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AWM: Nutrient Adequacy and Caloric Restriction (2013)

Citation:

Truby H, Hiscutt R, Herriot AM, Stanley M, Delooy A, Fox KR, Baic S, Robson PJ, Macdonald I, Taylor MA, Ware R, Logan C, Livingstone M. Commercial weight loss diets meet nutrient requirements in free living adults over 8 weeks: a randomised controlled weight loss trial. Nutr J. 2008; 7: 25.

PubMed ID: 18764946
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To investigate the effect of commercial weight loss programs on macronutrient composition and micronutrient adequacy over a two-month period.

Inclusion Criteria:
  • Between the ages of 18 and 65 years of age
  • Body mass index between 27kg/m2 and 40kg/m2
  • Not actively dieting and lived within a 30-mile radius of their corresponding test center
  • Provided consent from their general practitioner to take part in the study.
Exclusion Criteria:
  • Prior history of coronary heart disease
  • Known type 1 or type 2 diabetes
  • Liver or respiratory failure or gout
  • Taking lipid-lowering or anti-hypertensive drugs
  • History of obesity with known cause (i.e., Cushing's disease or hypothyroidism)
  • Previous gastric or weight-loss surgery
  • Taking any weight loss drug (i.e., Orlistat)
  • Clinical depression
  • Eating disorders, drug or alcohol abuse or any malabsorptive state
  • Treatment for a malignancy
  • Pregnancy or breastfeeding.
Description of Study Protocol:
  • Recruitment: 300 subjects were recruited via media advertisements across the UK and were assigned to attend one of the five regional centers (60 at each center)
  • Design: Randomized controlled trial
  • Blinding used: Implied with measurements.

Intervention:

  • Subjects were randomized to one of five diets for two months:
    1. Slim Fast Plan
    2. Weight Watchers Pure Points Programme
    3. Dr. Atkins' New Diet Revolution
    4. Rosemary Conley's "Eat Yourself Slim" Diet & Fitness Plan
    5. Control.
  • The Control Group was asked not to alter their current diet or exercise levels and were offered the diet of their choice free of charge for six months after the study was completed
  • Subjects were not given any individual dietary counseling by the study staff. No attempt was made to standardize energy intake across groups, as the overall purpose of the study was to determine the relative effectiveness of commercial diet programmes in overweight, but otherwise healthy subjects, who were free to interpret the dietary regimen as they chose.

Statistical Analysis

  • Differences between groups at baseline for continuous outcomes were compared using Students' T-tests, except where the Shapiro-Wilk test indicated non-normal distribution of the data, when the non-parametric Mann Whitney U-test was used
  • For categorical variables, the chi-square test was used to investigate between group differences
  • For normally distributed data where homogeneity of variance was confirmed, ANOVA was used to explore between group differences and where the overall result provided evidence of significant group differences, post-hoc comparison was conducted
  • Changes over time for each diet group (baseline to two months) were explored using generalizing estimating equations (GEEs) with an identify link function and an exchangeable correlation structure
  • Robust variance estimate techniques were used to calculate standard errors and confidence intervals
  • All P-values were two-sided
  • To account for multiple comparisons, a P-value of less than 0.01 was considered statistically significant
  • Data were analyzed using Stata Version 10.0 (StataCorp College Station, TX, USA).
Data Collection Summary:

Timing of Measurements

Measurements made at baseline and at two months.

Dependent Variables

  • Subjects were asked to complete a seven-day food record with estimated weights and concurrent with a seven-day activity diary, which enabled subjects to record what they were doing minute-by-minute across a 24-hour period and provided with an extensive list of activities from which to allocate their time
  • When subjects returned to the test centers for anthropometric measurements, they were individually debriefed as they returned their diary and any queries regarding food or drink consumption or activities were resolved
  • All diaries were analyzed centrally at the University of Surrey
  • Energy intake was validated by activity diaries that were coded into minutes per day of time spent in sleeping, light, moderate or vigorous activity. Minutes in each category per day were multiplied by a metabolic equivalent value to give a total daily MET value.
  • Nutrient intake assessed using WinDiets by registered dietitians or supervised students
  • Micronutrient intakes were compared to current UK reference nutrient intake (RNI values)
  • In addition to the nutrient analysis, the number of fruit (including fruit juice) and vegetable portions were counted assuming a standard portion size of 80g
  • Totals per week were then divided by seven to provide an average daily intake of fruit and vegetables. 

