Dear Mark: Young Guy, Low Testosterone; RS for Babies; and Sprints vs Tempo Runs

White PotatoFor today’s edition of Dear Mark, I answer three questions. First up is a young guy with low testosterone. He eats the right foods, does the right exercises, and has lived the right number of years, but he’s saddled with the testosterone of a much older man and wants to know why. Next, I discuss whether resistant starch is suitable or important for infants. The parents are benefiting from it, but does that mean an infant needs it, too? And finally, I explore the value of tempo runs – tough but doable runs maintained at the anaerobic threshold pace – for fat loss. How do they compare to my favorite fat burning exercise – sprints?

Let’s go:

Hey Mark. Your site is great! I’ve learned a lot. I just have a question. Despite the fact that I lift weights (squats, ring dips, pullups) 3x a week and do jiu jitsu 2x a week, along with eating plenty of chicken, beef, eggs, etc. my testosterone at 19 years old is 270 (low end of normal). All my doc said was remove GMOs, perhaps increase my calories (I’m 145 lbs with 1500 daily calories) and carbs, and to check back in a few months. But this makes no sense to me. Any suggestions?


Thanks for the kind words! Much appreciated.

What your doc said makes perfect sense to me, actually. Well, not the GMO thing. It’s not that I’m necessarily a fan of them, but I don’t see how they’d impact testosterone unless we’re talking about GMO soy.

You’re lifting heavy using compound, full-body movements three times a week. That takes a lot out of you, and it should be increasing your testosterone levels. You’re practicing jiu jitsu, one of the more calorically-demanding martial arts (and most instructors include conditioning workouts along with skill training, so that’s even more energy you’re expending). You’re eating plenty of protein, animal fat, and getting ample amounts of dietary cholesterol from eggs that the strength-training body can leverage into testosterone, hypertrophy, and strength – so you should be enjoying healthy levels of potent testosterone flowing through your veins.

Assuming you’re taking care of the other important determinants of testosterone levels, like zinc intake (eat your oysters), vitamin D/sunlight exposure, and excessive stress/cortisol, I think I know the problem.

You’re just eating too few calories for your situation. 1500 calories is drastically low for a 19 year old male trying to support your level of activity.

In obese guys? Yeah, a low calorie diet will improve sexual function and raise testosterone. But you’re not obese or probably even overweight. The obese guys make up for the lack of calories by consuming the thousands of calories stored in their body fat as they lose weight. Their calorie intake is low, but their calorie usage remains high.

If you’re lean, you don’t have that luxury. Ultra low calorie diets – which for an active youngster, your diet qualifies – take their toll. Recall what happens to the hormonal profile of bodybuilding competitors as they approach competition. They’re dieting hard and working out harder. Their testosterone plummets. Overall, the hormonal profile of a competition-adjacent pro bodybuilder resembles that of an 80-year old man. The good news? Their testosterone recovers once competition ends and they resume eating enough food. I’m confident the same is true for you.

You’ve got everything going for you. Just eat enough to support everything you’re doing. Somewhere in the range of 2,500-3000 calories is a good target. You can always reduce it if you’re gaining body fat, but I strongly suspect you will not. Try it for a month and re-test. It’s only a month, and it’s not the end of the world if it doesn’t go well. At least then you’ll know that it’s not the amount of food you’re (not) eating.

I should note that testosterone levels among adult males have been dropping for some time, independent of age, health, or established lifestyle factors (though they may not include “low calorie intake” or “overtraining” as factors), at least in America and Finland.

Hi Mark,
Just curious if you knew of any information on how much resistant starch a 1-year old should eat per day. My wife and I are experimenting with 1 tsp of potato starch a day (with intent to increase up to 4 tbsp to see how we feel) and want to give some to our baby as well.
She gets a lot of probiotic foods (milk kefir, sauerkraut and natto) and is still breastfed.
Any thoughts would be appreciated!
Thank you,

I don’t have a specific dosage for you, but I do know that as infants are weaned they begin to display gut bacteria that can degrade resistant starch, so they can make use of it. Also, mother’s milk comes prepackaged with a type of prebiotic known as human milk oligosaccharide, so babies can definitely benefit from prebiotics.

