As a dietitian, there is no question I get that is more difficult to answer than this one. What causes obesity? Why do people have obesity? I have worked with thousands of people with obesity by now, and I know that the easy answers to this question do not suffice. They do not explain the full picture.
I also have seen enough patients that it is clear to me that obesity is not monolithic. All obesity is not the same. I think there is more than one cause of obesity. Of course, a person can have more than one of those factors playing into their own condition, but I see obesity as having distinct causes.
Cause of Obesity: Drive to Eat
Let's first address the portion of obesity that is caused by "simply" eating too much junk food. In my experience of working with thousands of patients, people who eat more energy dense foods like snack foods seem to have a much stronger drive to eat than people who don't eat those foods often.
It is not a lack of self control or willpower that leads people to eat more snack foods. It is just a much stronger drive to eat. The person who tends not to eat snack foods is not looking at snack foods and thinking, "I need to eat that," and then refraining. It just never occurs to their mind to desire the food in the first place, and if the desire does occur to them, it is not a very strong desire. On the other hand, the person who tends to eat snack foods very often has strong thoughts of wanting to eat those foods all day long.
It is also important to understand what underlies the drive to eat. In some people, it seems to be primarily a genetic-based tendency. In a vast majority of cases, there is not one specific gene that leads to an increased drive to eat. Rather, a combination of genes ups the liklihood a person will exprience a higher drive to eat. This drive to eat is hormonally-mediated, and genetics seem to play a role in having that increased hormonally-mediated drive to eat.
For others, the drive to eat seems to be turned on by stress factors such as poor sleep, depression, and anxiety. Physical and emotional stress lead to hormonal changes, some of which increse the hormones that cause a drive to eat. For this group, a change in lifestyle or treating the underlying stresses might dial down the drive to eat.
Cause of Obetity: Obesogenic Environment
The obesogenic environment is definitely a strong factor in obesity for some people. Those who consider the food industry at fault for obesity are in essence considering the obesogenic environment to be the only cause of obesity.
There are many factors that can make an environment obesogenic. Abundance of available fast food, convenience stores with mostly snack foods, and families that lack the time to cook homemade meals are a perfectly obesogenic environment.
Poverty is also a factor for a complex array of reasons. When money is scarce, families may feel forced to buy something they can afford now rather than something that is more expensive upfront, but cheaper in the long run. For families with little children, a meal at a fast food place or a snack food is an affordable gift parents can provide for their children. Especially when much of the other things children may request are expensive, this is a way parents can feel they are providing for their kids. Additionally, sometimes the mere perception that healthy foods are expensive discourages people to look for cheap nutritious food.
I consider the way someone's life is set up as part of their environment. Sitting in cars or trains for long commutes and sitting at desks all day makes a sedentary environment. When children's entertainment is limited to screen time, playing outside gets forgotten. These life routines cause people to be very inactive.
Another part of a person's environment is their culture. Food is central to many cultures. Over the years, as people move from their family's home country to the United States, parts of the culture remain, and parts get left in the home country. Unfortunately, many times the aspects of the culture that get left behind are the features of healthy eating and physical activity. When the remainder of the culture gets meshed with American culture and lifestyle, the result is often poor nutrition and inactivity.
Cause of Obesity: Food Addiction
The idea of addiction to food is not a concept that is completely accepted in the scientific world. While addictive-like behaviors people experience with food lack some of the characteristics of an addiction to a drug, there are similarities. Some of the similarities between what is termed as food addiction and other addictive behaviors are the constant obsession with the substance, behaviors geared at obtaining more of the substance, use in large quantities, hiding the use, and inability to stop using the substance.
One factor that separates addiction to substances and addiction to food is the concept of abstinence. While it may be a goal with typical substance use to be completely abstinent, with food, that can't be the goal. Some people argue that there are certain food components that those with food addiction can and should completely abstain from, such as sugar.
While I am not qualified to decide whether or not someone can have a true addiction to food, it is clear that people experience it as an addiction. It also seems to me that food addiction is distinct from binge eating disorder, which I would characterize under obesity disorders of drive to eat.
Many proponents of healthy eating promote the idea of "everything in moderation." While that is a noble idea and may work for some, for those with food addiction, complete avoidance of the particular foods they find addictive is more likely the appropriate goal.
What Causes Obesity?
This article clearly can't do justice to the topic of causes of obesity. As a dietitian who has cared for thousands of patients with obesity, I believe that understanding the causes of obesity can inform treatment.