Your body responds to what you usually eat by making enzymes (like protease) and hormones (like insulin) to deal with your daily food intake. This goes for all food components, fat, carbohydrates and protein. I personally don't eat very many carbs, usually. I still need to lose about twenty pounds, so I'm going to keep on the very low carb band wagon until I lose all the weight. Now, yesterday, if you read my post about what we ate for lunch, you'll know that we all felt like crap afterwards. This is because your insulin production is based on what you ate for the last meal and maybe overall on what you ate in the last day or two. If you do very low carb and want to eat sugar again, just like with a vegetarian who hasn't eaten meat in a while, you have to go gradually off of it. If you are vegetarian and decide that you're going to eat meat again, and you eat a double Whopper, you're probably going to be sick. And it isn't because of the food itself. The same happens if you're a low carber. Say for instance, you go to France on holiday and you eat half a dozen pain au chocolat, you're going to be sick. I suggest ramping up for that LOL
According to Lippincott's Illustrated biochemistry text, the things that stimulate insulin synthesis (production) are glucose, amino acids, and gastrointestinal hormones, and it says that "the synthesis and release of insulin are decreased when there is a scarcity of dietary fuels [i.e. carbohydrates]..." p.310
In other words, if you don't eat carbohydrates, your body isn't making very much insulin. Why would it? That would be inefficient. Luckily the body is highly adaptable, and in the case of former vegetarians will go back to making the enzymes for digesting meat in a couple of days. Same for the low carb folks. Fall off the wagon, and your body will start making insulin again. If we weren't so adaptable, you wouldn't be sitting here reading this because your ancestors wouldn't have lived.
And a little tangential thing I read today while I was researching the above, for your amusement. It's about the stupidest thing I've ever read actually. From a study,
Protein dietary reference intakes may be inadequate for vegetarians if low amounts of animal protein are consumed:
"The health benefits of vegetarian diets are well-recognized; however, long-term adherence to these diets may be associated with nutrient inadequacies, particularly vitamins B12 and D, calcium, irno, zinc and protein...
Results and Discussion...
Furthermore, two food groups (nuts/seeds and fruits/vegetables) contributed to nearly 20% of dietary protein, sources not recognized by the DRI report. These are important distinctions because protein from cereals and vegetables (particularly if these foods are less refined) has poor digestibility. Traditional vegetarian diets (e.g., Indian and Guatemalan vegetarian diets) with low amounts of animal proteins and large proportions of cereal and vegetable protein have protein digestibility scores averaging 70% (range 54–77%) compared with plant-based diets with a large proportion of animal protein (mean 88%, range 78–93%)..."
Now you tell me how a diet is simultaneously healthy and yet long-term adherence causes deficiencies. And not only that, in the results of this paper, they even say that plant protein is not as digestible as animal protein. The prior is codswallop if I ever read it and the latter should really have some vegans and vegetarians raising an eyebrow about what they've been fed (hint: lies). Someone has an agenda, and it ain't in the interest of your health. If I eat meat only, as Stefansson (and the Inuit) did, no supplements are required. Chew on that.