So That's Why

Your brain builds a convincing world every night, then clears nearly all of it before you wake. So why do we dream? Most of us have between four and seven separate dreams a night and forget up to 95% of them within minutes. Jen, Chris and Matt work through what is actually happening in the brain during REM sleep, why the forgetting is a consequence of the mechanism rather than a memory failure, and what the best current evidence says dreaming is for. The episode covers the four regions that swing out of balance during REM, the 2024 Scientific Reports study on dreaming and emotional memory, why babies spend so much more time in REM than adults, the simple line that separates a bad dream from a nightmare, and whether what you eat can genuinely change what you dream about. By the end you should be able to explain the whole thing in one sentence. Chapters 00:00 Why do we dream 01:34 How much we actually dream and why we forget it 02:26 What is happening in the brain during REM sleep 07:37 Dreaming as emotional processing 10:44 How dreaming changes with age and how you wake 12:46 What separates a bad dream from a nightmare 15:15 Can food actually change your dreams 17:22 The verdict on why we dream Four Regions Swing Out of Balance During REM Sleep (02:26) Most vivid dreams happen during rapid eye movement sleep, and what makes REM unusual is not simply that the brain is busy. Several regions shift at once. The prefrontal cortex, which handles logic and self awareness, powers down. That is why nothing in a dream seems questionable while it is happening. The amygdala, involved in processing emotions, becomes more active, which helps explain the emotional intensity. The visual cortex fires with no real input coming in, generating the images fresh rather than replaying old footage. The hippocampus keeps feeding the dream real material from recent memory. Underneath it all, the brainstem fires bursts of signals and the rest of the brain builds a story around them, which is why a dream lurches from your kitchen to a beach with no join. "My brain's improvising over random noise and pretty much hoping that I don't notice." Matt The Same Switch Explains the Strangeness and the Forgetting (06:46) The prefrontal cortex is not only the region that would normally question a dream. It is also the part that bookmarks a memory as worth keeping. With it turned down, dreams barely get flagged, so they are hardly stored. "The one night your brain does its most vivid work, it keeps no receipts." Chris Dreaming Looks Like Emotional Sorting (07:37) The leading theory is that dreaming is emotional and memory processing. The brain holds onto the memory of something that upset you while turning down the emotional charge attached to it. A 2024 study published in Scientific Reports found people who dreamed kept their emotionally charged memories, let neutral material fade, and rated the charged memories as less upsetting by morning. Older work from sleep researcher Rosalind Cartwright found people going through a painful breakup who dreamed about it recovered their mood noticeably faster. The hosts are careful with the limits here. This is still open science, and much of it shows a link rather than a nailed down cause. A Nightmare Is the Same Process Running Hot (12:46) The dividing line is simple. A nightmare wakes you. A bad dream is unpleasant and you sleep through it, whereas a nightmare pulls you out of REM with the fear still running. Roughly two thirds of dreams carry sadness, worry or anger, and only about a fifth are clearly happy. "A nightmare isn't your mind failing. It's that same system working on something heavy and getting stuck partway through." Chris Stress is the biggest trigger, and lost sleep does it too, because the brain packs in extra REM to catch up. Frequent nightmares are common after trauma, affecting up to 70% of those living with it. If nightmares become frequent and start wearing you down, it is worth speaking to a GP, as treatments such as imagery rehearsal therapy genuinely work. About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website:

Pre-diabetes might be the only common diagnosis experts can't agree on, and a quarter of the people told they have it quietly recover on their own. In this episode, Jen, Chris and Jamie unpack why we develop pre-diabetes, why it builds in near silence for a decade or more, and why a warning that lands while you feel perfectly fine is still genuinely good news. The team dig into the two changes at the heart of it: muscles that stop listening to insulin, and insulin-making cells that go quiet rather than die off. They explain the "fat in the wrong place" idea that pulls it all together, why even slim people can be affected, and why three different tests can disagree so wildly that the experts still argue about the word itself. Then comes the hopeful part, which is the unusually deep evidence that modest, sustainable changes can shift the whole picture. As Chris puts it, pre-diabetes is best thought of as a stage, not a disease. In this episode Two Quiet Changes Drive Pre-Diabetes (03:14) It's Fat in the Wrong Place, Not Just How Much (05:41) Why Experts Still Argue Over the Diagnosis (07:01) What the Evidence Says Actually Works (10:12) (Timestamps are based on the transcript's section markers. Please verify against the final edit before publishing.) Two Quiet Changes Drive Pre-Diabetes 03:14 Pre-diabetes comes down to two things drifting slightly out of step over years, each making the other worse. The first is insulin resistance, where your cells stop listening to insulin as well as they used to. The cells that go deaf first are your muscles, the biggest customer for blood sugar, taking up about three-quarters of it after a meal. The second is in