Patients often reach out to me seeking a dietitian for weight loss. The person will tell me a story of slow weight gain over the years, difficulty losing weight with multiple tries, and putting in efforts at improving nutrition. They ask, "Do you do weight loss? Can you help me lose weight?" Unfortunately, my answer is that I don't have a high likelihood of helping the person lose weight with nutrition alone.
Research does not show that diet as an obesity treatment is successful. Studies show that in as short as one year after losing weight, you might see numbers as high as 20% of people who have maintained the weight loss, but those numbers decrease as time goes on, to less than 5%. Additionally, the degree of weight loss maintained is often in the 5-10% range. While that is clinically significant to improve health outcomes, it is often not enough for patients to feel they are at the weight they want to have. That means that maybe one in twenty people who I try to help lose weight with diet alone will be able to keep some weight off over time.
While I work with many patients who have obesity, and I have been working in obesity research for years, I still do not have the magical answer to weight loss with diet alone.
The goals of nutrition are primarily just that--improved nutrition behaviors. That is, eating in a way that promotes health. Secondary goals are improved health outcomes, such as blood sugars in goal range, lower blood pressure, better lipid profile, greater energy levels, and stronger cardiovascular fitness.
If you do find a dietitian who does weight loss, I would want to know their success rates. I would want to see data of what percent of their patients lose at least 5% of their weight and keep it off for more than 5 years. If they tell you that the patients who follow their advice lose weight, then I am not impressed.
The problem with diets for weight loss is that they are not sustainable for the average person. The fact that a small minority can stick to a diet for any length of time speaks more to that person's unique characteristics rather than the quality of the diet or dietitian.
In any other area of medical research, if a medical treatment is found to have mediocre effect on 5% of people, no one would want that treatment! Somehow with diets, that logic goes away.
Of course nutrition affects body weight. But a bigger question than what exactly someone should eat is what else is affecting that person's eating and body weight: What is the cause of this individual's obesity? Obesity is not a homogenous condition. Different causes are more prominent in some individual with obesity than others. Understanding that is the key to understanding the treatment of obesity.