Independent Variables

  • Subjects were randomized to one of five diets for two months
    1. Slim Fast Plan
    2. Weight Watchers Pure Points Programme
    3. Dr. Atkins' New Diet Revolution
    4. Rosemary Conley's "Eat Yourself Slim" Diet & Fitness Plan
    5. Control.
  • The Control Group was asked not to alter their current diet or exercise levels and were offered the diet of their choice free of charge for six months after the study was completed
  • Subjects were not given any individual dietary counseling by the study staff. No attempt was made to standardize energy intake across groups as the overall purpose of the study was to determine the relative effectiveness of commercial diet programmes in overweight, but otherwise healthy subjects, who were free to interpret the dietary regimen as they chose.
Description of Actual Data Sample:
  • Initial N: 300 men and women were recruited; 293 were allocated to one of the five diets
  • Attrition (final N): 240 completed; 46 on the Atkins, 52 on Weight Watchers, 46 on Slim Fast, 50 on Rosemary Conley's Eat Yourself Slim Plan, 46 on Control
  • Age: Average age, 40.3 years; range, 20 to 61 years
  • Ethnicity: Not reported
  • Other relevant demographics: Mean waist circumference was 101.4±10.4cm (range, 80cm to 128cm)
  • Anthropometrics: Mean BMI was 31.7kg/m2. There were no diet group or center differences in baseline characteristics.
  • Location: Multiple locations; University of Surrey, Bristol, Nottingham, Ulster and Queen Margaret University College, Edinburgh.
Summary of Results:

Key Findings

  • A significant shift in the macronutrient composition of the diet with concurrent alteration of the micronutrient profile was apparent with all diets
  • There was no evidence to suggest micronutrient deficiency in subjects on any of the dietary regimens
  • Those sub-groups with higher needs for specific micronutrients such as folate, iron or calcium may benefit from tailored dietary advice
  • Changes within diet groups are summarized as follows:
    • In the Atkins Group, there were significant declines in percentage RNI for folate, magnesium, calcium, iron and potassium and a significant increase in selenium, with a reduction in caloric intake from 9,550±404kJ to 6,809±415kJ per day (2,274±96kcal to 1,621±99kcal per day)
    • In the Weight Watchers Group, there were significant declines in percentage RNI for riboflavin, niacin, potassium, calcium, magnesium, iron and zinc, with a reduction in caloric intake from 9,706±427kJ to 6,084±239kJ per day (2,311±102kcal to 1,449±57kcal per day)
    • In the Slim Fast Group, there was a significant decline for niacin and a rise in percentage RNI for zinc, with a reduction in caloric intake from 9,512±456kJ to 6,076±316kJ per day (2,265±109kcal to 1,447±75kcal per day) 
    • In the Rosemary Conley Group, there were significant declines in percentage RNI for magnesium, potassium and zinc, with a reduction in caloric intake from 10,149±409kJ to 6,417±201kJ per day (2,416±97kcal to 1,528±48kcal per day)
    • In the Control Group, there were no significant alterations in micronutrient percentage RNI, despite a caloric reduction from 9,512±367kJ to 7,947±486kJ per day (2,265±87kcal to 1,892±116kcal per day).
Author Conclusion:
  • The diets tested all resulted in considerable macronutrient change and resulted in an energy deficit indicating dietary compliance
  • Health professionals and those working in community and public health should be reassured of the nutritional adequacy of the diets tested.
Funding Source:
Industry:
BBC
Other:
Reviewer Comments:
  • Some subjects following the Atkins diet may have been following advice and taking a daily multivitamin supplement, which is recommended in the book, but this was not analysed
  • The authors did identify some limitations:
    • Nutrient intake profiles are the result of self-reported measures of diet, which have a number of known limitations
    • Food was only recorded for seven days and this may not be enough time to ascertain habitual food intake
    • Not all subjects provided food records, so combined with the attrition rate, the sample size is small.
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? 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.) 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? 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