_edi.jpg)
Metabolism, Reclaimed:
What healthy aging asks of your metabolism,
and where whole-food nutrition can help
Getty Images
Metabolism might be the most used and least understood word in nutrition. Most of us have absorbed the idea that it means the rate at which we burn calories, and that some people are simply lucky to have a fast metabolism. This reduces a whole-body coordination system to a single number, misrepresenting the remarkable complexity of what is actually happening.
In reality, metabolism runs in two directions. Catabolism breaks down food and stored molecules to fuel everything from breathing to exercise. Anabolism uses that fuel to build and repair tissue. A healthy metabolism moves fluidly between the two depending on whether you have just eaten, trained, or slept. Coordinating that movement is a layered set of processes: hormonal signaling, energy conversion, cholesterol and lipid handling, waste clearance, and cellular renewal. Think of an orchestra, not an engine.
Metabolism also matters more than most health conversations acknowledge. Around 1 in 9 adults worldwide are living with diabetes, and 1 in 8 are living with obesity.¹ ² Both are, at their core, signs that the body’s metabolic balance has been disrupted.
The quiet change most people experience
Long before anything appears on a health chart, metabolic change shows up as something far less dramatic and much harder to name.
It is the afternoon energy dip that did not happen before. It is the weight that creeps on with no change to diet or exercise. It is recovery from a heavy meal taking noticeably longer than it used to.
For women especially, this shift can arrive faster and more abruptly. Falling estrogen through perimenopause and menopause changes where fat is stored, reduces insulin sensitivity, and alters cholesterol profiles, sometimes within a couple of years. A real physiological change, though often met with advice to simply eat less and move more. For men the drift tends to be slower and less openly discussed, which usually means it goes unnoticed until a blood test flags something.
Then there is the growing group told their numbers are “borderline” or “pre-” something, advised to monitor it, and sent home without much of a plan. And a growing number of people taking GLP-1 medications, navigating an entirely new set of questions: what is happening to my muscle mass, and what does nutrition look like if I stop?
These are the people behind metabolic health. Not a category, but a universal experience of bodies that change with time.
Why the same habits stop working
Several interconnected biological shifts drive this, and they compound on each other. Most of them are recognized hallmarks of aging, the biological processes researchers have identified as the underlying drivers of how we age.³ Metabolism is where many of them converge.
The first key driver is inflammation. Chronic low-grade inflammation – “inflammaging” – interferes with insulin signaling and pulls the wider hormonal network out of sync. Once that coordination slips, other problems follow.
Insulin sensitivity begins to fall. Insulin and glucagon form the primary axis managing how sugar is stored and released, with cortisol, thyroid hormones, leptin, ghrelin, and gut peptides including GLP-1 fine-tuning the rest. These hormones are not metabolism itself. They are its language. As cells respond less readily to insulin, that language gets harder to hear: glucose regulation loses precision and energy delivery becomes less reliable. Researchers call this “deregulated nutrient sensing” – another hallmark. That afternoon crash is the result, felt rather than measured.
Mitochondria become less efficient too. Carbohydrates, fats, and protein each follow their own route – glycolysis, beta-oxidation, deamination – but all roads lead to the mitochondria, where fuel becomes ATP, the energy currency that powers every cell. With age that conversion slows, and the most energy-hungry tissues (brain, heart, and skeletal muscle) feel it first. Mitochondrial dysfunction is, unsurprisingly, also in the hallmarks of aging.
Cholesterol handling also drifts. Cholesterol itself is a necessity, needed to form cell membranes, steroid hormones, bile acids, and vitamin D. But with age LDL clearance slows and HDL function deteriorates, while inflammation disrupts the liver’s regulation of cholesterol traffic. The result is a slow, largely silent rise in circulating LDL. This is not a cholesterol problem in isolation. It is a signal that the clearance system is losing precision.
Cellular clean-up slows alongside it. AMPK and mTOR are the internal sensors switching cells between catabolism and anabolism: build, break down, or recycle. With age that balance tips, and autophagy, the process clearing damaged proteins and worn-out mitochondria, becomes less efficient. Disabled macroautophagy is itself a hallmark of aging. Waste accumulates and mitochondrial function drops further as a result.
Finally, muscle loss compounds everything. Skeletal muscle is the body’s largest site of glucose uptake, so as lean mass declines, so does the capacity to clear glucose from the blood, accelerating the insulin resistance already underway.
None of this is fixed or destiny. These are dynamic processes, and every one of them responds to how we eat, move, and live.
The gut is a metabolic organ
The previous post in this series established the gut as the foundation – the system through which every other nutrient, supplement, or longevity intervention must operate. What it did not explore is the gut’s role as a metabolic organ.
Beyond digestion and microbial diversity, the gut actively shapes how the body handles energy, blood sugar, and appetite. It processes nutrients before they reach circulation, and the metabolites it generates have direct consequences for insulin sensitivity and inflammatory tone. The gut does not just support metabolism. In several meaningful ways, it runs it.
Those metabolites are short-chain fatty acids (SCFAs), produced when gut microbes ferment dietary fiber. Their effects reach beyond the gut: propionate plays a role in liver glucose metabolism, butyrate strengthens the gut barrier and helps regulate inflammation, and acetate serves as an energy source throughout the body. As the previous post covered, different fibers ferment in different places and produce different SCFA profiles, which is why fiber diversity matters as much as quantity. When that balance is disrupted – “dysbiosis,” another recognized hallmark of aging – SCFA production falls, and the metabolic benefits fall with it.
