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Sweet Potatoes for Diabetes?

August 8, 2012 Written by JP       [Font too small?]

Are sweet potatoes really healthier than regular, “white” potatoes? In a word: yes. For starters, the most obvious difference between the two relatives is the vibrant orange color of the so-called “sweet” variety. Carotenoids, much like those found in carrots, are naturally occurring pigments which impart this easily identifiable characteristic of sweet potatoes. Apart from their well established antioxidant properties, select carotenoids, such as beta carotene are used by the body in the manufacture of Vitamin A, an essential nutrient. But, that’s not all that sets sweet potatoes apart from paler potatoes. Sweet potatoes are also higher in fiber and Vitamin C, and equivalent in most other nutrients including potassium. However, before you feel too good about ordering a side of sweet potato fries, you should also be aware that they’re not all they’re cracked up to be – especially for diabetics.

There is a fair amount of confusion about the relative health benefits of sweet potatoes. In reality, they’re a mixed bag of both harmful and healthful properties. When eaten in moderation, sparingly and in the context of an otherwise healthy, low-glycemic meal, they can contribute valuable antioxidant protection and nutrition. Apart from the aforementioned carotenoids and Vitamin C, sweet potatoes also possess protective phytochemicals, such as chlorogenic acid. What’s more, in some countries where malnutrition is common, incorporating sweet potatoes into the daily diet is effective as insurance against Vitamin A deficiency. Arguing against the judicious use of sweet potato in either circumstance seems foolhardy. Having said that, the way that sweet potatoes are often promoted nowadays often veers too far in the opposite direction.

Numerous doctors and nutritionists endorse the inclusion of sweet potatoes in menu plans intended for diabetics and healthy individuals alike. I generally disagree with this position for two primary reasons. Firstly, sweet potatoes are loaded with fructose – a form of sugar which has been associated with a variety of health concerns ranging from fatty liver disease to high blood pressure. In addition, the positive studies published in relation to sweet potatoes and blood sugar control have mostly been conducted using a specific extract of a South American sweet potato known as Caiapo (Ipomoea batatas). To be clear, this isn’t the type of sweet potato most people traditionally consume. Also, the dosage used in the published studies (4 grams of a proprietary extract) is near impossible to equate to the amount of sweet potato eaten as a food source. This leads me to believe that many of the assertions made about the health benefits of conventional sweet potatoes are based on evidence derived from studies using Caiapo. Incidentally, at the moment, Caiapo extracts are relatively difficult to acquire and are exclusively produced by Fuji-Sangyo, a Japanese nutraceutical manufacturer.

If you enjoy sweet potatoes and want to derive the greatest possible benefit from them, here’s what I suggest you do. Data from at least two studies indicates that boiling sweet potatoes results in the lowest glycemic index – nearly half that of baking or roasting. It’s also important to note that boiling sweet potatoes actually increases their total antioxidant capacity. Leaving the skin on sweet potatoes and adding a good source of fat (grass fed butter, unrefined olive oil, etc.) will also assist in moderating their glycemic index and load, while simultaneously enhancing the absorption of the carotenoids present in the orange flesh. Finally, eating a relatively small quantity of sweet potato is fine for almost everyone. For instance, a small sweet potato (60 grams or 2 oz) contains only 10 grams of non-fiber carbohydrates and a trivial glycemic load of 5. In this case, employing moderation truly does help to transform a potentially harmful food into a reasonably healthy option.

Note: Please check out the “Comments & Updates” section of this blog – at the bottom of the page. You can find the latest research about this topic there!

To learn more about the studies referenced in today’s column, please click on the following links:

Study 1 - Nutrition Facts: Sweet Potato, Cooked, Baked in Skin (link)

Study 2 - Antioxidant Capacity and Antioxidant Content in Roots of 4 Sweet (link)

Study 3 - A Household-Level Sweet Potato-Based Infant Food to Complement (link)

Study 4 - Sweet Potato-Based Complementary Food for Infants in Low-Income (link)

Study 5 - Improved Metabolic Control by Ipomoea Batatas (Caiapo) is Associated(link)

Study 6 – Efficacy of Ipomoea Batatas (Caiapo) on Diabetes Control in Type 2 (link)

Study 7 – Mode of Action of Ipomoea Batatas (Caiapo) in Type 2 Diabetic Patients (link)

Study 8 - Isolation of Antidiabetic Components from White-Skinned Sweet Potato (link)

Study 9 - Relationship Between Processing Method and the Glycemic Indices of (link)

Study 10 - Effects of Baking and Boiling on the Nutritional and Antioxidant (link)

Processing Method Affects the Glycemic Index of Sweet Potatoes

Source: Journal of Nutrition and Metabolism Volume 2011 (link)

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3 Comments & Updates to “Sweet Potatoes for Diabetes?”

  1. JP Says:

    Update 05/26/15:

    http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD009128.pub3/full

    Cochrane Database Syst Rev. 2013 Sep 3;9:CD009128.

    Sweet potato for type 2 diabetes mellitus.

    BACKGROUND: Sweet potato (Ipomoea batatas) is among the most nutritious subtropical and tropical vegetables. It is also used in traditional medicine practices for type 2 diabetes mellitus. Research in animal and human models suggests a possible role of sweet potato in glycaemic control.

    OBJECTIVES: To assess the effects of sweet potato for type 2 diabetes mellitus.

    SEARCH METHODS: We searched several electronic databases, including The Cochrane Library (2013, Issue 1), MEDLINE, EMBASE, CINAHL, SIGLE and LILACS (all up to February 2013), combined with handsearches. No language restrictions were used.

    SELECTION CRITERIA: We included randomised controlled trials (RCTs) that compared sweet potato with a placebo or a comparator intervention, with or without pharmacological or non-pharmacological interventions.

    DATA COLLECTION AND ANALYSIS: Two authors independently selected the trials and extracted the data. We evaluated risk of bias by assessing randomisation, allocation concealment, blinding, completeness of outcome data, selective reporting and other potential sources of bias.

    MAIN RESULTS: Three RCTs met our inclusion criteria: these investigated a total of 140 participants and ranged from six weeks to five months in duration. All three studies were performed by the same trialist. Overall, the risk of bias of these trials was unclear or high. All RCTs compared the effect of sweet potato preparations with placebo on glycaemic control in type 2 diabetes mellitus. There was a statistically significant improvement in glycosylated haemoglobin A1c (HbA1c) at three to five months with 4 g/day sweet potato preparation compared to placebo (mean difference -0.3% (95% confidence interval -0.6 to -0.04); P = 0.02; 122 participants; 2 trials). No serious adverse effects were reported. Diabetic complications and morbidity, death from any cause, health-related quality of life, well-being, functional outcomes and costs were not investigated.

    AUTHORS’ CONCLUSIONS: There is insufficient evidence about the use of sweet potato for type 2 diabetes mellitus. In addition to improvement in trial methodology, issues of standardization and quality control of preparations – including other varieties of sweet potato – need to be addressed. Further observational trials and RCTs evaluating the effects of sweet potato are needed to guide any recommendations in clinical practice.

    Be well!

    JP

  2. JP Says:

    Updated 07/16/15:

    Note: While not related to diabetes, this is an interesting study that may be applicable to those not living with leukemia as well …

    http://journals.lww.com/cancernursingonline/pages/articleviewer.aspx?year=9000&issue=00000&article=99450&type=abstract

    Cancer Nurs. 2015 Apr 15.

    Improvement of Constipation in Leukemia Patients Undergoing Chemotherapy Using Sweet Potato.

    BACKGROUND: Leukemia patients undergoing chemotherapy commonly develop constipation, which is difficult to treat using routine methods.

    OBJECTIVE: The aim of this study was to determine whether sweet potato can alleviate constipation in leukemia patients undergoing chemotherapy.

    METHODS: Leukemia patients receiving their first chemotherapy were randomized to an intervention group (n = 57) or a control group (n = 63). The control and intervention groups were managed by using routine nursing methods and routine methods plus dietary sweet potato consumption (eating sweet potato 200 g/d, from admission to discharge), respectively. Related data regarding patients’ defecation were collected on the second and fifth days after chemotherapy initiation, which included rates of constipation, frequency and duration of purgative usage, constipation status assessed by Rome III criteria, and scores on defecation satisfaction.

    RESULTS: On the second day, the rate of constipation and the rate of having first defecation within 24 hours after chemotherapy initiation were significantly improved in the intervention group, but the difference of the defecation satisfaction and “almost no loose stools without purgative use” in Rome III criteria were not significantly changed. On the fifth day, except for “the sensation of anorectal obstruction” and “requirement of manual assistance” in Rome III criteria, other items regarding defecation were significantly improved.

    CONCLUSION: This study demonstrates that sweet potato had a positive impact on the prevention of constipation and the defecation satisfaction in leukemia patients receiving their first chemotherapy.

    IMPLICATIONS FOR PRACTICE: As sweet potato is inexpensive, abundant, tasty, and easy to prepare, it can be widely used in leukemia patients undergoing chemotherapy.

    Be well!

    JP

  3. JP Says:

    Updated 07/16/15:

    https://www.jstage.jst.go.jp/article/jnsv/59/4/59_272/_pdf

    J Nutr Sci Vitaminol (Tokyo). 2013;59(4):272-80.

    Sweet potato [Ipomoea batatas (L.) Lam. "Tainong 57"] starch improves insulin sensitivity in high-fructose diet-fed rats by ameliorating adipocytokine levels, pro-inflammatory status, and insulin signaling.

    The aim of this study was to investigate the effects of low-glycemic index (GI) sweet potato starch on adipocytokines, pro-inflammatory status, and insulin signaling in the high-fructose diet-induced insulin-resistant rat. We randomly divided 24 insulin-resistant rats and 16 normal rats into two groups fed a diet containing 575 g/kg of starch: a low-GI sweet potato starch (S) or a high-GI potato starch (P). The four experimental groups were labeled as follows: insulin-resistant P (IR-P), insulin-resistant S (IR-S), normal P (N-P) and normal S (N-S). After 4 wk on the experimental diets, an intraperitoneal glucose tolerance test (IPGTT) was conducted, and the homeostasis model assessment (HOMA), adipocytokines, pro-inflammatory cytokines levels, and insulin signaling-related protein expression were measured. The homeostasis model assessment values were significantly lower in the IR-S than in the IR-P group, suggesting that insulin sensitivity was improved among sweet potato starch-fed rats. Levels of tumor necrosis factor-α, interleukin-6, resistin, and retinol binding protein-4 were significantly lower in the IR-S versus the IR-P group, indicating an improvement of pro-inflammatory status in sweet potato starch-fed rats. The sweet potato starch diet also significantly enhanced the protein expression of phospho-Tyr-insulin receptor substrate-1 and improved the translocation of glucose transporter 4 in the skeletal muscle. Our results illustrated that sweet potato starch feeding for 4 wk can improve insulin sensitivity in insulin-resistant rats, possibly by improving the adipocytokine levels, pro-inflammatory status, and insulin signaling.

    Be well!

    JP

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