Carbohydrate constitutes one of the three macronutrients in the diet, along with protein and fat, which provide you with energy. Total carbohydrate corresponds to the sum of starches, sugars and fiber in a serving of food. This nutrient is found in a variety of foods, from grain products, legumes and starchy vegetables to fruits, milk, yogurt and sugar.
Around 45 percent to 65 percent of your daily calories should come from carbohydrates, which corresponds to an intake ranging between 225 and 325g of carbohydrates, based on a 2,000-calorie diet. The U.S. Department of Health and Human Services recommends a minimum of 130g of carbohydrate a day. However, the Food and Nutrition Board of the Institute of Medicine claims that "the lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed." The current recommendations emphasize the consumption of carbohydrate-rich foods, but it appears that this nutrient is not essential to life, as long as the diet provides enough protein and fat.
One of the reason why people advocate diets with approximately half the calories from carbohydrates is to prevent ketosis. The body's cells can use glucose, or the sugar obtained from the digestion of carbohydrates, or fat, whether it is dietary fat or stored body fat, for fuel. When the daily carbohydrate intake falls below 100g, the body starts using more fat than carbohydrate through a metabolic pathway called beta-oxidation, which results in the production of ketone bodies that can also be used for energy by various organs, such as the brain. Many people criticized diets low in carbohydrates because they induce this condition called ketosis. However, ketosis itself is not harmful, but is unfortunately often confounded with ketoacidosis, a dangerous medical condition associated with extremely high concentrations of acidic ketone bodies in Type 1 diabetes.
Carbohydrate-rich foods, mainly the minimally processed and refined ones, such as whole grains and fruits, constitute the main source of fiber and antioxidants for most people. Eliminating all carbohydrates can result in a lack of fiber, antioxidants, vitamins and minerals, which can lead to constipation in the short-term and nutritional deficiencies in the long-term. However, it is possible to get enough fiber and important micronutrients by consuming low-carbohydrate vegetables, such as leafy greens, broccoli, cauliflower, asparagus, zucchini, mushrooms, onions and tomatoes. Although non-starchy vegetables do contain some carbohydrate, it is a good way to get fiber and antioxidants for fewer carbohydrates than with whole grains and fruits. Most of the carbohydrates in non-starchy vegetables are fiber, which does not influence your blood sugar levels and does not provide calories.
No-Carb Vs. Low-Carb Diets
Excluding most carbohydrates from your diet is not dangerous for your health if you include sufficient amounts of protein and fat into your diet and the ketogenic effect of low-carb diets is not harmful. However, it may be difficult to obtain enough fiber, vitamins and minerals by completely eliminating all carbohydrates from your diet. This is why including a minimum amount of carbohydrates, corresponding to approximately 20g a day, from high-fiber, low-carb vegetables is recommended to stay healthy. In addition to vegetables, a healthy low-carb diet should include foods like fish, poultry, eggs, meat, cheese, olive oil, avocado, nuts and seeds.