EAL

DLM: Diet Composition (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To compare the effects on blood pressure and serum lipids of three healthful diets, each reduced in saturated fat:

A carbohydrate-rich diet, similar to the DASH diet
A diet rich in protein, approximately half from plant sources
A diet rich in unsaturated fat, predominantly monounsaturated fat.

Inclusion Criteria:

Healthy adults
Aged 30 years and older
Systolic blood pressure of 120mm to 159mm Hg or a diastolic blood pressure of 80mm to 99mm Hg.

Exclusion Criteria:

Diabetes
Active or prior CVD
LDL cholesterol greater than 220mg per dL (above 5.70mmol per L)
Fasting triglycerides greater than 750mg per dL (over 8.48mmol per L)
Weight more than 350lb (more than 159kg)
Taking medications that effect blood pressure or blood lipid levels
Unwillingness to stop taking vitamin and mineral supplements
Alcoholic beverage intake of more than 14 drinks per week.

Description of Study Protocol:

Recruitment

Mass mailing of brochures and advertisements
Based on self-reported race and ethnicity, attempts were made to achieve a cohort 50% African-American.

Design

Baseline data were collected at screening visits
After a six-day run-in period, in which participants ate two days of meals from each study diet, they were randomized to one of six sequences of the three diets. Randomization by computer and stratification by clinic was conducted at a central location.
An unblinded person at each site opened a sealed opque envelope with the randomized diet sequence
Each feeding period lasted six weeks with a two- to four-week washout period in between
Participants ate their own food during the washout period.

Blinding Used

Participants and personnel involved in collection of outcome data were masked to diet sequence.

Intervention

Three diets with reduced saturated fat, cholesterol and sodium and rich in fruits, vegetables, fiber, potassium and other minerals at recommended levels.

Diet One (carbohydrate): Contained 27% fat (6% saturated, 13% monounsaturated, 8% polyunsaturated), 58% carbohydrate and 15% protein (5.5% meat, 4% dairy and 5.5% plant)
Diet Two (protein): Contained 27% fat (6% saturated, 13% monounsaturated, 8% polyunsaturated), 48% carbohydrate and 25% protein (9% meat, 4% dairy and 12% plant)
Diet Three (unsaturated fat): Contained 37% fat (6% saturated, 21% monounsaturated, 10% polyunsaturated), 48% carbohydrate and 15% protein (5.5% meat, 4% dairy and 5.5% plant).

Statistical Analysis

Between-diet differences in end-of-period measurements were used to perform paired T-tests of the hypothesis that the mean between-diet difference was zero
Statistical significance was P<0.05 (two-sided) without adjustment for multiple comparisons
Mean (95% confidence interval) change from baseline to the end of feeding period is reported
ANCOVA was used to assess the effects of weight change on outcomes
The target sample of 160 provided 90% power to detect a mean between-diet difference of 1.7mm Hg in systolic blood pressure and 5.9mg per dL (0.15mmol per L) in LDL cholesterol.

Data Collection Summary:

Timing of Measurements

Baseline and end of study.

Dependent Variables

Systolic blood pressure
Diastolic blood pressure
LDL-cholesterol
HDL-cholesterol
Total cholesterol
Non HDL-cholesterol
Triglycerides.

Independent Variables

Carbohydrate diet
Protein diet
Unsaturated fat diet.

Control Variables

Weight
Alcohol intake.

Description of Actual Data Sample:

Initial N: 191 randomly assigned to intervention
Attrition (final N): 161
Age: Mean, 53.6±10.9 years.

Ethnicity

African-American: 90 (55%)
Non-Hispanic white: 65 (40%)
Other: Nine (6%).

Other Relevant Demographics

Not high school educated: 33 (20%).

Anthropometrics

Mean weight (SD): 87.3kg (18.7)
Body mass index, mean (SD): 30.2 (6.1)
Obesity status
- Not overweight or obese: 34 (21)
- Overweight: 57 (34)
- Obese: 73 (45).

Location

Boston, MA
Baltimore, MD
Blacksburg, VA.

