Is sweet potato a superfood or nutritional bust

Is sweet potato a super-food or nutritional bust?

If you eat sweet potatoes because you think they are nutritional power houses and do your body good, you may be surprised with the info below. Sweet potatoes are neither as nutritious as previous thought, nor as good for you as they are claimed to be.

Below you will find the most common nutritional claims about sweet potatoes together with some thought-provoking info. If you don’t care about numbers, data, stats, and research and prefer more entertaining form of delivery, please watch our video. You will see us trying to make sense out of the tuber nonsense. Have fun!

But… if you are a nerd… head to the data department below the clip, where percentages, milligrams, RDA, GI and GL numbers dominate.


CLAIM #1: Sweet potatoes provide more than 5x daily requirement of vitamin A

But…beta carotene is not vitamin A

Despite nutritional labels listing vitamin A, sweet potatoes do not have any vitamin A. They only have beta carotene. Beta carotene converts to vitamin A in the liver, but the process isn’t straightforward, and it is subject to significant losses.

How much vitamin A do you really get from 100 grams of sweet potatoes?
  • Sweet potatoes are said to have more than 300% RDA for vitamin A[1]
  • RDA for vitamin A for adults (averaged data) = 800 RAE = 2,700 IU[2]

However, once processing, absorption and conversion rate are taken into consideration it appears than the final count of vitamin A is much smaller than suggested by the nutritional claims. Below is a breakdown of how much beta carotene remains in sweet potatoes after processing and how much of the remaining beta carotene gets converted to vitamin A in a human body.

  • Total carotenes in raw sweet potatoes– approx. 10,000 mcg/100g[3]
  • Beta carotene in raw sweet potatoes– approx. 7,000 mcg/100g[4]
  • Beta carotene after boiling, frying, baking – (beta carotene retention rate – approx. 87%) – approx. 6,000 mcg/100g[5]
  • Recent studies indicate that bioconversion of beta carotene from food is much lower than previously thought. Bioconversion of beta carotene to retinol activity equivalents (RAE) from sweet potatoes is estimated to be 13:1; this is lower than bioconversion from spinach at 8:1, and much lower than from supplementation of beta carotene at approx. 2:1[6].
  • RAE equivalents after bioconversion – approx. 460 mcg from 100g of boiled and mashed potatoes
    1. Average absorption rate of beta carotene in the intestine is 5-65%[7]
    2. Average conversion rate of beta carotene to retinol (vitamin A) from vegetables is 3-30%[8], [9]
  • 100 g of sweet potatoes provide 57% of RDA (460 mcg RAE in 100g)
  • Oops! One serving of boiled and mashed sweet potatoes (130 g) provide only 74% of RDA for vitamin A, not 300% as frequently stated

Other considerations:
  • Bioavailability and amount of beta carotene in sweet potatoes varies with geolocation and agri-practices[10]
  • Beta-carotene to vitamin A conversion depends on human genetic variability, e.g. good converters vs poor converters
  • Absorption is lower in case of gastrointestinal problems, compromised gut integrity, and diseases of gastrointestinal tract
  • Commercial processing affects beta carotene content: e.g. canned sweet potatoes have half of beta carotene of freshly boiled sweet potatoes[11]
  • Nutrient load matters: the bigger the dose of beta carotene the lesser its conversion to vitamin A[12]
  • Vitamin A status matters: conversion of beta carotene is lowered by nutritional adequacy of vitamin A[13]
  • Lack of fat prevents absorption. For carotenoid absorption a minimum of 2.4g of fat per meal is required[14]
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Sweet potatoes and vitamin A deficiency
  • Average consumption of sweet potatoes in USA, Canada, & Australia is 6 lb per person per year
  • USA, Canada, Australia don’t have widespread vitamin A deficiency
  • The highest consumption of sweet potatoes in the world is in Angola (100 lb per person per year)
  • Oops! 65% of Angola’s population is vitamin A deficient[15]


CLAIM #2: Sweet potatoes are high in nutrients

  • Sweet potatoes are one of the richest sources of vitamin B6 among all plant staples [16]; One serving provides 10% of vitamin B6; therefore, to get 100% RDA one needs to eat 10 servings or 5 cups.
  • Oops! One needs to eat over 2 kg (4 lb) of sweet potatoes to get RDA for most of B vitamins (avg 4% RDA in 100g) or 10 kg (20 lb) to get RDA of vitamin E (1% RDA in 100g)

  • For minerals such as calcium, iron (avg 3% RDA in 100g), one needs to eat more than 3 kg (7 lb) to arrive at RDA;
  • Most people don’t eat more than 4 lb of food a day (less than 10 cups)[17],[18]
  • Sweet potatoes lack two essential macronutrients: proteins and fats; however, they are high in carbs, carbs are not essential
  • Oops! Sweet potatoes lack many essential nutrients including vitamin B12, vit E, sel, or zinc

