I know these kind of brain morphometry analyses (I published an article using them). I would not trust the results too much. Those analyses are really straight-forward to setup once you have access to a MRI dataset, which makes them very popular. It can be easy to get a significantly positive result when you toy with the statistical thresholding techniques, especially with a rather low sample-size which is the case here with the sub-group "depression + child sex abuse".

Also it feels strange that the brain region specifically associated with child sex abuse would be in the occipital cortex, which is responsible for visual processing. The authors probably had to make mental gymnastics in the discussion to justify this piece of results.

I would wait for other studies to confirm this before having any opinion on this.

Most calories came from bread in Europe until the middle of XXth century but diabetes and obesity skyrocketed with the modern diet. I would not exaggerate the role of wheat in the current obesity epidemic.

From the abstract, they don't seem to differentiate between starchy foods and (refined) sugars. Intuitively and from my limited knowledge, I would assume that sugar is the real culprit of health decline, unless starchy foods are consumed in lieu of a diverse diet (including various protein sources, vegetables and nuts).

Starchy foods are still at the basis of many diets over the world, including in countries with high life expectancy (e.g. Japan and their high white rice consumption).