Dear Mark: Exercising (and Eating) in the Heat; Post-Antibiotics Gut Health Support

For today’s edition of Dear Mark, I’m answering a pair of questions from you folks. First up, what with the crazy heat wave sweeping much of the planet, a reader writes in asking about the best way to eat and move in the heat. Should you cease all activity? Should you modify your normal movement patterns and eat and drink differently to keep the heat at bay? Read on to find out. Next, how should a person deal with and support the post-antibiotics gut biome? What can we do to mitigate the negative effects broad-spectrum antibiotics have on our gut bacteria?

Let’s go:

Hi Mark,

Thanks again for all the great work you’re doing here. Having been introduced to Primal living – my latest discovery has been kettlebells, and I’m so happy about it – has been one of the best things in my life.

Now, I have a question that might interest quite some people for this summer: do you have specific thoughts and recommendations about how to manage life during a heat wave? Drinking more of course; but should it impact our diet and exercise too?

Thank you so much!


Thanks for the kind words. Much appreciated.

When it’s hot out, you have to be really careful with your activity levels. Extreme heat stress reduces the blood flow to the brain by about 30%. By “extreme” I mean extreme — body temperatures approaching 40° C — but any degree of heat stress will reduce blood flow to the brain and increase it to the lower body, albeit not to the same degree. Throwing exercise into the mix, however, will raise your body temperature further, and throwing dehydration into the mix compounds the inhibition of cerebral blood flow.

You know how I rail against the potential dangers of dropping dead from heart attacks during extreme endurance events? Heat stroke is a larger danger. One study in a cohort of endurance athletes found that for every serious cardiac event occurring during a race, ten life-threatening instances of heat stroke occurred. Some researchers even think elevated core body temperature is the proximate cause of most endurance-related events.

A few things to keep in mind regarding heat stress and activity:

Larger people actually have a higher heat tolerance during exercise; whether it’s hot-humid or hot-dry, a larger body mass improves heat loss.

Stay hydrated. I’m not one to freak out about drinking eight glasses of water a day — that’s pretty silly and unnecessary in most cases — but things change when you’re dripping sweat. Exercise in said heat makes it even more crucial. I like a pinch of sea salt and a splash of trace minerals in my water, for the electrolytes and to replace any sodium lost. Coconut water is also helpful, especially if you’re working hard and burning through both glycogen and fluids. But the absolute greatest supplement for hard exercise in hot weather is a glass of fresh squeezed orange juice with a large pinch of sea salt mixed in. I know, I know. Juice is bad, right? No, it’s a tool to be used in special circumstances. And this is a special circumstance. It ends up tasting like really good Sunny-D (not purple stuff). I can remember a backpacking trip where a liter of salted orange juice cobbled together from materials purchased from a small stand along the trail saved me. When I say a pinch, I mean a pinch. Don’t put too much salt in, as its effects on blood flow during heat-stressed exercise are unclear.

Don’t do anything you don’t have to (like marathons). Keep exercising, but do the intense stuff inside, and if you do it outside do it under a tree or an umbrella. I’m totally on board with walking in intense heat. Just let your body be the guide when you do it. If your hands are swelling up, if you feel woozy or dizzy, if you’re not urinating no matter how much you drink, cool it. Take a break. Go inside, read a good book or watch a movie. Find a shady spot under a big green leafy thing growing out of the ground. Take a nap, even.

As for diet, I always heed the traditions of the people who live and cook and eat in warm climates for their entire lives: spicy food. Whether it’s Thailand, Mexico, Ethiopia, Nigeria, India, or Jamaica, the hotter the climate, the spicier the cuisine. Sweating is your body’s way of cooling off, and sweating because you just took a face full of chili paste works, too. I’m not sure if adding chilis to everything when it’s deep summer improves your physiological resistance to the damaging effects of heat stress (though it can reduce microbial growth, another problem common in the tropics), but it sure makes me feel cooler.