  • Sweet potatoes lack many brain nutrients: creatinine, carnosine, taurine, omega-3, haem iron, vitamin B12, vitamin D3[19]
  • Oops! The highest sweet potato consumption per capita is in Angola 100lb per capita per year [20] Angola’s averaged IQ is 68.[21]


CLAIM #3: Sweet potatoes are high in antioxidants

  • Antioxidants detected in sweet potatoes: phenolic acids (caffeic acid, ferulic, sinpic, coumaric acid, etc.) tend to be poorly absorbed;[22]
  • ORAC (Oxygen Radical Absorbance Capacity), a measure of antioxidant activity, for sweet potatoes is 2,720; most apples have ORAC over 3,000[23]

CLAIM #4: They are very good for the immune system

Many sweet potato advocates claim that they are excellent immune system boosters due to their high vitamin A content. However, vitamin A is only one of many nutrients required by the immune system.

  • The immune system relies on variety of nutrients including, zinc, vitamin D, selenium, iron, etc. Sweet potato lacks adequate amounts of all the above. It also lacks cholesterol, which is a vitamin D precursor.[24]
  • For comparison: all the above nutrients can be found in beef liver (see chart below)

CLAIM #5: Sweet potatoes support eyes and good vision

  • Besides vitamin A, good vision requires the following nutrients: vitamin E, zinc, omega-3, lycopene, astaxantin.[25]
  • Oops! None of the above nutrients are present in sweet potatoes in adequate amounts. Beta carotene must be converted to A; vitamin E, zinc and omega-3 are present in very low amounts; studies aren’t conclusive about lycopene, astaxantin, and lutein presence and bioavailablity in sweet potatoes.[26]


CLAIM #6: Sweet potatoes are recommended to diabetics to stabilize sugar due to low GI and GL

It has been suggested that sweet potatoes are a good choice for diabetics due to their low glycemic index and glycemic load. That, however, may not be a good advice given the fact that most North Americans bake rather than boil the tubers and opt for more than one serving. Processing and portion changes both the glycemic index as well as glycemic load to such extent that recommendations of sweet potatoes to diabetics become inappropriate.

Glycemic index

Classification of glycemic index:[27]

  • Low: 55 or less
  • Medium: 56-69
  • High: 70+

*Glycemic index of sweet potatoes: [28]

  • Boiled – 61 (medium GI)
  • Roasted – 82 (high GI)
  • Oops! Baked – 94 (high GI)

  • Fried in vegetable oil (don’t do it!)- 76 (medium GI)
  • For comparison: glycemic index of sucrose (table sugar) is 65
Glycemic load

Glycemic load estimates blood sugar surge after eating a specified portion (e.g. one servings) of food

Classification of glycemic load (GL)

  • Low: 10 or less
  • Medium: 11-19
  • High: 20+

Glycemic load of sweet potatoes

  • GL of one serving of boiled sweet potatoes is 11 (medium, similar to honey)
  • Oops! GL of baked sweet potatoes is 42 (very high)[29]

  • For comparison: GL for carrots is 2, for dates 18, for of bagel 25, for raisins 28[30]
Carbohydrate content

Serving sizes and real life seldom match; for most of us 1/2 cup of sweet potatoes isn’t sufficient. On the average we eat minimum ½ pound at the dinner table, which is about three servings.[31] Doubling or tripling the portions dramatically increases carbohydrate content of the meal.

  • One serving = 130g or 5” sweet potato
  • One serving of potatoes has approx. 20g of carbs (mostly starch)
  • Starch breaks down to sugar
  • 20g of sugar = 7 packs of sugar
  • Three serving of potatoes have approx. 60g of carbs
  • Oops! 60g of sugar = 20 packs of sugar

Insulin index

Insulin index measures the surge of insulin after eating. High insulin index number indicates high insulin production. Elevated insulin prevents weight loss and leads to weight gain.

  • Oops! Insulin index of sweet potatoes is 98[32]. Insulin index for glucose is 100

  • For comparison, insulin index for oatmeal is 40, for beans 38, and for cauliflower 60
  • Due to high insulin index sweet potatoes produce a substantial drop in blood sugar within one to two hours post meal
  • Oops! An insulin surge after a sweet potato meal may cause reactive hypoglycemia

  • The drop in blood sugar and reactive hypoglycemia is more pronounced when eating sweet potatoes with the skin[33]
Resistant starch

Resistant starch present in food helps lower absorption and breakdown of dietary carbohydrates. Due to its carb-blocking properties, resistant starch can help with blood sugar management. Resistant starch is present in potatoes.

