EAL

DM: Prevention and Treatment of CVD (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

Subjects participated in either the San Luis Valley diabetes Study (SLVDS) (Colorado) or the Insulin Resistance Atherosclerosis Study (IRAS), a multicenter study (Oakland, CA, San Antonio, TX, and San Luis Valley, CO).

This paper is an evaluation of associations between macronutrient intake and lipoprotein profile and time of diabetes diagnosis (undiagnosed prior to study vs. previously diagnosed) in individuals with type 2 diabetes. Analyses were conducted separately for the 2 studies.

Inclusion Criteria:

1. Adults with type 2 diabetes from SLVDS (1984-1992) or the IRAS (1992-1994).

2. Diagnosis of diabetes with 75 g glucose OGTT using WHO criteria.

3. Diagnosis of diabetes based on current use of diabetes medications

Exclusion Criteria:

1. On lipid lowering medications

2. Missing data

Description of Study Protocol:

Recruitment

SLVDS- Hispanic and non-Hispanic men and women in rural southern Colorado
IRAS- multicenter study in Oakland CA, Los Angeles CA, San Antonio TX, and San Luis Valley CO.

Design

SLVDS- subjects were followed for 8 years. Of 421 participants, 140 were seen once, 277 were seen twice, and 152 were seen 3 times.
IRAS- no details given, but reader is referred to reference 14.

Blinding Used (if applicable):

Not used.

Intervention (if applicable):

Analysis of dietary intake.

Statistical Analysis

Simple correlation coefficients were obtained between the percentage of total calories from each nutrient available and each lipoprotein.

Regression modelling was used for hypothesis testing to accomplish adjustment for potentially confounding variables.

Because nutrient intake was assessed with different methods in the two studies, all analyses were performed separately but in a parallel manner.

Data Collection Summary:

Timing of Measurements: few details of original studies included in this article

Dependent Variables

SLVDS:

HDL by dextran sulfate magnesium precipitation
Triglyderides via an enzymatic method
LDL cholesterol using the Friedewald formula when triglyceride values were <400mg/dl
total cholesterol

IRAS:

LDL and HDL by isopyknic ultracentirfugation
VLDL top and bottom fractions were measured for cholesterol and triglyeride concentrations
total cholesterol

Independent Variables

Total fat
Saturated Fat
Oleic acid
Polyunsaturated fat
total carbohydrates
simple carbohydrates
starch
Dietary intake:
- SLVDS: 24-h dietary recall administered by bilingual interviewers trained & certified by the Nutrition Coordinating Center, U of Minnesota. Two dimensional food models and 3 dimensional measuring devices were used to identify serving sizes.
- IRAS: 1-yr FFQ (NCI Health Habits and History Questionnaire) modified to include ethnic foods.
Weight history
- weight gain group (gain of 5 or more pounds in previous 6-12 months)
- weight-loss group (loss of 5 or more pounds in previous 6-12 months)
- stable weight group

Control Variables

Total calories
alcohol intake
BMI
vigorous activity
diabetes medication
age
sex
ethnicity
education

Description of Actual Data Sample:

Initial N:

Of the 430 subjects classified with type 2 diabetes in the SLVDS, 421 were used in this analysis.
Of the 537 subjects classified with type 2 diabetes in the IRAS, 437 were included in this analysis.

Final N: not specified

Selected demographics and anthropometrics of study samples

	SLVDS	IRAS
age, years	58.6± 10.5	57.0± 8.4
women, %	56.8	52.6
Hispanic, %	65.3*	33.4
African-American, %	NA	34.6
Non-Hispanic white, %	34.7	32
previous dx of diabetes, %	83.6*	61.6
previously undiagnosed for diabetes, %	16.4	38.4
duration of diabetes among those diagnosed, %	8.7± 7.9	6.8± 6.4
BMI < 25, %	18.8	9.4
BMI 25-29.99, %	44.7	36.6
BMI > 29.99	36.6	54*
Weight loss > 5 lb, %	30.9	31.8
weight gain > 5 lb, %	12.8	19.9*
stable weight,%	56.3	48.3

* P<0.05 between SLVDS and IRAS

Summary of Results:

Unadjusted Pearson correlation coefficients between nutrients (percentage of calories) and LDL cholesterol

Nutrient	SLVDS	IRAS
Total fat	0.09*	0.03
Saturated fat	0.02	-0.02
Polyunsaturated fat	0.09	0.11*
Oleic acid	0.11*	0.02
Total Carbohydrate	-0.03	0.01
Starch	0.00	0.00
Simple carbohydrates	-0.06	0.01

* P<0.05

Higher reported intake of total dietary fat was related to significantly higher levels of LDL cholesterol (P<0.05) in both studies and all subgroups.

Higher reported intake of carbohydrate intake was associated with increased TG (P<0.01) only among individuals with previously undiagnosed diabetes in the SLVDS (n=69) and only among subjects who gained weight (>5 lb, n=87) during the previous year in the IRAS.

Author Conclusion:

Data from these two large epidemiological studies emphasize the potential importance of low dietary fat to lower LDL cholesterol.

This is consistent with recommendations for low fat intake toward the goal of weight loss, which is a key element of metabolic management of type 2 diabetes mellitus.

The potential negative effect of excess carbohydrate intake is an increase in TG, especially in individuals with recent diagnosis of type 2 diabetes and those who are gaining weight.

Funding Source:

Reviewer Comments:

The two study groups were significantly different for ethnicity, level of education, previous diagnosis, and obesity. Weight history and previous diagnosis were controlled for in the analysis.There were over 50% in the IRAS group that were obese, and over 50% in the SLVDS group that were Hispanic.

Nutrient intake was measured differently in each group and the methods of lipid analyses were different for all lipids.

This epidemiological study shows that high fat intake contributes to higher LDL cholesterol in people with diabetes while high carbohydrate intake contributes to higher TG in newly diagnosed type 2 diabetes mellitus or with weight gain.

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)	N/A
	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)	N/A

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?	???
2.	Was the selection of study subjects/patients free from bias?		Yes
	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?		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.)	N/A
	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?	No
	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?		No
	4.1.	Were follow-up methods described and the same for all groups?	No
	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	No
	4.4.	Were reasons for withdrawals similar across groups?	???
	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?		No
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	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.)	???
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	No
	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?		No
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	No
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	No
	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?	???
	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?	No
	7.7.	Were the measurements conducted consistently across groups?	No
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)?	No
	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