I guess everyone has seen this:
Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion The DIETFITS Randomized Clinical Trial
How do you sum up the trial (apart from tedious)? These quotes do it up for me:
"The intervention involved 22 instructional sessions held over 12 months in diet-specific groups of approximately 17 participants per class. Sessions were held weekly for 8 weeks, then every 2 weeks for 2 months, then every 3 weeks until the sixth month, and monthly thereafter. Classes were led by 5 registered dietitian health educators who each taught 1 healthy low-fat class and 1 healthy low-carbohydrate class per cohort"
"...an emphasis on high-quality foods and beverages"
"...focus on whole foods that were minimally processed, nutrient dense, and prepared at home whenever possible."
This should be a good intervention.
Except decision making was then handed to the participants:
"Then individuals slowly added fats or carbohydrates back to their diets in increments of 5 to 15 g/d per week until they reached the lowest level of intake they believed could be maintained indefinitely"
End result of this is that 10% of the participants weighed more at the end of 12 months of closely supervised healthy eating by a Registered Dietitian Health Educator than they did at the start. Cracking intervention for these poor folks.
And in both the low fat and the low carb groups just under 5% (LF 4.3%, LC 3.6%) of participants developed metabolic syndrome, who had been relatively healthy before the start of the intervention. How can you manage this with "healthy" food and 22 meetings with a Registered Dietitian Health Educator? I'm impressed. If a Registered Dietitian Health Educator ever comes your way, RUN. Especially if they use the words "healthy" and "diet" in the same sentence.
Bottom line: Low carb diets only work when you limit the amount of carbs you eat. However "healthy" those carbs you add back in might be, depending on the opinion of a Registered Dietitian Health Educator, it's no longer a low carb diet. You'll get fat again.
Of course the same applies to low fat diets, especially if they are sugar restricted at the same time. Ultimately if you follow a low fat diet with as much added fat as you feel comfortable with, you're going to be disappointed with the results too. Adding back sugar will be even more disastrous. Sad but true.
Addendum: Gardner did essentially the same study in 2007 but made the mistake of publishing the weights alongside the carb intakes at each assessment interval. I wrote all over his graphs here. He didn't repeat the mistake. No one should imagine he's stupid. Or honest.