Nutrition Without the BS (Part IV— Weight Gain and Loss)

This is the part IV of my extensive notes from the course on Nutrition. It starts with Part I here.

When energy intake exceeds energy expenditure, the excess energy is stored as body fat, and an individual will experience weight gain. When energy intake exceeds energy expenditure by a certain margin (for instance 600 kcal), weight shoots up initially but tends to level off after a while.

Body weight is not increasing in a linear fashion because energy expenditure also increases weight gain, and as a consequence, a new equilibrium is reached between energy expenditure and energy intake, except at a higher body weight.

Why is energy expenditure going up when you gain weight? There are two main reasons:

1) the basal metabolic rate (BMR) will increase as weight increases. People gain fat but also lean body mass as they gain weight. The basal metabolic rate is mainly determined by the amount of lean body mass.

2) the energy cost of physical activity will be higher with greater weight. Lifting up your arm, walking, maintaining posture all take more energy as the weight of the limbs and overall body mass increases.

Non-obese adult males have a body fat percentage between 10–20% while non-obese adult females carry around 20–30% body fat. Morbidly obese individuals can have a body fat percentage exceeding 50%. The percentage body fat gradually increases as people age because muscle is being replaced by fat.

Body fat distribution

Excess body fat can be stored at multiple sites in the body. Most of the body fat is stored below the skin as so-called **subcutaneous fat**. A relatively small — but a clinically relevant amount of body fat is located within the abdominal cavity connected to the intestine, pancreas, and other organs. This so-called intra-abdominal or visceral fat is believed to be more detrimental to health compared to the subcutaneous fat. People that carry a lot of visceral fat have a comparatively large waist and are considered to have central or abdominal obesity. However, it should be realized that not all the fat around the waist/abdomen is visceral fat. The fat on the outside that can be pinched is subcutaneous fat. Proper estimates of the amount of subcutaneous and visceral fat can be obtained using Magnetic Resonance Imaging. With this technique, the cross-sectional image is made of the abdomen visualizing the different fat depots and allowing calculation of the visceral and subcutaneous fat surface area.

The amount of visceral fat is relatively well correlated with waist circumference or waist to hip ratio (ratio of waist circumference to hip circumference), which can be much more easily assessed using a tape measure.

Causes of Obesity

1. Psychological Factors

There are two broad categories of psychological reasons for overeating:
 
 — Emotional/comfort eating happens when people eat because they are upset or stressed.
 — External factors are involved when people eat due to external cues, such as sight or smell of food.

Because people differ in their psychological makeup, strategies to manage psychological eating have to be found on an individual level. There are no one-size-fits-all solutions.
 
2. Social Factors

In many developed countries, obesity rates are reversely correlated with the socio-economic class.

It is also connected to the social network individual belongs to. Social norms in the group dictate what is acceptable regarding eating habits and obesity.
 
3. Environmental factors

We are surrounded by food, images of food and ads for food. Portions in restaurants are increasing. More of us have desk jobs, and commute in a car/train/bus instead of walking, etc.

4. Genetic Factors

Hereditary factors in obesity have been confirmed by twin, adoption, and twin adoption studies. All these study approaches reveal that the influence of genetics on obesity is very large, whereas the environment in which a child is raised has a surprisingly little impact.

A defect in leptin production is relatively rare, but the people who have it, are always hungry, which leads to severe obesity.

So far, about seventy-five common genetics variants have been linked to obesity, but these explain only about 2–4% of the variability in BMI that is attributable to genetics, which means there is still a lot we don’t know.

Genetic factors also determine body fat distribution. Lipodystrophy is a condition where individual store very little fat on their lower extremities, whereas the amount of fat stored around the waist is normal or elevated. Scientists are trying to find these fat distribution genes.

CONCLUSION:

• People with unfavorable genetics are more prone to overeat
• Environmental factors explain an overall increase in obesity, genetic factors explain inter-individual differences.