the pancreas, where the insulin-making beta cells gradually stop keeping up. Insulin tells your cells to take sugar in and use it. When they stop listening, sugar hangs around in the bloodstream. This can build for ten or even twenty years before anything shows on a test. It's a drift, not a breakdown. The reassuring twist: the beta cells largely don't die. They seem to change job and go quiet, so there is a route back. Chris: "Pre-diabetes is a stage, not a disease." Jamie: "They've downed tools. They're still in the building, they're just not doing the skilled bit." It's Fat in the Wrong Place, Not Just How Much 05:41 The idea that pulls everything together is a domestic one. Picture your body's fat as something you store in a cupboard. Most of it is meant to live there, under the skin, safely. But every cupboard has a size, and that size is different for everyone. The trouble starts when it overflows into places it was never meant to go. This explains why you can be fairly slim and still develop pre-diabetes. Your personal storage cupboard might just be a small one. It's part of why people of South Asian heritage can be affected at lower body weights, and why screening thresholds are set lower for some groups. The cupboard hasn't shrunk. Many of us are simply filling it faster and emptying it less than a couple of generations ago. Jamie: "So the bathroom scales are never really telling the interesting story." Why Experts Still Argue Over the Diagnosis 07:01 Whether you count as having pre-diabetes depends heavily on which test you happen to get, and that is where the debate comes from. There are three common ways to diagnose it, and the share of people who count swings wildly between them. The most common, the HbA1c test, adds a further wrinkle, because it reads a touch higher in Black patients for the very same blood sugar. One analysis found the proportion of a group counted as pre-diabetic ranged from about 4% to over 40%. Same people, different test. Over a few years, very roughly a quarter of people progress, half stay put, and a quarter drift back to normal. This busts the biggest myth, that pre-diabetes means diabetes is definitely coming and nothing can be done. It's a real signal, just drawn with a slightly blunt pencil. What the Evidence Says Actually Works 10:12 After all the uncertainty, this is one of the most changeable situations in medicine, and the evidence is unusually deep. In a landmark prevention trial, people making modest changes cut their chance of developing diabetes by getting on for 60% over about three years, which was clearly better than the medication group in the same trial. The levers are reassuringly dull: roughly 7% weight loss and about 150 minutes of movement a week, the equivalent of a brisk 20 to 25-minute walk a day. Movement helps on its own. People who missed the weight target but kept moving still cut their risk by over 40%. A Mediterranean-style diet of veg, beans, whole grains and olive oil meaningfully cut new diabetes in one big trial, even when people barely lost weight. A responsible note from the team: the pre-diabetic range is typically an HbA1c of 42 to 47. If it's on your radar, that's a good reason for a chat with your doctor, not a cue to panic or self-diagnose. Jamie: "So the walking and eating group beat the drug? That's not how these stories usually go." About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Ask anyone what makes us cry and they'll say sadness. When researchers track real crying episodes, they find something else entirely. Jen, Chris and Matt unpack why we cry when we're sad, and discover the answer isn't the sadness at all. It's powerlessness. The triggers people actually report are far smaller than anyone assumes, turning up as conflict, criticism, rejection and minor personal failures rather than bereavement and tragedy. The team follows the signal from the limbic system to the brainstem to the tear glands, explains why tears spill over your eyelid at all, and looks honestly at the evidence behind the popular idea that crying flushes stress toxins out of the body. They also tackle the biggest contradiction in this research. Over 70% of people say crying makes them feel better, while controlled lab studies found the opposite. The resolution comes down to timing, and to who else is in the room. Chapters 00:00 Why do we cry when we're sad 00:51 Powerlessness, not sadness 04:20 What happens in the brain and body 08:33 What emotional tears are made of 10:51 Why crying varies so much between people 16:02 Does crying actually make you feel better 19:03 When crying isn't good for you 21:29 The verdict on why we cry The Real Trigger Isn't Sadness, It's Powerlessness (00:51) Sadness is almost always present when we cry, but rarely on its own. It turns up blended with anger, fear, frustration or disappointment, and the common denominator underneath is not being able to do anything about the situation. One psychologist frames the tipping point as the moment psychological demands exceed your sensory effective threshold. In other words, the emotion has outpaced whatever coping mechanism was available at the time. "So it isn't then about how bad the thing is, it's the gap, I guess, between that and what you've got left in the tank." Matt This is also why the same event can floor you one week and barely register the next. Sleep deprivation, alcohol, stress and mental health all lower the threshold. Why Tears Actually Run Down Your Face (04:20) The sequence starts in the limbic system. The amygdala helps determine how intense an emotion feels, while the anterior cingulate cortex helps you recognise and respond to it. From there the signal travels to the pons in the brainstem, which activates the tear glands through a facial nerve. The