Why Does Alcohol Affect People So Differently?

In any group, one person is merry after two drinks while another seems untouched all evening. So why does alcohol affect people so differently? It turns out to be one of the most individual pieces of biology there is. In this episode, Jen, Chris and Matt unpack why the same few drinks can land completely differently on two people sitting side by side. They follow alcohol through the liver's two-step, single-lane processing system, explain why more than 500 genetic variants are involved before you've even had a sip, and look at how biological sex, body water, age, food, drink type, medications and mood all stack on top. Along the way they clear up the idea that water cures a hangover, explain why drinks really do hit harder in your 40s, and look at how drinking habits are shifting. No judgment and no rules, just the reasons behind something we've all witnessed. In this episode 02:12 The genetics behind your response 03:27 How the liver breaks down alcohol 06:51 Sex, body composition and body water 08:37 Age, medications and tolerance 09:40 Food, drink type and the water myth 13:12 Changing drinking trends and lower-risk approaches Over 500 Genetic Variants, Before You've Had a Sip (02:12) The scale of the variation is the first surprise. Researchers have identified over 400 genomic regions and more than 500 genetic variants linked to how people experience and metabolise alcohol. That's an enormous amount of difference set before anyone takes a single sip. It's also why blanket advice fits so badly. Two people can drink the same amount at the same pace and end up with very different blood alcohol levels. Even "I know my limits" is only partly true, because those limits shift with sleep, food, stress, age and medications. "There's over 500 genetic factors influencing how you respond before you've even had a sip. Which is a lot of variation, baked in right from the start." — Matt The Liver's Single-Lane Road (03:27) Most of what happens comes down to how the liver processes alcohol, and it does so in two steps. First, an enzyme called alcohol dehydrogenase (ADH) converts the alcohol into acetaldehyde. Then a second enzyme, aldehyde dehydrogenase (ALDH), turns that acetaldehyde into acetate, which is broken down into water and carbon dioxide. Acetaldehyde is the toxic, carcinogenic in-between product. The headaches and nausea come from this, not the alcohol itself. The genes ADH1B and ALDH2 set how fast each step runs. When one runs fast and the other slow, the toxic middle product builds up. The liver can only clear roughly one standard drink per hour. Anything faster simply backs up. "Acetaldehyde is the nasty part, so it's toxic and carcinogenic, and it's responsible for a lot of the unpleasant effects of drinking." — Jen "It's not that the liver is struggling per se. You've got to think of it more like a single-lane road, with traffic building up behind it." — Matt Sex, Body Composition and Body Water (06:51) Genetics is the foundation, and biological sex is one of the most consistent layers on top, much of it down to body water. Alcohol is water soluble, so it spreads through the body's water. On average men have more total body water, so the same drink is more diluted. Men also have ADH activity in the stomach lining, breaking down some alcohol before it reaches the bloodstream. Women have far less. Muscle holds more water than fat, so two people of the same weight can respond very differently depending on body composition. "Alcohol is water soluble, so it distributes evenly through the body in its water. And on average, men have more total body water." — Chris Age, Food, Drink Type and the Water Myth (08:37) Age shifts the whole system, and a few in-the-moment factors change the response too. After 30 we lose roughly 3 to 8% of lean muscle mass per decade, which lowers total body water, while the liver becomes less efficient. That's the real reason drinks hit harder in your 40s than your 20s. Food slows gastric emptying, so a meal with fats and carbs can significantly lower peak blood alcohol levels. Lining your stomach genuinely works. Spirits and carbonated drinks absorb faster than beer or wine. And water helps hydration and comfort, but it doesn't lower blood alcohol or do much for a hangover. "It's a real physiological shift. And that's why people often say drinks hit harder in their 40s than their 20s." — 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.