Dear Mark: Dairy Inhibiting Magnesium Absorption, Trampoline Training, and Max Aerobic Heart Rate

Dear Mark Dairy-Magnesium Absorption Final

For today’s edition of Dear Mark, I’m answering three questions. First, does dairy inhibit magnesium absorption, thus negating the utility of adding blackstrap molasses to milk? There’s a good deal of evidence that points to a probable answer. Next, is mini trampoline training actually good for you, or is it just a silly way to pass the time and look ridiculous (or all of the above)? And finally, how should someone calculate (and train under) their max aerobic heart rate?

Let’s go:

Hi mark, in regards to your recent post and another previous post about blackstrap molasses and some suggestions to how it can be taken, you mention a couple of ways that include dairy.

I have read that the absorbtion of magnesium is affected (decreased) when taken with dairy, I was wondering if there was any truth behind this and if so to what degree?



I’ve heard that too but never saw it substantiated. You spend enough time in alternative health circles and it starts to seem like dairy inhibits the absorption of everything. The calcium content of dairy blocks iron absorption. The dairy protein prevents you from absorbing the polyphenols in blueberries. Dairy supposedly even prevents you from absorbing the calcium it contains, if you listen to the more rabid of the vegans.

So, does dairy inhibit magnesium absorption, as the Weston A Price Foundation has asserted?

Lactose doesn’t block magnesium absorption. A study in live healthy human subjects found that the presence of lactose, even in large amounts, had no effect on magnesium absorption.

Calcium doesn’t block magnesium absorption. The body uses separate pathways to absorb each. The biggest determinant of magnesium bioavailability is your magnesium status. If you’re low, absorption is high. If you’re replete, absorption drops. It’s totally context-dependent.

Casein doesn’t block magnesium absorption. Researchers actually use casein as the control when studying the effects of various proteins on magnesium bioavailability.

I don’t see any route by which dairy would block magnesium absorption. Have at it!

What is your opinion of exercising on a rebounder or mini trampoline? There doesn’t seem to be much research. But webpages and blogs all report glowing benefits. The only research that all sites use is a NASA report about how beneficial rebounding is for returning astronauts. What are your thoughts?

I’ve actually seen a decent amount of research. I’ll go through some of it and then give my thoughts after.

A group of Thai working women performed aerobic dance moves on a hard wooden surface or mini trampoline. Both produced good training effects and improved bone metabolic parameters, but the trampoline produced more leg strength and forced better balance.

A moderate intensity exercise session on a mini trampoline has the ameliorative effect on blood glucose you’d expect.

In patients recovering from a stroke, mini trampoline training improved postural control to a greater degree than balance training. It also led to greater improvements in daily functioning and mobility. Another study in stroke patients found that trampoline training (30 minutes a day, 3 times a week for 6 weeks) led to fewer falls, greater balance, and improved gait.

In elderly women, trampoline training ranks among the best ways to improve balance (and thus reduce falls and catastrophic injuries).

In athletes with ankle instability, training on a mini trampoline improves postural control and reduces sway.

There’s evidence it’s not just good for the elderly and health-compromised. In a group of male gymnasts, training on a mini trampoline for 12 weeks improved sprint speed, standing broad jump, vertical leap, and anaerobic power output.

They’re a little risky, too, particularly the big backyard ones. If you’re going to bounce around on a trampoline, observing the following rules seems to minimize the risk of injury:

  • Bounce alone. One at a time, please. Most injuries involve collisions with other people.
  • Don’t jump off of an elevated surface onto the trampoline. Roof to trampoline, bad. Trampoline to roof, awesome (if you can pull it off, but you may need to be a comic book character).
  • Use a safety net to prevent falls.
  • Most importantly, trampolines are fun. I have fond childhood memories of bouncing on my buddy’s backyard trampoline. We were reckless, of course, which I wouldn’t recommend. We probably got lucky. But man was it fun.

    Dear Mark,
    I must precede my question with a tremendous note of gratitude. I am a fitness trainer and health coach, age 67, and having followed the advice of “Primal Blueprint” and “Primal Endurance”, I’ve gone from 18.3% body fat to 12.3% body fat in 4 months. I feel much better, am stronger and faster, and suffer much less injuries. Before I met you, I was overtraining junky that would yoyo between peaks and painful setbacks. God bless you, Mark, and thanks ever so much.

    Here’s my question:
    According to various calculations, my heart-rate max should be somewhere between 153 – 161. My HR at rest is about 68 (here in hot Israeli summers). Yet, I jog at 153, run at 180, and at all-out sprints can hit as high as 212. Understandably, I’m confused as how to stay in my aerobic zone. What we be your recommendation.

    A million thanks and blessings for your continued success,

    Lazer from Israel

    Using the Maffetone method outlined in Primal Endurance, you calculate your max aerobic heart rate by subtracting your age from 180. That gives you 113. It means in order to maximize fat burning and minimize sugar burning, you have to keep your heart rate at or under 113 during exercise. It doesn’t sound like much. It probably feels way too easy. But bear with me. It works. This is where the magic happens, where you accumulate easy volume, where the “base” is built, where you begin building more fat-burning mitochondria. It probably feels way too easy, especially for a guy like you with so much experience.

    The hard truth: if jogging spikes your heart rate past your aerobic max, you’re not very good at burning fat during exercise. Even if you don’t “mind” pushing that heart rate up. Even if you “feel fine” jogging at 153 bpm. 180 minus age is where you have to be to improve fat burning.

    You might be awesome at burning sugar all day at a much higher HR, and even feel quite comfortable for long periods of time (until you burn out), but you will not be improving your fat-burning efficiency if you simply keep doing that. Most endurance athletes find that high-end sugar-burning HR zone and get “comfortable” in it several times a week, but then never really improve race speed (read: efficiency) from that point. It takes patience to stay at the aerobic zone, but over time everyone notices that they are able to handle a higher and higher work load at that rate, which means that you are going faster while still burning mostly fat.

    If you’re just interested in immediate objective performance results—fast times, feeling like you “did something” after every training session—keep at it. Just know that you will be undercutting lasting benefits to your fat-burning efficiency, boosts to your fitness, and improvements in your long term health trajectory. You know where I stand on this one.

    Thanks for reading, everyone!

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