| Study |
Bias |
| Randomisation process |
Deviations from intended interventions |
Missing outcome data |
Measurement of the outcome |
Selection of the reported results |
Overall |
| Authors' judgement |
Support for judgement |
Authors' judgement |
Support for judgement |
Authors' judgement |
Support for judgement |
Authors' judgement |
Support for judgement |
Authors' judgement |
Support for judgement |
Authors' judgement |
Support for judgement |
| Subgroup 3.6.1 Without diet/food industry funding |
| Guldbrand 2012 |
Some concerns |
"Randomisation was not stratified and was based on drawing blinded ballots." No information describing allocation concealment. No significant differences were present at baseline (P > 0.1 for all characteristics). |
Low risk of bias |
"Non‐blinded study". n=4 in low carbohydrate diet group and n=3 in balanced diet group discontinued interventions (did not attend group meetings). Primary intention‐to‐treat analysis, with secondary completers analysis also done. |
High risk of bias |
4/30 (13%) participants in the intervention group and 3/31 (10%) in the control group did not have data for this outcome. Discontinued diets in both groups as had "severe difficulty" in following the diets, which may be related to change in weight (missingness possibly and likely influenced by true value). |
Some concerns |
No information about method used for body weight measurements. Weight is not an observer‐reported outcome involving judgement. |
Some concerns |
No mention of pre‐specified analysis plan, but trial registry at date prior to study publication mentions the outcome and timepoint. The time point mentioned in trial registry at date prior to publication is reported on in publication. Analysis intentions are not reported in sufficient detail to enable an assessment. |
High risk of bias |
No specific information on allocation concealment. Attrition in both groups due to "severe difficulty" following diets, possible and likely that the missingness is dependent on the true value of the outcome. Lack of information in the pre‐registered methods. |
| Krebs 2012 |
Low risk of bias |
"Baseline measures completed prior to randomisation. Computer randomised sequence undertaken by an independent biostatistician at a distant site and random allocation of each individual emailed to personnel independent of those assessing outcome measures. These personnel organise allocation of the individuals into the two groups according to random allocation." No statements or statistical tests about differences between groups, large sample size and baseline characteristics table showed similar weight and BMI. |
Low risk of bias |
"Allocation of randomisation was concealed from the participant until after written informed consent and baseline assessment." "If two members of the same household were enrolled they were both allocated to the same intervention group." "Dieticians delivering the intervention were notified of the dietary allocation after baseline assessment and before the first group session" Modified intention‐to‐treat analyses were undertaken, regardless of intervention adherence (missing outcome data excluded). Deviations reported are expected to arise in usual care e.g. disliked diet, missed visit. |
Low risk of bias |
63/207 (30%) participants in the intervention group and 61/211 (29%) in the control group did not have data available for this outcome. "Generalized mixed linear models were used... including baseline as a co‐variate." "Both the ‘intention‐to‐treat’ analysis and the analysis that only included those who completed the study found no difference between the groups in any outcome." (data not shown). |
Low risk of bias |
Tanita electronic scale was used to measure weight. No evidence that a different method was used across intervention groups to measure weight. "...research assessors remained blind to intervention allocation at all assessment points and until after database lock" |
Some concerns |
No mention of pre‐specified analysis plan, but trial registry at date prior to study publication mentions the outcome and timepoint. The time point mentioned in trial registry at date prior to publication is reported on in publication. Analysis intentions are not reported in sufficient detail to enable an assessment. |
Some concerns |
Lack of information in the pre‐registered methods. |
| Samaha 2003 |
Some concerns |
"...randomly assigned to either the low‐carbohydrate diet or the low‐fat diet, with use of a pre‐established algorithm generated from a random set of numbers." No information describing allocation concealment. "Subjects in the two groups were well matched with regard to base‐line characteristics (Table 1)." No formal hypothesis test, but no apparent significant differences in Table 1 |
Some concerns |
"The study was not blinded." Total attrition is 34%. No reasons or details about deviations from intended interventions reported. A modified intention to treat analysis was conducted, including weight data for most participants, though some of this information was obtained from medical records. |
Low risk of bias |
Total attrition was 34%, but weights from missing participants were obtained from medical records. Consequently, weight data were only missing for 6/132 (4.5%) of the total group. |
Low risk of bias |
