Continuing weight loss may deteriorate into wasting, a vaguely defined condition called cachexia.[31] Cachexia differs from starvation in part because it involves a systemic inflammatory response.[31] It is associated with poorer outcomes.[26][31][32] In the advanced stages of progressive disease, metabolism can change so that they lose weight even when they are getting what is normally regarded as adequate nutrition and the body cannot compensate. This leads to a condition called anorexia cachexia syndrome (ACS) and additional nutrition or supplementation is unlikely to help.[28] Symptoms of weight loss from ACS include severe weight loss from muscle rather than body fat, loss of appetite and feeling full after eating small amounts, nausea, anemia, weakness and fatigue.[28]
Are you like Old Faithful when it comes to your morning walk or evening jog? Know this: The more you do an activity, the more your body adapts to it, so you burn fewer calories. If you want to light a fire under your metabolism, consider cross-training. For example, if you normally walk, try biking instead. "Since you're not used to working all those different muscles, it's a more intense workout, which can translate into a greater metabolic after-burn because your body is working harder to recover and get oxygen to all your tissues," says Carol Espel, M.S., an exercise physiologist for Equinox Fitness Clubs in New York City.

The the induction phase gets people used to losing weight at a fast rate, which will not last and is not healthy. Faster weight loss does not mean healthy weight loss. Any diet that emphasizes fast, easy weight loss is one to approach with caution. The guidelines are clear that a safe, healthy rate of weight loss is to lose 1 to 2 pounds per week after the first couple of weeks. The Atkins diet states you will lose "only body fat" by eating regular meals, taking in adequate calories, and keeping your insulin levels down. There is no way to only lose body fat when losing weight. Each pound you gain from consuming excess calories is 75% fat and 25% muscle, and each pound you lose from cutting back 3,500 calories is the same ratio of fat and muscle. Claims that you will lose only fat are not based on science despite the fact that the Atkins diet claims to be scientifically based.
Setting the right goals is an important first step. Most people trying to lose weight focus on just that one goal: weight loss. However, the most productive areas to focus on are the dietary and physical activity changes that will lead to long-term weight change. Successful weight managers are those who select two or three goals at a time that are manageable.