Dear Mark: When Walking Is No Longer Enough; Fermented Foods and Depression

Walking FinalFor today’s edition of Dear Mark, I’m answering two questions. First up, what happens when a brisk walk isn’t enough to attain the optimal fat-burning heart rate zone? It’s a good problem to have—better fitness—but it still needs a response. What activities can a person do to slightly increase the intensity without going over the target heart rate? And second, are fermented foods a potential cause of depression? If they have any effect on serotonin, could this cause problems rather than improvements?

Let’s go:

Dear Mark,

I love walking and have lost 65 pounds over the last year and a half with that, combined with some basketball and, of course a primal diet. But walking no longer gets me into my “180-my age” range anymore, my heart rate stays 110 or so even at 4 mph. Running/jogging hurts my knees, so should I try the elliptical for my aerobic work, or just stick with fast walking even at a lower heart rate? Thanks and love the blog and podcast!


I’ve got good news and bad news, Vance.

The good news is that you’re officially fitter than when you started. If you’re able to walk at the same pace with a lower heart rate, you’re building that aerobic base, those new mitochondria. You’re becoming fat-adapted. Nice work.

The bad news (that isn’t really bad news) is that you’ll have to step it up a bit. But here’s another piece of good news: the “harder” work will only be as hard as walking used to be at your old heart rate because you’re more efficient at burning fat and you’ve got all those new mitochondria to play with. This is how an aerobic base opens up new doors and promotes the exploration of new types of movement. If last year a 5 mile uphill hike made you wheeze with regret, today that same hike will be a breeze. You’ll actually get to enjoy yourself, take in the views, and hold a conversation. The physical effort will be an afterthought.

That’s why the aerobic base is so important even for regular folks and non-elites: it improves your default mode of transportation. If before a slow walk along a sidewalk was as fast as you could go and still be comfortable, now a fast walk is your default. Your new normal becomes faster, better, stronger.

As for what you can do to hit that heart rate?

The elliptical is okay. I’m not a big fan, personally, especially for the high-volume, low-intensity movement you’ll be doing. The treadmill’s linearity is bad enough. Ellipticals are totally linear. Your movements literally follow a track, forcing repetition and replication. Any repetitive motion adds up. Sprinting on an elliptical? Sure. It’s over in a jiffy and provides the desired stimulus.

Try rucking. Load up a backpack with books and walk around wearing it. Start small, maybe 10-15 pounds. Move up as dictated by your heart rate. If things get heavy, use a pack with a hip belt to redistribute the weight. Weighted vests also work well here.

Do you have any hills near you? Go walk them.

As for the machines, an inclined treadmill can work.

Rowing is great. Just keep it nice and leisurely, like you’re a 19th century Manhattan fop taking his sweetheart out on the pond. Wouldn’t want to sweat through your linen suit.

Skipping is great, too. Kids know what they’re doing. If skipping’s too intense, skip for 10 paces, walk for 20.

A nice easy bike ride.

Swimming, too. Don’t forget about the pool.

Anything works. Just explore the different types of movement and watch your HR.


Fermented foods, like kefir and kimchi, are often praised for their health benefits, one of which is their affect on serotonin and mood.

I’m wondering, concerned even, about possible long-term effects like serotonin depletion. This is something I observe in myself after prolonged periods of enthusiastic coffee consumption, short-term indulgences with wine, and (unfortunately) even a single dose of 90% dark chocolate. It also something I’ve read about in association with BCAA supplementation.

Should we be wary of a daily kefir habit too?


There are some strange things going on with serotonin and depression. It’s not a straightforward relationship. The common “neurotransmitter imbalance” model of depression where low serotonin causes depression isn’t quite accurate and has little actual evidence to support it. Anti-depressant drugs and supplements that don’t target serotonin, as well as non-pharmacological interventions like exercise, may be more effective than SSRIs against depression. If SSRIs work, it’s probably not by “increasing serotonin.”

In mice, probiotic administration increases serotonin turnover in the brain and reduces some of the inflammatory biomarkers associated with depression. Yet in humans, elevated serotonin turnover in the brain is a common feature of depression. Weird, eh?

