Answers Rubric for Assignment 5
Bazzano et al.
# Questions Answers Points
1. Title of article, Journal name, and your name Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial
Annals of Internal Medicine
Your name
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2. What is the research question addressed in this study? What are the effects of a low-carbohydrate diet compared with a low-fat
diet on body weight and cardiovascular risk factors?
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3. Identify the dependent variable(s) Cardiovascular disease risk factors, body weight 5
4. Identify the independent variable(s) Type of diet: low-carbohydrate vs. low-fat diet 5
5. What is the research design used? Randomized parallel group trial. Cohort is also correct if included in the
answer since all RCTs are by definition a couple of cohorts followed
over time.
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6. What type of sampling design was used? Convenience or volunteer sampling 5
7. Describe the intervention. Was it adequately described?
Note: for the purpose of this article, since it’s a parallel
design, it does not matter which diet is labeled as
intervention or comparison. Technically, the low-carb diet
is the intervention.
Both diets and details for the intervention were adequately and clearly
described.
Low-carb diet: maintain an intake of digestible carbohydrate (total
carbohydrate minus total fiber) of less than 40 g/d. weekly meetings with
a dietitian for 1st 4 weeks, followed by small group counseling sessions
every other week for the next 5 months (a total of 10 sessions) and
monthly for the last 6 months of the intervention.
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8. Describe the control or comparison condition. Was it
adequately described?
Both diets and details for the intervention were adequately and clearly
described.
Low-fat diet: maintain less than 30% of daily energy intake from total fat
(with <7% from saturated fat) and 55% from carbohydrate, based on
National Cholesterol Education Program guidelines; weekly meetings
with a dietitian for 1st 4 weeks, followed by small group counseling
sessions every other week for the next 5 months (a total of 10 sessions)
and monthly for the last 6 months of the intervention.
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9. Were the participants fully informed about the nature of the
research?
Yes. Each participant signed an approved consent form. Consent forms
usually have all the components to help participants be fully informed
about the study.
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10. Was ethical permission granted for the study? Yes. The study was approved by the Institutional Review Board at
Tulane University.
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11. Were randomization procedures adequately explained?
Describe them.
Yes. Participants were assigned to one of the two diet groups using a
computer-generated, blocked randomization, stratified by sex.
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12. Does the article provide evidence that randomization was
successful - that is, it resulted in groups that were
comparable prior to the intervention?
Yes. Table 1 shows that the two groups were similar on demographic
characteristics and cardiovascular risk factors.
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13. Was the study longitudinal? How many data collection Yes, the study followed participants over one year. There were four data 5
points were there? collection points: at baseline and at 3, 6, and 12 months.
14. Was blinding used? If yes, who was blinded - and was this
adequate? If not, is there an adequate rationale for failure
to blind/mask?
Outcome assessors (data collectors) were blinded to the diet group
assignment.
Dietitians were not blinded to the study hypothesis. This may have
resulted in potential differences in dietary counseling. Training, detailed
scripts, and intermittent observations were used to minimize any
differences. No rationale is provided to why the dieticians were not
blinded to the study hypothesis.
Obviously, participants were not blinded. That would not be possible
because each group had to follow the recommended dietary intake so
they knew the type of diet they were on.
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15. What are the results of the study? Did the results answer
the research question(s)?
Overall, a low-carbohydrate diet resulted in greater weight loss and
reduction in cardiovascular risk factors than a low-fat diet among obese
black and white adults. Table 3 reports the detailed results for the low-
carb (LC) vs. the low-fat (LF) diets (please note that only differences
between the two groups that had p-values <.05 are considered
significant differences that can be attributed to the program and not
chance):
- Body weight: LC lost more weight than LF
- Waist circumference: LC lost more waist circumference at 3 and 6
months but no significant differences between the two groups at 12
months.
- Lean mass: LC group gained more lean mass
- Fat mass: LC group lost more fat mass at 6 and 12 months
- Cholesterol: no significant differences in total and LDL. For HDL (the
good cholesterol), there were significant increases for the LC group
relative to the LF group at 6 and 12 months.
- Triglycerides: LC decreased more at the 3 data collection points
- Blood pressure, plasma glucose, insulin, serum creatinine: no
decreases or significant differences
- C-reactive protein level: LC reduced more at 6 and 12 months
- 10-year Framingham risk score: LC improved their score, i.e., reduced
it.
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16. Was outcome data reported even for treatment group
members who did not complete the program (intention-to-
treat analysis)? If not, what was the rationale? If not
applicable, indicate that in your answer.
There were several individuals who did not complete the program (10,
11, and 7 at 3, 6, and 12 months, respectively) as shown in Figure 1.
However, in Table 3, results were reported only for those who completed
the programs. No rationale was provided. The most common is the
difficulty and cost of tracking down people who are lost to follow-up. We
also don’t know if those lost to follow-up are different from those who
completed the program.
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17. What were the study limitations? (1) Self-reported dietary information may be subject to memory and
recall issues; (2) dietitians were not blinded to the study hypothesis; (3)
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no CVD clinical end points (example a fatal or non-fatal CVD event such
as a heart attack) ; (4) multiple statistical tests were performed,
potentially resulting in statistical significance due to chance; (5)
generalizability is limited to situations where intensive and repeated
dietary counseling is available; (6) the characteristics of those lost to
follow-up are not reported.
18. Do you consider the outcomes measured to be important
policy or practical outcomes? Were they measured over a
long enough period?
With obesity prevalence reaching epidemic proportions and with CVD
being the number one cause of death, it is important to assess different
types of diets and their impact on body weight and CVD risk factors. A
one-year time period is reasonable to see changes in the outcome
measures used. A 3-months period would have been too short to see
the effect of dietary changes on some of the cardiovascular risk factors.
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