overflow itself is simpler than most people expect. The glands produce fluid faster than the tear ducts can drain it, so the drainage isn't failing, it has just been outpaced. "So think about it like a sink with the tap on harder than the plug hole can cope with." Jen The team also covers the three tear types (basal, reflex and emotional), and why there's no rigorous evidence that any other species produces the third kind. The Stress Toxin Idea Doesn't Hold Up (08:33) Some studies have reported higher levels of prolactin and adrenocorticotropic hormone in emotional tears, alongside compounds including leucine enkephalin, potassium and manganese. Chris and Jen are careful to flag that these findings still need stronger replication. That matters, because they're the foundation of the popular idea that tears flush stress toxins out of the body. One of the influential early studies supporting it was not successfully repeated by later researchers. The chemistry that is present, including oxytocin, vasopressin and endogenous opioids, points at stress regulation and social connection rather than detox. Whether a Cry Helps Depends on Who's in the Room (16:02) Over 70% of people say crying makes them feel better. Controlled lab studies found criers felt worse immediately afterwards. The resolution appears to be timing. One study tracked mood after a sad film and found criers felt worse straight away, recovered within 20 minutes, and by 90 minutes were better than before the film began. Context does the rest. Social support is the biggest single factor. There's also a finding about numbers that will be familiar to anyone who has cried at work, because people tend to feel better crying alone or with one other person, and worse with two or more. "There's a real permission in that, isn't there? You're not actually then doing crying the wrong way." Matt The episode closes on what tears are actually for. Researchers photographed faces and digitally removed the tears, and the same faces with tears visible were judged as sadder and more in need of help. "So a good cry isn't a system failing, it's a message going out, and whether you feel better depends far more on who's around to answer it." Jen About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Nearly all of us blame the calendar for wrinkles, but the science says the calendar is mostly innocent. Estimates put at least 80% of visible facial ageing down to sun exposure, not birthdays. In this episode, Jen, Chris and Matt go one layer beneath the surface of the skin to find out what a wrinkle actually is. They cover the slow collagen decline that starts in the late twenties, the fibroblasts that build the skin's scaffolding, and the MMP enzymes that break it down again. They explain how UV light manages to speed up demolition and quieten repair in a single move, why not all wrinkles are the same thing, and the sharp collagen drop that arrives around menopause. There is also a straight answer on collagen drinks, and the cheap, unglamorous product that outperformed everything else in a four-year controlled trial. Key Point Timestamps 00:04 The question and the 80% figure 01:51 The collagen timeline, decade by decade 03:15 Collagen, elastin, fibroblasts and MMPs 08:18 How sunlight causes most of what we see 10:06 Dynamic, static and sleep wrinkles 12:22 What the evidence says about collagen supplements 14:28 SPF, retinoids and vitamin C 18:02 Injectables, lasers and the lifestyle stuff Wrinkles Form in a Layer You Cannot See (03:15) Wrinkles do not start in the visible surface of the skin. They form in the dermis underneath, where three things do the structural work. Collagen provides firmness and tensile strength, elastin lets skin stretch and spring back, and hyaluronic acid holds water and keeps the layers plump. All three are made and maintained by one type of cell, the fibroblast. In young skin, fibroblasts lay down fresh collagen and elastin about as fast as the old material wears out. Two things change that with age. A growing share of fibroblasts become senescent, meaning they largely stop producing and start giving off low-level inflammatory signals. At the same time, a family of enzymes called MMPs becomes more active. Their normal job is useful, clearing out worn collagen so fresh collagen can replace it, but the balance tips. "Collagen and elastin get broken down and disorganised faster than the fibroblasts rebuild them." — Chris Sunlight Speeds Up Breakdown and Slows Repair (08:18) When ultraviolet light hits the skin, it generates a burst of unstable molecules called free radicals. Within minutes, those free radicals switch on the MMPs, the very enzymes that break collagen down. Each unprotected sunny hour becomes a small spike of collagen loss. Then it does a second thing simultaneously. It quietens the signal that tells fibroblasts to make new collagen. That is why sunlight accounts for so much of what shows up on skin. It is not vague damage. It drives both ends of the same process, and the effect is cumulative rather than dramatic. "The sun isn't ageing our skin in some vague way, it seems to be driving the two exact processes you've both just described at both ends, which kind of makes it feel less like fate and something that we can actually deal with." — Matt The Collagen Drop Nobody Talks About Enough (10:06) Individual variation matters enormously here. How much protective pigment skin produces is largely down to genetics, and that pigment strongly affects how much UV gets through in the first place. Hormones matter too, and this part is badly under-discussed. Around menopause, as oestrogen falls, women can lose up to about 30% of their skin's collagen in roughly the first five years. By the age of 50, nearly 50% can be gone. Set against the background