Dr. Mark

Education

Energy balance

Units of energy

Calorie

A calorie is a unit of energy approximately equal to the energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.

In practice, “calories” almost always mean kilocalories.

1 food calorie = 1 kcal = 1 Cal = 1000 calories = 1000 cal.

In scientific papers you may also see another measure of energy — the joule (or kilojoule). 1 kcal = 4184 joules = 4.184 kilojoules (kJ).

Why does your body need these calories? The body needs energy for movement, heat production, and chemical reactions.

Total energy expenditure

Total energy expenditure looks like this:

  1. BMR (Basal Metabolic Rate) – the minimum amount of energy the body spends at complete rest to maintain vital functions: breathing, circulation, maintaining body temperature, and organ work.
  2. NEAT (Non-Exercise Activity Thermogenesis) – energy spent on everyday movements that are not workouts (walking, cleaning, cooking, involuntary movements (fidgeting), moving around the office, taking the stairs instead of the elevator. Accounts for 15–30% of total energy expenditure.
  3. TEF (Thermic Effect of Food) – energy spent digesting, absorbing, and processing nutrients and food. About 10% of total daily expenditure.

Components of total daily energy expenditure.

  • BMR = basal metabolic rate.
  • NEAT = non-exercise activity thermogenesis
  • TEF = thermic effect of food.

The body cannot digest or absorb all total energy consumed from food. Some components of food pass through the digestive system and are lost in feces (2–10%), and some is lost in urine (1–2%).

What remains is actual metabolizable energy: energy the body can use to produce heat, movement, or chemical reactions.

The most commonly used estimates of metabolizable energy today are based on the general Atwater factor system.

Atwater factors are:

  • 4 kcal per gram of protein or carbohydrate
  • 9 kcal per gram of fat
  • 6.9 kcal per gram of alcohol.

Thermodynamics

Energy cannot be destroyed. It can only be converted into another form.

  • Chemical energy is the stored form of energy in food and body tissues.
  • Kinetic energy, which produces mechanical work.

For example, the goal of muscle cells is to convert chemical energy into mechanical work — movement.

  • Thermal energy is the energy we feel as temperature. When we “burn” body energy, chemical energy is converted into thermal energy.

Energy balance

Based on the laws of thermodynamics, we can formulate the principles of energy balance.

  • If you consume more calories than you expend, your body stores energy (weight increases).
  • If you expend more calories than you consume, your body loses energy (weight decreases).
  • If you are in energy balance, your body maintains the same amount of energy (weight stays at the same level).

Why the scale often lies:

You will often see weight "fluctuations" that have nothing to do with fat:

  • Water and Glycogen: When starting a diet, you deplete glycogen. Since 1g of glycogen binds 3–4g of water, you experience a sharp drop in weight (water), not fat.
  • Bloating and Hormones: Menstrual cycles, excess salt, stress, and certain medications cause water retention. The scale goes up even though you are in a caloric deficit.

4. The Paradoxes of Recomposition: Deficit vs. Growth

Can you build muscle while losing fat? Yes.

Muscle tissue consists of water and protein. To build it, you need amino acids, water, and ATP (energy). The body can successfully "borrow" this energy from existing fat stores.

Fat Math:

To lose 1 kg of pure fat, you need to create a cumulative deficit of approximately 8,260 kcal. Fat is an extremely energy-dense "battery."

The Paradox of Gaining Weight in a Deficit:

If you train, you can lose fat while gaining muscle. Because muscle is less energy-dense than fat, the total number on the scale may even increase, despite your waistline shrinking.

The Inverse Paradox (Gaining Fat in a Deficit):

This is only possible through catastrophic muscle loss (e.g., complete cessation of training). If muscle is breaking down faster than you are burning fat, your body fat percentage increases — all while in a caloric deficit. This is a result of a lack of stimulus, not a caloric deficit.

5. Refeeds and Diet Breaks

When a deficit persists for too long, the body activates defense mechanisms: hunger rises and energy levels drop.

Refeed (1–3 days): Increasing calories to maintenance level (primarily via carbohydrates). This is not a "metabolic cure" but a tool for psychological relief and replenishing muscle glycogen before a heavy training session.

Diet Break (1–2 weeks): A complete pause of the deficit. It helps lower cortisol, "shed" stress-related water, and mentally prepare for the next phase of dieting.

The Bottom Line:

Don’t search for "metabolic magic." Success is built on protein control, structured resistance training, and a consistent weekly energy balance, which does not depend on "meal timing" or "glycemic index," but on the total energy intake over time.