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Sweet potato for type 2 diabetes mellitus

  1. Cheow Peng Ooi1,*,
  2. Seng Cheong Loke2

Editorial Group: Cochrane Metabolic and Endocrine Disorders Group

Published Online: 3 SEP 2013

Assessed as up-to-date: 20 FEB 2013

DOI: 10.1002/14651858.CD009128.pub3


How to Cite

Ooi CP, Loke SC. Sweet potato for type 2 diabetes mellitus. Cochrane Database of Systematic Reviews 2013, Issue 9. Art. No.: CD009128. DOI: 10.1002/14651858.CD009128.pub3.

Author Information

  1. 1

    Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Endocrine Unit, Department of Medicine, Serdang, Selangor DE, Malaysia

  2. 2

    Universiti Putra Malaysia, Institute of Gerontology, Serdang, Selangor DE, Malaysia

*Cheow Peng Ooi, Endocrine Unit, Department of Medicine, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor DE, 43400, Malaysia. cpooi07@gmail.com.

Publication History

  1. Publication Status: Edited (no change to conclusions), comment added to review
  2. Published Online: 3 SEP 2013

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Characteristics of included studies [ordered by study ID]
Ludvik 2002

MethodsParallel RCT

Randomisation ratio: 1:1

Superiority design


ParticipantsInclusion criteria: clinically stable T2DM on diet only

Exclusion criteria: no information

Diagnostic criteria: authors' criteria


InterventionsNumber of study centres: no information

Treatment before study: diabetic diet

Titration period: nil

Experimental intervention groups:

  1. Tablets each containing 168 mg powdered white-skinned sweet potato (Ipomoea batatas)
  2. Tablets each containing 336 mg powdered white-skinned sweet potato (Ipomoea batatas


Participants in each group received 4 tablets 3 times daily after meals for a period of 6 weeks. A total of 2 g and 4 g/day were ingested by participants in each group, respectively

Control intervention:

Placebo tablets. No information on the contents of these tablets

All patients were on diet regimen during the study


OutcomesOutcomes reported in abstract of publication:

Primary outcome(s): (as stated in the publication) change in fasting blood glucose

Seondary outcome(s): (as stated in the publication) change in plasma insulin level, serum cholesterol and weight

Additional outcome(s): incidence of adverse events


Study detailsRun-in period: no information

Was s tudy terminated early (for benefit/because of adverse events): no


Publication detailsLanguage of publication: English

Commercial funding: grant from manufacturer

Publication status: peer review journal


Stated aim of studyQuote from publication: "To assess the effect of caiapo on glucose metabolism, its tolerability and mode of action in male Caucasian type 2 diabetic patients".


NotesLetter to editor. Pilot study


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskQuote from publication: "randomised to receive placebo or 2 (low dose) or 4 g (high dose) caiapo"
Comment: there was no description of generation of the random sequence; furthermore, reports of 2 other trials by the same principal investigators that used a similar intervention also provided no information about sequence generation

Allocation concealment (selection bias)Unclear riskComment: there was no information provided about the method of allocation concealment

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskQuote from publication: "double-blind"

Comment: there was no other information available concerning blinding

Blinding of outcome assessment (detection bias)
All outcomes
Low riskComment: fasting blood glucose was specifically accessed at each visit for each participant

Incomplete outcome data (attrition bias)
All outcomes
Low riskComment: all participants completed the study, no treatment withdrawals or major adverse events reported

Selective reporting (reporting bias)Low riskComment: primary outcomes were stated

Other biasUnclear riskComment: there was no information about the sample size calculation or exclusion criteria; there was also insufficient information to assess other important risks of bias

Ludvik 2004

MethodsParallel RCT

Randomisation ratio: 1:1

Superiority design


ParticipantsInclusion criteria: clinically stable T2DM on diet only

Exclusion criteria: renal, hepatic, cardiovascular, hematological, respiratory, autoimmune, neurological diseases or other endocrine dysfunction that could interfere with the study

Diagnostic criteria: authors' criteria


InterventionsNumber of study centres: no information

Treatment before study: oral hypoglycaemic agents withdrawn 2 weeks before trial

Titration period: nil

Intervention group:

4 g of Caiopo (Ipomoea batatas) once daily

Control intervention:

Placebo tablets; no information provided regarding the content of these tablets

All participants were on diet regimen during the study


OutcomesOutcomes reported in abstract of publication:

Primary outcome(s): (as stated in the publication) change in fasting blood glucose and 2-hour postprandial blood glucose; change in HbA1c

Seondary outcome(s): (as stated in the publication) change in cholesterol and triglyceride levels

Additional outcome(s): incidence of adverse events


Study detailsRun-in period: 5 participants on antidiabetic medication (metformin and/or glibenclamide) had their medications withdrawn 2 weeks before the start of the study

Was s tudy terminated early (for benefit/because of adverse events): no


Publication detailsLanguage of publication: English

Commercial funding: grant from manufacturer

Non-commercial funding: nil

Publication status: peer review journal


Stated aim of studyQuote from publication: "... assessment of the efficacy and tolerability of Caiapo (4 g/day) compared with placebo when administered for 12 consecutive weeks for type 2 diabetic patients ..."


