EAL

MUFA and PUFA - CNPP

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To compare two ad libitum diets in patients with type 2 diabetes [one high in monounsaturated fat (MUFA) and the other low in fat and high in fiber and complex carbohydrates] to ascertain which diet would lead to greater weight loss and greater improvements in dyslipidemia and glycemic control.

Inclusion Criteria:

Type 2 diabetes
Treated with oral glucose-lowering medications, diet, or both.

Exclusion Criteria:

Insulin therapy within the previous two months
HbA1c higher than 12%
Medical conditions affecting plasma lipoprotein metabolism
Use of lipid-lowering medications within the previous six weeks
Proliferative retinopathy or nephropathy
Coronary events within the previous six months
Treatment with glucocorticosteroids
Fasting plasma cholesterol concentrations higher than 300mg per dL
Triglyceride concentrations higher than 700mg per dL.

Description of Study Protocol:

Design

Subjects were fed low-fat or high-monounsaturated fat metabolic diets in random order for six weeks, with the two diets separated by a six- to 12-week washout period
Both diets were offered at 25% above estimated energy requirements to allow for self-selection of quantity of food.

Blinding Used

Fat and carbohydrate (CHO) content were changed by modifying recipes and portion sizes so that participants were blinded to diet so far as possible.

Intervention

Low-fat diet: 20% fat, 65% CHO
High-mono diet: 40% of energy from fat (25% of energy as MUFA), 45% CHO
Refined sugar made up 19% of calories for both diets
The low-fat diet was higher in fiber and water
Both diets were low in saturated fat, but the low-fat diet had less saturated fat and cholesterol than the high-MUFA diet; this difference was intentional because it mirrors the composition of these types of diets in the "real world."

Statistical Analysis

Changes in body weight, plasma lipids and lipoproteins and glycemic variables were analyzed with the use of a two-factor analysis of variance model with repeated measures on time and diet
Power calculations were made (80% power and an alpha of 5%) for detecting a difference of 1% in HbA1c, a difference of 20% in plasma fructosamine and a difference of 15% in fasting plasma glucose
P-values were calculated for the main effects of time, diet and the time-x-diet interaction
Time-x-diet interaction was tested for differential responses to the two different diets over time.

Data Collection Summary:

Timing of Measurements

Blood samples collected before and after each dietary period.

Dependent Variables

Weight change, based on the differences between the mean weights on the first three days and on the last three days of the dietary phase
Fasting plasma lipids and lipoproteins using the Lipid Research Clinics program methods
Fasting plasma glucose using the glucose oxidase method
HbA1c using HPLC on a Diamet analyzer
Plasma fructosamine using automated colorimetric assay
Glucose disposal and insulin sensitivity by hyperglycemic and euglycemic clamp studies.

Independent Variables

Energy balance
Dietary intake
All meals were prepared by a metabolic kitchen staff at a clinical research center
Subjects consumed one meal at the research center and other meals, including weekend meals, were packaged for home consumption

Description of Actual Data Sample:

Initial N: 11; eight females and three males
Attrition (final N): 11
Age: 50.4±4.8 years
Other relevant demographics:
- Fasting plasma glucose: 141±33mg per dL
- HbA1c: 6.8±1
- Plasma fructosamine: 2.31±0.65mmol per dL
Anthropometrics:
- Weight: 101.0±17.8kg
- BMI: 37.2±7.0kg/m²
Location: United States.

Summary of Results:

Weight

The statistically significant time-x-diet interaction for the body weight changes indicated a differential response to the two diets, with weight loss being significantly greater on the low-fat diet
Weight loss was statistically significant only on the low-fat diet (-1.53±1.21kg; P<0.001).

Changes in Weight, Plasma Lipids and Plasma Lipoprotein Diets from Initial to Final Values

Variables	Low-fat Diet	High-monounsaturated Diet	P-value for Time	P-value for Diet	P-value for Time-x-Diet Interaction
Body weight, kg	-1.53±1.23	-0.47±0.93	0.002	NS	0.045
Total cholesterol, mg per dL	-9.6²	-10.2	0.011	NS	NS
LDL, mg per dL	-10.2	-7.5	0/008	NS	NS
HDL, mg per dL	-7.1	-4.5	0.016	0/003	NS
VLDL, mg per dL	-10.5	-23.7	NS	NS	NS
Triglycerides, mg per dL	-13.0	-23.2	NS	NS	NS

Nutrient Intake

The subjects consumed 212 fewer kcal per day during the low-fat diet than during the high-MUFA diet (P<0.02)
The subjects consumed significantly more (P<0.05) calories, fat, saturated fat, MUFA and cholesterol while on the high-MUFA diet; they consumed significantly less (P<0.05) CHO and fiber while on that diet compared to when on the low-fat diet.

Glycemic control

Plasma glucose, fructosamine and HbA1c concentrations and glucose infusion rates during the clamp studies did not differ between the two diets; the changes were very small and unlikely to be of clinical importance.

Author Conclusion:

An ad libitum, low-fat, high-fiber, high-complex-carbohydrate diet resulted in greater weight loss than did a high-MUFA diet, and the former did not increase plasma triacylglycerol concentrations from baseline or worsen glycemic control in patients with type 2 diabetes.

Funding Source:

University/Hospital:

General Clinical Research Center Grant PHS 5MOIRR00334 and and by the Oregon Health & Science University Foundation

Reviewer Comments:

Power calculations made
Food provided by metabolic kitchen.

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?	???
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?	N/A
	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?	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?	Yes
	6.6.	Were extra or unplanned treatments described?	Yes
	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?	Yes
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