I’ve been paleo since I experienced the benefits of going gluten-free 30 months ago and dug deeper into the contrarian diet (counter to “accepted” diets) it espouses.  The benefits have been life changing (I promise I’ll send in a success story soon), but include blood pressure normalization (no more pills), “cured” my osteoarthritis, lowered my uric acid (no more episodes of gout), and I don’t get colds regularly.

Unfortunately, I’ve reinjured myself and see an arthroscopic surgery on the horizon, and I know this will include antibiotics. Is there anything I can do to protect my precious microbiome, hasten its recovery, and reintroduce what might have been compromised, outside of more fermented foods (dairy and vegetable), raw foods (including oysters and other bacteria-rich yummies)?


Great question. Prophylactic antibiotics given during surgery are broad-spectrum and thus target just about everything without discrimination. Good for infectious microbes, bad for commensals. There isn’t a ton of research into countering these negative effects. What the literature tends to focus on is preventing or treating antibiotic-related diarrhea. But, since antibiotic-related diarrhea is generally caused by the trashing of the gut biome, any treatment that works against it will probably also benefit your post-antibiotics gut in a more general sense.

Fermented dairy should absolutely appear in your post-surgery (and, heck, pre-surgery) diet. It just works. Yogurt is a good option to try, if a bit inconsistent. Kefir is probably better; it’s been shown to improve patients’ tolerance to triple antibiotic therapy during treatment for H. pylori infection.

Fermented vegetables like sauerkraut are also must-eats. The fermented cabbage contains ample amounts of L. plantarum, a bacteria strain that’s been shown to prevent antibiotic-related diarrhea in piglets. Good options exist in stores, and even more are available in farmer’s markets, but the best way to get the most bacteria-rich vegetable ferments is to make your own. While you’re at it, consider making your own yogurt and kefir as well.

Supplemental probiotics are fantastic here, too: large doses of the desired microorganisms delivered directly to your gut. Some of the strains used in Primal Flora, like B. clausii and S. boulardii, have been shown to be effective against antibiotic-related diarrhea, so that could be a good choice.

Don’t forget the food for your gut bugs: prebiotics. You need to eat fermentable fibers and other prebiotics like resistant starch. Consider eating cooked and cooled potatoes, unheated potato starch, leeks, garlic, onions, green bananas, apples, pears, berries, and pretty much any fruit or vegetable you can get your hands on. Here’s where a wide variety of plant foods becomes even more important to consume because it introduces a wide variety of fermentable substrates for your gut bugs. Oh, and dark chocolate is a great source of fiber and polyphenols which have prebiotic effects in the gut.

Get dirty, too, to introduce potentially helpful bacteria. Go out and garden. Go barefoot at the park and practice tumbling, or roughhouse with your kids (or friends). Don’t immediately rush to wash your hands before eating (unless you’ve been handling raw meat and/or dog poop).

Whatever you do, don’t stress too much about the antibiotics you have to take. Stress is awful for gut health and the antibiotics are actually helpful here. Overall, it sounds like you’re on the right track. Good luck!

That’s it for today, everyone. Thanks for reading and be sure to help out with your own answers down below.

Take care!

TAGS:  dear mark

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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27 thoughts on “Dear Mark: Exercising (and Eating) in the Heat; Post-Antibiotics Gut Health Support”

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  1. Growing up in Florida I thought the heat wave last week in Alabama wasn’t anything to think twice about. Well, I neglected to realize how differently my body would react to it now that I’m pregnant! I ended up in labor and delivery at 29 weeks due to pre-term contractions triggered by dehydration. I thought I was drinking enough water, but was clearly mistaken. I’ve started actually writing down how many glasses I drink, and supplementing with coconut water.

      1. +1! Also drink something every time you sit down to nurse (guessing you are breastfeeding since you are at this site!).

  2. I’ve been primal for about a year and four months and I’ve lost about fifty pounds. I’m also a very avid backpacker and one of my favorite places to visit is the Grand Canyon. Living on the front range in Colorado, I’m exposed to a variety of weather conditions and heat factors. From the cool mountains to the hot lower elevations. The GC is another animal though. I’m well experienced there but I have been wondering how weighing in at so much less would effect my ability to deal with the increasing heat in that area. This article helped me hone in on that. I’ll attempt that salted water/juice trick here at home to see how it works for me too. Hiking the GC on the primitive only trails and being secluded from people is my favorite thing ever. It will be an all new trip this year going full primal on the food and experiencing the new weight and it’s effects. Thanks for everything.

