Energy-PTC-2025-1 (1)

Energy

  • Energy = theoretical construct explaining movement & chemical reactions; understood by predictive power.

  • Human body stores chemical energy; converts it into kinetic (mechanical work) & thermal (heat) energy.

  • First law of thermodynamics: energy cannot be created/destroyed, only transformed.

Calories

  • Calorie = heat required to raise 1 g1\,g water by 1∘C1^{\circ}C at 1 atm.

  • In nutrition: always kilocalories (kcal).
    • 1 kcal=1000 cal=4184 J=4.184 kJ1\,\text{kcal}=1000\,\text{cal}=4184\,\text{J}=4.184\,\text{kJ}

  • Food labels may list kJ; convert via kcal=kJ4.184\text{kcal}=\frac{\text{kJ}}{4.184}.

  • Atwater general factors (metabolizable energy):
    • Protein & carbohydrate: 4 kcal⋅g−14\,\text{kcal·g}^{-1}
    • Fat: 9 kcal⋅g−19\,\text{kcal·g}^{-1}
    • Alcohol: 6.9 kcal⋅g−16.9\,\text{kcal·g}^{-1}

Energy Expenditure (EE)

  • Components (average sedentary person):
    • Basal/Resting Metabolic Rate (BMR/RMR) ≈ 60–70 % of EE.
    • Non-Exercise Activity Thermogenesis (NEAT).
    • Exercise Activity Thermogenesis (EAT).
    • Thermic Effect of Feeding (TEF) ≈ 10 % (varies 10–25 %).

  • EE functions: movement, heat, chemical reactions.

Energy Intake

  • Gross energy of food measured via bomb calorimetry.

  • Digestive & urinary losses (2–12 %) → Metabolizable Energy (ME).

  • Atwater factors approximate ME; protein net ≈ 3.2 kcal⋅g−13.2\,\text{kcal·g}^{-1}.

Thermodynamics & Energy Balance

  • Equations:
    • ΔBody Energy=Intake−Expenditure\Delta\text{Body Energy}=\text{Intake}-\text{Expenditure}

  • Principles:
    • Surplus → energy stored.
    • Deficit → energy lost.
    • Balance → maintenance.

Substrate Metabolism vs. Energy Balance

  • Acute “fat burning” not equal to long-term fat loss.

  • Body constantly stores & oxidizes multiple substrates; conversion among macros possible.

  • Effective diet must: A) raise EE, B) lower intake, or C) improve nutrient partitioning.

Energy vs. Mass

  • Body weight ≠ body energy exactly.
    • Water, glycogen, GI contents, electrolytes, menstrual cycle, drugs alter weight without energy change.

  • Nutrient partitioning (P-ratio):
    • P=0P=0 → all weight change = fat; P=1P=1 → all = lean mass.

  • Muscle gain + fat loss can co-occur within same energy state (recomposition).

  • Requirements for muscle synthesis: protein, water, energy (which can come from stored fat).

  • Even at 6 % bf, ~49 000 kcal remain for building tissue.

Body Recomposition Evidence

  • Numerous studies in novices, elderly, overweight & even elite athletes demonstrate simultaneous fat loss & muscle gain.

  • Advanced lifters can still recomp with optimized training & nutrition (DXA-verified cases).

Calculating Energy Balance from Composition Change

  • Human tissue energy densities (Hall 2008):
    • Glycogen 42074207 kcal·kg⁻¹
    • Protein 47084708 kcal·kg⁻¹
    • Fat 94419441 kcal·kg⁻¹
    • Average Lean Body Mass 18161816 kcal·kg⁻¹

  • Example: +3 kg LBM & –1 kg fat → 3×1816−9441=−3993 kcal3\times1816-9441=-3993\,\text{kcal} i.e. deficit.

3500 kcal Rule & Variants

  • Pure adipose tissue (~87 % TG) ≈ 8260 kcal⋅kg−18260\,\text{kcal·kg}^{-1} (≃ 3750 kcal·lb⁻¹).

  • Traditional 3500 kcal·lb⁻¹ assumes 20 % LBM loss.

Surplus/Deficit Paradoxes

  • Weight gain in deficit possible when lean mass ↑ faster than fat ↓ (energy density difference 5.2 : 1).

  • Fat loss in surplus possible if muscle gain ≥5.2× fat loss.

  • Fat gain in deficit possible with severe muscle loss (detraining, illness, drugs).

“Maintenance Intake” Misconception

  • Stable scale weight ≠ energy balance; recomp can mask true deficit/surplus.

Adaptive Thermogenesis (AT) vs. “Metabolic Damage”

  • AT: EE adapts (±10 %, up to −40 % in very lean contest prep).

  • Driven mainly by body-fat %, also current intake, hormones (leptin, thyroid).

  • No permanent metabolic damage; EE resets with body composition.

  • Yo-yo weight regain explained by return to old habits, not damaged metabolism.

Refeeds & Diet Breaks

  • Refeed rationale: transient leptin/EE bump → largely TEF; EE ↑ only ~7 % on 40–50 % surplus.

  • Overfeeding stores majority of energy; little persistent metabolic lift.

  • RCTs: intermittent restriction ≈ continuous when cumulative deficit equal.

  • MATADOR & later studies: diet breaks aid adherence, not metabolism.

Estimating Energy Expenditure

Basal Metabolic Rate

  • Preferred formula: Cunningham 1991 (aka Katch-McArdle):
    BMR=370+21.6×FFMkg\text{BMR}=370+21.6\times\text{FFM}_{kg}

  • Alt. physique-athlete formula (Tinsley 2018): RMR=24.8×BWkg+10\text{RMR}=24.8\times BW_{kg}+10 (for very lean/muscular).

Physical Activity Level (PAL)

  • Categories & multipliers (sedentary≈1.2, somewhat active≈1.35, active≈1.55, very active≈1.75).

  • Validate client self-report; 60 % overestimate activity.

Strength Training EE

  • Intense lifting ≈ 0.1 kcal⋅kg−1⋅min−10.1\,\text{kcal·kg}^{-1}\text{·min}^{-1}

  • Shortcut: RT EE=0.25×BWkg×work sets\text{RT EE}=0.25\times BW_{kg}\times \text{work sets}

  • Add TEF on workout calories.

Activity Trackers

  • Reasonable for step counts; poor for kcal (errors 20–60 %).

  • Step-based PAL guide: <7500 sedentary; 7500–9999 somewhat; 10 000–12 500 active; >12 500 + intense = highly active.

Thermic Effect of Food (TEF)

  • Mixed meals TEF 10–25 %.
    • Higher (≈25 %) in lean, high-protein, whole-food diets with unsaturated fats/MCTs.
    • Lower (≈10 %) in overweight, processed diets.

  • Protein TEF ≈20 %, carbs/fats ≈15