| 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 |
| Dyson 2007 |
Low risk of bias |
"Randomization was undertaken by means of sealed envelopes equivalent to the number of subjects and filled fifty‐fifty with an indicator of either a low‐carbohydrate diet or healthy‐eating advice. Two separate sets of envelopes were prepared for both diabetic and non‐diabetic subjects. An independent observer witnessed randomization." Author reported in correspondence that no formal test of hypothesis was done for difference at baseline for non‐diabetic participants. Baseline characteristics table showed differences which were consistent with differences resulting by chance with very small sample sizes. |
Low risk of bias |
No information, however, blinding of participants and people delivering these dietary interventions is highly unlikely. Deviations reported are expected to arise in usual care. n=3 of randomised participants in balanced group refused follow‐up as not allocated to low carbohydrate diet (missingness possibly influenced by true value). Modified ITT analysis conducted. |
High risk of bias |
In low carbohydrate diet group, 0% and in balanced diet group, 43% (n=3/7) of randomised participants did not have data available. Modified ITT with last observation carried forward conducted. High attrition in the control group, and differential attrition; refusal of follow‐up as not allocated to low carbohydrate diet may be influenced by expected change in weight, therefore missingness could be and was likely influenced by the true value. |
Low risk of bias |
Body weight recorded at each monthly interval up to 3 months and at 3 months intervals for the next 21 months. No evidence that a different method was used across intervention group to measure weight. No details about blinding of outcome assessors. Weight is not an observer‐reported outcome involving judgment. |
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 |
Differential attrition and high attrition in the control group due to withdrawals related to disappointment with not being assigned to the low carbohydrate diet; therefore missingness could and is likely related to the true value of the outcome. Lack of information in the pre‐registered methods. |
| Haufe 2013 |
Low risk of bias |
"For allocation of the subjects, a computer‐generated list of random numbers was used. The randomization sequence was created using SPSS 18 (Chicago, IL) statistical software and subjects were assigned to reduced carbohydrate or reduced fat diet with a 1:1 allocation using random block sizes of 2, 4, and 6. Study nurses and physicians screening and enrolling volunteers were blinded for the randomization sequence." "Both groups were well matched for gender, age, body weight, body mass index, blood lipid profiles, glucose metabolism, and cardiorespiratory fitness." |
High risk of bias |
"Blinding of participants for the allocated dietary intervention was impossible." "Except for the dieticians, study nurses and physicians were blinded for the treatment assignment". Deviations reported are expected to arise in usual care e.g. lost to follow up, withdrew consent. Per protocol analysis conducted. 24/28 participants in the intervention group and 30/33 in the control group excluded from the analysis for reasons including protocol violations and "other". |
High risk of bias |
57/80 (71%) participants in the intervention group and 56/83 (67%) in the control group did not have data. Very high attrition in both groups, with limited reporting of reasons, but it is likely that with such high attrition, missingness is possibly and likely to depend on the true value. |
Low risk of bias |
"We measured body weight, waist circumference,and height in a standardized manner after an overnight fast." No evidence that a different method was used across intervention groups to measure weight. "...study nurses and physicians were blinded for the 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 |
Some participants in both groups were excluded form analyses due to protocol violations. Very high attrition in both groups, with limited reporting of reasons; therefore missingness could and is likely to be related to the true value of the outcome. Lack of information in the pre‐registered methods. |
| Keogh 2007 |
High risk of bias |
Clinstat used to generate sequence; "allocation concealment: No" (trial registry). From Table 1 there appeared to be no large differences between groups at baseline. |
High risk of bias |
Open (masking not used). Deviations reported are expected to arise in usual care e.g. personal reasons, unable to comply. Per protocol, 8% participants excluded from analysis as they did not comply with the diet protocol. |
High risk of bias |
6/13 (46%) participants in the intervention group and 6/12 (50%) in the control group did not have data. 2/25 participants withdrew as unable to comply with diet, which may be related to change in weight (missingness possibly influenced by true value). Attrition is very high, therefore missingness could and is likely to depend on the true value of the outcome. |
Low risk of bias |
Weight was measured in light clothing and no shoes on a Mercury digital scale at baseline and every 2 weeks. No evidence that a different method was used across intervention groups to measure weight. Open label. Weight is not an observer‐reported outcome involving judgement. |
Some concerns |
No mention of pre‐specified data analysis plan. Analysis intentions are not reported in sufficient detail to enable an assessment. |
High risk of bias |
Allocation was not concealed. Some participants were excluded from the analysis as they did not comply with the diet protocol. Very high attrition in both groups, therefore missingness could and is likely to be dependent on the true value of the outcome. No pre‐registered document available to assess analysis intentions. |
