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Vitamins and Antioxidants and the Prevention and Treatment of CVD


Christensen AS, Viggers L, Hasselstrom K, Gregersen S. Effect of fruit restriction on glycemic control in patients with type 2 diabetes: A randomized trial. Nutr J. 2013; 12: 29.

PubMed ID: 23497350
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To investigate whether an advice to reduce the intake of fruit to patients with type 2 diabetes affects HbA1c, body weight, waist circumference and fruit intake.

Inclusion Criteria:
  • Adults with type 2 diabetes (duration less than 12 months)
  • HbA1c values 12.0% or less and who accepted to adhere to the protocol
  • Provided written informed consent.
Exclusion Criteria:
Clinically significant cardiovascular, renal or endocrine disease.
Description of Study Protocol:


Volunteers were selected from patients referred to MNT by their general practitioner to the Outpatient Clinic at Department of Nutrition, Regional Hospital West Jutland.


Randomized controlled trial with two parallel groups 

Blinding Used

Implied with measurements.


Subjects randomized to one of two groups for 12 weeks:

  • Medical nutrition therapy and advice to consume at least two pieces of fruit a day (high-fruit)
  • Medical nutrition therapy and advice to consume no more than two pieces of fruit a day (low-fruit).

Statistical Analysis

  • Analysis was performed using Stata Statistical software package (version 11.1)
  • All analyses were performed on an intention to treat basis with a two-sided 0.05 significance level (alpha 0.05)
  • A paired T-test was used to analyze if a variable changed significantly from before to after an intervention
  • For the primary outcome, multiple regression analysis was used controlling for potential confounders.


Data Collection Summary:

Timing of Measurements

Measurements made at baseline and at 12 weeks.

Dependent Variables

  • Height was measured at the first visit only
  • Body weight and waist circumference were measured at both visits. Subjects were weighed barefooted and in light clothing on a calibrated scale. Waist circumference was measured horizontally at the level of the umbilicus in a relaxed standing position.
  • Blood samples were taken from the subjects to analyze HbA1c using high performance liquid chromatography (HPLC)
  • Fruit intake was measured by a weighed three-day fruit record before and after the intervention. At each visit, the fruit intake was estimated using dietary recalls. Portion sizes were estimated and translated to grams using pictures and table values of mean weight for a given standard portion.

Independent Variables

Subjects randomized to one of two groups for 12 weeks:

  • Medical nutrition therapy and advice to consume at least two pieces of fruit a day (high-fruit)
  • Medical nutrition therapy and advice to consume no more than two pieces of fruit a day (low-fruit).

Control Variables

Physical activity was measured by a self-reported questionnaire at each visit to estimate activity level.


Description of Actual Data Sample:
  • Initial N: N=63 subjects
  • Attrition (final N): N=63 (32 females, 31 males), 32 in high-fruit, 31 in low-fruit
  • Age: Mean age in high-fruit group 59±12 years vs. 57±12 years in low-fruit group
  • Other relevant demographics: Mean duration of diabetes (days) in high-fruit group 22 vs. 33 in low-fruit group
  • Anthropometrics: Mean BMI (kg/m2) in high-fruit group 32±5 vs. 32±6. At baseline, significantly more subjects were taking oral anti-diabetic drugs on the high-fruit diet than on the low-fruit diet (22 vs. 12; P=0.02). There were no significant differences between the groups for any of the other baseline variables.
  • Location: Denmark.


Summary of Results:

Key Findings

  • The high-fruit group increased fruit intake with 125g (95% CI: 78 to 172) and the low-fruit group reduced intake with 51g (95% CI: -18 to -83)
  • HbA1c decreased in both groups with no difference between the groups (difference: 0.19%; 95% CI: -0.23 to 0.62)
  • Both groups reduced body weight and waist circumference; however, there was no difference between the groups.




Author Conclusion:

A recommendation to reduce fruit intake as part of standard medical nutrition therapy in overweight patients with newly diagnosed type 2 diabetes resulted in eating less fruit. It had, however, no effect on HbA1c, weight loss or waist circumference. We recommend that the intake of fruit should not be restricted in patients with type 2 diabetes.

Funding Source:
University/Hospital: Department of Nutrition, Regional Hospital West Jutland, Denmark
Reviewer Comments:

The authors noted the study had some weaknesses. The authors did not control the intake of medication and a difference in baseline use of OADs could bias the results. Finally, fruit intake and physical activity were self-reported and therefore could have been subject to under-reporting or over-reporting. Measurement of biomarkers of fruit intake such as plasma vitamin C and plasma carotenoids would have strengthened the study.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? No
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes