Energy expediture and its role in weight gain and lose

We use our net energy for maintenance (average daily expediture is 2000 kcal for female, 2500 kcal for male), for physical activity (exercising) and for growth. Our daily energy expediture can be higher or lower, depending on body size, illness or physical activity. The maintenance part is essential for our survival (things such as heart beat, brain function, respiration).

Now i will introduce some new terms. Basal maintenance in fasting state is called Basal Metabolic Rate (BMR). To this we will add the energy cost of digestion and absorption (dietary induced thermogenesis - approx. 10% of the caloric value of the meal). BMR covers 60-70% of the daily energy expediture and it is different between individuals, depending of the lean body mass (body mass remaining after we subtract the fat). Tall people with lot of muscle will have a much higher BMR than short fat people.

Physical activity is measured by PAL (Physical Activity Level) and is defined by the daily amount of physical activity of a person. This vary from 1.4 for sedentary people to 2.0 for athletes, with 1.6-1.7 being the average Joe. Can be measured though the oxygen consumption (indirect calorimetry).

As for growth, we will think at the net energy required to make extra tissue. It is close to zero for weight stable adults, relevant for children and pregnant women.

We store energy as fat, a dense and easy to use form of energy. The average amount of fat stored by a normal individual is 90.000 kcal (enough to support us for 30 days of fasting, but this can last for months if you are obese). Average amount of proteins stored is 36000 kcal, but you can use only 12000 kcal in case of emergency, before you start to compromise some of the normal body functions. Average amount of carbohydrates stored is 1400 kcal in the muscle and 350 kcal in the liver as glycogen, and it is used to maintain the blood glucose level in between meals.

When the energy intake is exceeding the energy expediture, the excess is stored as fat and we will experience weight gain. After a certain margin (let's say 600 kcal), the body weight tends to level off after a while, even if initially will go up, as the energy expediture also increase with the weight gain, until a new equilibrium is reached at a higher body weight. Why, you will ask? Because the BMR will increase as the body weight increase, even if the BMR is mainly determined by the lean body mass. The energy cost of the physical activity will be higher with greater body-weight (you need more energy to use your body as your overall body mass increase.

The opposite happens if we lose weight. Weight loss is rapid at first, but progressively slows down as the energy deficit decrease. Losing weight, the energy expediture decrease as well as BMR and the energy required for physical activity decrease, until a new equilibrium point is reached. This is the reason why every diet will work well at first, but lose efficiency over time.

Next post will be about weight management and obesity.

Energy balance (food related)

As i was talking quite a lot about proteins, i will stop here. I will start a new series of articles, related to energy homeostasis and balance.

First i need to underline some definitions.

Energy balance is defined as the balance between energy intake (in) and energy expediture (out).

We have three situations:

Energy intake is bigger than the energy expediture, you are gaining weight (energy is stored as fat).
Energy intake is lower than the energy expediture, you are losing weight (fat used as energy).
Energy intake is equal to the energy expediture, you keep the same weight.

Energy intake - via macro-nutrients (carbohydrates, fat and protein) - they contain energy, used as fuel or stored as body fat.

Now i will speak about the food intake and some specific qualities.

Satiety - is the feeling of satisfaction that occurs after a meal. This will prevent you from eating until next meal.
Satiation - feeling of satisfaction and fullness that occurs during a meal. This will make you to stop eating.
Hunger - uncomfortable sensation caused by lack of food.
Appetite - integrated response to the sight, smell, thought or taste that triggers eating.

Now, understanding these four notions is the key to any successful diet. 

While the satiety determines how much time passes between meals, the satiation determines how much food is consumed during a meal. Foods promoting satiation are very bulky, high water content and fiber, and they got strong sensory attributes. Veggies for example, eating them causes satiation. Thinking about texture, a watermelon is more satiating than watermelon juice. Calories ingested quickly are not properly sensed (think about fizzy drinks). Prolonged exposure time to the food (chewing) causes people to quit sooner and consume less energy overall.

Energy from fluids is less satiating than the energy from solids. That's why the consumption of sugary beverages may lead to over-eating, increasing the occurrence of obesity in many occasions. This is not accepted by the beverage industry and there is misleading advertising and powerful lobby against it. But, if we use our common sense, we can realize that it is true.

Enough for today, I will post soon about the factors determining the food intake (physiological, sensory, psychological and social, to name a few).

See you!
G.