rate of one to 1.5% a year, that is a very different order of change arriving in a very short window. The Cheapest Bottle in the Shop Wins (14:28) For collagen drinks and powders, a recent pooled analysis of 23 peer-reviewed trials found the strongest independent studies do not show a clear effect on wrinkles or elasticity. The gut cannot absorb collagen whole, so it breaks it into amino acids first. What does have strong evidence is considerably less exciting. In a well-known controlled trial, people using a daily broad-spectrum sunscreen showed no measurable increase in skin ageing over four years, while the comparison group aged visibly. Retinoids and topical vitamin C form the next tier down. "The cheapest and most ignored bottle in the shop beats the 40 quid miracle serum sitting right next to it." — Matt "It's never too late to start, because you're always preventing the next decade of damage even if you can't undo the last one." — Jen About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast

Your metabolism has an alibi. A study of over 6,000 people found metabolic rate is essentially flat from 20 to 60. Most of us start blaming our metabolism somewhere in our thirties. The largest study ever done on human energy expenditure suggests we have been accusing the wrong party. Using doubly labelled water, the gold standard for measuring energy expenditure in real life, researchers tracked over 6,000 people aged from eight days old to 95 across 29 countries. Between 20 and 60, metabolic rate holds steady. No dip in the thirties, no crash in the forties, and no measurable effect of pregnancy or menopause once size and body composition are accounted for. A real decline does arrive after 60, at around 0.7% a year, and Jen, Chris and Matt unpack the five things driving it. They also cover what actually holds it off, from resistance training and protein targets to where creatine, caffeine and green tea genuinely sit in the evidence. Chapters 00:00 Why we all blame our metabolism 00:54 What the biggest study on energy expenditure found 04:58 So why do we gain weight in midlife 07:03 The five things that change after 60 13:07 Resistance training at any age 14:14 The protein numbers that have shifted 16:55 Creatine, aerobic activity, caffeine and green tea 22:07 The verdict on metabolism and age Metabolic Rate Is Flat From 20 to 60 (00:54) The doubly labelled water technique tracks heavy forms of hydrogen and oxygen as they leave the body, which tells researchers how much CO2 someone is producing and therefore how much energy they are burning. Crucially, it measures ordinary life rather than a treadmill test. Over 6,000 participants, aged eight days to 95, across 29 countries Energy expenditure peaks at around eight or nine months old, when babies burn roughly 50% faster than an adult relative to body size The rate settles at around 20 and then stays flat for four decades "You've been blaming an innocent party, so it's like accusing a housemate who moved out years ago of finishing all the biscuits." Jen Why Midlife Weight Gain Happens Anyway (04:58) If the rate is flat, the weight gain needs another explanation. Tom Sanders, professor of nutrition at King's College London, said findings like these support the view that rising obesity is driven by excess energy intake rather than falling energy expenditure. Alongside that, muscle mass tends to fall, and a body with less muscle burns less energy in total. "So your machinery isn't getting worse with age. There may simply be less of the expensive machinery in your body." Jen The Five Things That Change After 60 (07:03) After 60, total energy expenditure falls by around 0.7% a year, which reaches roughly 26% lower by the age of 90. Five mechanisms run at once. Sarcopenia. Inactive adults can lose 3 to 5% of their muscle per decade from their thirties. Muscle is metabolically active tissue, so it costs energy even at rest. Jen compares it to the standing charge on an energy bill, the bit you pay whether or not you switch anything on. Mitochondria. Mitochondrial DNA accumulates mutations and oxidative damage, so ATP production becomes less efficient. Mitophagy, the process that clears out damaged mitochondria, also slows. Hormones. Growth hormone, IGF-1 and testosterone decline alongside changes in thyroid function and insulin sensitivity. Reduced output per kilo. The remaining tissue does less per kilogram than it used to. Anabolic resistance. Ageing muscle responds less strongly to protein and to being used. "So it's wear and tear, plus the maintenance team that's also slowing down." Matt What Actually Holds It Off (13:07) Resistance training is the single most evidence-backed intervention because it targets the biggest modifiable driver. Muscle protein synthesis machinery stays responsive to training into very old age, so there is no point at which starting stops being worthwhile. Protein targets for older adults now sit at roughly 1 to 1.2 grams per kilogram of body weight, rising to 1.2 to 1.5 for those training Around 25 to 40 grams of good quality protein per sitting, spread across three meals, does more than one large evening portion A 2025 systematic review and meta-analysis found creatine plus resistance training improved lower limb strength and lean muscle mass more than training alone Caffeine and green tea have real but small and short-lived effects If you have kidney disease or are on a medically restricted diet, protein targets are a conversation for your doctor "Keep the muscle you've got and feed it properly. Your body stays responsive to training and diet far longer into life than people assume." Chris About So That's Why So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research. Website: https://www.vegetology.com/so-thats-why-podcast