NotesOriginal research journal article


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskQuote from publication: "randomly divided into two groups"
Comment: the process of randomisation was not specified

Allocation concealment (selection bias)Unclear riskComment: there was no information about the adequacy of allocation concealment

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskQuote from publication: "double-blind"

Comment: there was no other information available about blinding

Blinding of outcome assessment (detection bias)
All outcomes
Low riskComment: fasting blood glucose and HbA1c were specifically measured

Incomplete outcome data (attrition bias)
All outcomes
Low riskComment: all participants completed the study, no treatment withdrawals or major adverse events reported

Selective reporting (reporting bias)Low riskComment: primary outcome measures were stated

Other biasLow riskComment: none detected

Ludvik 2008

MethodsParallel RCT

Randomisation ratio: 1:1

Superiority design


ParticipantsInclusion criteria: clinically stable T2DM on diet only

Exclusion criteria: no information

Diagnostic criteria: authors' criteria


InterventionsNumber of study centres: multiple centres (no information on exact number)

Treatment before study: no hypoglycaemic drugs 4 weeks prior to baseline visit

Titration period: nil

Intervention group:

4 g of Caiopo (Ipomoea batatas) once daily

Control intervention:

Placebo tablets; no information provided about the content of these tablets

All participants were on diet regimen during the study


OutcomesOutcomes reported in abstract of publication:

Primary outcome(s): (as stated in the publication) change in fasting blood glucose and 2-hour postprandial blood glucose; change in HbA1c

Seondary outcome(s): (as stated in the publication) change in cholesterol and triglyceride levels

Additional outcome(s): incidence of adverse events


Study detailsRun-in period: medications that affect blood glucose levels such as corticosteroids, high-dose diuretics or beta-blockers were stopped during the 2 weeks prior to screening and for the duration of the study; screening for participants took place 1 month prior to start of study; hypoglycaemic drugs were withdrawn 4 weeks before the start of the study

Was s tudy terminated early (for benefit/because of adverse events): no


Publication detailsLanguage of publication: English

Commercial other funding: grant from manufacturer

Non-commercial funding: nil

Publication status: peer review journal


Stated aim of studyQuote from publication: "To further evaluate the mode of action of Caiapo on insulin sensitivity over an extended period of time as well as the effects on fibrinogen and other markers of low-grade inflammation".


NotesOriginal research journal article


Risk of bias

BiasAuthors' judgementSupport for judgement

Random sequence generation (selection bias)Unclear riskQuote from publication: "randomised"
Comment: there was no information provided about the process used to generate the random sequence

Allocation concealment (selection bias)Unclear riskComment: there was no information provided about the adequacy of allocation concealment

Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskQuote from publication: "double-blind"
Comment: there was no other information available about blinding

Blinding of outcome assessment (detection bias)
All outcomes
Low riskComment: the primary and secondary outcomes were measured objectively

Incomplete outcome data (attrition bias)
All outcomes
High riskQuote from publication: "27/88 patients dropped out (due to pregnancy (1) and non-compliance to follow-up visits)"
Comment: there was no information about the number of participants who dropped out of the intervention and the control groups

Selective reporting (reporting bias)Low riskComment: important primary and secondary outcomes were adequately reported

Other biasLow riskComment: none detected

 
Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion

Ludvik 2003The objective was evaluation of the mechanism of action of Ipomoea batatas and not the effects of the intervention on T2DM. This paper did not contain relevant outcome data for assessment

 
Comparison 1. Sweet potato (Caiapo) tablets versus placebo

Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size

 1 Fasting blood glucose (final values)3Mean Difference (IV, Random, 95% CI)Subtotals only

    1.1 Sweet potato (2 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)0.0 [-2.23, 2.23]

    1.2 Sweet potato (4 g/day) at 6 weeks and below 3 months
273Mean Difference (IV, Random, 95% CI)-0.65 [-1.43, 0.13]

    1.3 Sweet potato (4 g/day) at 3 to 5 months
2122Mean Difference (IV, Random, 95% CI)-0.68 [-0.84, -0.52]

 2 Postprandial blood glucose (final values)1Mean Difference (IV, Random, 95% CI)Subtotals only

    2.1 Sweet potato (4 g/day) at less than 3 months
161Mean Difference (IV, Random, 95% CI)-0.98 [-2.07, 0.11]

    2.2 Sweet potato (4 g/day) at 3 months
161Mean Difference (IV, Random, 95% CI)-1.01 [-2.19, 0.17]

 3 HbA1c (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    3.1 Sweet potato (4 g/day) at 3 to 5 months
2122Mean Difference (IV, Random, 95% CI)-0.30 [-0.57, -0.04]

 4 Fasting plasma insulin (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    4.1 Sweet potato tablets (2 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)0.30 [-3.94, 4.54]

