Dear Mark: Resistant Starch, Zinc Deficiency, and Something New

FloursFor today’s edition of Dear Mark, we’ve got a three-parter. In the first section, I discuss the extremely hot (and then allowed to cool off) topic of resistant starch, explaining who might benefit from it, who might not, and where you can find further information on the subject. Second, I briefly go over how a zinc deficiency might arise and how you can address it on a Primal eating plan. The third section is bit of a surprise, featuring a very special guest writer. Since this is text and you guys can just skip ahead to see who it is, there’s admittedly very little suspense. But still. It’s a surprise that I think you’ll enjoy and appreciate.

Let’s go:

What about so-called resistant starch, that is, starch that passes undigested through the stomach but arrives in the colon? There’s some emerging evidence that the good bacteria that live in the colon need to feed on this starch in order to thrive. In other words, if everything is processed by the stomach and small intestine, the good “microbiome” is underfed, and the bad guys can multiply. An unhealthy microbiome may be tied to all sorts of auto-immune diseases. Do we need some resistant starch in our diets?

Resistant starch has really been making waves in the Primal health community. Lots of talk in the MDA forums and elsewhere.

So what’s the deal?

Resistant starch is a starch that resists digestion by regular digestive enzymes, passing through to the colon for fermentation by gut flora. In a post way back in the day, I addressed resistant starch and lumped it in with other prebiotic fibers like inulin, with the reasoning being that while it was certainly helpful and important, it was not some essential, magical nutrient. It seems I underestimated it. Resistant starch offers some interesting properties unique among other prebiotics.

Remember that starch post from a couple week’s back where I compared the fiber content of the kind of wild tubers our ancestors would have encountered to modern cultivated tubers? Much of the “fibrous material” would have been resistant starch, a highly efficient, durable method of energy storage for a plant’s underground storage organ. In the wild, where a plant isn’t protected from pests by agricultural chemicals or physical barriers, resistant starch makes sense. And so when we ate these tubers, we’d get a nice dose of resistant starch, particularly if we ate them raw or undercooked (cooking degrades the majority of resistant starch into regular old highly digestible starch).

Before agriculture, our ancestors obtained resistant starch and other fermentable fibers by eating a diversity of wild plant foods, bulbs, corms, tubers, cattails, cactuses, and medicinal barks – foods that by and large are not available to us nowadays (and if they were, they wouldn’t be very desirable or delicious). According to some estimates, they consumed up to 135 grams of fermentable fiber a day, and their gut flora would have reflected that. Nowadays, the most common sources of resistant starch in the modern diet (PDF) include various legumes, raw oats, and even certain types of bread that’s been frozen for 30 days. Raw potatoes, green bananas, and raw plantains are also quite high in resistant starch, but few people are eating them in their raw state. It’s much more delicious to cook them. We also have reliable means to cook our foods well enough to break down most of the resistant starch, like microwaves, ovens, and stoves. So, the result is many people following a Primal lifestyle – avoiding legumes and grains while cooking and reheating their starches – are also missing out on an important source of prebiotics and, perhaps, optimal gut health.

There’s a quandary, then. Resistant starch seems to promote ancestral-esque gut health and floral composition. How do we get resistant starch without foraging for wild foods or eating ungodly amounts of legumes, raw grains, and previously-frozen bread (thus incurring many of the negative aspects of these foods, like gut-damaging lectins, phytic acid, and/or gluten) or raw plantains and potatoes?

Unmodified, raw potato starch is probably the easiest way to get resistant starch, since each tablespoon contains about 8 grams of RS. Richard Nikoley has spearheaded the promotion of resistant starch via unmodified potato starch as a way to approximate or emulate the ancestral microbiome over at his blog. He’s been covering the benefits and relaying lots of anecdotes from readers who’ve seen great improvements in sleep quality and blood sugar control, even when diabetic or while remaining in ketosis). He even came up with a way to make mashed potatoes that don’t spike your glucose. Interesting, compelling stuff.

