What should be the effect of losing ones sight on the ability to digest food

One mechanism is enzyme induction.

Enzymes are proteins, which are metabolically expensive to produce. It makes evolutionary sense that your body makes less digestive enzymes such as lactase and sucrase when they're not needed. If your diet changes, your body can gradually increase the production of some enzymes through a process of enzyme induction.

For example, the production of lactase enzyme can be increased in some lactose-intolerant individuals by feeding them lactose . Also, studies in rats have shown that other carbohydrate-digestiYour body makes more of what it needs, and less of what it doesn't need--brilliant!ng enzymes, such as sucrase-isomaltase, trehalase, and maltase-glucoamylase--can be induced by hydrocortisone administration.