I've read a lot of research lately that ascertains that permanent weight loss is impossible to maintain for most people. There is a blog run by a PhD that explains a lot of the more complex literature in plain terms. Here is a post that explains their main point quite succinctly:
There is little scientific support for the notion that diets lead to lasting weight loss
A recent meta-analysis (a study that examines the results of many other studies) of over 50 years of weight-loss research revealed that people can initially lose about 5% to 10% of their weight on virtually any diet program.
This means that a 250 lb. woman can typically lose between 12 and 25 lbs. by dieting. This loss is often presented as “success” by diet companies, even though such a woman would still be categorized as “obese” according to the Body Mass Index (BMI).
But… “These losses are not maintained. As noted in one review, “It is only the rate of weight regain, not the fact of weight regain, that appears open to debate” (Garner & Wooley, 1991, p. 740). The more time that elapses between the end of a diet and the follow-up, the more weight is regained…”
“Among patients who were followed for under two years, 23% gained back more weight than they had lost. Among patients who were followed for two or more years, 83% gained back more weight than they lost (Swanson & Dinello, 1970). Even in the studies with the longest follow-up times (of four or five years postdiet), the weight regain trajectories did not typically appear to level off (e.g., Hensrud, Weinsier, Darnell, & Hunter, 1994; Kramer, Jeffery, Forster, & Snell, 1989), suggesting that if participants were followed for even longer, their weight would continue to increase…”
“The amount of weight loss maintained [after 5 years] in the diet conditions of these studies averaged 1.1 kg (2.4 lb).”
Reference: Mann, T., Tomiyama, A.J., Westling, E., Lew, A.M., Samuels, B., Chatman, J. (2007). Medicare’s search for effective obesity treatments: diets are not the answer. American Psychology, 62, 220-233.
The site is super pro-SJW but still have some very valid and very thorough dissection of current literature.
Me--I don't know how I feel about the topic at hand. I'm not fat and have always found that I can easily maintain a low weight through diet and exercise, but don't see any reason to shame people who are overweight.