I am low carb. Depending on how low the carb content is, I take 3 or 4 units prior to meal, if my sugar level is around 5. If higher than 5 I might take a little more, if less than 5 definitely less, maybe 2. Often at lunch I take nothing, especially if exercising after a meal. Same thing in the morning, less insulin if exercising after. But every now and then, maybe once a month, for some unknown reason, I get it wrong (or maybe my body reacts differently). In my opinion it’s not an exact science. Quantity of fat also makes a difference, eg lean meat and less quantity means less insulin. Fatty meat and greater quantity will need more insulin. But we are all different, so everybodies insulin intake will be different.