6.2) Weight Response
Your weight depends on the number of calories you consume, how many of those calories you store, and how many you burn up. But each of these factors is influenced by a combination of genes and environment. Both can affect your physiology (such as how fast you burn calories), as well as your behavior (the types of foods you choose to eat, for instance). The interplay between all these factors begins at the moment of your conception and continues throughout your life.
The balance of calories stored and burned depends on your genetic makeup, your level of physical activity, and your resting energy expenditure (the number of calories your body burns while at rest). If you consistently burn all of the calories that you consume in the course of a day, you will maintain your weight. If you consume more energy (calories) than you expend, you will gain weight.
Excess calories are stored throughout your body as fat. Your body stores this fat within specialized fat cells (adipose tissue) — either by enlarging fat cells, which are always present in the body, or by creating more of them. If you decrease your food intake and consume fewer calories than you burn up, or if you exercise more and burn up more calories, your body will reduce some of your fat stores. When this happens, fat cells shrink, along with your waistline.
Genes contribute to obesity in many ways, by affecting appetite, satiety (the sense of fullness), metabolism, food cravings, and body-fat distribution. Emotional eating can also play a large part in this. Some individuals are predisposed to eat more during emotional or stressful times and will need to factor that in when implementing healthy eating and exercise routines.
6.2.1 Body Mass Index
Your ability to regulate your body mass index
Body Mass Index (BMI) is commonly used to assess obesity. BMI has two components, weight and height, and can be influenced by body fat and body composition. BMI does not take into account body-fat percentage, muscle mass, bone thickness or genetic predisposition to a certain frame. Genetic factors account for around 40–70% of variability in BMI. As much as 21% of BMI variation is accounted for by common genetic variations.
BMI is one of many factors that you and your healthcare provider can use to help assess your health. The formula is BMI = kg/m2 where kg is a person’s weight in kilograms and m2 is their height in meters squared. There are many tools available online to calculate your BMI. A BMI of 25 or more is considered to be overweight, while the healthy range is 18 to 25.
If you have variations in this panel, you may want to consider the following to improve your health:
- Eat smaller food portions and increase your activity level.
- Eliminate trans fats by avoiding fried foods, baked goods, mixes, candy and chips.
- Replace trans and saturated fats with unsaturated fats. Foods rich in unsaturated fats include avocados, nuts, fish, and plant-based oils.
- Increase your daily activity by taking the stairs, going for a walk, joining an exercise program or a gym.
- For more information on dietary changes, talk to your healthcare professional.
Some examples of genes that have been associated with ability to regulate body mass index are:
FAIM2: Produces a protein which protects cells from apoptosis (death of cell). Variation is associated with an increase of 0.82 kg/m2 in BMI, 2.12 cm in waist circumference, and 2.82 kg weight.
FTO: Encodes the fat mass and obesity-associated protein. Affects the hypothalamus region of the brain which regulates appetite, energy intake, and satiety. Associated with difficulty feeling full, and risk of obesity. Each variation is associated with an increase of 0.33-1.12 kg/m2 BMI.
MC4R: Plays an important role in eating behaviour and obesity. Variations in this gene are linked to dominant obesity, increased BMI, problematic eating behaviour, insulin resistance, and type 2 diabetes. Each variation is associated with a 0.20-1.00 kg/m2 increase in BMI.
MTCH2: Associated with increased BMI and obesity. Variation is associated with an increased risk of gaining fat tissue following short-term dieting, including yo-yo/starvation dieting.
SH2B1: Expressed particularly in the hypothalamus, a crucial center for energy balance and regulation of food intake. Variations can disrupt hormonal signaling and are associated with obesity, increased snacking and increased fat intake. Variation is also associated with type 2 diabetes independently of BMI.
TMEM18: Associated with insulin and blood sugar levels. This gene affects energy levels through insulin and glycogen signaling. Variation is associated with a 0.26 kg/m2 lower BMI.