Dear Mark: Swimming Pool Chemicals, Washing Veggies, and Carb Blockers

Who doesn’t like a lovely day at the pool? Unless you can’t swim, there’s no reason not to love the cool water, the bright sun, the ping pong (every swimming club worth a dime has a ping pong table, or several of them), the face dunking, the high dive, and the chicken fights. But what if something sinister churned within the depths of the chlorinated water? What if by entering that pool you were risking life, limb, and the pristine alabaster of your eyeball? In today’s edition of Dear Mark, I’ve gone back to the roundup format. I begin with the question of swimming pool chemical safety, follow with a query about washing vegetables, and I finish the post with a short section on carb blocking agents. Sound good?

Let’s go:

Dear Mark,

I was wondering about possible negative effects of pool water. I enjoy a good sprint workout in the pool, especially when traveling and staying in a hotel. Could the chlorine or other chemicals be harmful since they do sometimes make me itch a little afterwards and burns my eyes (especially if I open them underwater)?

Thanks and Grok on,


I hate to be the bearer of potentially bad news, but there’s probably something to this. Most pools use chlorine as a disinfectant, to keep the water clear of bacteria and other microbes, and it’s darn good at that. Reason? Chlorine, in its pure form, is toxic. The chlorine in the pool is obviously diluted, so it’s not going to burn or kill you outright, nor are you a microbe, but toxicity concerns remain. Your first clues that it might be doing something untoward, of course, are the burning eyes and itching skin. That’s pretty normal, albeit disconcerting. As a kid, I used to get red, burning eyes when I’d spend the day at the pool. Nowadays, I think back to that and wonder…

Anyway, red eyes clear up and itchiness subsides, but could other problems be lurking beneath the surface? Maybe. Chlorine reacts with other substances, including bodily fluids and various organic matter, to form disinfection byproducts (DBPs), which may have novel – and unwanted – health effects. Let’s take a look at some evidence:

  • When chlorinated pool water meets dimethylamine (found in urine and sweat), nitrosamine carcinogens (the same type of compound that forms when we overcook bacon) form, and appear in pools at concentrations up to 500-fold higher than drinking water. Though it’s unclear whether or not these particular nitrosamines are absorbed by pool users, some nitrosamines are absorbed through (rat) skin. Why should you care? Well, nitrosamines are used to induce bladder cancer in rodents, and chlorinated pool and bathing water usage have been linked to bladder cancer in humans (though it’s just observational).
  • Chloramine, another DBP, has been linked to asthma in pool workers and elite swimmers.
  • A recent study found over 100 chemical byproducts in swimming pools, many of them toxic. Before and after 40 minutes of swimming laps in such a pool, healthy subjects’ biomarkers were tracked and recorded. One marker suggested increased lung permeability and inflammation, while another marker indicated a kind of DNA damage that, if unchecked, might lead to cancer. Subjects had also accumulated elevated levels of four of the most common DBPs after 40 minutes in the pool.

The good news is that you’re probably okay. Problems may arise when we absorb and uptake these DBPs (like chloroform) via inhalation, dermal absorption, and the ingestion of affected water on a regular basis. The populations that seem to suffer most from pool-related maladies are the ones who spend significant amounts of time at, in and around the pool – competitive swimmers (with their infamously long daily workouts), lifeguards, and other pool workers – and it doesn’t sound like you’re living in the water. If you stick to short, intense sprints, performed only when you have access to a pool on business or vacation, I wouldn’t worry.

Hello Mark,

Can I wash my veggies with dish washing solutions? Or must I use special vegetable washing solutions?

Thank you for your time,


Actually, you don’t have to use either. Tap water will work just as well. But don’t take my word for it. Check out the results of this study that explored this exact question. They used tap water, Palmolive, and four different vegetable washes to process unwashed, pesticide-laden produce and found no differences in pesticide residues when all was said and done. Luckily, washing the produce – whatever the solution used – took care of most of the surface pesticide residues (not all of them, though, not to mention the pesticides that are integrated within the produce).

So, yes, dish washing solution will work just as well as special vegetable washing solution, but so what? Water does the job, too.

Hi Mark,

Whats the deal the Carb-inhibitor/blocker pills, do they work? Are they safe? If so, which ones do you recommend? Thanks.


Carb blockers use an extract of the white kidney bean that inhibits alpha-amylase, a digestive enzyme that breaks down starch. Without alpha-amylase doing its work, we can’t effectively digest starches, and they pass through to the small bowel to be fermented by gut flora. Sounds great, right? You get to eat carbs and you don’t digest them. They don’t turn into glucose, they don’t get absorbed, and insulin stays low.

I kid, but actually, a study shows that this is pretty much what happens. On the first day, subjects ate 50 grams of rice starch. On the second day, they were administered an amylase-inhibitor that inhibited 95% of amylase activity and fed another 50 grams of rice starch. Postprandial (post-meal) delivery of carbohydrate to the small bowel was increased after eating the carb blocker, meaning less was absorbed. Blood glucose spike was reduced by 85%. Insulin was “abolished.” What’s not to like?

I’m a little suspicious of something that “blocks” a normal physiological function. Just because I think we should reduce our reliance on carbohydrates as energy sources doesn’t mean I no longer value our natural, inherent ability to digest them. I’m also suspicious of shuttling all those fermentable carbohydrates to our gut flora. Giving some soluble prebiotic fiber? Cool, that’s great and we evolved eating fibrous vegetable sources, so our “normal” gut flora is likely used to it. But it sounds like providing a massive dose of something like sweet potato starch to our eager gut flora is a potential recipe for small intestine bacterial overgrowth (SIBO), which we definitely don’t want. There’s evidence that blocking amylase action indeed increases short chain fatty acid production by our gut flora, a marker for gut flora activity, but instead of absorbing the healthful fatty acids, those with impaired amylase activity excrete most of them. That tells me that maybe the gut flora are biting off more than they can chew, that maybe providing all that cheap starch to our small bowels is too much of a good thing.

But that’s just speculation off of a few related studies. We can’t know for sure, of course. Still, if you want to block carbs, just don’t eat so many of them. That’s certainly safer than messing with a vital, inherent part of our physiology, don’t you think?

Thanks for reading, folks. Let me know what you think in the comment board. Grok on!

TAGS:  dear mark, toxins

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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