Weight data for participants remaining in the study were obtained using a single calibrated scale. Weight data for missing participants were obtained from medical records, with authors reporting that these were obtained using different scales and were likely 'obtained in a nonuniform manner with regard to clothing'. No evidence that a different method was used across intervention groups to measure weight. "The study was not blinded." Weight is not an observer‐reported outcome involving judgement. |
Some concerns |
No mention of pre‐specified analysis plan. Outcome data were never blinded. Analysis intentions are not reported in sufficient detail to enable an assessment. |
Some concerns |
No specific information on allocation concealment. The study was not blinded, and it is not clear whether deviations from intended interventions may have been influenced by this. Though weight data were available for nearly all participants randomised, some of these were obtained from medical records and may have been measured in a non‐uniform manner. No pre‐registered document available to assess analysis intentions. |
| Saslow 2017a |
Low risk of bias |
"Eligible participants provided written, informed consent and were randomly assigned following block randomization procedures (computerized random numbers in blocks of four) to either the MCCR or LCK diet..." "An assistant, not associated with any other aspect of the research, concealed the sequence in opaque envelopes, which were opened by other research assistants unaware of the sequence." No statements of statistical tests or differences between groups. Baseline characteristics table showed differences which were consistent with differences resulting by chance with very small sample sizes. |
Low risk of bias |
"For this trial, it was not possible for the participants and staff to be blinded to group allocation." Deviations reported are expected to arise in usual care e.g. moved away, work responsibilities. Modified ITT was conducted: "This primary analysis was conducted on an intention‐to‐treat basis, including all participants who were randomly assigned and had data at both baseline and 3 months." |
High risk of bias |
1/16 (6%) in the intervention group and 4/18 (22%) in the control group did not have data. Modified ITT conducted: "This primary analysis was conducted on an intention‐to‐treat basis, including all participants who were randomly assigned and had data at both baseline and 3 months." Flowchart for longer timepoint also indicates a modified ITT. Differential attrition and very high attrition in the control group, reasons vague and citing work schedules and/or family responsibilities; thus missingness could depend on its true value for weight but difficult to say if this is likely based on the reasons provided. |
Low risk of bias |
"Subjects were weighed with no jackets or shoes using the same calibrated scale at each time." No evidence that a different method was used across intervention groups to measure weight. "For this trial, it was not possible for the participants and staff to be blinded to group allocation." Weight is not an observer‐reported outcome involving judgement. |
Some concerns |
No mention of pre‐specified data analysis plan, and trial registry and protocol does not mention the outcome and timepoint in any versions thereof. Analysis intentions are not reported in sufficient detail to enable an assessment. |
High risk of bias |
Differential and high attrition in the control group with vague reasons, missingness could be and is likely dependent on the true value of the outcome. Lack of information in the pre‐registered methods. |
| Tay 2014 |
Some concerns |
Randomization procedures (sequence generation and allocation concealment) were performed by research associates independent of outcome assessments and intervention delivery and was done "...using random varying block sizes before random computer‐generated assignment to either an LC or HC diet in a 1:1 ratio." Baseline characteristics were "...not significantly different between diet groups (p>0.05) in independent‐samples t‐test...or Chi2 test" |
Low risk of bias |
"...diet assignment was discernible by participants and interventionists..." Deviations reported are expected to arise in usual care e.g. moved away, work responsibilities. Modified ITT, all participants except those who withdrew or were LTFU, were analysed in group to which they were assigned. |
High risk of bias |
31/64 (48%) participants in the intervention and 39/67 (58%) participants in the control arm did not have data available. Very high attrition in both groups; reasons vague and include work commitments, time constraints and change in life situation; thus missingness could depend on its true value for weight but difficult to say if this is likely based on the reasons provided. |
Low risk of bias |
"Body mass was measured using calibrated electronic scales..." No evidence that a different method was used across intervention groups to measure weight. "The researchers involved in outcome assessment and data analysis were blinded to treatment assignment." |
Some concerns |
No mention of pre‐specified analysis plan, but trial registry at date prior to study publication mentions the outcome and timepoint. The time point mentioned in trial registry at date prior to publication is reported on in publication. Analysis intentions are not reported in sufficient detail to enable an assessment. |
High risk of bias |
No specific information on allocation concealment. Very high attrition reported, with missingness possibly and likely dependent on the true value of the outcome. Lack of information in the pre‐registered methods. |
