The role of protein, carbohydrates, and insulin on muscle growth and preservation

Attia frames this as asking whether you can 'hit it at both ends' — reduce degradation AND increase synthesis — by combining macronutrients. Norton confirms the mechanism is real but notes the evidence base comes from only two protein/calorie-equated studies (Vargas and one other). The strength outcome (1RM squat and bench press) in the second study was the more compelling evidence that the difference involves contractile tissue rather than glycogen-stored water.

Attia's account is the most granular first-person description of elite keto-adaptation in the public domain. His mistakes: no volume reduction, cycling and swimming at elite levels from day one. The aerobic base recovered at 12 weeks. The anaerobic recovery took 18 months — with perfect dietary compliance over three years. He notes he wishes he had taken serial muscle biopsies for future proteomics/metabolomics work, which might have illuminated the molecular substrate of the extended adaptation.

Attia extends the same filter to protein dosing: 50 g/day prevents negative nitrogen balance (answering 'can you survive on 50 g?'), but optimal for lean body mass and health requires substantially more. Norton applies it to the Game Changers documentary: every dietary intervention compared against the Standard American Diet will 'look amazing because the standard american diet is such an awful diet' — the comparator is the real variable, not the intervention.

Norton's synthesis represents a practical integration of the sometimes-conflicting literature on keto and exercise. Ultra-endurance studies show parity or personal-preference-level differences. Studies on high-intensity or strength performance show consistent disadvantages in ketogenic conditions. The mechanism follows substrate economics: fat oxidation is simply too slow to supply ATP for the glycolytic demands of high-intensity work, regardless of how well-adapted the athlete becomes.

Attia's framing makes the point elegantly: 'you only need about 50 grams a day if we're talking about preventing you from being in a negative nitrogen balance but what's optimal for health or lean body mass so that's a very different question.' This is also the frame Norton uses to explain why a bodybuilder 'not needing' exogenous testosterone to build muscle is consistent with testosterone being the biggest single driver of maximum muscle mass.

The exchange starts with Attia asking Norton whether combining carbohydrate and protein post-resistance training — rather than protein alone — would 'hit it at both ends' by simultaneously reducing degradation and increasing synthesis. Norton explains that there is probably some degradation that is needed for remodeling, but on balance the anti-catabolic effect of insulin is a real pathway. The practical implication is that if your goal is maximizing net protein accretion rather than just maximizing synthesis, the carbohydrate + protein combination after training has a theoretical edge — though the magnitude in real-world protein-equated trials is modest.

Norton is careful to emphasize that the keto group still increased lean body mass — the finding is 'less accrual,' not 'no accrual.' The glycogen-water confound is real: carbohydrates cause glycogen storage which stores roughly 3 g water per gram of glycogen, so some of the lean mass difference could be water. The second study's strength difference (1RM squat and bench press) is the more compelling data point because strength gains track contractile protein accretion more closely than DEXA-measured lean mass.

Attia describes making 'all the standard mistakes' entering the keto diet — primarily, making zero reduction in his already 'maniacal' training volume. By week five he was 'staggeringly and upsettingly miserable.' At 12 weeks he finally recovered his aerobic base, but anaerobically was still far below pre-keto baseline. He stayed on the diet for three years with only a single deviation, which means the 18-month anaerobic recovery happened under perfect conditions. His biggest regret is not having taken muscle biopsies throughout for proteomics and metabolomics work. He acknowledges the 18-month timeline could include psychological components but suspects there is a deeper physiological explanation not yet identified in the literature.

Attia says: 'what i'm saying is we need a hard metric for it we really need some kind of hard metric to explain this because if we look at things like okay let's look at blood ketosis yeah it's clearly not... it's clearly not blood ketones... it's not lipolysis... we see fat oxidation within six days.' His regret is not having collected muscle biopsies during his personal experiment, which might have revealed differences in mitochondrial enzyme profiles, substrate transporter expression, or other molecular adaptations that take months to develop. Norton agrees this is a major gap.

Attia applies the same frame to protein: 'you only need about 50 grams a day if we're talking about preventing you from being in a negative nitrogen balance but what's optimal for health or lean body mass so that's a very different question.' Norton uses it to address the Game Changers documentary: comparing any deliberate diet to the Standard American Diet will produce apparent benefits because the SAD is the worst possible comparator. The 'relative to what' principle is the corresponding research design version of the same point.

The mechanistic explanation is substrate availability: fat oxidation can supply ATP fast enough to sustain output up to roughly the lactate threshold (which sits around 60–70% VO2max in trained athletes). Above that threshold, glycolytic flux is required, and the glycolytic pathway is rate-limited in keto-adapted athletes by reduced glycogen stores and blunted glucose oxidation enzyme expression. Attia's 18-month anaerobic-recovery story is a personal illustration of exactly this ceiling.