Metabolomic studies identify elevated levels of ketone bodies, branched-chain amino acids, and trimethylamine-N-oxide (TMAO) in individuals consuming habitual meat-rich diets, reflecting a metabolic shift toward fat oxidation and protein catabolism, which may have provided evolutionary advantages during periods of carbohydrate scarcity but are now associated with metabolic and cardiovascular risk in modern contexts.

When a person eats mostly meat and very few carbohydrates, the body stops using sugar for energy and starts breaking down fat and protein instead. The liver turns fat into ketones to fuel the brain and muscles, and it uses amino acids from meat to make new glucose. Gut bacteria that digest protein become more active and produce a compound called TMAO, which enters the blood. The liver also becomes less responsive to insulin, which keeps glucose production high. These changes help the body survive without carbs but can damage blood vessels and increase disease risk over time.