Yes it absolutely is, since he claims he doesn't eat sugar for all the reasons he cites, yet he's fat and looks metabolically unhealthy:

https://www.wnycstudios.org/podcasts/heresthething/episodes/...

>Robert Lustig: I carry a few extra pounds and I’m not happy about it. I don’t eat sugar.

>Alec Baldwin: You don’t.

>Robert Lustig: No. I have dessert twice a year. When I’m in New York I have a piece of Junior’s cheesecake and when I’m in New Orleans I have bread pudding -

Notice his twice yearly dessert sugar indulgences are high in fat.

> If dietary fat is more easily stored as fat,

You seriously believe your body preferentially uses de novo lipogenesis to convert carbohydrate to fat (which entails some energy loss) rather than just storing fat as fat? DNL on a typical mixed macro diet is rare, to the point that something like 90% of your bodyfat came from fat you ate, and the fatty acid profile of your body mirrors that of your diet: https://pubmed.ncbi.nlm.nih.gov/12324287/

Even in low-carb circles, this is tacitly acknowledged now by warning against eating meat from animals fed a high-PUFA diet, like poultry.

I'm not saying overeating carbs won't make you fat, but arguing that it somehow makes you fatter, calorie-for-calorie, than fat is ridiculous considering that eventually your body runs out of fat and has to use DNL (which is inefficient), and that fats require the least energy for your body to digest of any macro.

> why do keto diets work?

They don't, at least not any better than low-fat diets. They seem to work better initially because keto dieters lose a lot more weight early, but that weight is disproportionately fat-free mass, i.e., water, glycogen, and probably at least some lean body mass (muscle and bone density). See the graph on p. 4 of Kevin Hall's NIH study comparing the diets:

https://sci-hub.se/10.1038/s41591-020-01209-1