I ran across Don Matesz’ video where he cites the O. Lammert et al paper, Effects of isoenergetic overfeeding of either carbohydrate or fat in young men, to suggest that DNL can make you fat. More specifically, Matesz says the study refutes the claims of HCLF advocates (Durianrider, Dr. John McDougall) that you can’t get fat from all-the-carbs-you-can-eat.
In the study, normal weight males ate about +1200 extra calories per day above their habitual diet (@ 78/11/11 low-fat macros) for 21 days. In the end, the analysis estimates that the average subject produced only 10g fat per day via hepatic DNL, or 16g/day from total body DNL (adipose + hepatic + muscular sources, etc.).
But these numbers are in line with the HCLF diet claims, which say even if you continually overeat a massive amount of carbs, DNL will only produce “in the low 10’s” of fat grams per day. In fact, one of the paper’s authors is professor Marc Hellerstein, who’s UC Berkeley lab has studied DNL for decades. These results don’t change the picture of DNL as a minor contributor to fat accumulation in the scheme of things.
Now, the subjects did gain an average of 0.9 kg of fat by overeating for these 21 days. The model implies that DNL produced (21 days)(16 g fat/day) = 0.336 kg of fat from the excess carbohydrates, and that the “fat-sparing” effect of carbohydrates caused the storage of the rest (0.9 kg – 0.336 kg of dietary fat into adipose tissue). Note that the majority of the fat gain came from dietary fat, not DNL.
Of course in real life, people eating HCLF aren’t trying to continually overeat, and they’ll stop when they’re full. Plus, they may exercise more than these college student subjects, and might oxidize (burn) more fat each day than these overeating subjects. So for many, eating ad libitum HCLF is a great weightloss strategy.
Ok, now for the surprising part.
The experiment was conducted as a kind of “twin” study, where they paired subjects into a high-carb (78/11/11) and a high-fat (31/11/58) partner. The “twins” would follow each other around, and perform the same physical activities, including sleep. Each would eat +1200 calories over their respective baselines for 21 days, one eating only 11% fat, and the other eating 58% fat.
The big (fat) surprise was that there was no statistical difference between the fat gain of the low-fat twin vs. the high-fat twin after 21 days of overeating. So once again, we see that different macro ratios of a diet don’t produce different results under isocaloric conditions. This is the same conclusion time after time, making advocates for specific macro ratios scramble to find “design flaws” in every experiment confirming this outcome.
So how can the high-fat twin overeat 1200 calories/day, including 290 g/fat day, totaling 4600 cal/day, and only gain 0.9 kg of fat after 21 days? Ironically, these numbers are pretty similar to all the Sam Feltham overeating self-experiment stunts, which HCLF adherents are quick to dismiss.
So what is the conclusion here? I think these results fit in with all of the other overfeeding studies, that show A) the average weight gain is always less than the theoretical max of 1 kg per 9000 extra calories, and B) that even very different macronutrient ratio diets produce about the same net weight results.