The studies were small and short term. Study settings, participants and interventions varied widely. Participant drop-out rates were high and some primary studies reported that long-term dietary adherence was poor.
An investigation of clinical differences between the studies found no significant relationship between any of the outcomes and participant age, inclusion of participants on insulin, or duration of dietary intervention.
Glycaemia.
All 12 studies (n=251) that measured this blood glucose reported a greater reduction in the intervention group than in controls, and 9 studies (out of 11; n=214) that reported HbA1c reported a lower (or more greatly reduced) level in the intervention group. When studies were pooled there was a significantly greater mean reduction in the intervention group in both fasting blood glucose (p=0.013) and HbA1c (p=0.013) than in controls. Interventions with lower levels of carbohydrates resulted in greater reductions in both measures. Regression analyses found that weight change attenuated the effect of the reduction in glycaemia associated with a restricted-carbohydrate diet, though the association remained statistically significant when controlling for weight.