Very low calorie diets (VCLDs) and low calorie diets (LCDs) are often recommended for those trying to lose weight or those that have just had Bariatric surgery. As long as you are under the guidance of a physician these diets can help a person lose weight, but there can be some harmful effects long term. With starting any type of new diet you should have approval of your physician or surgeon to make sure that it’s not going be harmful to you.
It’s very difficult to get all the nutrients your body needs for good health on only 500 calories a day. Diets that provide fewer than 800 calories are called very low-calorie diets, or VLCDs. They generally consist of a liquid supplement that provides an adequate amount of protein, plus vitamins and minerals to help meet nutritional needs. VLCDs are usually reserved for people who are severely obese, and a person on such a diet requires close monitoring by his doctor. The diets are only meant to be followed short term, about 12 weeks, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
Low-calorie diet are diets below 1200 calories a day. These diets again should only be under the supervision of a nutritionist or dietician. Then it should only be done if its also recommended by a doctor. Post bariatric surgery you are generally only on 800 to 900 calories per day. This like VLCD should only be done on a short term basis. They can be done a little longer than VLCDs but again are not sustainable long term and tend to end up regaining that you have already lost. It’s the same issue that restrictive diets can have like ketogenic, etc.
When you eat so few calories your body goes into what’s often referred to as “starvation mode.” Thyroid hormones, which are hormones that regulate your metabolism, decrease to help limit calorie burning. While your body does burn fat when you reduce your intake, it also breaks down your muscle. And because you’re eating so little on your 500-calorie diet and not getting enough protein, you’ll continue to burn muscle for fuel.
That being said, intermittent fasting is a recent diet trend that alternates between periods of normal eating and fasting to help promote weight loss. Some of these diets count a 500-calorie eating day as fasting. Although you still need to discuss the diet with your doctor, limiting your intake to 500 calories one or two days a week may allow you to use real food instead of a liquid supplement, since you’ll be able to get the nutrients you need on the other days of the week.
In any event, you want to make wise food choices when you’re limiting your intake and include low-calorie, nutrient-dense foods periodically throughout the day. And fill in with calorie-free foods and drinks such as sugar-free gelatin and ice pops, fat-free broth, black coffee, plain tea and sugar-free lemonade to help control hunger.
Not only is it easier to limit your intake to 500 calories only a couple of times a week, but it may also serve as an alternative way for you to lose weight, especially around your middle, according to a 2014 review paper published in Translational Research. This review found that although people lost more weight on regular calorie-restricted diets, intermittent fasting was just as effective at helping decrease belly fat. Restricting your intake for short periods of time causes your body to release hormones that help you burn fat and build muscle. It also releases hormones that give your metabolism a little boost too.
If you have a medical condition such as diabetes or low blood pressure, or if you take prescription medications, you shouldn’t fast without your doctor’s approval. Intermittent fasting is also not recommended for people who are underweight or women who are pregnant or nursing.