PDM: Prediabetes (2013)


Sarkkinen E, Schwab U, Niskanen L, Hannuksela M, Savolainen M, Kervinen K, Kesaniemi A, Uusitupa MIJ. The effect of monounsaturated-fat enriched diet and polyunsaturated-fat enriched diet on lipid and glucose metabolism in subjects with impaired glucose tolerance. Eur J Clin Nutr. 1996; 50(9): 592-598.

PubMed ID: 8880038
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 compare the effects of a high-fat monounsaturated-enriched diet and a reduced-fat polyunsaturated-enriched diet on glucose and lipid metabolism in free-living subjects with well-defined impaired glucose tolerance.

Inclusion Criteria:
  • Impaired glucose tolerance according to WHO (1985) criteria
  • Participation in a Finnish FinMonica Survey.
Exclusion Criteria:
  • Normal glucose tolerance
  • Previously diagnosed diabetes
  • History of thyroid, kidney or liver disease
  • Currently taking lipid-lowering medication.
Description of Study Protocol:


Subjects were recruited from a Finnish FinMonica Survey in which an oral glucose tolerance test was performed with a 75g glucose load on 225 subjects from the Kuopio area in Eastern Finland. 


Randomized clinical trial in which subjects were randomized into one of two test diet groups following a three-week period during which all subjects consumed a run-in diet.

Blinding Used

Dietary fats and oils were provided to the subjects on a single blind basis.


  • The composition of the run-in diet was 36% total fat, 18% saturated fat, 12% monounsaturated fat, 6% polyunsaturated fat
  • After three weeks of consuming the run-in diet, subjects were randomized into one of two test diet groups:
    • A reduced fat, polyunsaturated-fat enriched diet (30% total fat, 10% saturated fat, 10% monounsaturated fat diet, 10% polyunsaturated fat)
    • A high-fat, monounsaturated-fat enriched diet (36% total fat, 10% saturated fat, 18% monounsaturated fat, 8% polyunsaturated fat).
  • Diets were planned to be isocaloric
  • A dietitian gave detailed written and oral instructions on the dietary regimen.

Statistical Analysis

  • Differences in the means and in the absolute and percentage changed (zero and eight weeks) between the two diet groups were analyzed with Student T-test
  • Changes in serum total and lipoprotein lipids and apolipoproteins during the test diets were analyzed by analysis of variance for repeated measurements
  • Paired T-test was used for analysis of within group changes in glucose metabolism and fatty acid composition of serum triglycerides.
Data Collection Summary:

Timing of Measurements

  • Four weeks before the onset of the study the subjects had a second OGTT and a clinical examination including medical history, use of medication and the basic laboratory measurements (routine hematology, TSH, urinary albumin, liver enzymes, serum creatinine)
  • Once the subjects were randomized into one of the two test diet groups, subjects visited the research unit at baseline, two weeks, four weeks and eight weeks
  • Weight, blood pressure and concentrations of serum total cholesterol, triglycerides and HDL-cholesterol were measured at each visit
  • Insulin sensitivity index, glucose effectiveness and first-phase insulin secretion and serum total and lipoprotein lipids, apolipoproteins, free fatty acids, plasma cholesterol ester transfer protein activity and fatty acid composition were measured at baseline and week eight.

Dependent Variables

  • Insulin sensitivity index measured by intravenous glucose tolerance test (IVGTT)
  • Glucose effectiveness measured by IVGTT
  • First-phase insulin secretion measured by IVGTT
  • Serum total and lipoprotein lipid levels measured by fasting blood sample
  • Apolipoproteins measured by fasting blood sample
  • Free fatty acids measured by fasting blood sample
  • Plasma cholesterol ester transfer protein (CETP) activity measured by fasting blood sample 
  • Fatty acid composition of serum triglycerides measured by fasting blood sample. 

Independent Variables

Randomization to one of two test diet groups (low-fat, high polyunsaturated-fat composition or high-fat, high monounsaturated-fat composition) for eight weeks.