    4.2 Sweet potato tablets (4 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)4.5 [-0.93, 9.93]

    4.3 Sweet potato tablets (4 g/day) at 5 months
161Mean Difference (IV, Random, 95% CI)1.11 [-1.85, 4.07]

 5 Body weight (final values)1Mean Difference (IV, Random, 95% CI)Subtotals only

    5.1 Sweet potato (4 g/day) at 3 months
161Mean Difference (IV, Random, 95% CI)-1.0 [-5.32, 3.32]

 6 BMI (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    6.1 Sweet potato (4 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)-1.10 [-4.43, 2.23]

    6.2 Sweet potato (4 g/day) at 5 months
161Mean Difference (IV, Random, 95% CI)1.0 [-0.81, 2.81]

 7 Total cholesterol (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    7.1 Sweet potato (4 g/day) at 3 to 5 months
2122Mean Difference (IV, Random, 95% CI)-0.47 [-1.10, 0.16]

 8 Triglycerides (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    8.1 Sweet potato (4 g/day) at 3 to 5 months
2122Mean Difference (IV, Random, 95% CI)-0.03 [-0.41, 0.35]

 9 HDL-cholesterol (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    9.1 Sweet potato (2 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)-0.26 [-0.63, 0.11]

    9.2 Sweet potato (4 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)-0.31 [-0.64, 0.02]

    9.3 Sweet potato (4 g/day) at 5 months
161Mean Difference (IV, Random, 95% CI)-0.14 [-0.31, 0.03]

 10 LDL-cholesterol (final values)2Mean Difference (IV, Random, 95% CI)Subtotals only

    10.1 Sweet potato (2 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)0.02 [-0.95, 0.99]

    10.2 Sweet potato (4 g/day) at 6 weeks
112Mean Difference (IV, Random, 95% CI)-1.06 [-1.92, -0.20]

    10.3 Sweet potato (4 g/day) at 5 months
161Mean Difference (IV, Random, 95% CI)-0.13 [-0.60, 0.34]

 
Summary of findings for the main comparison. Ipomoea batatas (Caiapo) tablets compared to placebo for type 2 diabetes mellitus

Ipomoea batatas (Caiapo) tablets compared to placebo for type 2 diabetes mellitus

Patient or population: people with type 2 diabetes mellitus
Settings: out-patients
Intervention: Ipomoea batatas (Caiapo) tablets
Comparison: placebo

OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of Participants
(studies)
Quality of the evidence
(GRADE)
Comments

Assumed riskCorresponding risk

PlaceboIpomoea batatas (Caiapo) tablets

MorbiditySee commentSee commentNot estimableSee commentSee commentNot investigated

Adverse effects
Follow-up: 1.5 to 5 months
See commentSee commentNot estimable140
(3)
⊕⊝⊝⊝
very lowa
2 out of 3 studies reported adverse eventsb

Health-related quality of lifeSee commentSee commentNot estimableSee commentSee commentNot investigated

Well-beingSee commentSee commentNot estimableSee commentSee commentNot investigated

Functional outcomesSee commentSee commentNot estimableSee commentSee commentNot investigated

CostsSee commentSee commentNot estimableSee commentSee commentNot investigated

HbA1c [%] (final values)
Follow-up: 3 or 5 months
Final values for HbA1c across control groups ranged from 6.5 to 7.1Final values for Hba1c in the intervention groups were 0.3 lower (0.6 to 0.04 lower)-122
(2)
⊕⊝⊝⊝
very lowc
-

*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: confidence interval;

GRADE Working Group grades of evidence
High quality: further research is very unlikely to change our confidence in the estimate of effect
Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate
Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate
Very low quality: we are very uncertain about the estimate

 aDowngraded by three due to high risk of bias (insufficient information on the process of randomisation, blinding, selective outcome and incomplete data reporting), small number of trials and participants and no replication of trials by other authors (same investigating team throughout)
bMild gastrointestinal symptoms such as nausea, diarrhoea, constipation, gastric pain and abdominal distension
cDowngraded by three due to imprecision, high risk of attrition bias and indirectness
 
Table 1. Overview of study populations

CharacteristicIntervention(s) and comparator(s)Sample
size
[N]
Screened/
eligible
[N]
Randomised
[N] Safety[N]
ITT
[N]
Finishing study
[%]
Randomised finishing study
Follow-upa

Ludvik 2002I1: 2 g powdered white-skinned
sweet potato (Ipomoea batatas)
tablet
--66-61006 weeks

I2: 4 g powdered
white-skinned
sweet potato (Ipomoea batatas)
tablet
666100

C: Placebo666100

Total:181818100

Ludvik 2004I: 4 g of Caiopo
(Ipomoea batatas) tablet
--3030-301003 months

C: Placebo313131100

Total:616161100

Ludvik 2008I: 4 g of Caiopo
(Ipomoea batatas) tablet
21----27N/A5 months

C Placebo21--34N/A

Total:4288-6169.3

Grand totalAll interventions I1: 63 + ?
I2: 6
I1: 63
I2: 6

All c omparators 71 + ? 71

All interventions and c omparators 140 + ? 140

 aDuration of intervention and/or follow-up under randomised conditions until end of study
"-" denotes not reported
"+ ?" denotes number of unreported participants who took part in the study
C: comparator; I: intervention; ITT: intention-to-treat; N/A: not applicable