-event profile — nausea, vomiting, constipation, diarrhoea — generally manageable with slow dose titration, but real enough that a meaningful number of patients discontinue.

One of the quieter but more clinically useful findings of 2025 comes from a post-hoc analysis of the SURPASS programme, published in Diabetes Therapy. The researchers pooled participants from SURPASS-1 through -5 and looked specifically at adults aged 65 and over with type 2 diabetes and a body mass index below 30 — a group often under-represented in obesity-focused trials. In that subgroup, tirzepatide produced HbA1c reductions of roughly 1.97% to 2.10% regardless of the maintenance dose assigned.

Weight loss in this leaner, older group was, as one might expect, more modest in absolute terms than in the overall trial population, and dose-proportional. The safety picture was broadly reassuring: overall adverse-event incidence was low, and hypoglycaemia rates were consistent with the broader cohort. The notable caveat is that older participants without obesity were somewhat more likely to discontinue because of adverse events — a reminder that tolerability, not just efficacy, drives real-world outcomes.

The practical takeaway is narrower than the data: when the priority is glycaemic control rather than weight reduction, tirzepatide appears to retain meaningful efficacy in older adults who are not obese. That is a conversation worth having with a clinician, not a prescription delivered by a magazine.

Perhaps the most genuinely new territory is the use of second-generation incretin analogues in autoimmune forms of diabetes. A 2025 review in the Journal of Clinical Medicine examines the emerging — and explicitly off-label — evidence for semaglutide and tirzepatide in type 1 diabetes and latent autoimmune diabetes in adults (LADA). Neither drug is currently approved for these conditions.

The rationale is that the type 1 population has changed. Overweight and obesity are increasingly common alongside T1D, and clinicians now talk about "double diabetes" — patients with T1D who also carry features of insulin resistance, metabolic syndrome, or a family history of T2D. The review summarises a growing body of work suggesting that, as add-ons to insulin, semaglutide and tirzepatide may improve glucose control, support weight loss, and potentially help preserve residual beta-cell function in selected patients.

The language matters here. "May," "growing body of evidence," and "add-on" are doing real work in that sentence. The evidence base is still early, the populations studied are heterogeneous, and the risks specific to type 1 diabetes — including the potential for diabetic ketoacidosis when insulin needs shift — make this firmly a decision to be made with an endocrinologist, not by analogy from a friend's experience with weight loss.

Even within the established uses of GLP-1 medicines, important questions remain open. The most pressing, flagged squarely by the 2025 pipeline review, is maintenance of weight loss. The current expectation is that pharmacological treatment may need to be long-term, possibly indefinite, to preserve the benefit. That has implications for cost, adherence, side-effect tolerance over years rather than months, and the still-young evidence base on very long-term safety.

The gastrointestinal side effects that dominate the early weeks for most patients can usually be reduced by slow up-titration, but they are not trivial, and they are a common reason for stopping. And while the cardiovascular and hepatic signals so far are encouraging, particularly in steatotic liver disease, they need to be confirmed across the newer multi-agonists.

The researchers, writing in a peer-reviewed journal devoted to the biology of aging, introduce a clinical clock they call LinAge2. The pitch is straightforward. Most of the epigenetic clocks sold to consumers were trained to guess chronological age from patterns in DNA methylation. They are, in effect, very expensive birthday-guessers. LinAge2 was trained instead to predict something we actually care about: mortality and functional decline. The authors report that clocks trained on survival and functional aging outperformed those trained on chronological age at forecasting who lives and who does not.

That distinction sounds academic. It is not. If a clock is graded on how closely it matches the number on your driver's license, the best it can ever do is tell you what you already know. If it is graded on how well it sorts the resilient from the frail, it has a chance — at least in principle — to flag something useful before the body announces it on its own.

Imagine two weather forecasters. One is judged on how closely his daily forecast matches yesterday's weather. The other is judged on whether he correctly called the storm. Both will get good at their respective jobs, but only one of them is useful if you are deciding whether to put the boat in the water. The first generation of epigenetic clocks — the ones that powered most consumer tests on the market — were graded on yesterday's weather. They learned to read methylation patterns that drift predictably with the years and to spit back a number close to your age. Impressive engineering. Limited use.

The newer wave, of which LinAge2 is the latest entrant, is graded on the storm. The npj Aging team explicitly frames biological aging as a decline in resilience that drives an exponential increase in mortality risk, and they trained accordingly. The result, in their hands, is a clock that predicts mortality more accurately than chronological-age-trained competitors and one the authors argue can inform clinical decision-making and promote strategies for healthy longevity.

LinAge2 is described by its authors as an enhanced clinical clock. That word — clinical — is doing work. It signals that the model leans on the kinds of measurements your doctor already orders: routine bloodwork, functional indicators, the unglamorous numbers that show up on a printout after an annual physical. The team benchmarked it against several established clinical and epigenetic clocks and reported that it predicts mortality more accurately and provides actionable insights for guiding personalized interventions.

The actionable-insights phrasing is the most interesting part, and also the part to read with the most caution. A clock that says you are biologically 72 when your birth certificate says 68 is a curiosity. A clock that says your number is being pulled upward by, say, a specific inflammatory or metabolic signal is at least pointing somewhere. Whether those pointers translate into longer or stronger lives when acted on — that is a different study, and it has not yet been run at the scale that would settle the question.

If you have sent off a kit in the last few years, the result you received was almost certainly produced by a clock trained on chronological age, or a hybrid that leans heavily on it. That is not a scandal — it is the state of a young field. But it does mean the number you taped to the fridge is best read as an interesting data point, not a verdict, and certainly not a treatment plan. Ask the company what their clock was trained to predict. If the answer is your age, you now know what that buys you. If the answer is mortality or functional decline, ask what evidence supports it and whether it has been benchmarked against peers in the published literature.

