A very low-carb diet (VLC) normally refers to a diet where the carbohydrate intake is no more than 50 grams of total carbs / 20 grams of net carbs a day.
This type of diet has many help treating some health conditions and it also be a very effective tool for weight loss, especially if you have metabolic syndrome. For example, the Restricted ketogenic diet, which is a VLC, is used to manage and try improve diseases such as cancer, Alzheimer's and epilepsy. But it is not suited for everyone.
If you’re following a VLC you have to make sure you are ingesting sufficient micronutrients such as magnesium, calcium and potassium. Lack of certain micronutrients might cause health issues in the future. Also keep an eye on your levels of vitamin E, A, C, iron, thiamin, folate and zinc.