Eating is not only for nutrition, but is also an act of self-love that includes pleasure. Nonetheless, one must never intend to eat and vomit to impede its natural end of digestion.

Likewise, sex is not only for procreation, but also for love, and this includes pleasure. Nonehteless, one must never intend to have sexual union and impede its natural end, which is semination for potential procreation.

So let’s line up the parrellels:

eating ———- sex     (Both are life-giving and love-giving acts; both are pleasurable)
digestion —— semination
nutrition —— procreation
bulimia ——– contraception

Hence, contraception, like bulimia, is a violation of natural law and the matter of grave sin.

Other parrellels between food and sex to consider that can be understood through reason:

Eating food you have not paid for is akin to fornication (nonmarital sex). Eating someone else’s food is adultery. Both are akin to taking a bite of fresh fruit in the grocery store and placing it back on the shelf.

Eating things that are by nature not edible, like plastic, rocks, or sand is akin to homosexual behavior, bestiality, pedophilia, and msturbation. All pervert sexual behavior and negate its natural end, violating natural law. All are the matter of mortal sin.