DLM: Diet Composition (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • The study was designed to compare three diets: An average American diet (AAD), a Step 1 diet and a low-SFA (Low-Sat) diet
  • The goal of DELTA-1 was to determine the effects of reducing total fat and SFAs on plasma lipids, lipoproteins and thrombogenic factors.

 

Inclusion Criteria:
  • Healthy, normolipidemic subjects between the ages of 22 and 65 years
  • Recruitment goals were aimed at achieving a final study population that was composed of 60% women, with equal numbers of pre-menopausal and postmenopausal women; 30% blacks; and similar numbers of men >40 and less than 40 years of age
  • Subjects were required to be in good health, taking no medications known to affect plasma lipid levels or thrombotic factors, and available for the entire duration of the study
  • Mean plasma total cholesterol between the 25th and 90th percentiles for age, race and sex
  • Plasma triglycerides and HDL cholesterol had to be below the 90th and above the 10th percentile, respectively
  • Subjects willing to eat meals provided by the diet center and instructed not to change either smoking (fewer than 10% smoked cigarettes) or exercise habits
  • Participants willing to participate in each diet period for eight weeks long, with breaks of four to six weeks between diet periods.
Exclusion Criteria:

Not applicable

Description of Study Protocol:

In this double-blind study of three diets used a crossover design with three feeding periods. Each subject was randomized to one of six diet sequences (ABC, ACB, BAC, BCA, CAB or CBA). Each diet period was eight weeks long, with breaks of four to six weeks between diet periods.

The staff prepared each subject’s meal individually, with all items containing fat weighed to the nearest 0.1g and all other foods weighed to the nearest gram. Subjects ate two meals each weekday (either breakfast and dinner or lunch and dinner, depending on the research center) in a supervised cafeteria setting.  

Compliance was assessed by tray checks at meals eaten on site and by self-report on standardized forms for packed meals. Subjects were weighed twice weekly; if needed, adjustments were made in caloric intake to maintain stable body weight. Participants were instructed not to change either smoking (fewer than 10% smoked cigarettes) or exercise habits.

Blood samples were obtained once each week during weeks five, six, seven, and eight of each diet period. This design was chosen to ensure that there was adequate time to achieve steady-state levels of lipids, lipoproteins and thrombogenic factors. Subjects fasted overnight before blood sampling. Standardized blood sampling and processing procedures were validated and used at all four clinical centers.

The goal of DELTA-1 was to determine the effects of reducing total fat and SFAs on plasma lipids, lipoproteins and thrombogenic factors.

Three diets were designed:

 

Diets Total fat SFA MUFA PUFA Dietary carbohydrates Dietary protein
(percent of kcal)
AAD 37 16 14 7 48 15
Step 1 diet 30 9 14 7 55 15
Low-fat diet 26 5 14 7 59 15

The proportions of individual SFAs were designed to be similar in all three diets and to reflect the diet of free-living Americans. To avoid confounding of our results, we maintained trans-fatty acids at levels, 1.5% of total calories on all three diets.

The diets were prepared from the same foods with different amounts of various fats and oils added to otherwise low-fat menus, and all the diets were kept isocaloric. All fat sources (meats, margarines, oils, etc.) were procured centrally in single lots that were used for the duration of the study.

The statistical computations for longitudinal analysis of the repeated measurements were performed separately for each of these response variables. The linear statistical model, the set of primary hypotheses, the strategy for controlling type I error and the estimation. The statistical computations were performed by the mixed-model procedure of the SAS software system

 

Data Collection Summary:
  • T-Chol, LDL-Chol, HDL-Chol,
  • TG, apo B, apo A-I, Lp(a).
Description of Actual Data Sample:

Four Research Centers (Columbia University, Pennington Biomedical Research Center, Pennsylvania State University and University of Minnesota recruited 25 to 30 healthy, normolipidemic subjects 22-65 years of age.

  • 118 subjects were randomized to the study. 103 subjects completed the study
  • 55% women, 45% men.
Summary of Results:
  • 118 subjects were randomized to the study. 103 subjects completed the study
  • 55% women, 45% men
  • 30% women and 20% men were black; 32% of women were postmenopausal
  • Mean age: 37.9 years.

Diet effects on lipids and apolipoproteins

Lipids/lipoproteins AAD Step 1 Low-sat
TC 202.16±2.8*† 191.06±2.7‡ 183.462.7
LCL-C 131.46±2.7*† 122.26±2.6‡ 116.962.6
HDL-C 52.26±1.1*† 48.56±1.1‡ 46.261.0
TG 85.16±3.4* 92.46±3.7 93.063.7
Apo B 116.86±2.4† 113.66±2.6 111.66±2.6
Apo A 142.26±2.0*† 135.46±2.0‡ 130.46±1.9
Lp(a) 15.56±1.8*† 17.06±1.8‡ 18.26±1.9
TC/HDL 4.07±0.10 4.16±0.11 4.21±0.11

TC indicates total cholesterol; LDL-C, LDL cholesterol; HDL-C, HDL cholesterol; and TG, triglyceride. These values are mean six SEM, for the overall group of 103 subjects. They have been adjusted only for slight period effects observed. The TG values are antilogs of ln(TG) data. The Lp (a) values are squares of square-root data.

All values are mg/dL.