None of this is reason to chase the newest acronym down the internet. LinAge2 itself is a research tool at the moment, not a product on a shelf, and the broader category of mortality-trained clocks is still being kicked around by people whose job it is to kick. The honest summary is that the science is moving in a direction that should eventually make these tests worth the money — and that day is closer than it was, but not here.

The arrival of mortality-trained clocks is real progress, and the LinAge2 paper is a credible step. It is not a green light to overhaul anything. The interventions with the best evidence behind them for staying strong, sharp, and independent into the eighth and ninth decades have not changed: regular resistance work, walking that occasionally makes you breathe harder than you would like, sleep you actually defend, blood pressure and lipids kept honest, and a primary care doctor who has read your chart more than once. A better clock, when it arrives in consumer form, will be a useful instrument on that dashboard. It will not be the engine.

For now, the most sensible posture is the one this column tends to recommend on most fronts: pay attention, stay skeptical, and keep doing the boring things that work. The clocks are getting better. So, with any luck, are we.

For decades, fat was treated like a storage closet — a place the body stashed extra calories for a rainy day. That picture is changing. A 2025 review in Life Medicine synthesizes a growing body of work suggesting adipose tissue behaves more like an endocrine organ: it listens, it signals, and as we age, it begins to broadcast inflammatory and metabolic messages that ripple out to the rest of the body.

If you're reading this with a baby monitor crackling in the background, here's the short version: where your body stores fat, and how that fat behaves, may matter more than the number on the scale. And while the evidence is still building, the practical takeaways are gentle, doable, and — mercifully — do not require a 6 a.m. spin class.

The shift in thinking comes partly from new tools. Single-cell and spatial transcriptomics let researchers zoom in on individual cells inside fat tissue and ask what each one is doing. The picture that emerges from this work, as summarized in the Life Medicine review, is of a tissue that undergoes significant remodeling with age — altered fat distribution, visceral expansion, impaired thermogenesis, and chronic low-grade inflammation.

Three cell populations keep coming up. Adipose progenitors, the stem-like cells that normally refresh healthy fat, become less effective. Immune cells shift toward a more inflammatory posture. And senescent cells — cells that have stopped dividing but refuse to quietly exit — accumulate and leak signaling molecules that nudge neighboring tissues toward dysfunction.

None of this is destiny. The review is careful to frame adipose tissue as both an early sensor of aging and a potential driver of it, meaning interventions aimed at fat health may have effects that travel well beyond the waistline.

Not all fat is created equal. The soft layer under the skin — subcutaneous fat — appears relatively well-behaved. The fat that wraps around the liver, pancreas, and intestines is a different story. With age, the body tends to redistribute fat inward, and that visceral compartment is where much of the inflammatory chatter seems to originate, according to the synthesis of remodeling and inflammaging patterns described in the review.

Translation for the school-pickup crowd: a body composition that quietly shifts over the postpartum years and into your forties isn't just a wardrobe issue. It may also be a signaling issue. That's worth knowing — not to add another worry to the pile, but because the levers that influence visceral fat (sleep, movement, what's on the plate) are the same ones that tend to make you feel better day-to-day anyway.

"Inflammaging" is the unlovely word researchers use for the slow simmer of low-grade inflammation that tends to rise with age. It's not the sharp, useful inflammation of a healing cut. It's quieter, more diffuse — and increasingly implicated in the cluster of conditions that show up later in life, from insulin resistance to cardiovascular disease.

The new framing places aging adipose tissue near the center of that simmer. As fat cells age and senescent cells accumulate, the tissue's inflammatory and metabolic signaling disrupts metabolic and immune homeostasis. It's a feedback loop: tired fat tissue contributes to systemic inflammation, and systemic inflammation makes fat tissue more tired.

This is where the evidence is still maturing. The mechanisms are well-described in cells and in animal models, and the human associations are real, but the leap from "adipose tissue drives aging" to "here is the pill that fixes it" hasn't been made. Several therapeutic ideas — senolytics that clear senescent cells, drugs that revive thermogenic brown fat, approaches that recalibrate immune cells within adipose tissue — are in earlier stages of investigation, as the review itself frames them: opportunities, not arrivals.

So what does a sleep-deprived parent actually do with all this? The honest answer is: the basics, but with a bit more respect for why they matter.

Move most days, even briefly. Walking after meals, a few sets of squats while the pasta water boils, a stroller loop around the block — none of it is glamorous, and all of it nudges visceral fat in the right direction. Muscle is one of the most metabolically helpful tissues you can build.

Protect sleep where you can. Easier said than done with a newborn, but on the nights you have agency, treat sleep as a metabolic intervention, not a luxury. Inflammation and sleep deprivation travel together.

Build plates around protein and fiber. Not a diet, not a rulebook — just a default that crowds out the ultra-processed snacks the day will otherwise hand you.

Talk to a clinician about your actual numbers. Waist circumference, fasting glucose, lipid panel, blood pressure. They're imperfect proxies for adipose health, but they're the ones we have, and they're worth knowing.

If there's a quiet gift in this research, it's a reframe. The soft middle that so many parents quietly resent isn't a moral failing or a cosmetic problem. It's a tissue — a working, signaling, occasionally cranky organ — that responds, slowly but reliably, to the way you live.

You don't have to overhaul anything tonight. You probably can't. But the next walk, the next plate with something green on it, the next night you turn the lights off ten minutes earlier — those are the inputs the body is actually listening for. The science is still catching up to where they lead. The direction, though, looks promising.