Do infants “need” resistant starch? Maybe. Their gut bacteria still need to eat, and RS has been shown to be a good source of food for bacteria in adults and infant pigs. Yep, pigs. You’re not one, but the omnivorous pig is a fair proxy for humans. Infant pigs who eat resistant starch enjoy increased calcium, zinc, iron, and phosphorus absorption compared to infant pigs eating digestible starch.

Here’s what I’d do: once the baby’s getting the majority of his calories from solid food rather than milk/formula/breastmilk, start including tiny amounts of RS. I’m talking tiny – like a quarter teaspoon at a time – just to see how he reacts. If you’re up for chewing food (which is “weird” but also pretty normal on a global, historical scale), try a small amount of chewed green banana.

Actually, scratch that. Green bananas are awful unless incorporated into smoothies. Why not stick to whole foods that taste good? Once your kid starts eating starches, you can give him small amounts of cubed cold leftover potatoes. 100 grams of cooked and cooled potato has about 5 grams of RS, so start small.

If the kid doesn’t have any problems like extreme amounts of gassiness, constipation, diarrhea, or other symptoms of an upset stomach, the RS is probably beneficial and definitely harmless. Just go slowly.

Hi Mark,

I know tempo runs are great for increasing your race-running pace and lung capacity but are they as effective at fat-burning as sprinting is?



Great question. For those who don’t know, a tempo run is a sustained effort at or around the anaerobic threshold, also known as the lactate threshold. You’re at maximum aerobic/fat-burning capacity and juuust starting to flirt with obtaining significant energy from the anaerobic pathway. Tempo runs are tough but manageable – they’re “comfortably hard.” They’re intense enough to push training adaptations without being so unpleasant that you quit before it’s over.

There are actually different kinds of tempo runs. Most people, when they use the term, refer to 5-10 mile runs at close to race speed. But sprinters do them too. Sprinters do tempo runs for active recovery and building/maintaining the aerobic base (yes, even sprinters need an aerobic base). For a tempo day, they might run a total of 2000 meters in 100s, 200s, or 400s. Easy-ish pace, enough to get their heart rate up a bit. They look a lot like sprints, only at 60-75% intensity.

Tempo runs can get you into trouble. First of all, there’s not a switch that blocks the aerobic pathway and turns on the anaerobic pathway. It doesn’t work like that. You’re always burning bits of everything and there are no hard barriers, so it’s very easy to go harder than you’d intended and get into almost pure sugar burning territory. That’s cool if you want to do that to improve your fitness and you accept the consequences, but I’d advise against using such a run on a regular basis for fat burning/body composition alterations/health maintenance.

Don’t get me wrong: if you do them right, tempo runs are great for burning body fat. But they burn lots of other stuff, too. And if you do too many of them with too little rest in between, you’ll burn out. Tempo runs got me into trouble. My absolute intensity was significantly different than the rest of the population, but my relative intensity wasn’t necessarily higher than an enthusiastic amateur runner. I just did too much.

I’d say sprinting still gets the nod. Sprinting isn’t so much a pure burner of calories in a mechanistic sense (although it does that too). What it really does is get the “furnace” going better than almost anything else, allowing you to make better use of energy substrates without them turning into fat, and increases insulin sensitivity so glucose replenishes glycogen without requiring as much insulin. Plus, a recent study found that two minutes of sprinting resulted in the same 24 hour oxygen consumption (a marker of post-exercise metabolism) as 30 minutes of steady state endurance training (akin to a tempo run). So yeah, a tempo run is good, but sprints are just so much more efficient.

Make sure you’re doing tempo runs right and they can be very helpful. If you find yourself bonking and craving sugar/carbs afterwards, you’ve probably ventured far afield of the aerobic pathway and should go easier next time. Or just focus on sprints for fat loss and do tempo runs for fun.

Thanks for reading, folks. Got any comments or advice for the readers who asked today’s questions? Leave ’em in the comment section!

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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26 thoughts on “Dear Mark: Young Guy, Low Testosterone; RS for Babies; and Sprints vs Tempo Runs”

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  1. I made the mistake of doing a sprint interval workout and a tempo run two weeks ago after doing a marathon a few weeks prior (and on shoes that had about 500 miles on them) and my calf is still hurting me! I just got over excited about working on speed work now that it’s summer and I have a break until Fall race season. Been icing, wearing compression socks, and doing trigger point.

