Understanding Obesity: Causes, Effects & Treatment

When we eat more calories than we burn, our bodies store this extra energy as fat. While a few extra pounds may not seem like a big deal, they can increase your chances of having high blood pressure and high blood sugar. These conditions may lead to serious health problems, including heart disease, stroke, type 2 diabetes, and certain cancers.

What Is Obesity?

More than two-thirds of adults are considered to be overweight or obese, and more than one-third of adults have obesity. Obesity is a condition in which a person carries an excess amount of body fat to a degree that increases the risk of health problems. Understanding whether you’re at risk of weight-related health problems is the first step toward managing your health — at any weight.

How Is Obesity Measured?

Body mass index (BMI) is one way to tell whether you are at a normal weight, overweight, or obese. BMI measures your weight in relation to your height.

• A BMI of 18.5 to 24.9 is in the normal range.
• A BMI of 25 to 29.9 is considered overweight.
• A BMI of 30 or greater is considered obese.

However, because BMI doesn’t measure actual body fat, a very muscular person, like a bodybuilder, may have a high BMI without having a lot of body fat. Review your findings with your healthcare provider if your BMI is outside the normal range.

What Causes Obesity?

Our bodies need calories (energy) to keep us alive and active. To maintain weight, we need to balance the energy we take in with the energy we use. When a person eats and drinks more calories than they burn, the energy balance tips toward weight gain, overweight, and obesity. The tipping point at which calories in and calories out become unbalanced may differ from one person to another. Genes, the world around you, and other factors may all affect weight gain.

Genetics and Family History

Research shows that obesity tends to run in families, suggesting that genes may contribute to obesity. Families also share diet and lifestyle habits that may affect weight. However, it is possible to manage your weight even if obesity is common in your family.

Environment and Lifestyle

Where people live, play, and work may also strongly affect their weight. Obesity rates were lower 30 years ago — our genetic makeup hasn’t changed since then, but our world has. Many people drive rather than walk, and living in areas without sidewalks or safe places to exercise may make it tough to be more active. Many people eat out or get takeout instead of cooking, which may lead to eating more calories, and most vending machines do not offer low-calorie, low-fat snacks.

Overweight and obesity affect people in all income ranges. However, people who live in low-income areas may face even greater barriers to eating healthy foods and being active than other people, since high-calorie processed foods often cost less than healthier options like fruits and vegetables.

A person’s culture may also affect weight — some cultures have foods with a lot of fat or sugar, making weight management difficult, and family events where people eat large amounts of food may make it tough to control portions.

Sleep and Obesity

Research suggests that lack of sleep is linked to overweight and obesity. Recent studies have found that sleeping less may make it harder to lose weight. In these studies, adults who were trying to lose weight and who slept less ate more calories and snacked more.

Medications and Weight Gain

Certain drugs may cause weight gain. Steroids and some drugs to treat depression or other mental health problems may make you burn calories more slowly or feel hungrier. Be sure your healthcare provider knows all the medicines you are taking, including over-the-counter drugs and dietary supplements — they may suggest an alternative that has less effect on weight.

What Are the Symptoms of Obesity?

Obesity itself is usually identified through BMI and waist size rather than a single “symptom,” but common signs that often go along with excess weight include:

• A BMI of 30 or higher, or a waist size greater than 40 inches (men) or 35 inches (women)
• Breathlessness or fatigue during routine activity
• Joint and lower-back pain from carrying extra weight
• Snoring or disrupted sleep, which can point to sleep apnea
• Skin issues such as chafing or rashes in skin folds
• Difficulty losing weight despite diet and exercise efforts

If you notice several of these signs together, it’s worth getting your BMI, waist size, and blood pressure or blood sugar checked by a healthcare provider.

Does Body Shape Matter?

Healthcare providers are concerned not only with how much body fat a person has, but where the fat is located on the body. Women tend to collect fat in their hips and buttocks, giving them a “pear” shape, while men usually build up fat around their bellies, giving them more of an “apple” shape. Some men are pear-shaped and some women are apple-shaped, especially after menopause.

Extra fat around your midsection may put you at greater risk for type 2 diabetes, heart disease, and other health problems — even if you have a normal weight. Your provider can help you assess your risk.

What Health Problems Are Linked to Obesity?

Weighing too much may increase the risk of several health problems, and it may also contribute to emotional and social difficulties.

Health Risks

Type 2 diabetes, heart disease, high blood pressure, stroke, kidney disease, and certain cancers are some of the diseases linked to excess weight. Obese men are more likely than other men to develop cancer of the colon, rectum, or prostate, while obese women are more likely than other women to develop cancer of the breast (after menopause), gallbladder, uterus, or cervix. Cancer of the esophagus may also be linked to obesity.

Other health problems linked to excess weight include breathing problems such as sleep apnea, fatty liver disease (also called nonalcoholic steatohepatitis or NASH), gallbladder disease and gallstones, and pregnancy problems such as gestational diabetes, high blood pressure, and an increased risk of cesarean section.

Emotional and Social Effects

Excess weight may also contribute to emotional suffering. Because physical appearance is highly valued in society, people who don’t fit society’s view of beauty due to their weight may be seen as less attractive. Some people in our culture may also view a person with obesity as lacking willpower, so people with obesity may face limited options in the job market, at school, and in social situations — and may feel rejected, ashamed, or depressed as a result.

Who Should Consider Losing Weight?

Healthcare providers generally agree that people who are considered obese (BMI of 30 or greater) may improve their health by losing weight.