The evidence is quite clear, though: fermented food intake is usually associated with low rates of depression in humans, not high rates.

Among pregnant Japanese women, high yogurt intake is protective against depressive symptoms.

Among Spanish university students, high-fat yogurt (but not low-fat yogurt) is protective against depression.

A recent trial in humans even found that a multi-species probiotic supplement made subjects more resistant to sad moods. These were healthy humans, not depressed ones, and depression is more than “sad mood,” but it’s promising.

The serotonin/fermented food question is up in the air. I’m not convinced, personally. But we have a conceivable mechanism by which fermented foods might exert protection against depression: improved gut health.

Leaky gut is common and seems to play a pathophysiological role in major depression; up to 35% of depressed patients have leaky gut. If your gut is too permeable, bacterial endotoxins/lipopolysaccharide (LPS) gain admittance to general circulation. And at least in mice, LPS induces depression.

Fermented food and probiotics can help. L. rhamnosus and L. reuteri supplements reduce leaky gut, and L. rhamnosus also helps restore the gut barrier in kids with acute gastroenteritis. In rats with leaky gut, yogurt improves gut barrier function.

I don’t think you should worry about this until it actually becomes a problem. Keep drinking that kefir and fermenting that cabbage.

That’s it for this week, folks. Now let’s hear from you.

Anyone had depressive symptoms worsen with fermented food intake? Improve?

What else can Vance do besides walk faster?

Thanks for reading!

TAGS:  mental health

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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38 thoughts on “Dear Mark: When Walking Is No Longer Enough; Fermented Foods and Depression”

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  1. Wow, great questions! The walking one was helpful, since walking is what I do every day (since I have an active dog). Love the idea of the backpack to make things a little harder. Sometimes I just drive to an area with more hills for a more intense walk. And agree with Mark about the elliptical. Too linear and it is BORING. I’ll take fresh air any day!!

  2. Yea, the correlation between serotonin and depression (and other mood disorders) is complicated. The old model of “more is better and less is worse” just isn’t panning out. Now doctors are looking at neurotransmitter receptor activation and distribution throughout the brain, other neurochenicals (glutamate), and even voltage intensity and frequency between brain cells. Those are just a few factors. Anyhow, for what it’s worth anecdotally, I haven’t had any bad psychological effects from fermented drinks (or heard of anyone who has).

  3. Way to build that aerobic base, Vance. I’m there with you, hence why I’ve had to up my game a bit to hit those same markers.

  4. There’s been some researchers who have looked at categorizing at least some of the features of depression/anxiety as byproducts of immune health. For example, folks with depression often have higher levels of inflammatory markers, indicative of an overactive immune system. So if drinking fermented drinks replenishes your gut health (and puts your immune system back on track) it makes conceptual sense that it may calm some depressive symptoms.

  5. Two great questions! Love the tip about skipping. It is so fascinating the direct role food plays in the health of our minds.

  6. I have a connection with depression and fermented foods. If I don’t have any around the house, I get depressed. All kidding aside, I feel much better stomach wise and defecating wise when I get my ferment on.

  7. Although fermented foods are great for the gut, there are a few of us who can’t eat them due to histamine intolerance. Fermented foods are loaded with histamine. When I get too much histamine in my diet (unfortunately, many great Paleo foods are high histamine), my body can’t break it down fast enough. Symptoms can include itchiness, hives, dandruff, and many more, including feelings of anxiety.

    1. Lynda, thanks for your comment! I’ve heard of histamine intolerance but don’t know anything about it. I’ve been making kefir and even one spoonful and I have diarrhea. I know fermented foods are good for us so kept trying. Also put spinach in my AM smoothie every day. Going to see if eliminating those for a few days solves the GI problems and would not have thought of that possible trigger unless I had read your comment! So many thanks!

  8. If running causes pain, give race walking a try. There are plenty of “how to race walk” videos on the Internet. Race walking has lower impact and a different motion than running, so you may find that it’s easier on the joints. It’s a distinct style that you need to learn and practice to obtain the smooth speed that competitive race walkers achieve (sub-20 10K).