*P<01 AAD vs. Step 1, based on adjusted values from the linear regression model described in “Methods.”

†P<01 AAD vs. Low-Sat, based on adjusted values from the linear regression model described in “Methods.”

‡P<01 Step 1 vs. Low-Sat, based on adjusted values from the linear regression model described in “Methods.”

With a few exceptions, significant effects (P<0.01) were observed in each sub-group for all variables when diet was changed from AAD to either Step 1 or Low-Sat. The reductions in total cholesterol on the Step 1 diet compared with the AAD ranged from 4.7% to 5.9% for the different sub-groups, with a mean of 5.5%. The differences between AAD and the Low-Sat diet ranged from 7.6% to 10.0%, with a mean of 9.1%.

Each diet effect on total cholesterol in each of these groups was significant at P<0.01. The differences in plasma LDL cholesterol levels for each of the sub-groups on the Step 1 or Low-Sat diets were compared with those on AAD. These results paralleled those for total cholesterol. LDL cholesterol levels decreased '7.0% (6.3% to 7.4% for the various sub-groups) when subjects changed from the AAD to the Step 1 diet. The average difference between the AAD and the Low-Sat diet was approximately 11% (8.8% to 12.4%).

Diet effects on LDL cholesterol were significant in all sub-groups (P<0.01). Plasma concentrations of apo B, essentially the only protein in LDL, changed in a similar, albeit more modest, manner as dietary saturated fat was reduced. Significant reductions in apo B levels (P<0.01) were observed only when the AAD was compared with the Low-Sat diet, although this comparison was not significant in postmenopausal women or in older men.

Plasma HDL cholesterol concentrations also were lower on the Step 1 and Low-Sat diets than on the AAD (P, 0.001) in all sub-groups except blacks (AAD vs. Step 1) and older men (AAD vs. Step 1). Overall, plasma HDL cholesterol levels decreased by 7.0% (5.9% to 8.6%) when subjects changed from AAD to Step 1.

The change from AAD to Low-Sat was associated with a mean reduction of 11.3% (10.0% to 12.9%) in HDL cholesterol concentrations. Plasma levels of apo A-I changed in parallel with levels of HDL cholesterol; significant reductions were observed for all comparisons except AAD vs. Step 1 in blacks, postmenopausal women and older men.

Plasma triglycerides, presented as antilogs of natural log triglycerides, increased significantly in women and non-blacks changing from AAD to Step 1 and in non-blacks changing from AAD to Low-Sat; this increase was approximately 10%. In all other sub-groups, increases in plasma triglycerides were not statistically significant, ranging from 1% to 12% as dietary fat was reduced.

Of interest, there was no further increase in plasma triglyceride between the Step 1 and the Low-Sat diets despite an additional reduction of 4% in total fat and a concomitant further increase in dietary carbohydrate.

Lp(a) levels, depicted as the squares of square roots of plasma concentrations, increased in all subgroups (P<0.01) except postmenopausal women and older men as dietary saturated fat was reduced from AAD to Step 1. Lp(a) levels increased in all groups as diet changed from AAD to Low-Sat.

Author Conclusion:

DELTA-1 has demonstrated clearly that reduction of total fat and SFAs in the diet is accompanied by clinically important reductions in total and LDL cholesterol concentration in all the groups studied, despite differences in levels of these variables on the

AAD. Decreases such as those we have observed should be associated with 10% to 20% reductions in ASCVD in the population. Consumption of Step I and Low-Sat fat diets were also associated with significant reductions in HDL cholesterol and significant increases in Lp(a) concentrations. Plasma TG rose minimally in our normolipidemic subjects. The impact of these potentially atherogenic changes in response to reducing dietary total and saturated fats must be weighed against the clearly demonstrated benefit of reducing LDL cholesterol levels and the beneficial outcomes of clinical trials in which dietary SFAs were reduced.

Funding Source:
Government: NHLBI, NCRR, NIH
Industry:
AARHUS, Bertoli, USA; Best Foods; Campbell Soup Co; Del Monte Foods; General Mills; Hershey Foods Corp; Institute of Edible Oils and Shortenings; Kraft General Foods; Land O’Lakes; McCormick Inc; Nabisco Foods Group; Neomonde Baking Co; Palm Oil Research Institute; Park Corp; Proctor and Gamble; Qua
Food Company:
Other:
University/Hospital: Columbia University College of Physicians and Surgeouns, Pensylvania State University, University of North Carolina, University of Minnnesota School of Public Health, Pennington Biomedical Research Center, Mary Imogene Bassett Hospital, Louisiana State Unviersity School of Medicine, Virginia Polytec
In-Kind support reported by Industry: Yes
Reviewer Comments:

Very well designed and controlled study.

The statistical power is not enough to do sub-group analysis in the current study. Further studies are required to study the effect of different diets (AAD, step 1 and low fat diets) on lipids and lipoproteins in different population groups, men age <40 and >40 years; pre- and postmenopausal women and different races. Information on other risk factors such as family history, blood pressure and blood sugar levels of the subjects also will be helpful.

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? 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? 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.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? ???
4. Was method of handling withdrawals described? ???
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  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? 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? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? ???
  5.5. In diagnostic study, were test results blinded to patient history and other test results? Yes
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? ???
  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? ???
  6.6. Were extra or unplanned treatments described? ???
  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? ???
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)? Yes
  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