Summary of Results:

Key Findings

HTN

12 of 32 persons (38%) remained hypertensive on carbohydrate diet
Seven of 32 persons (22%) remained hypertensive on protein diet
- Protein diet compared with carbohydrate diet reduced systolic BP by mean 1.5 mm Hg (P=0.001)
Six of 32 persons (19%) remained hypertensive on unsaturated fat diet
- Unsaturated fat diet compared with carbohydrate diet reduced systolic BP by mean 1.4 mm Hg (P=0.003) for primary analyses.

Lipids

Protein diet significantly lowered LDL-cholesterol and HDL-cholesterol, while unsaturated fat diet had no effect when compared to carbohydrate diet
Both protein and unsaturated fat diets significantly lowered TG, total cholesterol and non HDL-cholesterol, when compared to carbohydrate diet.

Changes in Blood Pressure and Blood Lipids by Diet Type

Variable	Diet Intervention (Percentage energy from Carbohydrate, Protein, Fat)
	Carbohydrate (58-15-27)	Protein (48-25-27)	Unsaturated (48-15-37)
	Percentage Change from Baseline (95% CI)
BP: All	-8.2% (-9.6 to -6.8)	-9.5% (-10.9 to -8.2)	-9.3% (-10.6 to -8.0)
BP: Stage 1 HTN^b	-12.9% (-16.6 to -9.2)	-16.1% (-19.7 to -12.5)	-15.8 (-19.4 to -12.3)
BP: Pre-Hypertension^a	-7.0% (-8.5 to -5.6)	-8.0% (-9.3 to -6.6)	-7.7% (-8.9 to -6.4)
Diastolic BP: All	-4.1% (-5.0 to -3.3)	-5.2% (-6.1 to -4.4)	-4.8% (-5.6 to -4.0)
Diastolic BP: Stage 1 HTN^b	-6.3 % (-8.4 to -4.3)	-8.6 % (-10.9 to -6.4)	-8.2% (-10.4 to -6.0)
Diastolic BP: Pre-Hypertension^a	-3.6% (-4.5 to -2.7)	-4.4% (-5.3 to -3.6)	-3.9% (-4.7 to -3.2(
Total Cholesterol (mg/dL)	-12.4% (-15.7 to -9.1)	-19.9%* (-23.5 to -16.4)	-15.4%* (-19.1 to -11.8)
LDL-Cholesterol: All (mg/dL)	-11.6% (-14.6 to -8.6)	-14.2%* (-17.5 to -10.9%	-13.1% (-16.4 to - 9.8)
LDL-Cholesterol: ≥130 (mg/dL)	-19.8% (-24.2 to -15.5)	-23.6%* (-28.5 to -18.8)	-21.9% (-26.9 to -16.6)
LDL-Cholesterol: <130 (mg/dL)	-4.4% (-7.8 to -0.9)	-6.1% (-9.9 to -2.2)	-5.4% (-9.1 to -1.8(
HDL-Cholesterol (mg/dL)	-1.4% (-2.5 to -0.3)	-2.6%* (-3.6 to -1.6)	-0.3% (-1.3 to 0.7)
Triglycerides (reported as median and IQR) (mg/dL)	0.1% (-8.6 to 8.8)	-16.4%* (-25.5 to -7.3)	-9.3%* (-17.5 to 1.2)

^a Pre-hypertension defined as systolic BP 120mm to 130mm Hg or diastolic BP 80mm to 89mm Hg
^b Stage 1 hypertension defined as systolic BP 150mm to 159mm Hg or diastolic BP 90mm to 99 mm Hg
*Significant differences bolded.

Other Findings

Patterns were similar by race and sex
Compared to baseline, CHD risk was 16% to 21% lower, as estimated by Framingham risk equation; both protein and unsaturated diets further reduced risk.

Author Conclusion:

In the setting of recommended levels of saturated fat, cholesterol, fiber, fruit, vegetables and minerals, diets that partially replace carbohydrates with protein or monounsaturated fat can further lower blood pressure, improve lipid risk factors and reduce CVD risk.

Funding Source:

Government:

NIH

Industry:

The Almond Board, International tree Nut Council, Olivio Premium Products Inc, The Peanut Institute

Commodity Group:

In-Kind support reported by Industry:

Yes

Reviewer Comments:

Weight kept constant
Large study population and demographically heterogeneous
Dietary period only six weeks long.

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?	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?		N/A
	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