Metabolism Explained Simply

Metabolism is a term everyone uses without always understanding it. "I have a slow metabolism" is one of the most common excuses for weight gain, but the reality is often more nuanced. This guide demystifies metabolism and gives you the real tools to optimize it.

Steps

1

Calculate your Basal Metabolic Rate (BMR)

BMR represents the energy spent at rest to maintain vital functions: breathing, circulation, temperature regulation, and brain activity. It accounts for 60% to 75% of your total energy expenditure. It mainly depends on your lean mass, age, sex, and height.

2

Understand NEAT (Non-Exercise Activity Thermogenesis)

NEAT encompasses all non-sport activities: walking, cleaning, typing, or fidgeting in your chair. It represents 15% to 30% of total expenditure and varies wildly between individuals. The difference in NEAT between two people can reach 2,000 kcal per day.

3

Integrate structured physical activity

Voluntary physical exercise (sports, weightlifting, running) only represents 5% to 15% of total expenditure for most people. It's an important lever but often overestimated. One hour of jogging burns about 400-600 kcal—roughly the equivalent of a croissant and a hot chocolate.

4

Discover the Thermic Effect of Food (TEF)

TEF represents the energy spent to digest, absorb, and metabolize nutrients: about 10% of total intake. Protein has the highest TEF (20-30%), carbohydrates a moderate TEF (5-10%), and lipids the lowest (0-3%). A high-protein diet therefore burns slightly more calories.

5

Bust metabolic myths

No, eating 6 small meals doesn't speed up metabolism. No, some foods don't "burn" fat. No, skipping breakfast doesn't put your metabolism into "starvation mode." The real levers are muscle mass, daily NEAT, and diet quality.

BMR, NEAT, TEF: The components of your expenditure

Your Total Daily Energy Expenditure (TDEE) is the sum of four components. Basal Metabolic Rate (BMR) is the largest: between 1,200 and 2,000 kcal depending on your profile, it primarily depends on lean mass (muscle burns more energy than fat, even at rest).

NEAT is the most variable component and the most underestimated lever. A sedentary office worker has a NEAT of 200-300 kcal/day, while an active server can reach 1,000-1,500 kcal. Walking more, taking the stairs, and standing up are simple but effective strategies.

The Thermic Effect of Food (TEF) accounts for about 10% of total caloric intake. A 2,000 kcal diet generates about 200 kcal of TEF. Whole, protein-rich foods maximize this component, while ultra-processed foods minimize it.

Why metabolism slows down (and how to avoid it)

Metabolism naturally decreases with age, mainly due to the loss of muscle mass (sarcopenia). Starting at age 30, we lose about 3% to 8% of muscle mass per decade without resistance training. Strength training is the most effective remedy against this decline.

Very restrictive diets (less than 1,200 kcal) trigger a reduction in metabolism beyond what weight loss explains. The body reduces NEAT (you move less unconsciously), lowers thyroid hormones, and increases metabolic efficiency. This is the famous "metabolic adaptation."

To maintain an efficient metabolism: practice strength training regularly, don't drop too low in calories (never below BMR), maintain a high protein intake during weight loss, and keep a high level of daily activity (NEAT).

Metabolic adaptation during dieting

When you reduce your calories to lose weight, your body adapts to conserve energy. This metabolic adaptation is proportional to the severity and duration of the restriction. It manifests as a drop in BMR, reduced NEAT, and increased hunger.

The most famous study on this subject followed participants from "The Biggest Loser": 6 years later, their metabolism remained reduced by 500 kcal/day compared to what would be expected for their weight. Extreme diets leave lasting metabolic marks.

The strategy to minimize this adaptation: moderate caloric deficit (300-500 kcal below TDEE), high protein intake (1.6-2.2 g/kg), regular strength training, and periodic diet breaks (weeks at maintenance calories). Patience always beats severity.

FoodCraft Tip

Calculate your TDEE accurately

The FoodCraft TDEE calculator combines scientifically validated formulas (Mifflin-St Jeor, Harris-Benedict) with your actual activity level to estimate your daily energy expenditure. It's the essential starting point for any nutritional strategy.

Meal planning adapted to your metabolism

The FoodCraft AI meal planner takes your caloric goals and macronutrient distribution into account to suggest menus that support your metabolism. It prioritizes nutrient-dense foods and appropriate protein intake.

Frequently asked questions

Can you really "boost" your metabolism?
The real levers are muscle mass (strength training increases BMR), NEAT (moving more daily), and adequate protein intake (high TEF). Teas, spices, and "fat-burning" supplements have negligible effects (10-50 kcal/day), far below marketing promises.
Does intermittent fasting slow down metabolism?
With equal caloric intake, intermittent fasting does not slow down metabolism. Studies show that BMR remains stable during fasts of 24 to 72 hours. It is prolonged caloric restriction that slows metabolism, not meal frequency.
Does eating at night make you gain more weight than eating in the morning?
Meal timing has a minor impact compared to the total amount of calories consumed. However, some studies suggest that metabolism is slightly more efficient in the morning. In practice, eat when it suits you and allows you to control your total intake.
Is metabolism genetic?
Genetics influence BMR (about 40% variation), but differences between individuals of the same height, age, and body composition are generally less than 200-300 kcal/day. Environment and habits (activity, diet) have a much greater impact than genetics.
How do I know if my metabolism is slow?
A "slow metabolism" is often a perception rather than a measurable reality. Overweight individuals actually have a higher BMR than thin people (more mass to maintain). If you suspect a real metabolic problem, a thyroid check is the first test to perform.

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