    1. Some of my best hiking memories are from the Grand Canyon. Due to heat we chose to go in December. We waded in the Colorado river at the bottom… and sunbathed in our shorts… meanwhile there was a blizzard up at the rim. Best time of year to go, in my opinion.

      1. P.S. it wasnt a blizzard up top the whole time of course. Mostly sunny in the canyon. It was a 5 day hike with 3 days in warmth down low on the Tonto trail. Nights got cold, but that was normal for us since we are from Alberta, Canada and had hiked for years around Jasper in the northern Rocky Mountains.

  3. I make a really awesome lacto-fermented garlic radish pickle that goes on top of salads and burgers. Same process to make it as homemade sauerkraut.this has made my gut healthier and I feel just helps overall.

  4. Cold kimchi is great for hot weather and post antibiotic therapy. I use Napa cabbage, diakon radish, and leeks. I add siracha after the ferment for heat. It’s great with sliced hard cooked eggs and/or sliced smoked pork shoulder.

    1. Most of the chronic diseases start from a leaky gut! I think it is time for me to start making own fermented products as It is always the best way to get the most bacteria-rich ferments out from it~

      p/s: Never know that dark chocolate is a great source of fiber! LOL! ????

  5. Some people tolerate dairy less well in the heat.

    My husband is an outdoor entertainer and we work in the hot and humid Midwest & hot and dryish and windy high plains in the summer.

    He can take cream in his coffee in the early morning when it’s cool(er) but can’t have dairy during the day without getting sick. He says it feels like the dairy is curdeling in his belly.

    So no yogurt or hard cheese or cottage cheese or sour cream for him during work days.

    On the other hand, he does get to have pie. We get homemade pie at the fairground church stands, preferring fruit pies made with local wild fruits. Chokecherry, gooseberry, currents, damson plum and the like.

  6. Great tips for dealing with the extreme heat. We just had 3 weeks of 95-103 degree temperatures during the day, and our MMA school is a location without climate control. It easily reached 110 degrees inside by late afternoon and early evening. For the most part I handled it pretty well, but one day I had a couple dizzy spells and muscle cramping. Made sure to rehydrate right away and stay hydrated going into the next day. Might have to try the salted orange juice suggestion some day. Thanks Mark & crew!!!!

  7. i have SIBO, how can I recover from antibiotics without growing my SIBO further?

    1. Low-FODMAP, low-carb paleo + fermented foods at every meal (build up to the last part!)

  8. Interesting. I handle, subjectively, heat much better since losing 125 lbs. And I sweat much less. I can walk and feel fine, not jogging or running, whereas when obese it would feel like heck.

    So the summers, in Austin, Texas, are much more pleasurable now being much smaller. So I’ll take it.

  9. So interesting about the spicy food! I’ll definitely test it out. As for exercise in the heat, I’ll be marathon training, but always go super early before the sun is out and bring along my hydration pack. I overheat easily but recognize the signs right away to back off.

  10. I understand your concern about antibiotics. I had a similar worry a few years ago and I went all out. I made yogurt and sauerkraut ahead of time to be ready when the course was over (the only way to ensure that your yogurt and fermented veggies are active is to make them yourself), I bought unpasteurized, small batch miso, and I started drinking kombucha (which I now brew myself so I can ensure that’s active, too). I also stayed away from sugar, even in fruit, for a few days to avoid a yeast infection. I don’t know if any of these things were necessary, but it made sense to me.

