Tuesday, October 6, 2009

Troubling Tubers

Tubers are a point of contention in the paleo community.  The paleo diet as prescribed by Loren Cordain says tubers of all sorts are out.  They require processing (cooking) and are too nutrient dense and high on the glycemic index.  If anyone can find me more data on why Cordain rules them out when they were clearly eaten by many hunter-gatherers, please point me to a source.

Complex carbohydrates like tubers are quick energy, breaking down into glucose easily, starting with your saliva.  In saliva is amylase, a digestive enzyme designed to break down complex carbohydrates like starch into simpler ones for digestion and absorption.  The enzymes follow the food through your digestive system, breaking it down.  Amylase is interesting because there is a gene for it that has more copies on the chromosomes of starch-eaters (on average) than those that don't have starch as a large part of their diet, according to researchers.  Some speculate that amylase copying is a critical point in human evolution, the divergence between humans with more copies of the gene for improved starch digestion and other great apes with fewer copies.

Starches would be beneficial for human evolution because they are such a concentrated energy source.  Reliance on nutrient-dense tubers could fuel our brain growth and change our social interactions.  One article discusses the evidence and arguments surrounding this hypothesis.

One caveat discussed: tubers are not readily digestible until cooked, so human ancestors would have needed fire.  Evidence of cooking hearths and consistent use of fire doesn't show up in the archaeological record until later in human evolution.  Of course, just because we haven't found it doesn't rule it out, but more data is needed.  However, there is evidence in the teeth of our oldest ancestors, the Australopithecines, that show a diet of soft-tough food items, which could mean a diet of underground storage organs, namely bulbs and roasted tubers that are rendered soft and digestible.

Another caveat from my physical anthropology background: savanna-dwelling primates dig up roots and tubers, notably baboons and some chimpanzees.  Why haven't they become larger-brained? 

Perhaps it is not just the starch that fueled our evolutionary path.  Perhaps it was the combination of eating high energy sources like tubers, adding meat to our diet, cooking our food, and creating organized food redistribution that led our ancestors on a different path than our closest relatives.  While chimpanzees exhibit hunting and root acquisition, they lack cooking and food redistribution akin to hunter-gatherer groups.  

In my opinion, there is never going to be one thing to pinpoint and say "aha! that is what makes us human!"  My argument is that perhaps our reliance on roots and tubers is something that evolved with us and has been with us for millions of years.

You make up your own decision, but here are some pros and cons for eating tubers, namely the sweet potato:

1.  They are great energy sources for quick refueling after intense activity.
2.  They contain high concentrations of vitamins like B6, and especially vitamins A (beta-carotene) and C.  Carotenoids help stabilize blood sugar levels and play a role in many bodily systems, such as skin growth and repair.
3. They are high in potassium, essential to our bodies, namely cell function.   
4.  They are also high in fiber, so they promote digestive health and satiate your hunger.
5.  They are chock full of antioxidants, which are linked with reduced risk of cancer and disease. 

1.  They are relatively high glycemic foods (compared to other vegetables), which is great for getting energy fast, say after exercise, but not that great at more sedentary times.
2.  They are often fried and/or over-processed (i.e. those that come in bags and boxes).
3.  They require cooking to promote digestibility.
4.  They don't digest well when eaten in conjunction with protein.  Proteins require a more acidic stomach environment to digest them, while starches require a more alkaline environment.  This means that your stomach plays tug of war with its acid-base balance and thereby can't digest either efficiently.  The combining of these foods can lead to bloating, gas, indigestion, and heartburn, among other problems, described more here.   Starches are best with easily digested protein sources, such as whey, eggs, and milk (eggs being the most suitable on a paleo-style diet).

More on Sweet Potatoes

Sweet potatoes can be orange or white and most supermarket "yams" are really just orange sweet potatoes.  Yams have a lower glycemic load and glycemic index (more on those values in another post!), so they are preferable if you can find true yams.

There are a multitude of ways to prepare sweet potatoes, and I will definitely return to them in future posts.  I love them best in savory applications since their inherent sweetness needs no accentuation, at least to me.

The Most Basic Roasted Sweet Potato Wedges
Cooking Time: 1/2 hour start to finish
Zone Blocks: each medium sweet potato is 3 blocks, 1/2 T of olive oil is about 4-5 blocks.  Use less if desired, but beware of stickage.  

1 sweet potato per diner (each is 3 blocks on the zone diet)
1/2 T olive oil per sweet potato

Start heating your broiler on Low and remember to keep the oven door open a crack (I know, this has always weirded me out--if the oven can clean at ungodly temperatures, why am I cracking it and losing all this heat for broiling?).  Make sure one of your oven racks is in a high enough position to get right below the upper heating elements. 

Peel your sweet potatoes and slice lengthwise into thin wedges (say 1/4 inch), no need for a mandolin (unless you have one you really like to use), just a heavy chef's knife will do.  I am awful with anything sharp; I almost always grate part of my hand whenever using the grater, so I am especially careful with knives for my inherent idiot factor.  To make this easy: after peeling, cut your first 1/4 wedge off the sweet potato side furthest from your hand (smart, huh?).  Then, lay the rest of the sweet potato on the cutting board with the cut side down, making it steady and now a little thinner to slice.  Of course, this will leave you with wedges that aren't perfect ovals--they'll have a straight side, but really, do you care?  Slice them more if desired, but the wedges work fine for me. 

Once cut, pile them on a baking sheet, drizzle with oil, and sprinkle garlic, salt, and pepper (your discretion about how much to use--I like mine garlicy and salty).  Then, get your hands dirty by tossing the potatoes to evenly coat every one with oil, salt, garlic, and pepper--both sides.  Then, arrange in rows to allow for the most surface area exposure to the heat.  Whack in the oven (but leave the door open a crack!), and give them 10 minutes--more or less.  Look frequently for browning and remove to flip once you see any evidence of burning.  This is a fun game of how far can you let them go to get crunchy without going over the line to burnage.  Fun!  Flip and repeat on the second side noting that this side always takes less time.  Once done, remove and try not to burn yourself devouring them!  They are yummy!

Serving Suggestion:
I am naughty and still eat starches with beef and poultry, but perhaps eggs would be a better choice now that I have looked into it more.  Let me know what combinations work best!

Sweet Potatoes on FoodistaSweet Potatoes

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