    1. Same thing happened to me, I started doing speed work a week and a half after a 50 mile race and started feeling worn out. I backed off the speed work for a few days and was ready t race again. No ice for me though, all it does is delay healing.

  2. Ditto on the calorie boost for the 19 year old. I remember how much I ate at that age with a similar training level. What a burden! Six meals a day just to maintain. My massive calorie needs lasted all through my twenties. When I hit 30 it slowed down, which was a relief, and then slowed again at 40 ( which eventually lead to some fat gain which I promptly got rid of). My appetite, at 48, is now right in alignment with my calorie needs, or perhaps a little more, so I can’t be sloppy. But at nineteen, let it roll. If you’re eating clean, it’s almost impossible for an hard training teenager to overeat.

  3. I was in the same situation as the first guy a few years ago. Because I had the energy for the (brazilian in my case) Ju Jitsu, and I wasn’t super skinny/ ripped, I assumed I should be keeping calories low and didn’t really feel like eating that much anyway (that’s the effect of switching to a fairly-low carb diet/ restricted eating window etc.).

    I realized after a while I needed to add calories (and accept a bit of fat gain), but, as I’d just realized the psychological benefits of the primal way of eating, I didn’t know what to add or how to add calories without losing the ‘natural’ feel of the primal way of eating,

    Nuts are great, but according to Mark’s advice, not too healthy in the kind of 1000-calorie quantities that you need to supplement a low-calorie diet. Carby foods (sweet potatoes) in that kind of quantity (1000 calories) are also bad for someone with bad reactions to high-carb diets (like I was). Adding too much fatty meat or high fat dairy is also hard to get used to for some people (I had trouble sleeping if I ate too much fatty meat).

    My favourite solution was adding a tub of high-fat yogurt with a bit of fruit (maybe 800 cals) every day after my workout/ BJJ session, and making sure my two daily meals were slathered in butter/ beef dripping. I put on a good amount of muscle in that period, and still felt great, so I’d really recommend it.

  4. Mark, I am an elite long distance runner, and have been following your blog for a few weeks, I LOVE it! Seems like we are on the same page today, as I just did a guest post on Tempo runs on Thanks for sharing your knowledge 🙂 I am always looking for ways to improve!

  5. My guess on why his calories are so low (based on the limited info on his diet) is that it is too high in protein and low in fat and maybe low in carbs.

    When I first started the paleo diet, I was losing weight despite eating plenty of protein right after a workout. This didn’t work because your body also needs to replenish carbs and fats after a workout, which your muscles use for energy.

    The other problem with high-protein is that it is the most satiating macronutrient. Most people will feel full after eating just 300-400 calories of protein without regards to the rest of their diet. The solution is to increase good fats and good carbs and he will easily increase his calories. Also it will help to eat a lot right after working out.

  6. The guy with low testosterone should find out if they checked his prolactin level, as low testosterone can be indicative of a (usually benign) pituitary tumor. He should also make sure he sees an endocrinologist if he doesn’t feel confident in his GP.

    Source: I have a giant tumor on my pituitary that stopped my body from making testosterone (and am now on TRT).

    1. Great call, Jeff. Low T can be attributed to a lot of factors, outside of diet (some mentioned above, little sleep, stress, etc.). I too have high prolactin levels, which lower T levels (but no tumors – have had 2 scans with negative results). I take a medication to lower the prolactin – .5 mg of Cabergoline (Dostinex) twice a week – which lowers the prolactin. I have thought about TRT, but am nervous about.

      1. Interesting! I wonder if you have a tumor too small to detect or just and over zealous pituitary. Sounds like the treatment is the same either way (I’m on cabergoline/dostinex as well).

        TRT is rough, you should talk to your endo about off-label clomiphene – it raises testosterone if your pituitary is still healthy but just putting out prolactin, mine isn’t so it didn’t work for me but might for you. Clomiphene is a fertility drug for women, it isn’t approved for low T yet because there isn’t much money in it since it’s been generic for a very long time.

  7. Appreciate the info on tempo runs…I have found since using a heart rate monitor I have a better idea of my tempo pace, as well as my easy pace and, although it could be my imagination I feel that having a general idea of my HR helps me train smarter.

