Obesity is a complex health issue to address. It results from a combination of causes and contributing factors, including genetics and behaviors such as dietary patterns, physical activity, inactivity, medication use, and other exposures. Additional contributing factors in our society include the food and physical activity environment, education and skills, and food marketing and promotion.
In Part 2 of this article series, I will discuss many of the known factors and causes that contribute to obesity.
Behavior
The Food Factor
According to the Centers for Disease Control and Prevention (CDC), Americans are eating more calories on average than they did in the 1970s. Between 1971 and 2000, the average man added 168 calories to his daily intake, while the average woman added 335 calories. What’s driving this trend? Experts say it’s a combination of increased availability, bigger portions, and more high-calorie foods.
Practically everywhere we go – shopping centers, sports stadiums, movie theaters – food is readily available. You can buy snacks or meals at roadside rest stops, 24-hour convenience stores, even gyms and health clubs. Americans are spending far more on foods eaten out of the home: in 1970, we spent 27 percent of our food budget on away-from-home food; by 2006, that percentage had risen to 46 percent.
In the 1950s, fast-food restaurants offered one portion size. Today, portion sizes have ballooned, a trend that has spilled over into many other foods, from cookies and popcorn to sandwiches and steaks. And, research shows that people will often eat what’s in front of them, even if they’re already full. Not surprisingly, we’re also eating more high-calorie foods (especially salty snacks, soft drinks and pizza), which are much more readily available than lower-calorie choices like salads and whole fruits. Fat isn’t necessarily the problem; in fact, research shows that the fat content of our diet has actually decreased since the early 1980s. But, many low-fat foods are very high in calories because they contain large amounts of sugar to improve their taste and palatability. In fact, many low-fat foods are actually higher in calories than foods that are not low-fat.
The Exercise Equation
The government’s current recommendations for exercise call for an hour of moderate to vigorous exercise every day. But, fewer than 25 percent of Americans meet that goal.
Our daily lives don’t offer many opportunities for activity. Children don’t exercise as much in school, often because of cutbacks in physical education classes. Many people drive to work and spend much of the day sitting at a computer desk. Because we work long hours, we have trouble finding the time to go to the gym, play a sport, or exercise in other ways.
Instead of walking to local shops and toting shopping bags, we drive to one-stop megastores, where we park close to the entrance, wheel our purchases in a shopping cart, and drive home. The widespread use of vacuum cleaners, dishwashers, leaf-blowers, and a host of other appliances takes nearly all the physical effort out of daily chores.
The Calorie Equation
The balance of calories stored and burned by your body 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, or if you exercise more and burn more calories, your body will reduce some of your fat stores. When this happens, fat cells shrink – along with your waistline.
Genetics
Health care practitioners routinely collect family health history to help identify people at high risk of obesity-related diseases such as diabetes, cardiovascular diseases, and some forms of cancer. Family health history reflects the effects of shared genetics and environment among close relatives. Genetic changes in human populations occur too slowly to be responsible for the obesity epidemic. Nevertheless, the variation in how people respond to the environment that promotes physical inactivity and intake of high-calorie foods suggests that genes do play a role in the development of obesity.
Genes give the body instructions for responding to changes in its environment. Studies have identified variants in several genes that may contribute to obesity by increasing hunger and food intake.
Rarely, a clear pattern of inherited obesity within a family is caused by a specific variant of a single gene (monogenic obesity). Most obesity, however, probably results from complex interactions among multiple genes and environmental factors that remain poorly understood (multifactorial obesity).
Other Factors
Diseases and Drugs
Some illnesses may lead to obesity or weight gain – these may include Cushing’s disease, and polycystic ovary syndrome. Drugs such as steroids and some antidepressants may also cause weight gain. The science continues to emerge on the role of other factors in energy balance and weight gain, such as chemical exposures and the role of the microbiome.
Environmental Causes
Environmental influences come into play very early, even before you’re born. Researchers some-times call these in-utero exposures “fetal programming.” Babies of mothers who smoked during pregnancy are more likely to become overweight than those whose mothers didn’t smoke. The same is true for babies born to mothers who had diabetes. Researchers believe these conditions may somehow alter the growing baby’s metabolism in ways that show up later in life.
