DLM: Diet Composition (2010)

Citation:

Paniagua JA, de la Sacristana AG, Sanchez E, Romero I, Vidal-Puig A, Berral FJ, Escribano A, Moyano MJ, Perez-Martinez P, Lopez-Miranda J, Perez-Jimenez F. A MUFA-rich diet improves postprandial glucose, lipid and GLP-1 responses in insulin-resistant subjects. J. Am. Coll. Nutr. 2007; 26(5): 434-44.

PubMed ID: 17914131
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To study the effects of three weight-maintenance diets with different macronutrient compositions (a high saturated fat diet, a high MUFA diet and a carbohydrate-rich diet) on carbohydrate, lipid metabolism, insulin and incretin levels in insulin-resistant subjects. 

Inclusion Criteria:
  • Subjects had to be 35 to 75 years old
  • History of fasting glycemia (less than 125mg per dL) with glycosylated hemoglobin (HgbA1C) levels less than 6.5% without any drug or previous insulin treatment
  • BMI higher than 25kg/m2
  • Waist circumference of 102cm or higher for men, 88cm or higher for women
  • Inclusion criteria had to have been met and stable for at least six months prior to enrollment and remain constant throughout the course of the study.  
Exclusion Criteria:
  • Subjects were excluded if they exhibited signs of diabetic retinopathy, nephropathy, neuropathy or macrovascular complications
  • Cigarette smoking and alcohol consumption
  • Use of diuretics, steroids or β-blockers
  • Use of other medications that might affect glucose metabolism
  • All subjects had to have normal hepatic, renal, thyroid and adrenal function.  
Description of Study Protocol:

Recruitment

Subjects were recruited from diabetic patient records at primary care centers in Cordoba between 2003 and 2004 and were invited to attend a screening session where body weight, height, waist circumference, blood pressure and blood biochemistry indices were measured to determine eligibility. 

Design

A prospective, randomized, crossover design was implemented where each subject participated in each dietary intervention group. Subjects were randomly allocated into three groups, and underwent three dietary periods of 28 days each in the crossover design. Diets were designed to provide sufficient calories such as to maintain each participant's weight throughout the study, and dietary cholesterol was kept constant through each diet as well. 

Blinding Used

Blinding was not specified; however, subjects stayed home and prepared their own foodstuffs, and thus one can assume subjects were not blinded to their treatment group. 

Intervention

Three different experimental diets: 

  • A low-fat, high-carbohydrate diet consisting of 65% CHO, 20% fat (6% SAT, 8% MUFA, 6% PUFA)
  • A Mediterranean diet consisting of 47% CHO, 38% fat (9% SAT, 23% MUFA, 75% of which was provided in the form of extra virgin olive oil, and 6% PUFA); Fiber content, 29g.
  • A diet rich in SAT fat: 47% CHO, 15% protein, 38% fat (23% SAT, 9% MUFA, 6% PUFA). Fiber content, 27g.

Subjects were randomly allocated into the three groups with a 28-day intervention cycle. Total calories were calculated based on REE and individualized activity patterns aiming to provide 125% of the subjects' estimated energy needs. 

Statistical Analysis

  • Changes in anthropometry, calorimetry and biochemical determinations were analyzed using repeated-measures design, with one repeated-measures factor (diet: high-SAT, high-MUFA, and high-CHO) used
  • A power calculation was done with preliminary data (80% power with an α of 5%) for detecting a difference of 15% in fasting serum glucose and HOMA-IR. Data were tested for normality of distribution, and the Friedman test was used for variables that did not log transform. 
  • Plasma glucose, triacylglycerol, HDL-cholesterol, GLP-1, and insulin were analyzed by calculating the area under the curve (AUC) based on trapezoid rule with adjustment for baseline concentrations. P<0.05 was considered significant.
Data Collection Summary:

Timing of Measurements

  • Energy expenditure was measured before the start of the study with indirect calorimetry and a three-day food intake diary was completed
  • Body weight was measured twice weekly and intake adjusted such that weight could not vary by more than 1kg
  • A test breakfast was provided on the last day of each diet period and venous blood samples were taken at fasting, 10 minutes before eating, five minutes before eating and then 15, 30, 60, 90, 120, 150, and 180 minutes after eating the test meal. Plasma concentrations of glucose, triacylglycerol, HDL, insulin and GLP-1 were determined.

