At least 2 to 3 cups (16 to 24 ounces) of vegetables a day are recommended for most adults, depending on age, sex and level of physical activity. Any type of vegetable counts, including raw, cooked, fresh, frozen, canned and dried vegetables. One-hundred percent vegetable juice counts, too. You're right about the missing fiber, though. Vegetable juice has plenty of vitamins and minerals, but it's lower in fiber than is a serving of most whole vegetables. Without enough fiber in your diet, you may risk constipation, high cholesterol, high blood sugar and weight gain. Some types of vegetable juice are high in sodium, too.