In the overall study (Saveanu et al., 2015), the three antidepressants—escitalopram, venlafaxine extended-release, and sertraline—worked equally well.
In the analyses in this paper, participants who were morbidly obese were more likely than those of normal weight to have remission from their depression after treatment with venlafaxine extended-release.
With escitalopram or sertraline, the chances of remission were the same with high or normal BMI.
However, in persons with a higher BMI, venlafaxine did better than escitalopram.
This differential improvement was mainly explained by improvement in particular symptoms like sleep disturbance, somatic anxiety and appetite. Thus, in participants with greater BMI, venlafaxine-XR particularly reduced physical symptoms (sleep, appetite/weight changes) and somatic symptoms (fatigue, headache, muscle aches).
How much of a difference was there? The number needed to treat to achieve remission with venlafaxine-XR in obese III participants was 6.
Female participants with higher BMI were more likely to remit regardless of the medication given. This improvement in females was explained by changes in cognitive symptoms (including suicidal ideation and guilt) and by psychomotor changes. On the other hand, male participants who had higher BMI were not more likely to remit.
The authors argue that the findings of this study are not explained by the use of higher doses of medications in obese patients. Higher doses were used for obese patients in both genders and with each of the medications. Also, antidepressant dose was statistically controlled for. However, I have some reservations about this, as discussed below.