Dependent Variables

  • Plasma glucose: Measured with glucose oxidase method
  • Plasma insulin: Measured by microparticle enzyme immunoassay
  • Total HgbA1C was measured by HPLC
  • Total cholesterol and triacylglycerols were determined by enzymatic techniques. HDL was measured by dextran sulfate-magnesium precipitation procedure. LDL was calculated from the difference of total cholesterol, TG and HDL.
  • Apo A-1 and Apo B were determined by immunoturbidimetric method
  • Plasma GLP-1 were measured against standards of synthetic GLP-1
  • Insulin resistance was evaluated by the homeostasis model assessment method (HOMA-ir) using fasting glucose (FG) and fasting insulin (FI)
  • Fatty acids were extracted from plasma phospholipids and measured using a fluorometric method, and the relative amount of each fatty acid was quantified.

Independent Variables

Dietary treatment interventions:

  • A low-fat, high carbohydrate diet consisting of 65% CHO, 20% fat (6% SAT, 8% MUFA, 6% PUFA)
  • A Mediterranean diet consisting of 47% CHO, 38% fat (9% SAT, 23% MUFA, 75% of which was provided in the form of extra virgin olive oil, and 6% PUFA). Fiber content, 29g.
  • A diet rich in SAT fat: 47% CHO, 15% protein, 38% fat (23% SAT, 9% MUFA, 6% PUFA). Fiber content, 27g.

Subjects were randomly allocated into the three groups with a 28-day intervention cycle. Total calories were calculated based on REE and individualized activity patterns aiming to provide 125% of the subjects estimated energy needs.  

Control Variables

Total calories were controlled for in each diet group in hopes of subjects maintaining weight during each intervention. Weight was measured twice weekly and not allowed to vary by more than 1kg. Total cholesterol was kept constant in each intervention group. Fiber content was attempted to be kept constant in the higher fat diet groups as well.

Description of Actual Data Sample:
  • Initial N: 59 potential subjects were recruited to attend the initial screening session. 27 of these did not meet inclusion criteria (N=18) or refused to participate (N=9). 22 subjects qualified for the study and underwent an oral glucose tolerance test. Of those, 11 subjects were insulin resistant and were enrolled into the study.
  • Attrition (final N): N=11 
  • Age: Mean age 62.3±9.4 years
  • Ethnicity: Not specified, assumed Spanish ethnicity as all subjects were recruited from a clinic in Cordoba, Spain.
  • Other relevant demographics: Seven females, four males. Mean BMI 32.6±7.8.
  • Anthropometrics: Parameters did not change significantly during the course of the study (BMI, waist circumference, REE)
  • Location: Cordoba, Spain.
Summary of Results:

Key Findings

Serum fatty acid composition:

  • Dietary fatty acid profile reflects each dietary period
  • The proportions of myristic acid, palmitic acid, stearic acid and total saturated acids were significantly increased after the SAT diets compared to the MUFA and CHO dietary periods
  • Oleic acid was significantly increased after eating the high MUFA diet vs. the CHO-rich and SAT-rich diet (P<0.01). 
Selected Serum Fatty Acid Composition after the Three Diet Periods
  Fatty Acids SAT MUFA CHO P
Saturated fatty acids Myristic Acid (14:0) 0.59±0.07 0.42±0.05a 0.05±0.05 < 0.05
  Palmitic Acid (16:0) 23.30±0.47 21.40±0.46b,* 23.46±0.51 <0.01
  Stearic Acid (18:0) 10.00±0.47

9.23±0.28

10.07±0.37 <0.05
  Total saturated FAs 36.5±0.44 33.51±0.45 35.7±0.35 < 0.01
MUFA Oleic Acid (18:1, N=9) 20.37±1.22 24.91±0.67 21.83±0.59

<0.01

Data are expressed as mean ±SEM. * <0.05, compare MUFA vs. CHO. a <0.05, b <0.01 comparing MUFA and CHO vs. SAT.

