Written by Jason Prall.

It would appear that the general public here in the Western world is finally starting to come around to the understanding that perhaps the mainstream idea of a low fat, high carbohydrate diet may not have been the best advice. Like many reactions to an unsuccessful approach, the tendency is to do the exact opposite. And while taking that approach may produce profound benefits in the short term, often the real long-term success results are found somewhere in the middle of the spectrum — or at least by achieving some sort of balance.

Understanding this balance is where things get tricky, where science often missteps, and where poor conclusions get made. Why? Because there are infinite factors that come into play when trying to find the best approach for YOU. However, science can look at food with a broad lens in order to guide our decision-making for the general public. Here we’ll look specifically at the nutritional differences in the sweet potato versus potato debate.

Many nutrition professionals will denounce the incorporation of all carbohydrate sources for a variety of health reasons. And while not an absolute necessity by the human body, the truth is, for many people, carbohydrates can be very beneficial for overall health — specifically for those who are extremely active. But with so many natural carbohydrate forms, which foods should you eat?

Many nutrition experts tend to regard potatoes, sweet potatoes, and tubers in general as great forms of carbohydrates…but why? And are they all the same? And can the differences, if there are any, be applied to everybody? If you’ve read any of my other blogs floating around out there on the web, such as The Hormone Connection: Estrogen and Weight Loss or Chicken Versus Beef Protein, you already know the answer to the last question is most-often a resounding NO.

So let’s get to the meat and potaaa…uh…well let’s not jump the gun.

Sweet Potato Versus Potato: The Basics

As many of you probably suspect, potatoes and sweet potatoes are not in the same family. Sure they are both root vegetables, but potatoes are a nightshade in the Solanaceae family, along with and similar to peppers, eggplant, and tomatoes. Sweet potatoes, on the other hand, are in the Convolvulaceae family. And for those who are curious, yams are completely different than sweet potatoes.

Performing a search on micronutrient and macronutrient breakdown of sweet potatoes and potatoes, you’ll notice there are some immediate difficulties in comparing the two groups. Because of the wide varieties within each cohort, it becomes quite difficult to analyze all the combinations. In the sweet variety, your choices range from purple to garnet to whitish to deep orange — heirlooms and hybrids — hundreds of varieties. Regular potatoes contain even more diversity and include red-skinned, white, purple/blue potatoes, and fingerling — more than 4000 varieties are thought to exist.

But since most of us don’t see nearly this kind of variety, we can simply look at broad values and wrap our head around the general differences in nutrient composition in their raw state.

sweet potato versus potato
source: nutritiondata.com

As for macronutrient content, they’re pretty similar. In terms of micronutrients, aside from the beta-carotene and Vitamin C, there really isn’t a major difference. But when looking at the glaring difference in beta-carotene, it is crucial to understand that beta-carotene, which is often labeled as Vitamin A, actually requires some pretty significant conversion processes within the body to become usable Vitamin A (retinol). In the average person, it requires six units of carotene to make one unit of retinol. And of course the beta-carotene in sweet potatoes will vary drastically based on variety, as the lack of orange/red tends to indicate. Cooking does seem to lower overall beta-carotene. And while the bio-availability of beta-carotene is less than 10%, it appears that sweet potatoes cooked at home tend to have more bio-available beta-carotene than commercially prepared sweet potatoes. And as always with fat-soluble vitamins like Vitamin A, adding a fat source to your meal will help increase absorption and assimilation. Grass fed butter or ghee are wonderful additions. Coconut oil also lends a spectacular flavor. Add some sea salt, organic cinnamon, and cloves and you’ve added even more nutritional value.

Sweet Potato Versus Potato: Glycemic Scores

A common concern with potatoes and sweets alike revolves around how these two foods spike blood sugar. It’s tempting to directly compare the glycemic index (GI) and glycemic load (GL) of potatoes and sweet potatoes, but this just becomes an exercise in futility. According to the University of Sydney, potatoes tend to score a bit higher than sweets on the GI and GL scales. But there are so many factors that determine how these foods enter your blood stream. The way you cook each of these seems to have an effect on both the GI and GL. Are they roasted, baked, fried, or boiled? Are they whole, quartered or diced? Is the skin still on or are they peeled? Were they cooked in oil? And then of course, which variety was used?

As a general rule, sweet potatoes usually have lower GI and GL scores than potatoes. You can considerably reduce the GI and GL by pre-cooking and consuming either of these foods cold or reheated. And if you are consuming them hot, you have another reason to add some nice quality fats or oils like grass-fed butter, ghee, or coconut oil; as they’ll help lower the GI of your meal even further. If you are in the mood for potatoes, your best option is new (young) potatoes, as they have a relatively low GI due to their unique starch structure. But circling back, at the end of the day, GI and GL only mean so much. There are just so many more important aspects to food quality. In fact, I’ve probably belabored this aspect too much.