    You can race walk as fast as you’d like, and get your heart rate into any range you’d like. For short distances, I can walk considerably faster than most people can run (30 seconds at 10 mph and 11% grade on a treadmill). My form at that speed is probably a little shaky in terms of the judging you’d face in a real competition, but I’m just doing it for fun and exercise, so it doesn’t really matter.

    I don’t have orthopedic issues with running, but I enjoy it as a change of pace mode of transportation and exercise. I figure that it works slightly different muscles, and could be useful in preventing overuse injuries.

    From my understanding, a mix of slow or moderate running and walking is what persistence hunters tended to use. If you are tracking faint tracks or looking for prey, slowing up and reducing the vision-impairing bounce of running could be helpful. Cycling the use of different muscles could be helpful in terms of reducing fatigue as well. Unlike modern competitive runners, persistent hunters needed to stay alert to dangers along the trail (other predators, scavengers or tribes), and save something for a potential struggle at the end of the hunt.

  9. As far as fermented foods go, should we be trying to eat a variety? Or is just eating 1-2 fermented foods enough (i.e. Greek Yogurt and Sauerkraut)?

  10. Thanks for another interesting article Mark. As someone who suffers from debilitating panic attacks and anxiety who is 90+% primal diet compliant, exercises regularly, gets plenty of sleep and has gone to therapy and tried CBT, deep breathing, tried all of the natural supplementation recommendations … the only thing that seems to really work for me is one specific SSRI. I have no idea why. I’m in my 60’s and it is the ONLY pharmaceutical I take. It works really well for me, although it does make me fatigued and I’d love to quit taking it. The number of hours I’ve put in on researching the topic is ridiculous. If anyone has experienced the same and came across a “magic cure” I’m all ears … or I suppose all eyes would be more accurate LOL. 🙂

    1. As someone who went through all of that (debilitating anxiety, panic attacks, agoraphobia), my advice is to stick with what works. 🙂 I’ve tried lots of natural stuff and lots of pharmaceutical stuff. I take a small dose of something pharmaceutical and just try to live a good lifestyle otherwise. Good diet, good exercise, taking time to de-stress (even more important in our cases than the typical Joe) and a few supplements to dial it all in. Daily high dose EPA fish oil and some magnesium on occasion are pretty much my only standard nutritional supplements for mood. I’m a bit too sensitive for most other stuff that I’ve tried, and perhaps you’re the same way. In any case, I know how you feel about taking something “non-natural”. It would always nag at me for years. But in the end, we’re all here to live our best, fullest lives. So if modern medicine has given you something that helps, by all means, welcome it with open arms. Hahaha. Anyhow, if I ever come across something else that works well/is a good adjunct, I’ll circle back here!

      1. Dan I super appreciate your response, great advice, this makes me feel a lot better about my situation and I think you are a very wise man!

      2. Dan, HH, Mark, grateful to hear all this, not for me but for my 12-yo daughter. Went deep in depression last winter, much better now, but we can’t tell if it’s the SSRI, more exercise, or more sunlight…appreciate the insights. Will try more O3 and fermented foods. Hope these can help with her sleep too.

    2. For what is it worth…I’m in my mid-50’s and thought I had tried everything. A couple of years ago I found an excellent therapist who did EMDR (Eye Movement Desensitization and Reprocessing) with me over the course of several months. It has made a real difference in my quality of life.

  11. “Running/jogging hurts my knees, so should I try the elliptical for my aerobic work”

    I suggest you get a mini tramp and run in place. Better yet, do it to music. The springing of the tramp relieves the joint pain and you can still get a great workout.

  12. `Stair climbing! Easier than hill climbing in the heavy heat of summer. Here at the Metropolitan Museum in NYC one can easily encounter stairs that are equivalent to more than 2 levels in most building between floors.

    And yes, I have built myself up this way and with hill climbing when the weather allows.

    1. Stairs are great, but since this person is having joint problems they might have a hard time walking down the stairs. I suggest taking the stairs up, and the elevator down. Good luck!