  11. I live in Austin as well. For me, it’s about shade & air flow. I do crossfit, and as long as the fan is on, I’m good. I may be dripping sweat, but if it’s evaporating even a little, it’s cooling.
    If I must be in the sun, I wear very light colors; people from further north discount this, but it makes a big difference here. I can feel a shirt, or even a large dark logo, practically burning on my back. Blech… The best fabric was drysport by Insport, but it’s not made anymore. Nike dryfit is an attempt, but not as good as the original.
    For drink, even over 100, I stll just use tap water. For nighttime trail runs, which I love, I fill a camel with ice, and then pour in a bottle with nuun. But this is for extreme heat, distance, and no breeze. Evaporating sweat is the best coolant.

  12. I also had a close-encounter with antibiotics last month (Gave them the slip at the last moment!) and worried about the precious microbiome that I’ve been feeding for years. Now, this may sound kinda gross, but…I was thinking about spitting into a jar with some water and keeping it in the fridge to chug at regular intervals. (I bet some of you thought I was going to mention fecal material.)

  13. Just finished two weeks of combination of antibiotics for a facial cellulitis that caused half my face to swell and threatened my eye. I had combination antibiotics several years ago for colitis, and it was the worst experience. Diarrhea was actually worse. (Duh!)

    This time, I took Culturelle (L. rhamnosus) and Florastor (S.boulardii lyo) at twice the recommended dosage. Not only did I have no problems, but I had the first normal stools and bowel function in years.

    Now off treatment, I have added in a Bifidobacterium/Lactobacilli blend and backed off to once-daily dosing. All is good. The probiotics were perhaps the final piece of the puzzle, after going gluten-free, primal, and egg- and dairy-free.

    After a few more months, I am actually looking forward to carefully reintroducing eggs and dairy, and seeing how it goes.

  14. When I had to have the cleanse before the dreaded colonoscopy, I used as many probiotic foods as I could during prep–yogurt and kefir on the days of soft foods and liquid diet, kombucha and even some pickle juice on the clear liquid day (along with plenty of clear chicken broth). Then I made sure to load up on probiotics after the procedure.

  15. Given the option I always prefer to exercise on the heat
    I know I will do less and do not try to do more – try to not get to the stage of the lady on the grass fainted 🙂
    But the little I do feels super good!

  16. When it’s hot, at least out west where it’s relatively arid, what really works is to get your head wet and use an umbrella. Pour water on your head. Wear a wet bandana. If there’s any breeze, even just the breeze of you walking, you will feel so much cooler. Drinking liquids doesn’t cool you down. By all means drink if you are thirsty, but not just because you are hot.

  17. I work road construction in the summer months in humid conditions on 300 degree asphalt I’ve seen heatstroke and it’s not pretty I sometimes wear a wet towel on the head and another wet towel around the neck and reapply cold water every half hour or so

  18. In relation to the heat/stress/dehydration question, Im really curious to know what your thoughts would be on Bikram yoga. Is 90 minutes in a 110 degree heated room at 40% humidity too stressful for the body?

    I used to practice very regularly but ive taken a break in recent months as I was thinking that I might be overstressing my body with the heat and extreme sweating. Ive been trying to heal (naturally) from hypothalamic amenorrhea for the last 3 years and I thought that maybe the hot yoga was stressing my body out too much. Anyone have any thoughts on this?

    1. I know this comment is pretty old but I’m curious to know if you ever received a response.

      I started CorePower Yoga (about 98 degrees) about 5 months ago, and concurrently experienced amenhorrea and have not recovered yet despite being very healthy and active. I was probably even more active before I started the yoga so I don’t think it’s cause by excessive exercise. I’ve been to a doctor who brushed it off as normal due to being on low-dose birth control but I don’t think that’s the case since I’ve been on it for many years and never experienced that problem.

      Mark – any thoughts?

  19. So what’s up with the people who can eat spicy foods but don’t get the sweaty reaction? I can eat everything hot and it doesn’t effect my digestion nor does it make me sweat even though I fully feel the pain. I know there is a genetic component to it, but why does this difference exist? It’s weird. I also don’t react to poison ivy or oak (yet). I wonder if they’re linked?

  20. Hahahaha, omg did anyone catch that Dave Chappelle joke?!?! Props Mark, that’s one of my favorite comedic performances!