A small, but comprehensive, study from Stanford University researchers has pitted low-fat diets against low-carb diets. After one year the results are in and it's a draw. Frustrating anyone wanting a definitive result, the data compellingly suggests individual diet outcomes are much more subjective than many previously thought.

In recent years, the big dietary villain has prominently shifted from fat to carbohydrates, with some studies suggesting high-fat, low-carb diets could be the best way to shave off those pounds and keep healthy. But as more research accumulates, it is becoming increasingly clear that every individual's biology is so different that there is no single magic plan that applies to all.

"We've all heard stories of a friend who went on one diet – it worked great – and then another friend tried the same diet, and it didn't work at all," explains lead author of the study, Christopher Gardner. "It's because we're all very different, and we're just starting to understand the reasons for this diversity. Maybe we shouldn't be asking what's the best diet, but what's the best diet for whom?"

The new Stanford study followed 609 people for one year. The subjects were split into two groups, each directed to consume a controlled diet that was either low-fat or low-carbohydrate. One of the key focuses of the study was to understand how individual factors relate to weight loss and each participant's genome was examined at the start of the study.

After a year the results came in, and they may prove frustrating for those seeking an objective winner. The researchers found no significant difference in weight loss between the two diets, with the low-fat diet group losing an average of 5.3 kg (11.6 lb) and the low-carb group losing an average of 6 kg (13.2 lb).

Despite the similar overall averages, the researchers found huge individual variations in weight loss among the subjects and, interestingly, none of the variations correlated with either specific genotypes or a person's baseline insulin levels.

The interaction between genes and nutrition is a growing area of study called nutrigenomics. Several companies currently sell DNA tests that claim to identify certain genetic markers that can reveal whether a person is better suited to a low-carb or low-fat diet. This Stanford study looked at three specific genetic variants commonly utilized in nutrigenomic studies and known to be involved in fat and carbohydrate metabolism.

The results were stark. There was no difference in weight change between those genetically suited to the diet they were on and those genetically mismatched with their diet. Interestingly, these results challenged a smaller study Gardner and his Stanford team completed in 2010 that suggested genetically matched diets did indeed result in more weight loss.

"I had this whole rationale for why these three [DNA variants] would have an effect," Gardner says in an interview with Stat News. "But let's cut to the chase: We didn't replicate that study, we didn't even come close. This didn't work."

So what's the takeaway from this study, other than "eat less" or "eat healthy"?

Gardner and his team are determined to dig deep into the voluminous trove of data gathered from the study looking for some kind of clear signature that runs through all the participants. Is it microbiome, epigenetic or an undiscovered genetic pattern that explains the variability between all the participants?

"I'm hoping that we can come up with signatures of sorts," says Gardner. "I feel like we owe it to Americans to be smarter than to just say 'eat less.' I still think there is an opportunity to discover some personalization to it – now we just need to work on tying the pieces together."

Gardner discusses the results of the study in the video below.

The study was published in the journal JAMA.