  • Oops! Sweet potatoes have extremely low presence of resistant starch – 0.08g in 100g;

  • For comparison reheated white potatoes have 1.07g of resistant starch in 100g (13x more than sweet potatoes)
  • Foods rich in resistant starch are: lentils: 2.08g in 100g, ripe bananas – 1.23g, and green bananas 8.5g[34];

CLAIM #7: They help with weight loss because they are satiating

Sweet potatoes are said to be quite satiating and therefore aiding in weight loss. This however, may not be favorable as it may promote nutritional deficiencies. The feeling of satiety from sweet potatoes is not due to its nutrient density, but due to the amount of fibre and water it holds.

  • Satiety index of boiled potatoes is at considered to be very high (323); three time as high as white bread (100), and much higher than French fries (116), or cakes (65)[35]
  • Satiety index refers only to first two hours after eating[36]
  • The feeling of satiation is due to high amount of water and fibre, which makes the stomach feel full; unfortunately, water and fibre have no nutritional value
  • Oops! The combination of high satiety and low nutrient density facilitates malnutrition


CLAIM #8: They support gut health due to high fibre content

Fibre has become synonymous with good digestion. However, recent studies suggest that fibre may not only be non-essential, and besides lowering absorption of nutrients, it can be quite irritating to the gut.

  • Sweet potatoes are high in fibre – 3g in 100g portion
  • Oops! 80% of fibre in sweet potatoes is insoluble[37]; insoluble fibre may cause gut irritation

  • Insoluble fibre is said to be indigestible, does not bind to cholesterol, and does not feed gut microbiota;
  • New studies show that insoluble fibre (e.g. cellulose) can be broken down in humans by gut bacteria[38], which can result in gas and bloating
  • Low fibre diet may be beneficial for individuals with active diverticulitis, acute Crohn’s and colitis, bloating, cramping, constipation, nutrient malabsorption, IBS, candida overgrowth, narrowing of the intestines
  • Low fibre diet is naturally low in carbohydrates and may help with weight loss, oral health, heartburn, as well as many gut problems[39]
  • Sweet potatoes aren’t suitable for low fibre diets

Things seldom mentioned about sweet potatoes

Anti-nutrients

Anti-nutrients are substances that prevent nutrient absorption. Sweet potatoes have number of anti-nutrients present. Besides fibre, sweet potatoes also have oxalic acid, trypsin inhibitors, and phytic acid which bind to nutrients.

  • Oxalic acid binds mostly to calcium and forms calcium oxalate crystals. These can accumulate in various organs: kidneys, joints, muscles, thyroid, brain, arteries, bladder, etc. Development of kidney stones, stiffness, joint pain, thyroid disease, atherosclerosis, bladder and prostate inflammation, may be precipitated by excess dietary oxalate in sensitive individuals.
  • 80% protein is sweet potatoes is in the form of trypsin inhibitors, sporamin[40]. Trypsin inhibitors reduce absorption of amino acids as well as fat-soluble vitamins A, D, E, and K. Trypsin inhibitors are a plant’s natural pest repellent. Prolonged trypsin inhibition may increase in size and the number of pancreatic cells. These changes can lead to pancreatitis and even pancreatic cancer[41]
  • Phytic acid works similarly to fiber by binding to substances in the gut. Phytic acid reduces micronutrient absorption by binding to vitamin B3 (niacin), calcium, chromium, copper, iron, magnesium, manganese, and zinc. Additionally, phytic acid accelerates the metabolism of vitamin D and can cause its deficiency. Rickets and osteoporosis are common in populations with high phytic acid intake[42]
Pesticides

Sweet potatoes aren’t free of pesticides. According to USDA Pesticide Data Program sweet potatoes can contain 19 different pesticide residues. Dicloran, piperonyl butoxide, and chlorpyrifos are among the most commonly found.[43]

  • 47% of samples of sweet potatoes samples were found to contain dicloran, a possible carcinogen.
  • 7% of samples were positive for piperonyl butoxide, a possible carcinogen and suspected hormone disruptor
  • 4% of samples were positive for chlorpyrifos, a neurotoxin, suspected hormone disruptor, and bee toxin

 

My personal reasons why I don’t eat sweet potatoes:

  • I dislike the taste and texture/taste combination. They taste too sweet when baked and feel too watery when boiled
  • I choose the most nutritionally foods available. Sweet potatoes don’t have sufficient nutrient density.
  • I am not interested in poorly absorbed sources of vitamin A. I get it from eggs and butter
  • I don’t follow high carb diets. Carbohydrates make me put on weight and destabilize my blood sugar.
  • I avoid fibre. For me, fibre equals bloating and contributes to overgrowth of bacteria.
  • I am oxalate sensitive. I get joint pain and stiffness from oxalates.
  • I am immune to advice given by popular media. I prefer reading research and make conclusions myself.