    I think the key is not doing too many “workout runs” too close together. I have yet to find the proper placement of “sprint days” relative to my other runs for the best benefit/least stress but I’m working on it.

  8. That is the one issue with going low carb, if you want to call it an issue. I eat lots of animal fat and protein, and I feel full, but when I count calories at the end of the day I find that I often don’t meet the recommended daily caloric intake.

    Without carbs you have to push yourself to get to 2000-2500 calories a day. I’ve found that fat helps. I throw together several tablespoons of coconut oil and grass fed butter, top it with a tablespoon of shredded coconut, let it refrigerate, and then eat it much like a dessert. It’s yummy goodness. Sometimes I even drizzle on a teaspoon of local raw honey.

    1. That desert sounds absolutely delicious, glad I just read those words in that order. I think I already overdo it on the grass-fed butter and coconut oil though – so tasty.

  9. To the question about testosterone: I went from 673 to 1009 over one year after eating 100% primal. I suspect it was a combo of these things that contributed to the massive rise:
    – 2,500 – 3,000 cals per day, mainly fat (like Mark mentioned)
    – 5,000 iu vitamin D3 supplement on most days
    – zinc supplement on most days (an extra 50 mg on top of whatever’s in a multivitamin)
    – roughly 3 workouts a week (2 bodyweight & 1 sprint), plenty of resting/walking

    I’m 6’1, 168, ~8% body fat

    Wish I could narrow it down to exactly what caused it! If I wagered a bet, it would be on the weekly sprints & zinc supplement.

    1. Oh, and cod liver oil – I took lots of that (sometimes 3 teaspoons a day). I ate lots of grain fed meat/eggs (unfortunately), so I try to balance out that O3:O6 ratio.

  10. I’ll be searching the site for more info on testosterone. There are some of us for which no amount of exercise or perfect diet will solve the low T issue. My testosterone tested at 82 in march (33 years old). I lift 4x/week, play 3 rounds of disc golf a week, and incorporate one sprinting session. I am exceptionally active and still cant get my levels up. My doc tried clomid and after 6 weeks my T tested at 10 (no joke). He started me on TRT at that point which drastically improved my quality of life (i couldn’t believe the difference in the gym) but then I learned about the effects trt has on fertility. So now I have pituitary imaging scheduled and an appt made with a new endo. What a nightmare…it is really disheartening to my fiance and me.

  11. The low testosterone would be a great podcast subject. I recently submitted a question about it on the speak pipe. Please and thanks!

  12. That man with low testosterone should think about… ahem.. it’s an awkward topic… cutting out the porn. Something like 98% of the men in my generation are addicted to it and it certainly has it’s effects on health. The research isn’t there quite yet but it is something good to expirement with(or more accuratly expirement going without.)

  13. Avoiding GMO foods(grains, peanuts) probably was mentioned because of glycophosphate residue in crops. Glycophosphate is the weed killer that GMO
    crops were engineered for resistance to. It is also an endocrine disrupter in animal studies for testosterone, estradiol, testes formation and fetal formation in rats and rabbits( mammals, no ???) Of course they cannot do studies on humans.

    And if I was a young man, I would do all I could do to minimize endocrine dis-
    rupters–remnants mostly found in urban water supplies from birth control pills and
    insecticides in addition to avoiding soy products. There are plenty of references found when ‘googling’ glyphophosphate toxicology. Enough probability for me to
    recommend young people to avoid same.

    As a curiosity, glycophosphate was sprayed over coca crops(cocaine) in
    Columbia and the coca crops mutated quickly to resist glycophosphate and became more potent. If plants can mutate that fast, what might happen to other
    life forms? It is already known to affect some micro-organisms and some amphi-

  14. OOPs!!! glycophosphate is the chemical name. Use ‘glyphosate when searching.’

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  19. It’s wicked funny, as they say in Boston, that declining testosterone on “American” males finds substantiation from an endocrinology study of Boston males, and the fine print might even be a little wicked funnier as it might well be just some dudes in Watertown. Funny for me, too, as I used to get beat up around there. If Boston males are low in testosterone, what must all the others be like? Whoah.