EAL

DM: Prevention of Type 2 Diabetes (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To determine if dietary fat intake measured at a baseline exam in subjects with impaired glucose tolerance (IGT) predicted the subsequent development of type 2 diabetes. The San Luis Valley (southern Colorado) Diabetes Study was designed to determine the prevalence and incidence of type 2 diabetes mellitus in Hispanics and non-Hispanic white adults and the etiological and prognostic risk factors associated with type 2 diabetes mellitus.

Inclusion Criteria:

1. No previous diagnosis of diabetes mellitus

2. Impaired OGTT on 75-g OGTT, 1-hr and 2-hr using 1985 WHO criteria at baseline visit.

Exclusion Criteria:

Initial visit greater than 4 years before follow-up.

Description of Study Protocol:

Recruitment: All subjects were recruited from the San Luis Valley Diabetes Study. Original geographically based sample had 1,321 people 30-74 yr of age seen for a baseline visit May 1984 to August 1988.

Design: A cohort of 173 subjects with IGT were identified from a geographically based sample of 1321 persons included in the San Luis Valley Diabetes Study. Of these 134 were invited to follow-up before the clinic closed in January 1990. The remaining 39 subjects were excluded because more than 4 years had passed since their initial visit.

Blinding Used (if applicable): not applicable

Intervention (if applicable): 123 of the invited subjects had a second OGTT. Subjects were followed a mean of 22.6 months (range 11-40 months)

Statistical Analysis

Mean levels and percentage distribution of baseline risk factors for converters and nonconverters to type 2 diabetes were compared.
adjusted odds ratios were estimated by multiple logistic regression
baseline dietary risk factors were entered into multiple logistic regression models to evaluate importance after controlling for age, sex, ethnic grojp, BMI, waist-to-hip ratio, central obesity, fasting and 1-h postload insulin ratios, and fasting blood glucose to predict the development of diabetes
odds ratios were calculated from logistic regression to estimate the relative increase in risk associated with a 40 g/day increase in fat intake.

Data Collection Summary:

Timing of Measurements: All measurements taken at time of second OGTT

Dependent Variables:

Diagnosis of type 2 diabetes
Dietary fat intake

Independent Variables:

Dietary assessment: 24-hr recall by bilingual interviewers trained and certified by the Nutrition Coordinating Center, U MN. 3-dimensional food models and measuring devices were used during the interviews.

Control Variables

age
sex
ethnic grojp
BMI
skinfold measurements
waist-to-hip ratio
central obesity
fasting and 1-h postload insulin ratios
fasting blood glucose

Description of Actual Data Sample:

Initial N: A cohort of 173 subjects with IGT were identified from a geographically based sample of 1321 persons included in the San Luis Valley Diabetes Study. Of these 134 were invited to follow-up before the clinic closed in January 1990. The remaining 39 subjects were excluded because more than 4 years had passed since their initial visit.

Attrition (Final N): 123

Age: cohort means not specified

Ethnicity: cohort ethnicity not specified

Other relevant demographics: not specified for cohort as a group

Anthropometrics: those who converted to type 2 diabetes had mean BMI of 29.2±1.1

Location: United States

Summary of Results:

The mean percentage of energy as fat was 43.4% in 20 people subsequently developing type 2 diabetes mellitus compared with 40.6% in 43 people remaining IGT and 38.9% in 60 subjects who reverted to normal glucose tolerance.

Comparing the 20 subjects who developed type 2 diabetes melllitus with the 103 who continued to have IGT or normal, an increase in fat intake of 40 g/d was associated with an increase in risk of type 2 diabetes mellitus of 3.4 fold (95% CI, 0.8-13.6) adjusted for energy intake, age, sex, ethnicity, and obesity. The odds ratio increased to six fold (95% CI, 1.2-29.8) after adjustment for fasting glucose, insulin, and 1-hr insulin.

Means and percentage distribution for risk factors at baseline by follow-up glucose status.

	Changed to Normal	Converted to diabetes	P
Female (%)	48.3	75.0	0.02
Hispanic (%)	46.7	60	0.39
BMI	27.0	29.2	0.02
Glucose Fasting, Mm	5.6	6.1	<0.01
1-hr	10.1	12.6	<0.01
Insulin, PM Fasting	99.6	145.3	<0.01
Dietary fat (%)	38.9	43.9	<0.02
Fiber/1000kcal	10.1	7.6	<0.06

Author Conclusion:

Fat consumption significantly predicts type 2 diabetes mellitus risk in subjects with IGT after controlling for obesity and markers of glucose metabolism.

Relatively recent reviews have stated that there are no consistent data to support the hypothesis that diet modifies the risk of developing type 2 diabetes mellitus. However, evidence from animal and clinical studies, epidemiological studies, and evolutionary prospectives increasingly supports the hypothesis that high-fat/low carbohydrate diets prevalent in Westernized societies today are contributing to the excess obesity and type 2 diabetes mellitus seen in these same groups.

In epidemiological studies, multiple prospective assessments of diet and glucose tolerance are still needed to rule out the possibility that early sub clinical disease is altering dietary preferences and to better understand whether dietary composition is acting to increase risk for type 2 diabetes in all stages of the disease, in active and inactive, obese and lean.

Funding Source:

Government:	NIH
University/Hospital:	University of Colorado Health Sciences Center

Reviewer Comments:

A modifiable risk factor for decreasing the development of type 2 diabetes mellitus is reduced fat intake.

No information was given as to how the endpoint diagnosis of diabetes was determined. It may be included in a previous article about this 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?	???
	1.3.	Were the target population and setting specified?	Yes
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?	Yes
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)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	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?	Yes
	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?		N/A
	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.)	N/A
	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?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	Yes
	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?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	No
	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?	???
	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