Sweet Potato Versus Potato: Anti-nutrients & Inflammation

It is under this lens we can see the stark contrast between potatoes and sweet potatoes. Potatoes, being part of the nightshade family, can be problematic for some people and may cause inflammation, stiffness, and joint pain. As part of their natural defense mechanism, potatoes contain toxic glycoalkaloids like solanine and chaconine, most of which reside just below the skin’s surface.

The glycoalkaloid content is reduced after cooking, but does not completely get eliminated. These poisonous glycoalkaloids have been shown to contribute to intestinal permeability, aggravate inflammatory bowel disease, and destroy both cancer cells and normal liver cells. A nice thorough peeling can go a long way to reduce the toxic content of a potato. And if it appears green beneath the skin, or has begun to sprout, best to throw it out all together.

For those who consume potatoes as a way to avoid the anti-nutrient properties of phytic acid and lectins, I’m sorry to say that potatoes actually contain chitin-binding lectins. These lectins have properties very similar to the lectin found in wheat (wheat germ agglutinin), appear to behave similarly in the body and may have negative effects that contribute to inflammation, intestinal damage, immune dysfunction, and gene expression. Chitins are polymers of n-acetyl-glucosamine and the existence of these chitin-binding lectins in potatoes (and wheat germ agglutinin) may explain the perceived benefit of glucosamine supplementation, as the lectins bind to the glucosamine supplement instead of our own tissues, helping us avoid damage. Perhaps a better solution is to limit or avoid foods containing these chitin-binding lectins (barley, potato, tomato, rice, rye).

If you do consume potatoes, it is particularly important to buy organic. Regular commercial potatoes are usually treated with pesticides that are known carcinogens, cause neurological problems, and create hormonal issues. Sprout inhibitors are also used which cannot be scrubbed off since much of it ends up in the flesh.

Sweet potatoes don’t appear to have nearly the inflammatory or anti-nutrient properties. However, about 80% of the protein found in sweets is sporamin. This protein can interfere with proper digestion as it limits the action of the digestive enzyme trypsin, which assists in the digestion of protein.

The Winner? Sweet Potatoes

So why do some recommend potatoes over sweet potatoes? The answer lies in a recently admired and newly studied starch called resistant starch. The science is still in its infancy with regard to this supposed health-promoting component contained in a few particular plant foods. And while it does appear there is some validity to the health benefits of resistant starch, there are some major “ifs” that come into play as well. This complex topic will have to be saved for a later post. But suffice to say there are a lot of bio-individual components that need to be considered.

For now, the recommendation is to choose sweet potatoes over potatoes and load them up with some good fats, sea salt, or cinnamon and cloves. And it might be a good idea to mix things up and add some purple varieties in as well. It turns out the anthocyanins from purple sweet potatoes induce antioxidant enzymes via the Nrf2 pathway which help protect the liver and reduces inflammation by inhibiting nuclear factor kappa B.

(Image courtesy of rebootwithjoe.com)

 

Jason Prall has been a lifelong athlete with a continuing passion for all things health and fitness. During his time as a collegiate baseball and football player, he experienced numerous injuries and was frustrated with the shortsighted and ineffective treatment he continuously received from traditional medical avenues. With a deep interest in the inner-workings of the human body, he began my journey to thoroughly understand biology, physiology, exercise science, and nutrition in order to optimize his health and athletic performance.

References

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Fernandes, G., Velangi, A., & Wolever, T. M. (2005). Glycemic index of potatoes commonly consumed in North America. Journal of the American Dietetic Association, 105(4), 557-562.

Hwang, Y. P., Choi, J. H., Yun, H. J., Han, E. H., Kim, H. G., Kim, J. Y., … & Jeong, H. G. (2011). Anthocyanins from purple sweet potato attenuate dimethylnitrosamine-induced liver injury in rats by inducing Nrf2-mediated antioxidant enzymes and reducing COX-2 and iNOS expression. Food and chemical toxicology, 49(1), 93-99.

Juraske, R., Mosquera Vivas, C. S., Erazo Velásquez, A., García Santos, G., Berdugo Moreno, M. B., Diaz Gomez, J., … & Guerrero Dallos, J. A. (2010). Pesticide uptake in potatoes: model and field experiments. Environmental science & technology, 45(2), 651-657.

Patel, B., Schutte, R., Sporns, P., Doyle, J., Jewel, L., & Fedorak, R. N. (2002). Potato glycoalkaloids adversely affect intestinal permeability and aggravate inflammatory bowel disease. Inflammatory bowel diseases, 8(5), 340-346.

Search for Glycemic Index. (2015) The University of Sydney. Retrieved from http://www.glycemicindex.com/foodSearch.php

Soh, N. L., & Brand-Miller, J. (1999). The glycaemic index of potatoes: the effect of variety, cooking method and maturity. European journal of clinical nutrition, 53(4), 249-254.

Van Damme, E. J., Barre, A., Rouge, P., & Peumans, W. J. (2004). Potato lectin: an updated model of a unique chimeric plant protein. The Plant Journal, 37(1), 34-45.