Sunday, June 22, 2025

TEF and Metabolic Flexibility: Burning the right fuel at the right time with minimal waste

  1. Thermic Effect of Food (TEF)


Definition: The energy required to digest, absorb, and metabolize food.


๐Ÿ”ฅ Thermic Effect by Macronutrient:


Macronutrient TEF % of Calories Consumed


Protein 20–30%

Carbohydrates 5–10%

Fats 0–3%



➡️ Protein has the highest thermic effect—this is part of why it's key in body recomposition and fat loss.



๐Ÿ”„ 2. Metabolic Flexibility


Definition: Your body’s ability to switch between fuel sources: fat, glucose, ketones, and protein-derived substrates (GNG).


A metabolically flexible athlete can:


Burn glucose efficiently during sprints/lifting


Burn fat and ketones during long, steady-state efforts


Use gluconeogenesis (GNG) under carbohydrate scarcity (like on keto or carnivore)


๐Ÿ”‹ 3. Fuel Systems in Elite, Conditioned Athletes


๐Ÿ”น Glycolysis (Carbs → Glucose → ATP)


Anaerobic, fast


Used for short, high-intensity bursts (e.g., sprints, heavy lifts)


Creates lactate and potential fatigue



๐Ÿ”น Fat Oxidation (Lipolysis + Beta-Oxidation)


Aerobic, slow


Preferred during low to moderate intensity, long duration


Becomes more efficient on low-carb or keto diets



๐Ÿ”น Ketosis


Liver converts fat into ketones (BHB, acetoacetate)


Brain and muscles adapt to use ketones


Best suited for ultra-endurance, fasting states, or when carbs are chronically low


Can spare muscle glycogen during low/moderate output



๐Ÿ”น Gluconeogenesis (GNG)


Creation of glucose from non-carb sources (e.g., amino acids, lactate, glycerol)


Supports brain and red blood cell glucose needs in low-carb states


Highly active in keto-adapted athletes



๐Ÿง  4. Metabolic State in Highly Conditioned Athletes


Elite athletes often achieve:


Efficient fat oxidation, even when not in ketosis


Quick access to glycogen stores when needed


Better mitochondrial density and oxygen efficiency


Lower lactate accumulation at high intensities


Elevated GNG capacity without losing muscle due to hormonal signaling (like increased growth hormone and norepinephrine)


๐ŸŽฏ Carnivore / Keto Athlete:


When deeply adapted:


High TEF from protein can increase resting metabolic rate


Low insulin environment favors fat mobilization and ketone production


Metabolic flexibility improves if training stimulus remains high


GNG from protein and glycerol ensures brain + muscle glucose without carbs



➡️ Combine this with fasted training, strategic refeeding (cyclical keto), and hormone regulation, and you're training the body to become an engine of perpetual transformation—burning the right fuel at the right time with minimal waste.

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