Description of Actual Data Sample:
  • Initial N: 31 subjects (13 women, 18 men)
  • Attrition (final N): 31 subjects completed the study although some subjects did not have complete data sets. 14 subjects in the Mono group, 17 in the Poly group
  • Age: Mean age was 55.0±5.3 years for the polyunsaturated fat group and 55.4±5.7 years for the monounsaturated fat group
  • Ethnicity: Eastern Finnish
  • Anthropometrics: No significant differences were noted in baseline characteristics between the diet groups
  • Location: Kuopio area in Eastern Finland.
Summary of Results:

Dietary Compliance

  • According to the results of the food records, the compliance with the fatty acid modification of both diets was good
  • Those in the reduced-fat polyunsaturated fat-enriched diet actually consumed 34% total fat instead of 30%
  • Results on the fatty acid composition of serum triglycerides were in accordance with nutrient intake analysis from food records.

Serum Lipids

  • At the end of the study, there were no significant differences in any of the serum lipid variables between test diets
  • Serum total cholesterol decreased similarly and significantly in both diet groups
  • Apolipoprotein B and Apolipoprotein A-1 both decreased significantly in the monounsaturated group over time. No change was observed in the polyunsaturated group.
Polyunsaturated (N=17)

Monounsaturated (N=14)

Serum total cholesterol

Four weeks



Zero weeks
Eight weeks

Four weeks



Zero weeks
Eight weeks
Zero weeks

Eight weeks




Zero weeks

0.74 (0.17 to 3.56)

0.84 (0.28 to 3.92)

Eight weeks
0.68 (0.15 to 3.14)
0.55(0.13 to 2.71)***
Total triglycerides
Four weeks
1.79 (0.93 to 11.08)
1.72 (1.06 to 7.02)
Zero weeks
1.62 (0.83 to 10.29)
1.80 (0.96 to 11.3)

Eight weeks

1.71 (0.72 to 8.78)

1.45 (0.80 to 9.49)


Zero weeks



Eight weeks
Apolipoprotein A-1
Zero weeks

Eight weeks



Apolipoprotein B

Zero weeks



Eight weeks
Cholesteryl ester transfer protein activity
(mcmol x h-1 x L-1)
Zero weeks

Eight weeks




Glucose Metabolism and Insulin Response

  • No significant differences were found between the diet groups in the variables of glucose metabolism at baseline or in the changes of these variables during the test diets
  • The monounsaturated group had a lower fasting plasma glucose concentration at eight weeks than at zero weeks (6.4±1.3 vs. 6.0±0.8mmol per L, P=0.008). Glucose disappearance rate tended to be faster, but did not reach significance in this group over time.
  • Insulin sensitivity index or glucose effectiveness did not change significantly within either test diet group over time. Glucose effectiveness was significantly different between test diet groups at the end of the study due to the tendency of an increase in the glucose effectiveness in the monounsaturated group over time.
Author Conclusion:

Both the Poly diet and the Mono diet improved serum lipid profile in free-living subjects with impaired glucose tolerance, and the Mono diet seemed to improve glucose effectiveness as well.

Funding Source:
Government: Council for Health Sciences, Academy of Finland and the Ministry of Education Finland
Van den Bergh Foods and Valio Ltd, Finland
Food Company:
Foundation for Nutrition Research, Helsinki, Finland
Other non-profit:
In-Kind support reported by Industry: Yes
Reviewer Comments:
  • Small numbers of subjects in groups
  • The method of randomization was not described
  • The authors did not include a concurrent control group
  • Despite small numbers, a power calculation was not described.
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? ???
  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? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) ???
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  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? ???
  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%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  4.4. Were reasons for withdrawals similar across groups? N/A
  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? Yes
  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? N/A
  6.6. Were extra or unplanned treatments described? N/A
  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? Yes
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? N/A
  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? ???
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? ???
  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? No
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