I think it’s worth trying. Potato starch is only about $4 or $5 a bag (less if you order in bulk on Amazon), mixes well in water or smoothies without much of a taste. Start with a teaspoon or two and work your way up to as many as four tablespoons. Expect flatulence as your gut flora acclimatize to the influx of this food.

Anyone with digestive issues, particularly FODMAP intolerance or IBS, may want to exercise caution as fermentable carbohydrates often irritate or exacerbate those issues. On the other hand, there’s preliminary (and mostly theoretical, as it hasn’t been directly tested) evidence that resistant starch may actually treat small intestinal bacterial overgrowth by “flushing” the pathogenic bacteria out in the feces. Adding resistant starch to the rehydration formula given to cholera patients, for example, is an effective treatment because the cholera bacteria attach themselves to the starch granules almost immediately.

Anyone else try this? What have they noticed?

I attended a nutrition study course over the weekend and several vitamin deficiencies were discussed. Each delegate was also given a vial with a stopper of zinc solution to test ourselves for deficiency. I basically could taste nothing and despite being on an ancestral diet for over a year now, am apparently zinc deficient, which is worrying. I just wondered whether the zinc taste test had any merit? On a side note, this has since led me to investigate the whole nuts/phytic acid binding minerals issue and despite soaking and drying my nuts, I consume WAY too many which may be the cause of this deficiency if it indeed exists. Thanks for your attention to this matter.


The zinc test definitely has merit. In a study of pregnant women (whose zinc levels tend to drop as the pregnancy progresses), the accuracy of the zinc taste test ranged between 70-100%. Overall, the results of the test correlated strongly with zinc status. I see no indication that the test is only valid in pregnant women; anyone who’s deficient enough should qualify.

The nuts could be a problem. Low to moderate amounts (an ounce or two a day) aren’t an issue in the context of a nutritious Primal way of eating, but eating “way too many” will eventually impact nutrient absorption via phytate binding because, unfortunately, zinc is susceptible to phytate.

Meanwhile, adding phytase (which degrades phytate) to zinc-rich foods increases the absorption of zinc. It’s pretty clear that excessive phytate is a problem. How much phytate? I don’t have a hard figure for that, but being deficient in zinc despite eating Primally is a good indicator.

So, what should you do?

Eat enough selenium. It’s responsible for regulating the delivery of zinc to zinc enzymes throughout the body for proper zinc metabolism. Seafood like wild salmon is a good source of selenium. Eggs, too. And the very best of all is the Brazil nut. One or two Brazil nuts should get you to the RDA for selenium without giving too large a dose of phytate.

Make sure you’re actually eating enough zinc, of course. Oysters, red meat (beef, lamb, bison), and scallops are some of the richest sources.

Limit sources of phytate. Stick to the ounce or two of nuts per day, not however many you were eating previously. Consider subbing in some macadamias, which are among the lowest in phytates, and keep soaking the nuts you do consume (not mac nuts, though).

When you do eat phytate-rich foods, give yourself a couple hours in either direction before eating zinc-rich foods. This shouldn’t be too tough, since nuts are snacks more than meal components. It does mean that your oyster sliders on almond meal bread might not be a good option, sadly.

Eat zinc with animal protein. Studies show that animal protein can counteract the inhibitory effects of phytic acid on zinc absorption (PDF). Luckily, zinc usually comes with animal protein already attached. Handy!

Account for excessive sweating. Sweating is a good thing, usually, because it indicates vigorous physical activity, but it also depletes zinc. You may need to account for sweating by eating more zinc.

Supplement. In my view, Krebs cycle intermediaries (citrate, fumarate, succinate, etc.) are going to be your best bet for zinc.

Now for the surprise…

I get a lot of questions from women, and for the most part they’re very general, straightforward, and applicable to men, too. But there are times when a uniquely female perspective (that I simply cannot provide) would come in handy. Since I frequently bug Carrie for advice on this question or that one, I figured why not have her contribute directly to the blog and answer reader questions? She’s already done reader question roundupsdiscussed cellulite, and talked hot flashes in the past and she has a level of expertise on some topics that I don’t. In addition to being smart, beautiful, fearless, and kind, Carrie has a Master’s degree in Spiritual Psychology from the University of Santa Monica and serves as a group leader at intensive weekend spiritual psychology retreats on a monthly basis. She has participated in retreats in Los Angeles, and as far away as Norway. Carrie is hard at work on her long-awaited book, Primal Woman, which is due to be published in the fall of 2014.

Without further ado, let me introduce Carrie.

Mark, I really wish you would’ve addressed women’s cycles and necessary starch for menstruation. So many women lose their cycles only eating berries and salads. I know I did. Add back in a sweet potato, some bananas, and yes even some white potatoes and white rice. BAM! Flow city. ;)

Carrie here. I’m not Mark but I can handle this question.

First off, thanks for your question.

Personally, I never really had this issue, even though I’ve always been pretty active, because I always made sure to eat enough food. Not too much, not too little, just enough to keep me full, help me recover, and maintain my hormone levels. The only time I ever had any issues with my cycle was when I was on a strict low-fat, “heart healthy” diet full of whole grains and other starchy carbohydrates while doing tons of cardio. Of course, I wasn’t really Primal until menopause, so I can’t really say that it wouldn’t have happened if I’d been eating this way back then. That said, the research shows that the biggest variable for regular menstruation is sufficient calorie intake. Not sufficient potatoes, rice, or bananas. Not carbs. Calories. You need them if you want to maintain a normal cycle. Your body needs to know that you’ve got energy coming in before it decides you’re ready to conceive.

Study after study shows that dieting can have a negative effect on the menstrual cycle. Let’s go through some of the research.

Like here, a 1000 calorie high-carb diet caused menstrual irregularities. Women who lost the most weight (had the biggest energy deficit, in other words) had the most irregularities. All that starch wasn’t enough to overcome a super low calorie intake.

Or here, where a vegetarian diet caused 7 of 9 women to stop ovulating, while just 2 out of 9 women in the non-vegetarian group did. Both groups lost the same amount of weight (though they don’t give a calorie count), so it was something about the vegetarian diet, not just the energy balance.

Another study showed that an 800 calorie vegetarian diet disrupts menstruation. In fact, vegetarianism seems to be especially linked to menstrual cycle disturbances (although not so much in healthy, weight-stable vegetarian women eating adequate amounts of nutrient-dense food).

They’ve even found that something called a “drive for thinness” (which I’d never heard of) is strongly associated with disrupted cycles because it leads to huge energy deficits – too much exercise and not enough food.

See the common thread? Low calorie intake. The literature is rife with examples of young, healthy women losing their period after going on a low-calorie diet, whether high-carb or not. And that calorie requirement goes up the more you exercise, which is why the “female athlete triad” – excessive energy imbalance, loss of period, and bone weakening – is a common affliction.

That’s what jumps out at me when people talk about adding in sweet potatoes to jump start their cycle: they’re adding calories to their diet. They’re not substituting potatoes for something else. They’re adding it to whatever else they were eating, resulting in a net increase in calories, and that’s fixing the issue.

If carbs are the only way you can add enough calories to your diet to restart your cycle, then go for it. But it’s not a quality inherent to the carbs. It’s just the energy they provide. The calories. I hope this helps and I will also share about some other self-honoring choices I made during my cycle that I will post in a future column.

Keep the questions coming, folks. Carrie’s agreed to chime in every Monday, so send along any questions you might have for her, too. Thanks for reading!

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 more than three decades 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 flavorful and delicious kitchen staples crafted with premium ingredients like avocado oil. With over 70 condiments, sauces, oils, and dressings in their lineup, Primal Kitchen makes it easy to prep mouthwatering meals that fit into your lifestyle.

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