The gut also runs its own hormone system. Specialized cells in the intestinal lining, called L-cells, release GLP-1 and PYY in response to nutrients and the metabolites arriving from fiber fermentation. These hormones enhance insulin secretion, slow gastric emptying, and promote fullness. If GLP-1 sounds familiar, that is because it is the same pathway weight-loss drugs target. The pathway itself, though, is ordinary gut biology that food activates every time we eat.
Certain fibers also intervene directly in cholesterol metabolism. The liver uses cholesterol to make bile acids, which are released into the gut to aid fat digestion and then normally reabsorbed. Fibers such as chitosan, found in fungal cell walls, bind those bile acids before reabsorption, forcing the liver to make new ones from circulating cholesterol. The net effect is a reduction in LDL.
Where diet has real leverage
What we eat influences every layer described above: the hormonal environment, the quality of cellular fuel, cholesterol handling, microbiome composition, and the micronutrients every metabolic process depends on.
High-quality protein matters more with age, because it preserves skeletal muscle, the body’s largest site of glucose uptake, and supports stable blood sugar. With fat, quality beats quantity: monounsaturated and polyunsaturated fats support cell membranes, inflammation, and hormone signaling, while saturated and trans fats work in the opposite direction, promoting inflammation and impairing insulin signaling. Fiber feeds the microbes producing SCFAs and helps trigger the body’s own appetite hormones, with certain fibers reducing circulating LDL. Type and diversity both matter.
Micronutrients are the quiet enablers of metabolism. Phosphorus is required to form ATP. Zinc contributes to normal macronutrient and fatty acid metabolism. Choline is essential for exporting fat and cholesterol from the liver, and is consistently underconsumed in plant-forward diets; without it, fats accumulate there and compromise the liver’s central metabolic role. Beyond these, bioactives add another layer: spermidine induces autophagy and mitophagy, the clean-up processes that keep metabolic machinery, including mitochondria, functioning well.⁴ ⁵
Diet is by no means a quick fix – its power lies in consistency. It is not pharmacology, and diet alone will not reverse established metabolic disease. But the cumulative impact of whole-food nutrition is one of the strongest levers influencing long-term metabolic health.
Introducing Fermotein®: A whole-food metabolic matrix
Fermotein® is a whole-food ingredient built to support a metabolism-first approach to healthy aging and longevity.
The nutrient-dense mycelium powder is a complete protein containing all amino acids, including all nine essential amino acids. It also naturally provides around 30% fiber unique to fungi, including chitin and chitosan, which differ from plant-derived fibers in both structure and fermentation behavior. Beyond fiber, Fermotein® contains monounsaturated and polyunsaturated fats and is low in sugar and saturated fat. Fermotein® is among the richest known food sources of spermidine, with phosphorus, choline, and zinc supplying the micronutrient infrastructure that energy production, fatty acid, and macronutrient metabolism depend on.
In an ex vivo study with TNO using human intestinal tissue, Fermotein® consistently increased GLP-1 release in ileal tissue across three independent donors, with dose-dependent effects also seen in colon tissue .⁶ Because Fermotein® delivers both protein and fiber, two well-known triggers for GLP-1 secretion, it offers a plausible dual-trigger route to supporting the body’s own satiety signaling.
Clinical evidence is still building, and we will share more as it arrives. But a single whole-food ingredient bringing protein, fiber, healthy fats, spermidine, and micronutrients together in one matrix is well positioned to support metabolic health through several complementary pathways at once.
Metabolism as the connective tissue
Across this series we have looked at cellular health, performance nutrition for the aging athlete, and gut resilience. Metabolism is the underlying chemistry that runs through all three. It turns food into function, and when it loses precision, every other pillar of longevity feels it.
This brings us back to the person whose habits have not changed but whose body has. That is not a failure of willpower. It is a metabolic system asking for different inputs than it needed twenty years ago. Supporting metabolic health through consistent, nutrient-dense, whole-food eating is not a response to any cultural moment, it is the most foundational and cumulative investment nutrition can make for longevity.
The approaches that hold up as longevity moves into the mainstream will not be the ones chasing the latest mechanism or molecule. They will be the ones that answer with food built for the long arc of healthspan.
Interested in further insights, or trying Fermotein® in your own product?
(1) International Diabetes Federation. IDF Diabetes Atlas. https://diabetesatlas.org/.
(2) World Health Organization. Obesity and overweight fact sheet. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight.
(3) López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: an expanding universe. Cell. 2023;186(2):243–278. doi:10.1016/j.cell.2022.11.001.
(4) Borsky P, Holmannova D, Soukup O, et al. Distinct roles of urolithin A and spermidine in mitophagy and autophagy: implications for dietary supplementation. Nutr Res Rev. 2025;39:e8. doi:10.1017/S0954422425100292.
(5) https://pmc.ncbi.nlm.nih.gov/articles/PMC11673406/ — please confirm full citation details before publishing.
(6) The Protein Brewery / TNO Health & Work. Fermotein® stimulates GLP-1 release in ex vivo human intestinal tissue (InTESTine™). TNO Restricted Report No. 2026 R15096. Leiden, NL: TNO; 2026. Data on file.