Obesity is a condition that occurs when a person has excess weight or body fat that might affect their health. A doctor will usually suggest that a person has obesity if they have a high body mass index (BMI).
BMI is a tool that doctors use to assess whether or not a person has an appropriate weight for their age, sex, and height. It combines a person’s weight in kilograms divided by the square of their height in meters.
Having a BMI between 25 and 29.9 indicates that a person is carrying excess weight. A person has obesity if their BMI is 30 or over.
Certain other factors — such as a person’s waist-to-hip ratio, waist-to-height ratio, and amount and distribution of fat — also play a role in determining how healthy their weight is.
If a person does have obesity, it can increase their risk of developing a number of other health conditions, including metabolic syndrome, arthritis, and some types of cancer.
Maintaining a moderate weight or losing weight through diet and exercise can help prevent or reduce obesity. In some cases, however, a person may need surgery.
Read on to find out why obesity develops.
When a person consumes more calories than they use as energy, their body will store the extra calories as fat. This can lead toTrusted Source obesity.
Also, some foods and beverages — especially those that are high in fats and sugars — are more likely to lead to weight gain.
Items that tend to increase the risk of weight gain include:
- fast foods
- fried foods, such as french fries
- fatty and processed meats
- many dairy products
- foods with added sugar, such as baked goods, ready made breakfast cereals, and cookies
- foods containing hidden sugars, such as ketchup and many other canned and packaged food items
- sweetened juices, sodas, and alcoholic drinks
- processed, high carbohydrate foods, such as breads and bagels
Some processed food products, such as ketchup, contain high fructose corn syrup as a sweetener.
Eating too much of these foods and doing too little exercise can result in weight gain and obesity.
People with diets that consist mainly of fruits, vegetables, whole grains, and water are still at risk of gaining excess weight if they overeat or if genetic factors increase their risk.
However, they are more likely to enjoy a varied diet while maintaining a moderate weight. Fresh foods and whole grains contain fiber, which can encourage healthy digestion and help a person feel full for longer.
Leading a sedentary lifestyle
Many people lead a much more sedentary lifestyle than their parents and grandparents did.
Some examples of sedentary habits include:
- working in an office rather than doing manual labor
- playing games on a computer instead of doing physical activities outside
- going to places by car instead of walking or cycling
The less a person moves around, the fewer calories they burn.
Also, physical activity affects how a person’s hormones work, and hormones have an impact on how the body processes food.
Several studies have suggested that physical activity can help keep insulin levels stable and that unstable insulin levels may lead to weight gain.
One 2016 reviewTrusted Source noted that, although the designs of some studies make it hard to draw exact conclusions, “A lifestyle incorporating regular [physical activity] has been identified as a key factor for maintaining and improving many aspects of health, including insulin sensitivity.”
Physical activity need not be training in the gym. Physical work, walking or cycling, climbing stairs, and household tasks all contribute.
However, the type and intensity of activity may affect the degree to which it benefits the body in the short and long term.
Not sleeping enough
Some research has suggested that missing sleep increases the risk of gaining weight and developing obesity.
Researchers reviewed study evidence for over 28,000 children and 15,000 adults in the United Kingdom from 1977 to 2012. They concluded that sleep deprivation significantly increased the risk of obesity in both adults and children. The changes affected children as young as 5 years old.
The team suggested that sleep deprivation may lead to obesity because it can lead to hormonal changes that increase appetite.
When a person does not sleep enough, their body produces ghrelin, which is a hormone that stimulates appetite. At the same time, a lack of sleep also results in a lower production of leptin, which is a hormone that suppresses appetite.
One 2012 studyTrusted Source provided clues as to how liquid fructose, which is a type of sugar, in beverages may alter lipid and glucose metabolism and lead to fatty liver and metabolic syndrome.
Metabolic syndrome includes type 2 diabetes, cardiovascular disease, and high blood pressure. People with obesity are more likely to have metabolic syndrome.
After feeding rats a 10% fructose solution for 14 days, the scientists noted that their metabolisms were starting to change.
Scientists now believe that there is a link between high fructose intakes and obesity and metabolic syndrome. Authorities have raised concerns about the use of high fructose corn syrup to sweeten drinks and other products.
Animal studies have also found that when obesity occurs due to high fructose intakes, there is a close link with type 2 diabetes.
In 2018, researchers published the results of investigations involving young rats. They, too, experienced metabolic changes, oxidative stress, and inflammation after consuming high fructose corn syrup.
The researchers noted that “increased fructose intake may be an important predictor of metabolic risk in young people.” They called for changes in the diets of young people to help prevent these problems.
Avoiding high fructose corn syrup
Some items that contain high fructose corn syrup include:
- sodas, energy drinks, and sports drinks
- candy and ice cream
- coffee creamer
- sauces and condiments, including salad dressings, ketchup, and barbecue sauce
- sweetened foods, such as yogurt, juices, and canned foods
- breads and other ready made baked goods
- breakfast cereals, cereal bars, and “energy” or “nutrition” bars
A person can reduce their intake of high fructose corn syrup and other additives by:
- checking nutrition labels before buying
- opting for unsweetened or less processed items where possible
- making salad dressings and baking other products at home
Some foods contain other sweeteners, and these can also have adverse effects.
Medications and weight gain
Some medications can also lead to weight gain.
The results of a 2015 review and meta-analysisTrusted Source found that some medications caused people to gain weight over a period of months. These included:
- atypical antipsychotics, especially olanzapine, quetiapine, and risperidone
- anticonvulsants and mood stabilizers, especially gabapentin
- hypoglycemia medications, such as tolbutamide
- glucocorticoids for rheumatoid arthritis
- some antidepressants
However, some medications may lead to weight loss. Anyone who is starting a new medication and is concerned about their weight should ask a doctor whether or not the drug is likely to have any effect on their weight.
Is obesity self-perpetuating?
The longer a person has obesity, the harder it may be for them to lose weight.
One 2015 studyTrusted Source in mice suggested that the more fat a person carries, the less likely their body is to burn fat because of a protein known as sLR11.
It seems that the more fat a person has, the more sLR11 their body will produce. The protein blocks the body’s ability to burn fat, making it harder for them to shed the extra weight.
A faulty gene called the fat mass and obesity-associated gene (FTO) is responsible for some cases of obesity.
One 2013 study pointed to a link between this gene and:
- behaviors that lead to obesity
- a higher food intake
- a preference for high calorie foods
- an impaired ability to feel full
The hormone ghrelin plays a crucial role in eating behavior. Ghrelin also affectsTrusted Source the release of growth hormones and how the body accumulates fat, among other things.
The activity of the FTO gene might impact a person’s risk of having obesity because it affects the amounts of ghrelin they have.
In a 2017 studyTrusted Source involving 250 people with eating disorders, researchers suggested that aspects of FTO might also play a role in binge eating and emotional eating.
Many factors play a role in the development of obesity. Genetic traits can increase the risk in some people.
Eating a healthy diet that contains plenty of fresh foods and getting regular exercise will reduce the risk of obesity in most people.
However, those with a genetic predisposition to the condition may find it harder to maintain a moderate weight.