 

Nutritional comparison

Sweet potatoes vs beef liver (in 100g)[44],[45], [46], [47], [48], [49], [50], [51],[52], [53],[54]

Yellow highlights are to emphasize sweet potatoes’ nutritional inferiority when compared to beef liver

Sweet potato nutritional chart

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Sweet potato nutritional considerations

Sweet potatoes for diabetics

Are sweet potatoes good for you?


[1] https://www.healthline.com/nutrition/sweet-potato-benefits

[2] https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551189/

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551189/

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3551189/

[6] https://academic.oup.com/ajcn/article/80/3/705/4690550

[7] https://academic.oup.com/ajcn/article/96/5/1193S/4577160

[8] https://www.ncbi.nlm.nih.gov/pubmed/20200262

[9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854912/

[10] https://www.ncbi.nlm.nih.gov/pubmed/23053560

[11] https://ods.od.nih.gov/pubs/usdandb/VitaminA-Food.pdf

[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2855261/

[13] https://academic.oup.com/ajcn/article/96/5/1193S/4577160

[14] https://www.ncbi.nlm.nih.gov/pubmed/20200262

[15] http://siteresources.worldbank.org/NUTRITION/Resources/281846-1271963823772/angola1711screen.pdf

[16] https://www.bbc.com/future/article/20200127-how-a-vegan-diet-could-affect-your-intelligence

[17] https://en.wikipedia.org/wiki/Sweet_potato

[18] https://www.precisionnutrition.com/what-are-your-4-lbs

[19] https://www.bbc.com/future/article/20200127-how-a-vegan-diet-could-affect-your-intelligence

[20] https://www.potatopro.com/angola/potato-statistics

[21] https://new-iq-test.com/iq-by-country/

[22] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3052441/

[23] https://www.phytochemicals.info/list-orac-values.php

[24] https://www.ncbi.nlm.nih.gov/books/NBK22339/

[25] https://www.healthline.com/nutrition/8-nutrients-for-eyes#section2

[26] https://www.healthline.com/nutrition/8-nutrients-for-eyes#section4

[27] https://www.gisymbol.com/about-glycemic-index/

[28] https://www.healthline.com/nutrition/sweet-potato-glycemic-index#sweet-potatoes

[29] https://www.diabetesselfmanagement.com/blog/glycemic-index-confusion/

[30] https://extension.oregonstate.edu/sites/default/files/documents/1/glycemicindex.pdf

[31] https://parade.com/843520/tessmelchreit/how-many-potatoes-do-you-need-per-person-for-dinner/

[32] http://www.mendosa.com/blog/?p=3667

[33] https://fbns.ncsu.edu/USDAARS/Acrobatpubs/S114-150/S141.pdf

[34] https://www.precisionnutrition.com/regular-vs-sweet-potatoes

[35] http://www.mendosa.com/satiety.htm

[36] http://www.mendosa.com/satiety.htm

[37] https://www.healthline.com/nutrition/foods/sweet-potatoes

[38] https://academic.oup.com/femsec/article/74/1/205/2680467

[39] https://www.gutsense.org/fiber-menace/what-are-the-benefits-of-low-fiber-diet.html

[40] https://onlinelibrary.wiley.com/doi/full/10.1002/fsn3.110

[41] The Micronutrient Miracle: The 28-Day Plan to Lose Weight; by Jayson Calton, Mira Calton, p.73

[42] https://www.caltonnutrition.com/is-your-food-robbing-you/

[43] http://www.whatsonmyfood.org/food.jsp?food=SW

[44] https://fdc.nal.usda.gov/fdc-app.html#/food-details/168482/nutrients

[45] https://nutritiondata.self.com/facts/beef-products/3470/2

[46] https://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2666/2

[47] http://www.whatsonmyfood.org/food.jsp?food=BL

[48] http://www.whatsonmyfood.org/food.jsp?food=SW

[49] https://en.wikipedia.org/wiki/Insulin_index

[50] http://whatworks.site/hunger-food-insulin-index/

[51] http://ernaehrungsdenkwerkstatt.de/fileadmin/user_upload/EDWText/TextElemente/Ernaehrungswissenschaft/Naehrstoffe/Saettigung_Lebensmittel_Satiety_Index.pdf

[52] http://www.dietandfitnesstoday.com/water-in-beef-liver.php

[53] https://www.eatthismuch.com/food/nutrition/beef-liver,2767/

[54] https://www.myfooddata.com/articles/natural-food-sources-of-beta-carotene.php