Thursday, January 21, 2021

Interesting Study: "Effect of a Plant-Based, Low-Fat Diet versus an Animal-Based, Ketogenic Diet on Ad Libitum Energy Intake"

This is from Kevin Hall, who's a very polarizing figure in the LCHF/Keto diet community, and will be even more so after this!
"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."

"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."
The Keto diet people lost more weight, but it was "fat-free" weight, which in this case means water. (ABLC = Animal-Based, Low Carbohydrate; PBLF = Plant-Based, Low-Fat.)

"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. 

This study really wasn't testing this hypothesis, but it happens that the seemingly underperforming ABLC diet was 15% (by energy) n-6 PUFA, while the PBLF diet was less than 3%. The reigning animal model for inducing obesity used 8% energy as n-6 PUFA (more about that in a future post).

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!


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.

Goodrich, T. (2017, November 9). Omega-6 Fats: The Alternative Hypothesis for Chronic Disease. Yelling Stop.
Hall, K. D., Guo, J., Courville, A. B., Boring, J., Brychta, R., Chen, K. Y., Darcey, V., Forde, C. G., Gharib, A. M., Gallagher, I., Howard, R., Joseph, P. V., Milley, L., Ouwerkerk, R., Raisinger, K., Rozga, I., Schick, A., Stagliano, M., Torres, S., … Chung, S. T. (2021). Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nature Medicine, 1–10.


  1. The objective was weight maintenance so one could argue the LCHF diet won and the indigestible plant diet got the better of the subjects. Was it 80 g/day of fibre? As a whole food diet the insulin was relatively low on both arms and FFA elevated compared to SAD. The plant based diet showed a fat oxidation rate well above the fat intake by a factor of 3, leading to fat loss.

    15% protein isn't a standard LCHF diet as far as I'm aware.

    1. "15% protein isn't a standard LCHF diet as far as I'm aware."

      It's pretty typical of any human diet. LCHF diets go as high as 30% in the literature, Atkins recommends from 20% to 30%, for instance.

  2. It seems the time has passed for vilifying all carbohydrates. While it seems it’s becoming clear how much PUFAs are driving many of our metabolic disorders, I’m not sure I’m ready to write off processed carbs like refined sugars and wheat flours as a significant part of the problem.

    I’ve certainly seen people lose weight in many P-C-F permutations as long as the amount of energy they take in isn’t a toxic level of nutrient poor sources, whether it’s sugar, bread, or omega-6 fats.

    Ted Naiman’s P:E model is a great example where the energy can be carbs or fat, as long as it’s in balance with protein