Why fad diets work well for some, but not others

"There is no one-size-fits all solution to the diseases of obesity and type-2 diabetes," said Laura K. Reed, Ph.D, a researcher from the Department of Genetics at North Carolina State University, the lead investigator in the work. "Each person has a unique set of genetic and environmental factors contributing to his or her metabolic health, and as a society, we should stop looking for a panacea and start accepting that this is a complex problem that may have a different solution for each individual."

To make this discovery, the scientists studied 146 different genetic lines of fruit flies that were fed four different diets (nutritionally balanced, low calorie, high sugar, and high fat). Researchers then measured a variety of metabolic traits, including body weight, in each group. Flies in some of the genetic lines were highly sensitive to their diets, as reflected by changes in body weight, while flies of other lines showed no change in weight across diets. The scientists were able to ascertain what portion of the total variation in the metabolic traits was determined by genetics alone, by diet alone, or by the interaction between genotype and diet. Results showed that diet alone made a small contribution to the total variation, while genotype and genotype interactions with diet made very large contributions. This study strongly suggests that some individuals can achieve benefits from altering their dietary habits, while the same changes for others will have virtually no effect.

"The summer beach season often serves as a 'gut check' for many in terms of their weight," said Mark Johnston, Editor-in-Chief of the journal Genetics. "This research explains why the one-size-fits-all approach offered by many diet programs can have dramatically different effects for people who try them."