  13. I walk 3-5 miles several days a week, and it’s not been a heart rate pusher for quite some time. When the urge for a slight heartrate bump strikes, I scoop up my long-suffering 48 pound dog and carry him for awhile. Easy!

  14. The first thing I do before I start my day is “attitude,” I wake up smiling and that sets the tone and energy all day long. I love incorporating my work out sessions with my friends. And I love having a variety of options to a work out. Great article!

  15. Thanks Mark for answering my question, and those are great suggestions (as well as the discussion here)! I don’t know why I never thought of adding incline to the treadmill when I use one. I live in a very flat, very hot desert area and so during this time of the year I do use the treadmill. And I have plenty of backpacks I can try out as well. I think these will work!

  16. Walk off the beaten track. Walk on uneven ground – the less even the better. It uses a lot more and different muscles and is better for balance.

  17. Try swinging your arms around as you walk…a fitness instructor once told me that raising your arms over your head (up and down) raises your heart rate and also makes your core stronger as you are changing your balance up a bit. I don’t know about the core part, but if I’m on the treadmill, vigorously working my arms up and down really does elevate my heart rate. Also keeps it less boring, as does turning around and walking backwards….that’ll help your balance, and I find that my heart really pumps when I slip and catch myself! (Don’t do this) ;o)

  18. Nordic walking or walking with poles is another idea — you can give your arms as much of a workout as you want, and it can give some extra flexibility for trail hikes. Even walking the same route outside as usual, putting some push into the poles will give a noticeable heart rate boost.

  19. It depends on the severity of the joint issues but how about roller skating? It’s my go to combo low intensity, high intensity exercise/hobby.

    1. I in-line skate. It’s hard not to go too fast, but, nice to be outside. As you say, going all-out, up hills can serve as sprinting, too.

  20. I like to carry stuff when I walk, a medicine ball, sandbag, kettlebell, whatever, manipulate said object in new and interesting ways throughout your walk. Haloes, overhead unilateral carries, presses, throws, use thy imagination…..just plain carrying weight burns more calories.

  21. Vance as you are having knee problems it may be beneficial to get some professional advice from a physiotherapist before doing anything that has the potential to aggravate your knees, such as skipping and rucking.

  22. Hey Vance, Great job! I used to jog, and have now replaced it with long walks and hikes, as jogging bothers my knees. I find carrying a 25 lb pack to help increase the effort, but I’d work up to it gradually, and I don’t use it everyday. I also will often break up the walk with sprints, or 200-400 yrd interval runs. For some reason, sprinting and running intervals don’t bother my knees or low back like jogging. I don’t sprint with my pack.

    Another option is to literally carry some weight. Grab some dumbells, or throw a log or sandbag (deer carcass 😊) over your shoulder. That will get your heart singing! Good luck, it’s one big experiment!

  23. The extra weight and creating more movement during the walk are great ideas, I am going to experiment a lot (which is fun anyway!). One odd thing, Rich, is that playing basketball doesn’t bother my knees the way running or jogging does, even though it involves running. I think because it is more sprinting and more sporadic, mixed in with jumps, side movements, etc.

  24. I concur with loading up a backpack. My supermarket is only a kilometre away and I regularly walk down and load some heavy groceries like cabbage, pumpkin, cans, which are all good heavy things in compact forms.

    It’s pretty amazing how much harder you have to work with as as little as 5kgs on your back. But even more amazing is the realisation that just a couple of years ago I weighed eleven times (55kgs) that weight, which was the unintentional load I was carrying around.

    So it’s good to put some artificial weight back on. It also makes you stride differently and affects your balance in novel ways.

    Another tactic is to find an undulating route (I have a nearby gorge with walking tracks) and run up the short slopes instead of walking them. After a while you starting actively looking for short 20 or 30 metre inclines to run at. Even better if they are a little rocky and you have to shimmy around to keep your footing. It’s great for the flexors in the feet and lower legs because walking and running ain’t the same deal.

  25. I have a question: would common pickles (Vlasic, whatever) provide any of the benefits of fermented foods, or are they processed in a way that would nullify the effects?