Macro partitioning
Short-term fluctuations in energy balance (surpluses or deficits) are compensated almost exclusively by changes in fat stores, rather than carbohydrate or protein stores.
Your body uses fat stores to absorb day-to-day overeating or undereating, not muscle or glycogen. This means you can fluctuate in energy balance daily without immediately changing your body composition, but sustained surpluses will eventually increase fat stores because fat is the primary storage buffer. Do not panic over daily weight changes; they are mostly water and glycogen.
This study demonstrates that carbohydrate, fat, and protein stores are closely regulated by adjusting oxidation of carbohydrate or protein, rather than fat, in response to day-to-day fluctuations in energy balance.
Why this rating
High-quality controlled metabolic ward study with direct measurement of substrate oxidation via respiratory chamber, though limited to 24-hour periods.
Source
Short-term energy balance: relationship with protein, carbohydrate, and fat balances
William G.H. Abbott et al. · American Journal of Physiology-Endocrinology and Metabolism · 1988
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