If you are overweight (BMI between 25 and 29.9), experts recommend avoiding gaining any extra weight. If you are overweight and have other risk factors, losing weight may reduce these risks. Experts recommend trying to lose weight if you have two or more of the following:

• Family history of certain chronic diseases — close relatives with heart disease or diabetes may mean you’re more likely to develop these problems.
• Pre-existing medical problems — high blood pressure, high LDL (bad) cholesterol, low HDL (good) cholesterol, high triglycerides, and high blood sugar (prediabetes or diabetes) are warning signs of diseases linked to obesity.
• Large waist size — men with waist sizes greater than 40 inches and women with waist sizes greater than 35 inches are at higher risk of diabetes, unhealthy blood fats, high blood pressure, and heart disease.

Fortunately, losing even a small amount of weight can help improve your health, lower your blood pressure, and improve other risk factors. Research shows that people at high risk for type 2 diabetes who lose a modest amount of weight and increase their physical activity may prevent or delay the disease.

How Is Obesity Treated?

The best way to control your weight depends on how much excess weight you have, your overall health, and how ready you are to change your eating and physical activity habits. In some cases, if lifestyle changes don’t lead to enough weight loss to improve your health, doctors may recommend additional treatment, including weight-loss medication. In cases of extreme or severe obesity, doctors may recommend bariatric surgery.

If you’d like to understand the different types of weight-loss surgery, what they involve, and what recovery looks like, you can read more in our detailed guide on bariatric surgery definitions and facts.

How Can You Improve Your Health?

Although you cannot change your genes, you can work on changing your eating habits, physical activity levels, and other lifestyle factors.

Get Regular Physical Activity

Try these tips for starting or maintaining an exercise program:

• Get at least 150 minutes (2½ hours) of moderately intense aerobic activity each week that raises your heart rate and makes you sweat — brisk walking, biking, swimming, and playing tennis or basketball are good options you can do with others for support.
• Spread the 150 minutes out in short spurts over the week; brisk house or yard chores, walking the dog at a quick pace, or dancing for at least 10 minutes at a time all count.
• Aim for 300 minutes (5 hours) of aerobic activity a week to prevent gradual weight gain in adulthood. If you’re at a healthy weight now but used to be overweight or obese, experts encourage 60 to 90 minutes of exercise a day to keep the weight off.
• Most adults don’t need to see their doctor before starting a physical activity program. However, men older than 40 and women older than 50 who plan a vigorous program, or who have a serious health condition or risk factors for one, should check with a doctor first.

Eat a Healthy Diet

Eating healthy foods has vital health benefits, including weight loss. To start eating better, try these tips:

• Make half of what’s on your plate fruits and vegetables.
• Replace refined grains with whole grains, like oatmeal, whole wheat bread, and brown rice.
• Get your protein from healthy sources, like seafood, lean meats, poultry, eggs, beans, unsalted nuts, and seeds.
• Instead of sugary drinks, choose unsweetened tea, low-fat milk, or water.

Conclusion

Weight control is a lifelong effort, and understanding obesity — its causes, symptoms, and health risks — is the first step toward managing it. Small, consistent changes to your eating habits and activity levels can meaningfully improve your health at any weight. If lifestyle changes aren’t enough and your health is at risk, it may be worth discussing medical or surgical options with your doctor. You can contact us to book a consultation and get personalised guidance on managing obesity.

Frequently Asked Questions

1. What are the four types of obesity?

Obesity is generally classified by BMI: Class 1 (BMI 30–34.9), Class 2 (BMI 35–39.9), Class 3 or severe obesity (BMI 40 and above), and central/abdominal obesity, which is defined by excess fat around the waist rather than overall BMI alone.

2. What are 10 causes of obesity?

Common contributors to obesity include excess calorie intake, lack of physical activity, genetics and family history, poor sleep, certain medications, high-calorie processed foods, large portion sizes, sedentary work and lifestyle, stress and emotional eating, and limited access to healthy food or safe places to exercise.

3. What is the best treatment for obesity?

There is no single “best” treatment — it depends on the degree of obesity and overall health. Options range from diet and exercise changes, to medically supervised weight-loss programs and medication, to bariatric surgery for severe obesity when other methods haven’t worked.

4. What foods fight obesity?

Foods that support weight management include vegetables, fruits, whole grains, lean protein (fish, poultry, beans, eggs), and unsalted nuts and seeds. Reducing sugary drinks, refined carbohydrates, and heavily processed foods also helps.

5. What age is hardest to lose weight?

Weight loss can become harder with age, particularly after 40–50, due to a natural slowdown in metabolism, loss of muscle mass, and hormonal changes such as menopause. It’s still possible to lose weight at any age with the right approach.

6. What is the 3-3-3 rule to lose weight?

The 3-3-3 rule is a popular guideline suggesting 3 meals a day, each with roughly 3 food groups (protein, fibre, and healthy fat/carbs), spaced about 3 hours apart, to help control hunger and portion sizes. It’s a general habit-forming tip rather than a medically prescribed plan.

7. How do I trigger my body to burn fat?

Fat burning is primarily driven by maintaining a calorie deficit through a combination of regular aerobic exercise, strength training to preserve muscle mass, adequate protein intake, and enough sleep — there’s no single “trigger” that works without consistent lifestyle habits.

8. Is obesity a disease?

Yes, major health bodies classify obesity as a chronic disease, since it involves complex changes in metabolism and body function that increase the risk of other conditions like diabetes and heart disease — not simply a matter of willpower.

9. How is obesity diagnosed?

Obesity is typically diagnosed using BMI along with waist circumference measurement, and sometimes additional tests like blood sugar, cholesterol, and blood pressure checks to assess overall health risk.

10. Can losing a small amount of weight make a difference?

Yes, losing even 5–10% of body weight can meaningfully lower blood pressure, improve blood sugar control, and reduce the risk of conditions linked to obesity, even before reaching a “normal” BMI.