Followers must eat fat at each meal:

• Some healthy unsaturated fats are allowed: almonds, walnuts, seeds, avocados, tofu, and olive oil. But saturated fats from oils (palm, coconut), lard, butter, and cocoa butter are encouraged in high amounts.
• Protein is part of the keto diet, but it doesn't typically discriminate between lean protein foods and protein sources high in saturated fat such as beef, pork, and bacon.
• You can have certain fruits (usually berries) in small portions. Vegetables are restricted to leafy greens (kale, Swiss chard, spinach), cauliflower, broccoli, Brussels sprouts, asparagus, bell peppers, onions, garlic, mushrooms, cucumber, celery, and summer squashes. 

• It's high in saturated fat. It is associated with an increase in "bad" LDL cholesterol.
• Nutrient deficiency: deficiencies in micronutrients found in  vegetables, fruits, and grains;
• Liver problems, because of the amount of fat to metabolize;
• Kidney problems. The kidneys help metabolize protein; the keto diet may overload them;
• Constipation. The keto diet is low in fibrous foods like grains and legumes.
• Fuzzy thinking and mood swings: the brain needs sugar from healthy carbohydrates to function.