Ketosis, the body’s switch to fat metabolism as an emergency fuel, causes its own unpleasant and ultimately harmful side effects. In their fantastic and comprehensive review of popular diets, nutrition professor Marjorie Freedman, Ph.D., and her colleagues point out that the Atkins diet is not only disadvantageous for weight loss, it’s actually accompanied by the kinds of side effects you usually find on the flip side of magazine ads for pharmaceutical drugs: constipation, bad breath, headache, nausea, and fatigue, among others. With those kinds of side effects is it any wonder that virtually nobody can stick to the diet? Freedman, after an amazing review of the science behind popular diets, including Atkins, concludes that the best evidence for weight loss comes from a diet high in fruits, vegetables, and grains and low in fat (Freedman, King, et al. 2001).