After birth, babies who are breastfed for more than three months are less likely to have obesity as adolescents compared with infants who breastfeed for less than three months.
Childhood habits often stick with people for the rest of their lives. Kids who drink sugary sodas and eat high-calorie, processed foods develop a taste for these products and continue eating them as adults, which tends to promote weight gain.
The average American watches about four hours of television per day, a habit that’s been linked to overweight or obesity in a number of studies. Data from the National Health and Nutrition Examination Survey, a long-term study monitoring the health of American adults, revealed that people who are overweight and obese spend more time watching television and playing video games than people of normal weight. Watching television more than two hours a day also raises the risk of overweight in children, even in those as young as three years old.
Obesity experts now believe that a number of different aspects of American society may conspire to promote weight gain. Stress is a common thread intertwining these factors. For example, these days, it’s commonplace to work long hours and take shorter or less frequent vacations. In many families, both parents work, which makes it harder to find time for families to shop, prepare and eat healthy foods together. Round-the-clock TV news means we hear more frequent reports of child abductions and random violent acts. This does more than increase stress levels; it also makes parents more reluctant to allow children to ride their bikes to the park to play. Parents end up driving kids to play-dates and structured activities, which means less activity for the kids and more stress for parents. Time pressures – whether for school, work, or family obligations – often lead people to eat on the run and to sacrifice sleep, both of which can contribute to weight gain.
Some researchers also think that the very act of eating irregularly and on the run may contribute to obesity. Neurological evidence indicates that the brain’s biological clock – the pacemaker that controls numerous other daily rhythms in our bodies – may also help to regulate hunger and satiety signals. Ideally, these signals should keep our weight steady; they should prompt us to eat when our body fat falls below a certain level or when we need more body fat (during pregnancy, for example). They should tell us when we feel full and should stop eating. Close connections between the brain’s pacemaker and the appetite control center in the hypothalamus suggest that hunger and satiety are affected by temporal cues. Irregular eating patterns may disrupt the effectiveness of these cues in a way that promotes obesity.
Similarly, research shows that the less you sleep, the more likely you are to gain weight. Lack of sufficient sleep tends to disrupt hormones that control hunger and appetite. In a 2004 study of more than 1,000 volunteers, researchers found that people who slept less than eight hours a night had higher levels of body fat than those who slept more, and the people who slept the fewest hours weighed the most.
Stress and lack of sleep are closely connected to psychological well-being, which can also affect diet and appetite, as anyone who’s ever gorged on cookies or potato chips when feeling anxious or sad can attest. Studies have demonstrated that some people eat more when affected by depression, anxiety, or other emotional disorders. In turn, overweight and obesity themselves can promote emotional disorders: if you repeatedly try to lose weight and fail, or if you succeed in losing weight only to gain it all back, the struggle can cause tremendous frustration over time, which can cause or worsen anxiety and depression. A cycle develops that leads to greater and greater obesity, associated with increasingly severe emotional difficulties.
Healthy behaviors include a healthy diet pattern and regular physical activity. Energy balance of the number of calories consumed from foods and beverages with the number of calories the body uses for activity plays a role in preventing excess weight gain. A healthy diet pattern follows the Dietary Guidelines of America which emphasizes eating whole grains, fruits, vegetables, lean protein, low-fat and fat-free dairy products, and drinking water. The Physical Activity Guidelines of America recommends adults do at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous-intensity activity, or a combination of both, along with two days of strength training per week.
Obesity is a complex disease with a multitude of causes. Recognizing that many different factors contribute to the development of obesity can aid in better treatment options. As this series continues, we will look at the effects of obesity on a person’s physical and emotional health, as well as effects on their daily function. Later, we will discuss the metabolic syndrome that includes diabetes, hypertension and high cholesterol.
Obesity is a serious concern, because it is associated with
poor mental health outcomes, reduced quality of life, and the leading causes of death in the U.S. and worldwide, including diabetes, heart disease, stroke, and some types of cancer.
