The low-carb diet craze that reached a very popular following several years ago received criticism for the dangerous state of “ketosis” that some followers reached. One of the most famous (or infamous depending on who you ask) of these low-carb diets is the Akin’s Diet, more formally known as Dr. Atkin’s New Diet Revolution. Phases of the South Beach Diet, Complete Scarsdale Medical Diet, and many other restricted carbohydrate diets operate on the principle that restricting carbohydrate intake–usually to less than 100 g of carbohydrate/day–will help dieters lose weight.
In the short run, these diets do often help dieters shed pounds. Unfortunately, this loss is mostly due to the loss of lean muscle tissue, water (which makes up about 70% of lean tissue), and ions including potassium. Losing water weight can help people lose weight quickly but it is also quickly regained as soon as dieters return to a normal eating pattern.
Your fat tissue, on the other hand, stays right where you left it. You need carbohydrates to efficiently metabolize fat. (Specifically, you need glucose–from carbohydrates–to make pyruvate. You need pyruvate to make oxaloacetate. You need oxaloacetate to be present for the product of fatty acid oxidation, acetyl CoA to enter the TCA cycle. In essence, you can’t burn fat without having some glucose present.)
Part of the effectiveness (in the short run) of a very low carbohydrate diet also results from a loss of appetite many experience as a result of ketosis. Ketosis is a state in which ketone bodies accumulate in the body when not enough glucose (or insulin in diabetics) is present. Ketones are the byproducts of incomplete fatty acid oxidation (when fatty acids can’t be fully broken down and metabolized as a source of energy). When ketones accumulate, blood acidity rises. Mild ketosis may result in loss of appetite because it generally makes people feel sick. More severe ketosis can result in coma and death.
Instead of following a very low carbohydrate diet, it is best for most people to focus on consuming more complex carbohydrates from whole grain products and to reduce refined, highly processed simple carbs. Be skeptical of any diet that tells you to avoid eating nutrient-rich foods such as fruits and vegetables. Remember that any diet can appear to work in the short run but only adapting long-term healthy lifestyle habits and including regular physical activity can support sustained weight loss and maintenance.