The Pulse


Science, Human Health, and Asparagus Piss

by Patrick Reynolds

Let's talk about asparagus pee. We need to talk about it. Within its fluorescent ripples in the toilet bowl is the whole story of the scientific endeavor and our own journey towards wellness. I'm not taking the piss!

Asparagus. Braise it with a little olive oil and a touch of salt and you have a wonderful vegetable dish that goes with almost everything. When it's in season I have it almost everyday with my morning eggs. I love asparagus.

And an hour or two later I get a reminder of how much I loved it, as my piss smells a nose-wrinkling combination of sulphur and boiled cabbage.

Clearly I'm not alone in experiencing this phenomenon. Even Austin Powers has to deal with it.

When I was a kid I had a book about weird and wonderful facts about the human body. And I remember one of them was that some people (like me and Austin Powers) produce this smelly urine after eating asparagus, but other people don't have such a side-effect. I stored this bit of information amongst the other bits of useless trivia facts in my head and carried on.


Many years later, I trotted out this fact at a party and was corrected by a med-school friend. He told me that's what everyone used to think, but some researchers had gone back, run some tests, and come to a much more interesting conclusion.

The first "experiment" done in the 40s had consisted mainly of asking people, "Hey, when you eat asparagus does your piss smell bad?" 

Some people said yes, some people said no, and so the logical conclusion was that we don't all have the asparagus pee side-effect. But in a more rigorously controlled study, it was found that in fact ALL the participants had stinky urine, but that only some of them had the ability to SMELL it. As it turns out, if you're missing certain alleles of the olfactory genes you simply can't pick up that sulphury stinch.

This came home for me, literally, when my wife and I started living together. I told her one morning, "sorry about the bathroom, we ate all that asparagus earlier," and she looked at me like I was speaking Klingon. A few minutes later we were both standing in the bathroom, me saying "You really can't smell that!?" and her saying " What smell? What the hell are you talking about!?" The smell theory was true!

About 200 years ago we as a species started applying the scientific method to the world around us in an organized way. The idea was simple. Don't just guess at things, don't just accept what you've been told. Test your ideas, find the flaws in your theories, abandon ideas that don't fit the data and embrace those that do, even if it makes you uncomfortable. This is all science is. And by sticking to those basic principles we rocketed forward as a species, from horse and buggy to a rover on Mars, from the printing press to the global data network you're reading this on.

And here with the asparagus piss is a perfect little example. Everyone thought they knew the answer. But when we went back and checked that answer with data, we discovered a delightful new answer. And instead of me and my wife thinking the other was crazy and getting into a fight, we were able to understand that what was happening was an explained phenomenon. Science is cool. 

Everyone thought they knew the answer. But when we went back and checked that answer with data, we discovered a delightful new answer.

You would think that would be the end of the asparagus story, but  subsequent teams have done further research, and it appears that the reality might be a mix of the two theories. There are people who don't produce the stinky urine at perceptible levels, there are people who do, there are people who can smell it, and people who can't. Further research is needed. It's complicated.

Think about that. The asparagus smell seemed like a simple problem. You eat asparagus and you either have stinky pee, or you don't. But the reality turned out to be much more complicated. Now imagine instead of the smell of urine you were actually trying to prove a connection between eating something and having a better health outcome. The variables multiply by the dozens, the confounding factors are limitless, and the experiments are incredibly hard to set controls for.

This is why the science behind exercise and nutrition can seem so contradictory. In the 80's the "bad guy" was identified as fatty foods. But now we know that a healthy amount of fats in your diet is very beneficial. Carbs used to be the foundation of the food pyramid. Now we have a much better understanding that excess carbs are a huge part of the problem. Steady aerobic exercise used to be valued for its fat burning power. Now we know that occasional high intensity bursts mobilize fat even better.

People see how the scientific consensus zigs and zags, and a lot of them think "Stupid scientists! Get your story straight!" But the contradictions and reversals are actually a good sign that science is working. Human beings are messy, complicated things, and the science about us is going to be similarly complicated. There's going to be a lot of noise in the data.

What this all means for you is this. Don't get too wrapped up in the nutrition and exercise headlines. Every week you're going to see the results of a new study splashed across your browser page. These will be given sensational titles like  "High protein diets as risky as smoking!" or "Can drinking too much coffee kill you?". You'll be told this food is the new savior, and that one is the new enemy. Trying to eat according to the latest findings will drive you crazy.

Let me help you out. I spend time each week reading these studies and staying up to date on the latest research so you don't have to. Here's a summary of the best science we have on eating right and staying fit:

• Eat a wide variety of fresh foods. Most of them should be plants. This will completely cover your nutritional needs. Vitamins don't work.

• Everything besides fresh plants should be consumed in moderation. This includes carbohydrates, meats, dairy, sweets and alcohol.

• Exercise at a safe, moderate pace throughout the week. Your exercise routine should include some resistance training to keep your muscle mass and bone density at good levels.

And that's it. That's the culmination of our best science. Everything else is just the noise of research getting totzwiux7ammtw8f1adamg.jpg the bottom of things.

Perhaps in 50 years the baseline advice will be different. And in 200 years I'm sure we'll look back at our current practices the way we view bloodletting and leeching today. But for now, this is what we've got. It's not headline news, but the reality of how your body works never is. It's nuanced, has wide margins of error, and is different from person to person. 

Just like asparagus piss.




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