You can say that again!
Hot off the presses (Paoli et al., 2019).
Good paper. Nice background with information about muscle protein balance, anabolic & catabolic factors, and signaling pathways.
At one point the authors seem to have confused a study on starvation ketosis with nutritional ketosis, but in all fairness they also acknowledged the study showing beta-hydroxybutyrate can inhibit AKT which is important for skeletal muscle hypertrophy (Yamada et al., 2010).
Let's dive right in to Table 1 which is a summary of human studies on keto & lean mass:
Starting with the study by Wood and colleagues (2010), who studied: a low fat diet, low fat + exercise, keto, and keto + exercise. Everyone lost weight. The low fat group lost significantly more lean mass than any other group. The authors interpreted this to mean keto "had a protective effect on muscle mass."
LFD+ex, Keto, & Keto+ex all lost the same amount of lean mass although the keto groups were getting 50% more protein.
Another interpretation, one could say that 50% more protein and even resistance exercise weren't enough to prevent keto-induced muscle loss. They lost just as much lean mass as LFD+ex and Keto.
The authors concluded: "a general conservation of muscle mass."
Not acknowledging the control groups, as in Table 1, is a not-so-subtle-way of shifting goal posts imo.
It took nearly 3x more protein to maintain muscle mass in this population.
Green and colleagues controlled for protein and can you guess what happened to the group assigned to keto (Greene et al., 2018)?
Another rule of thumb: muscle shouldn't comprise more than 1/4 - 1/3 of the weight lost on any hypocaloric diet especially when combined with resistance exercise.
About two thirds of the weight they lost was lean mass. Man, I hope that was all water...
Side note: there's no definitive ruling on the influence of ketoadaptation on glycogen. Studies are mixed on this and there's no clear pattern, which is why I'm sticking with maximal fat oxidation rate as the indicator of ketoadaptation, not glycogen.
The study by Wilson and colleagues was an outlier (Wilson et al., 2017)... you rarely see increased fat gain in the keto group compared to control. CORRECTION (thanks, Mike!): this study had a unique design; weeks 1-10 keto, week 10-11 added back some carbs in an attempt to control for water/glycogen. Keto lost more fat in the beginning and then gained it back when they added back carbs. Lol.
Vargas and colleagues showed the same as above, "preservation of lean mass" on keto whereas the control group actually gained muscle (Vargas et al., 2018).
Kephart and colleagues showed modest muscle loss and blunted strength gains on keto vs. control (Kephart et al., 2018).
Hey, I'm just trying to be honest here... also, don't shoot the messenger but please let me know what you think!
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