A 600-calorie-a-day diet can help people suffering from Type 2 diabetes, high blood pressure or high cholesterol, but can also cause a slower metabolism, fatigue, nausea and gallstones. The risks of this diet are greater for people who are not being supervised by a doctor, pregnant or breastfeeding women, and children and teens, according to WebMD.
A 2011 study placed 11 people with Type 2 diabetes on a 600-calorie-a-day diet, reports WebMD. After three months of a diet consisting of liquids and non-starchy vegetables, seven of these people were free of diabetes. However, the study director attributes the reversal of diabetes to the weight loss rather than the specific diet.
People with a body mass index that is higher than 30 who go on a very low calorie diet can lose around 3 to 5 pounds a week, states WebMD. People who have a BMI of 27 to 30 should only go on such a diet if they suffer from health problems relating to being overweight. Also, the low calorie diet is not any more effective than other more modest diet plans, because once people go off this diet they still need to maintain a healthy diet and participate in physical activity.