Purpose of review - Quality or quantity of food has been at the heart of the diet debate for decades and will seemingly continue for many to come unless tightly controlled studies are conducted. To our knowledge, there has never been an overfeeding study comparing the effects of multiple diets.
Recent findings - This study reports a case study of an individual who ate 5800 Calories per day of 3 different diets for 21 days at a time. The 3 different diets were low-carb, low-fat, and very-low-fat vegan. The weight gain over 21 days was 1.3 kg for low-carb, 7.1 kg for low-fat, and 4.7 kg for very-low-fat vegan.
Summary - In this n-of-1 study, consuming 5800 Calories/day of 3 different diets for 21 days did not lead to the same amount of weight gain. Further research should be conducted on how the human body gains weight with an emphasis on how different foods affect physiology. If these findings are replicated, there would be many ramifications for obesity treatment and healthcare guidelines.
Full Text: https://doi.org/10.1097/MED.0000000000000668
Ben Bikman brought up this study, and made a nice summary slide for it

It is remarkable that such physiological changes occur even after a comparatively short period of only twenty-one days. Having tried all three also, my experience has been consistent with this in general; however I do not have asthma, and I was noticeably much more irritable on low-fat and very-low-fat vegan.
I'm curious as to how he "reset" his body state to keep the starting point consistent for the study. It would've also been interesting if he'd also adopted a high-fat animal-sources-only diet as part of this trial.
I also appreciate that the limitations are clearly stated. Interesting study!
Yeah! I would have liked to see more biomarkers too. But I think the point of this project was to illustrate how limited the current literature is.
The 3 month reset could have been better defined, to be sure. The fun thing is anyone can repeat this data finding experiment and collect better metrics.
This is exactly what I mean when I say the carnivore community, as a whole, is very scientifically minded. I.e. can they repeat the results