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So, will taking a daily multivitamin be okay? Yes, it's not going to harm or impede you in any way. However, you can get everything your body needs on a carnivore diet. If you add a little beef liver to your Lion Diet (which is what you are about to do), you will probably have your bases covered.
B1 (Thiamine) - beef liver, pork products, salmon, trout, mussels, tuna, chicken liver, fish roe. Biotin & Folate - beef liver and egg yolks. Vitamin A - beef liver, cod liver oil, butter, and a variety of cheeses. Vitamin C - beef, beef organs, and seafoods. Vitamin D - eggs, fatty fish, and you can make it by getting enough sun. Vitamin E - salmon and trout. Vitamin K - chicken, beef liver, and cheeses. Calcium - salmon, sardines, cheese, and milk. Chromium - beef and turkey Molybdenum - beef liver, yogurt, and milk. Magnesium - meat, but especially fatty fish. Iodine - eggs, dairy, and especially seafood. Admittedly, Vitamin D is one micronutrient that many people need to supplement.
I take magnesium because I would need to eat 2-2.5 lbs of beef a day to meet my magnesium needs, and that's a bit much for me. I also take vitamin D because I have a history of being deficient.