In randomized clinical trials, approximately half report improvement in A1C values with weight loss; whereas, approximately half report no improvement in A1C values despite fairly similar weight losses.  Eleven studies with more than 1 diet arm reported weight loss and A1C values at 12 months.  Six studies in diet arms reported no improvement in A1C despite weight loss (range: -0.8 to -4.4 kg) in all but one study which reported no weight loss.  Five studies in diet arms reported improvement in A1C ranging from -0.2% to -0.6% with fairly similar weight losses (range: -1.3 to -5.1 kg).

Studies using weight loss medications (orlistat and lifestyle, sibutramine) report consistent improvement in A1C.  Six studies with an orlistat arm reported improvements in A1C values (range: -0.3% to -1.1%) with orlistat and lifestyle intervention with weight loss (range:  -3.9 to -6.2 kg).  Four studies reported improvements in A1C values (range: -0.3% to -6.0%) with sibutramine with weight loss (range: -4.1 to -8.0 kg).

Ten studies reported significant improvements in at least one lipid value, generally in triglycerides and HDL cholesterol from weight loss either by diet alone or with weight loss medications.  Six studies reported improvement in blood pressure with weight loss; however, one study using sibutramine reported increases in blood pressure and one study using sibutramine reported no change in blood pressure.

• Grade I means there is Good/Strong evidence supporting the statement;
• Grade II is Fair;
• Grade III is Limited/Weak;
• Grade IV is Expert Opinion Only;
• Grade V is Not Assignable.
• High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
• Moderate (B) means we are moderately confident in the effect estimate;
• Low (C) means our confidence in the effect estimate is limited;
• Very Low (D) means we have very little confidence in the effect estimate.
• Ungraded means a grade is not assignable.