EAL

DM: Prevention of Type 2 Diabetes (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the long-term impact of a reduced-fat diet program on body weight, glucose tolerance, and conversion to type 2 diabetes.

Inclusion Criteria:

2-hr results of OGTT using WHO criteria:

a. impaired glucose tolerance 7.8-11.0 mmol/L

b. high normal blood glucose 7.0-7.8 mmol/L

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: Participants were recruited from the previous Workforce Diabetes Survey, in which OGTT were performed on 4833 workers from 41 worksites around Auckland, New Zealand.

Study Design: 5-year follow-up to a 1-year randomized controlled trial

Blinding: Participants were told that the study was testing the effect of fat intake on blood glucose levels.

Intervention: Subjects randomized to reduced-fat group or control group.

Statistical Analysis

Mean (SE) values, adjusted for age, sex, ethnicity, and baseline measurement
repeated measures model included time since baseline for each of the time points, treatment group, and the time by treatment interaction
unstructured variance-covariance matrix used to model the correlations between time points
categorical variables were compared using the chi-square test
Student's t test used for continuous variables
participants who dropped out before the end of the 12-month intervention period were not included in the analysis

Data Collection Summary:

Timing of Measurements

Subjects in both groups completed a comprehensive 3-day food diary before randomization and after 1 year.
OGTT at each review
Diabetes, impaired glucose tolerance, and impaired fasting glycemia were assessed at randomization, 6 months, and 1, 2, 3, and 5 years.
2-yr follow up of study groups

Dependent Variables

Glucose tolerance
Body weight

Independent Variables

Control diet group: received general dietary advice about healthy food choices upon entering the trial.
Reduced-fat group(RF) :
- Structured program to reduce total fat intake with personal goal setting, self-monitoring (food diaries) and monthly small group classes.
- Food diaries, 2 days per week, rotating days of the week for collection.
- Compliance of RF subjects was assessment at monthly meetings and completion of food diaries
- Compliance score= mean of the percentage of meetings attended and the percentage of diaries filled. Those with compliance scores above the median for the group were classified as compliers for the analysis.

Control Variables

age
sex
ethnicity
baseline measurements

Description of Actual Data Sample:

Initial N: Of 4833 workers, 276 had impaired glucose tolerance or high normal glucose concentrations. Of these, 237 could be contacted two years after the study; 176 entered the 1-year reduced-fat diet intervention.

Attrition (Final N):

136 completed the 1-year period (101 men, 36 women). The 40 dropouts during year one had a similar age, but a significantly higher BMI than those who completed the study.
104 at 2 years, 99 at 3 years, and 103 at 5 years.
the 33 lost to 5-year follow-up were were not significantly different from the rest of the participants, except that they were older

Age: 52±0.8 years

Ethnicity:

97 Europeans
12 Maori
22 Pacific Islander
5 other

Other relevant demographics and anthropometrics

	RF	Control
BMI	29.08±0.55	29.17±0.48
W/H ratio	0.944±0.008	0.954±0.00
Glucose (mmol/L) Fasting	6.7±0.2	6.6±0.2
2-hr	7.5±0.3	7.9±0.3
Insulin (mIU/L) Fasting	16.0±1.1	15.8±0.9
2-hr	50.2±4.2	47.0±3.8

Location: New Zealand

Summary of Results:

Change in nutrient intake over 1 year

	RF	Control	P
Kcal	-362	-59	0.016
Fat, g	-34.0	- 6.6	<0.0001
Fat (%)	-8.7	- 2.3	<0.0001
Carbohydrate, g	-1.0	-11	0.49
Carbohydrate (%)	+8.3	0.6	<0.0001

In the reduced fat group, fat decreased from 34.6% of energy to 25.9% of energy and in the control group from 36.1% of energy to 33.8% of energy. The fiber intake was 20 g/d in the RF group and 19 g/d in the control group.

Mean changes in anthropometrical and biochemical measurements (SEM) from baseline to year 5

	1 year	1 year	5 years	5 years
	RF	Control	RF	Control
weight, kg	-3.32±0.68*	0.59±1.61	1.06±0.64	1.26±0.68
BMI	-1.09±0.24*	0.22±0.15	0.72±0.28	0.59±0.27
Fasting glucose, mmol/l	0.08±0.16	0.17±0.13	0.02±0.18	0.29±0.30
2-h glucose, mmol/l	0.0±0.331	0.74±0.35	1.02±0.40	2.30±0.54

*P < 0.01

Compared with the control group, weight decreased in the RF group (P<0.0001); the greatest difference was at 1-yr (-3.3 kg), but was only –1.6 kg at 3-yr and no longer present by 5-yr.

Glucose tolerance improved in patients on the RF diet, a lower proportion had type 2 diabetes or IGT at 1 yr (47 vs. 67%, P<0.05) but in subsequent years, there were no differences between groups.

The more compliant 50% of the intervention RF group maintained lower fasting and 2-hr glucose at 5 years (P=0.04 and P=0.026, respectively) compared with the controls.

In both groups, the percentages with normal GTT was 32 to 36%, impaired fasting glucose, 17 to 21%, impaired GTT, 13 to 15% and diabetic, 32 to 33%.

Author Conclusion:

An intervention aimed at reducing dietary fat alone improved body weight and glucose tolerance over a 2-3-yr period but was only sustained to more compliant participants.

Those in the intervention group also seemed to increase physical activity; therefore, promoting healthy behaviors through dietary changes may have stimulated the participants to exercise more.

Funding Source:

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Although the goal of the RF group was not weight loss, this was the effect of the low fat diet. This group consumed fairly high intakes of fiber.

Those who continued the low fat diet over 5 years had lower fasting blood glucose and 2-hr blood glucose levels.

Motivating people to change lifestyle habits (diet and physical activity) over the long term continues to be a challenge for health professionals.

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?		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)	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?	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?	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?	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?	Yes
	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?	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)?	No
	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?	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