 

Biochemical results:

  • Fasting glucose was decreased during the MUFA and CHO periods compared with SAT
  • Fasting insulin concentrations were unchanged during the three diet periods
  • Mean HOMA-ir decreased during the MUFA diet compared with the SAT and CHO diets
  • Fasting total cholesterol, TG and LDL did not change during the three treatment diets
  • HDL, Apo A1 and APO B fell during the CHO diet
  • Postprandial integrated AUCs of glucose and insulin were significantly higher in response to the standard CHO breakfast than to the MUFA and SAT breakfasts
  • Postprandial TG AUC fell during the CHO diet. Postprandial HDL were increased after the MUFA and SAT diets.
  • Fasting GLP-1 were similar in all three diet groups, but postprandial AUC was significantly lower in response to the CHO diet than the MUFA and SAT diet.
  • Fasting serum proinsulin decreased after the MUFA diet as compared with the CHO and SAT diets. 

 

  SFA MUFA CHO P
Biochemical Determinations after the Three Dietary Periods
HBA1c (percent) 5.74±0.137 5.39±0.10b 5.40±0.10b  <0.01
Glucose        
    Fasting (mmol per L) 5.50±0.19 5.02±0.14a 5.03±0.13a  <0.05
    AUC, mmol•180 minutes per L 5.84±1.2 7.82±1.3 11.9±2.7*,b  <0.05
Plasma Insulin        
    Fasting, pmol per L 64.1±9.6 60.72±12.42 75.21±12.33 0.3
    AUC, pmoL•180 minutes per L 1253±140 1004±147 2667±329**,a <0.01
HOMA-ir, mmol per L x µU per ml 2.72±0.37 2.32±0.35*, a 2.52±0.37 <0.01
HOMA-i%β 103.1±12.2 109.1±12.5 126.6±18.4 0.2
GLP-1        
    Fasting, pmol per L 6.47±0.59 6.34±0.51 5.67±0.49 0.4
    AUC, pmol•180 minutes per L 4.34±1.10 4.22±0.66 1.85±1.14*,a <0.05
Proinsulin        
    Fasting (pmol per L) 11.0±2.6 8.72±2.3a 9.52±1.39 <0.05
    60 minutes PI/I ratio (percent) 1.64±0.57 2.59±1.21 1.44±0.43 0.17
Total Chol (mmol per L) 6.24±0.31 5.96±0.31 5.58±0.30 0.2
TG (mmol per L) 1.36±0.15 1.31±0.12 1.39±0.17 0.4
HDL chol (mmol per L) 1.22±0.12 1.22±0.14 1.09±0.11*, a <0.05
LDL chol (mmol per L) 4.24±0.25 3.99±0.22 3.85±0.28 0.6
Apo A1 (mg per dL) 151±9 156±9.41 136±9.87 <0.05
Apo B100 (mg per dL) 104±6 100±6 92±8a <0.05

Data are mean ± SEM. * <0.05, ** <0.01, comparing MUFA vs CHO. a < 0.05, b < 0.01 comparing MUFA and CHO vs. SAT.

 

Other Findings

  • Increasing the percentage of fat in the diet to approximately 40% of total energy did not increase body weight or adiposity when energy balance was maintained
  • Fasting plasma fatty acid composition reflects the composition of the types of fats consumed
  • Replacing saturated fat with MUFA improves fasting glycemic concentrations in insulin-resistant prediabetic patients. 

 

Author Conclusion:
  • Weight maintenance with a MUFA-rich diet improves HOMA-ir and fasting proinsulin levels in insulin-resistant subjects
  • Ingestion of a virgin olive oil-based breakfast decreased postprandial glucose and insulin concentrations, and increased HDL-C and GLP-1 concentrations as compared with CHO-rich diet.
Funding Source:
Government: Secretaria General de Calidad y Eficiencia, Junta de Andalucia, Exp 78/02 and 240/04
Reviewer Comments:

Small sample size.  Authors note excellent dietary compliance from subjects. 

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) Yes
  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? 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? 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? ???
  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? No
  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)? N/A
  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? N/A
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