In most cases, someone undertaking a diet with the goal of losing weight — regardless of what diet it is — will experience initial weight loss, followed by a significant amount of weight regain.[1][2] But do “95% of diets fail”, as is sometimes claimed?
This, of course, requires defining what is a “diet success”, and there is no universally accepted definition for what this means (and it likely varies according to each person’s needs and preferences). Nevertheless, some researchers have proposed a weight loss of ≥10% of one’s initial body weight after ≥1 year as successful weight loss.[3]
Using that definition, the percentage of people achieving successful long-term weight loss is variable in studies, with rates of 10%,[4] 20%,[3] 26%,[5] and 33%[6] reported over periods of 1–8 years.
These findings suggest that the failure rate of dieting is high, but not as high as 95%. Of course, it's important to note that the previous studies usually included people who were exercising (or were recommended to do so), and physical activity seems to enhance the effect of dietary interventions on weight loss.[2] Furthermore, these studies typically provided participants with counseling, education, and/or support sessions, which likely improves dietary adherence.