Insulin sensitivity didn’t make a difference. People who secreted more or less insulin lost no more or less weight in general on either a low-fat or low-carbohydrate diet. Genetics didn’t make a difference either. People who had genes that might indicate that they would do better on one diet or the other didn’t.

In fact, when you look at how every single participant in this study fared on the diet to which he or she was assigned, it’s remarkable how both diets yielded an almost identical, curving range of responses — from lots of weight lost to a little gained. It wasn’t just the averages.

Some have taken this study to prove that avoiding processed foods, eating more whole foods, and cooking at home leads to weight loss. While I’d like that to be true — I have advocated this healthful approach in my Upshot article on food recommendations and in a recent book — that’s not what this study showed. Although that advice was given to all participants, there was no control group in which that advice was omitted, and so no conclusions can be made as to the efficacy of these instructions.

Others have taken this study as evidence debunking the idea that counting calories is the key to weight loss. While that wasn’t the main thrust of this study, nor the instructions given, participants did reduce their intake by an average of 500-600 calories a day (even if they didn’t count them). This study didn’t prove the unimportance of calories.

The researchers also asked everyone, not just those in the low-carb group, to avoid “added sugars.” Therefore, we can’t really say anything new about added sugars and weight loss.

What this study does show is that people who have staked a claim on one diet’s superiority over another don’t have as strong a case as they think. It’s hard to overstate how similarly these two diets performed, even at an individual level.

It shows us that the many people, and the many studies, suggesting that we can tell which diets are best for you based on genetics or based on insulin levels might not be right either. Almost all of the studies that backed up such ideas were smaller, of shorter duration or less robust in design than this one. Granted, it’s still possible that there might be some gene discovered in the future that makes a difference, but those who think they’ve found it already might want to check their enthusiasm.