In 2012, up to 35% of US adults and 17% of teens were obese ().
Many people blame obesity on poor dietary choices and inactivity, but it's not always that simple.
Other factors can have powerful effects on body weight and obesity, some of which are outside of the person's control.
These include genetics, environmental factors, certain medical conditions and more.
This article lists 9 compelling reasons why obesity is not just a choice.
1. Genetics and Prenatal Factors
Health is especially important during early life, as this affects health later on. In fact, a lot can be determined while the fetus is still in the womb ().
The mother's diet and lifestyle choices matter a great deal, and may influence the baby's future behaviors and body composition.
Studies show that women who gain excessive weight during pregnancy are more likely to have heavy 3-year-olds (, ).
On the same note, children who have obese parents and grandparents are much more likely to be obese than kids with normal-weight parents and grandparents (, ).
Furthermore, the genes we inherit from our parents may determine our susceptibility to weight gain ().
Although genetics and early life factors are not exclusively responsible for obesity, they do contribute to the problem by predisposing people to weight gain.
About 40% of overweight children will continue to be heavy during their teenage years, and 75−80% of obese teenagers will become obese adults ().
Bottom Line: Genetics, the mother's weight and family history can all increase the likelihood of childhood and adult obesity.
2. Birth, Infancy and Childhood Habits
Although the reason is unknown, children born via C-section seem more prone to obesity later in life (, ).
This is also true for formula-fed infants, who tend to be heavier than breast-fed infants (, , ).
This may be because the two groups develop different gut bacteria, which can affect fat storage ().
It is important to note that these factors are generally not made of either the mother or baby, yet they seem to be linked to the child's obesity risk.
Additionally, forming healthy dietary and exercise habits during childhood may be the most valuable prevention against obesity and lifestyle-related diseases.
Bottom Line: Certain childhood factors may affect the risk of obesity later on. These include way of birth, breastfeeding and childhood dietary and exercise habits.
3. Medications or Medical Conditions
Many medical conditions and diseases require medication to treat.
Unfortunately, weight gain is a common side effect of many such medications. These include diabetes medications, antidepressants and antipsychotics (, , ).
These drugs may increase appetite, reduce metabolism or even alter the body's ability to burn fat — making it store fat instead of burning it.
Additionally, many common medical conditions can predispose to weight gain. A key example is hypothyroidism.
Bottom Line: Weight gain is a common side effect of many medications. These include diabetes medications, antidepressants and antipsychotics.
4. Powerful Hunger Hormones
Hunger and uncontrollable eating are not just caused by greediness or lack of willpower.
Hunger is controlled by very powerful hormones and brain chemicals, involving areas of the brain that are responsible for cravings and rewards (, ).
Many obese people have impaired function of these hormones, which alters their eating behavior and causes a strong physiological drive to eat more.
The brain has a reward center, which lights up and starts secreting dopamine and other feel-good chemicals when we eat.
This is the reason why most of us enjoy eating. This system also makes sure that we eat enough food to get all the energy and nutrients we need.
Junk food releases much more of these feel-good chemicals than unprocessed food. This yields a much more powerful "reward" in the brain (, , ).
Your brain may then seek more reward by causing powerful cravings for these junk foods. This can lead to a vicious cycle that resembles addiction (, , ).
Bottom Line: Hunger is controlled by powerful hormones. Obese people often have serious issues with many of these hormones, which causes a strong physiological drive to eat more and get fat.
5. Leptin Resistance
Leptin is a very important hormone that helps regulate appetite and metabolism ().
It is produced by fat cells, and sends a signal to the part of our brain that tells us to stop eating.
Leptin regulates the amount of calories we eat and expend, as well as how much fat our bodies store ().
The more fat contained in fat cells, the more leptin they produce. People with obesity produce very large amounts of leptin.
However, people with obesity tend to have a condition called leptin resistance ().
So even though our bodies are producing a lot of leptin, the brain doesn't see or recognize it. When the brain doesn't receive the leptin signal, it wrongly thinks that it is starving, even if it has more than enough body fat stored (, ).
This causes the brain to change physiology and behavior, in order to regain the fat that it thinks we're missing (, , ).
Hunger is increased, and energy expenditure is decreased, in order to prevent starvation. Trying to exert "willpower" against the leptin-driven starvation signal is almost impossible for many people.
Bottom Line: Leptin resistance is common in people with obesity. The brain doesn't sense the leptin that is produced, so it thinks that we are starving. This causes a powerful physiological drive to eat more.
6. Poor Nutrition Education
In our society, there are endless advertisements, health statements, nutrition claims and unhealthy foods.
Despite the importance of nutrition, children and adults are generally not taught how to eat properly.
Teaching children the importance of a healthy diet and proper nutrition has been shown to help them make better choices later in life (, , ).
Nutrition education is very important, especially when forming the dietary and lifestyle habits that you bring into adulthood.
Bottom Line: Teaching children the importance of proper nutrition is important, but nutrition education is generally lacking in society.
7. Addictive Junk Food
Some foods can be downright addictive.Food addiction involves being addicted to junk food in the same way drug addicts are addicted to drugs (, ).
This is actually much more common than you may think.
In fact, up to 20% of people may suffer from food addiction, and this number goes up to about 25% in overweight and obese people ().
When you become addicted to something, you lose your freedom of choice. Your brain chemistry starts making the decisions for you.
Bottom Line: Junk foods can be addictive, and up to 25% of overweight or obese people may suffer from food addiction.
8. The Effect of Gut Bacteria
Your digestive system hosts an immense number of bacteria, which are known as the gut microbiota.
Many recent studies show that these bacteria are incredibly important for health.
Interestingly, people with obesity tend to have different gut bacteria than normal-weight people ().
The gut bacteria in overweight or obese individuals may be more efficient at harvesting energy from food, increasing the total caloric value of the diet (, , ).
Even though our understanding of the relationship between weight and gut bacteria is limited, there is compelling evidence that these microorganisms do play an important role in obesity (, , , ).
Bottom Line: People with obesity have different gut bacteria than people who are at a healthy weight. This may cause obese people to store more fat.
9. The Environment
In some areas, buying healthy food is simply not an option.
These areas are often called food deserts, and are usually urban neighborhoods or rural towns without ready access to healthy, affordable food.
This is largely due to a lack of grocery stores, farmers markets, and healthy food providers within walking distance.
People in these regions are often poor, and may not have access to a vehicle to travel far to buy groceries.
Not being able to buy healthy and fresh foods limits the diet substantially, and increases the risk of problems like obesity.
Other environmental factors may also play a role in obesity, including artificial light from electric light bulbs, computers, phones and televisions.
Even though the link between screen use and obesity has been well established, most studies chalk this up to lack of exercise.
However, nighttime exposure to light and changes to the inner circadian rhythm may also contribute to obesity (, ).
Animal studies suggest that artificial light may alter the inner circadian clock, making rodents more susceptible to obesity and metabolic syndrome ().
Bottom Line: Several environmental factors can make us more susceptible to obesity, including food deserts and exposure to artificial light.
No One Chooses to be Obese
Obesity is a very complex problem.
It is not simply caused by greed, laziness or a lack of willpower. There are multiple factors at play, many of which occur within our brain and physiology.
A lot of these are completely out of our control, including genetics, childhood habits, medical conditions and hormones.