"The carbohydrate–insulin model of obesity posits that high-carbohydrate diets lead to excess insulin secretion, thereby promoting fat accumulation and increasing energy intake. Thus, low-carbohydrate diets are predicted to reduce ad libitum energy intake as compared to low-fat, high-carbohydrate diets....
"The primary outcomes compared mean daily ad libitum energy intake between each 2-week diet period as well as between the final week of each diet. We found that the low-fat diet led to 689 ± 73 kcal d−1 less energy intake than the low-carbohydrate diet over 2 weeks (P < 0.0001) and 544 ± 68 kcal d−1 less over the final week (P < 0.0001). Therefore, the predictions of the carbohydrate–insulin model were inconsistent with our observations."
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| "Figure 3. Body weight and composition changes. A) Both the ABLC and PBLF diets led to progressive weight loss over time with the ABLC diet resulting in more rapid weight loss during the first week. B) Fat-free mass decreased significantly only during the ABLC and accounted for the majority of the observed weight loss. C) Body fat mass decreased with the PBLF diet but was not significantly decreased with the ABLC diet." |
"Despite the substantial differences in energy intake between the PBLF and ABLC diets, total weight loss after two weeks was surprisingly similar. Greater weight loss during the first week of the ABLC diet as compared to the PBLF diet was likely due to differences in body water, glycogen, and gastrointestinal contents. Indeed, fat-free mass was decreased significantly with the ABLC diet whereas fat-free mass was relatively preserved with the PBLF diet."
Surprisingly, "Only the PBLF diet led to a significant body fat loss."
So the keto diet "won", but not in a meaningful way, as the knock on the LCHF diet has long been that the weight loss was water loss, and not really fat loss—which is of course what you want!
I have personally been on an intermittent keto diet for going on 10 years now. I can assure you that the initial weight loss was not water loss, as I've managed to maintain it for these 10 years. I've coached people who've seen significant weight loss, in one case 56 pounds over 10 weeks, which has so far also stayed off.
So these results don't reflect my experience.
But Hall structured this as a test of what's known as the Carbohydrate/Insulin Model of obesity, in other words that carbohydrate causes a rise in insulin, which causes fat accumulation. The CIM took a bit of a beating here, as indeed they had higher insulin, but they also ate less, without feeling hungry, and lost more fat.
I think that a ketogenic diet is the most efficient way to lose weight, but I don't think that our obesity epidemic is the result of eating carbohydrates. My hypothesis is that it's omega-6 fats that are the culprit.
Well, luckily the "underperforming" keto diet in this study was not one that I eat myself, or that I would recommend someone else eat.
So while a lot of LCHF advocates who think it's carbohydrate that is driving the obesity epidemic are a bit disgruntled with this paper, I'm happy to see that Hall didn't gore my ox!
Yet.
NB: I was working off a pre-print version of this paper. I may have to revise this post if it winds up that the published version is wildly different.
