Anywhere between 30 to 70% of our body weight is influenced by our genes. And the tendency to be obese is quite common among humans, as evident in high obesity rates, globally. This has led to the proposal of what is known as the thrifty gene hypothesis. According to this hypothesis, for most our existence as a species, food was scarce, necessitating opportunistic eating and storage of calories in the form of fat reserves for leaner times. Only in recent times do we have a wider array of food options and assured food supply throughout the day. Modern surplus and high caloric diet, combined with a crash in physical activity levels facilitated by motorization of various tasks, has led to a worldwide obesity epidemic.
A quick look around will tell you that children of overweight or obese parents, tend to be overweight too, demonstrating the heritability of body weight. Another example is that two people who are on the same weight loss program will respond differently. How our body responds to exercise stimulus and dietary restriction is variable and influenced by genes.
Studies carried out on twins help understand the association between genes and body weight better. Monozygotic, or identical twins share the same genes and the same prenatal environment and tend to have similar body weight while dizygotic twins, on the other hand, share the same prenatal environment but not the genes and could vary significantly in body weight.
There are many genes that influence body weight and our tendency to gain weight, notable among those genes is the the FTO gene. The FTO gene is thought to influence hypothalamic regulation of feeding behavior by modulating the “hunger hormone” ghrelin. For those who carry the “normal type” of this gene, feeding behavior is normal and well regulated. Those who carry the “abnormal type,” may be perpetually hungry due to elevated levels of ghrelin. These individuals may tend to overeat thus predisposing them to obesity. These individuals have also been shown to prefer high calorific food and a tendency for weight regain after weight loss.
However, knowledge of the presence of this polymorphism can help mitigate its deleterious effects. For example, a high fiber and high protein diet helps improve satiety. Exercise such as running or cycling has been shown to lower the hormone level and, thereby, hunger levels. Exercise lowers the effect of FTO variants on obesity by nearly 80%.
MC4R is another gene that is found to increase appetite and is associated with decreased feeling of fullness. Mutations in the MC4R gene was found to contribute to central obesity among Asian Indians. When people with this mutation consumed a high fat diet, it increased their risk for metabolic syndrome as against people with this mutation who ate healthy meals. Stress was another factor that compounded the effect of the mutation on the risk for obesity, studies show that increased mental stress and energy intake resulted in heightened risk for obesity among people with MC4R mutation.
Another factor that determines body weight is our body’s ability to store excess calories as fat and subsequent utilization of these calories when needed. The PPAR gamma genes are associated with this cycle and variations of these genes determine how much fat is stored and how quickly our body breaks down such fat for energy.
PPAR gamma plays an important role in the physiological response to dietary fat in humans. It mediates adipocyte differentiation and fat storage based on the diet. Body Mass Index (BMI) is an important indicator of obesity and the dietary fat that is consumed translates into BMI depending upon the type of PPAR gamma gene present in the body. A variant of the PPAR gamma gene is associated with higher BMI when the total fat intake was high.
People who carry the abnormal PPAR gamma gene and who have a high fat diet are found to be more obese than people who carry the normal gene. The abnormal PPAR gamma gene is also associated with insulin resistance, which in turn could increase obesity risk.
When you are trying to lose weight and you carry the abnormal PPAR gamma gene, a high fat diet can hinder weight loss. Therefore, such individuals would benefit from a low fat diet.
Obesity numbers are rising, with 20 million women in India estimated to be obese as against 9.8 million men, making it important to use available tools to understand one’s physiology better. Genetics is one such tool, among others. Body weight is defined, to a large extent, by genes and finding out about the gene variant that you carry can help you understand the effect of these variants.
Find out which variations of these genes you carry and more at www.xcode.in
Nutrigenetics, fitness genetics, health genetics are all nascent but rapidly growing areas within human genetics. The information provided herein is to be read and understood in that context.”