The Health Risks of Obesity in Adults, and How Much Weight Loss Helps

In brief: the main health risks of obesity include heart disease, stroke, type 2 diabetes, high blood pressure, some cancers, sleep apnea, osteoarthritis and fatty liver disease. Risk is higher when extra fat sits around the waist. The NHS estimates obesity is likely to cut 2 to 10 years from life expectancy. The encouraging part: a loss of 5% to 10% of body weight can bring health benefits.

The Health Risks of Obesity at a Glance

Obesity is a chronic disease, not a personal failing. The World Health Organization (WHO) estimates that in 2024 about 1 in 7 people worldwide lived with obesity, and it links higher-than-optimal BMI to an estimated 3.7 million deaths in 2023, mainly through heart disease, diabetes and cancer.

Adults are usually screened with body mass index (BMI). Both the WHO and the NHS class a BMI of 25 or more as overweight and 30 or more as obesity. The NHS uses lower thresholds for people of Black African, African-Caribbean, Middle Eastern, Chinese, South Asian or other Asian heritage.

The US National Institutes of Health (NIH) groups the risks into these areas:

Area	Linked conditions	What weight loss can do
Metabolism	Type 2 diabetes, metabolic syndrome	Losing 5–7% may prevent or delay type 2 diabetes in people at risk
Heart and circulation	High blood pressure, heart disease, stroke	Can lower blood pressure, cholesterol and blood sugar
Liver and digestion	Fatty liver disease, gallstones, pancreatitis	Losing 3–5% may reduce liver fat
Cancer	Colon, rectum and prostate in men; breast, womb lining and gallbladder in women	Gaining less weight with age is linked to lower risk of several cancers
Breathing	Sleep apnea, asthma	May ease sleep apnea, sometimes clearing it
Joints	Osteoarthritis, gout	Less stress on knees, hips and back; may improve symptoms
Kidneys	Chronic kidney disease	May help prevent or delay it
Fertility and pregnancy	Infertility, gestational diabetes, preeclampsia	Losing 5% may help periods and ovulation in women
Mental health	Stress, low self-esteem, depression, eating disorders	Linked to better body image and mood

Does Being Overweight Cause Health Problems?

Excess weight raises risk, but it doesn't guarantee illness. The NIH explains that risk climbs with more body fat, and especially with fat stored around the waist. Here's how some of the main links work:

• Type 2 diabetes: nearly 90% of people who have this form of diabetes also have overweight or obesity. Over time, high blood sugar can damage the heart, kidneys, eyes and nerves.
• Blood pressure and the heart: a larger body makes the heart work harder to pump blood, and excess fat can harm the kidneys, which help control blood pressure. Raised blood pressure is the top cause of strokes.
• Sleep apnea: fat stored around the neck can narrow the airway, causing snoring or pauses in breathing during sleep.
• Joints: extra weight puts more load on the knees, hips and ankles, and body fat can raise inflammation in the blood.

Day to day, the NHS notes obesity can also cause breathlessness, tiredness, joint and back pain, snoring, and difficulty moving around.

Health Risks of Obesity in Women

Women and men share most risks, but some are specific to women. According to the NIH:

• Cancer: women with overweight or obesity have higher rates of breast, womb lining and gallbladder cancers. The NHS also lists bowel cancer.
• Fertility: obesity is linked to irregular periods and ovulation problems, and can make some fertility treatments less effective. Losing 5% of body weight may improve the chances of regular periods, ovulation and pregnancy.
• Pregnancy: obesity raises the chance of gestational diabetes, preeclampsia (high blood pressure in pregnancy), a cesarean delivery and complications from anesthesia. It can also affect the baby's health.

If you're planning a pregnancy, talk to your doctor about reaching a healthier weight first. Don't try to lose weight during pregnancy without medical advice.

In men, the NIH lists higher risks of colon, rectal and prostate cancer, lower sperm count and quality, erectile dysfunction, and gout.

Why Waist Size Matters

Where you carry fat matters as well as how much. The NIH says fat around the waist adds to risk, and a large waist is one of the five markers used to diagnose metabolic syndrome. The NHS suggests keeping your waist to under half your height.

Example: Two Simple Checks

For an adult who is 170 cm (5 ft 7 in) tall and weighs 100 kg (220 lb):

• Waist check: half of 170 cm is 85 cm (about 33.5 in). A waist above that suggests too much fat around the middle.
• Weight loss goal: the NIH says losing 5% to 7% of starting weight may prevent or delay type 2 diabetes in people at risk. That's 5 to 7 kg (11 to 15.4 lb), taking them to about 93 to 95 kg (205 to 209 lb).

Find your own BMI with the BMI calculator, and see what each category means in our healthy BMI chart.

What Affects Your Risk

Weight is shaped by much more than willpower. The NIH lists factors including:

• Habits: high-calorie, sugary and fatty foods and drinks, and lots of time sitting.
• Sleep: adults aged 18 to 64 are advised to get 7 to 9 hours. Too little sleep is linked to hunger and weight gain.
• Medicines: some antidepressants, epilepsy drugs, steroids, diabetes and blood pressure medicines can contribute to weight gain.
• Health conditions: for example polycystic ovary syndrome (PCOS), an underactive thyroid, Cushing's syndrome, depression and long-term stress.
• Genes and family history: your chances are higher if one or both parents have overweight or obesity.
• Environment: access to affordable healthy food and safe places to be active.

The WHO describes obesity as a societal responsibility as well as an individual one, because food environments and daily routines strongly shape choices.

How to Lower the Health Risks of Obesity

Modest, sustained weight loss gives real benefits. The NHS says a loss of 5% to 10% of body weight brings health gains, and recommends aiming for 0.5 to 1 kg (1 to 2 lb) a week. Our guide on how to lose weight safely sets out a step-by-step plan.

Losing weight too fast has its own risk: the NIH notes rapid weight loss can increase the chance of gallstones. For people who need more support, treatment options include structured programs, weight loss medication and bariatric surgery.

Limits and When to Get Advice

BMI and waist size are screening tools, not diagnoses. BMI can't tell muscle from fat, and many people with a higher BMI are healthy. Your doctor can assess your actual risk using blood pressure, blood sugar, cholesterol and your family history.

The NHS advises booking a GP appointment if your BMI falls in the overweight or obese range and you'd like support with weight loss, your waist is more than half your height, or you have conditions such as diabetes, high blood pressure, sleep apnea or joint pain. Also speak to a doctor if you think you might have binge eating disorder or another eating disorder.

Frequently Asked Questions

What is the biggest health risk of obesity?

There's no single biggest risk for everyone, but type 2 diabetes and heart and circulation problems are among the most common and serious. The NIH reports that nearly 90% of people with type 2 diabetes also have overweight or obesity. Globally, the WHO links higher-than-optimal BMI mainly to deaths from heart disease, diabetes and cancers.

Can you be overweight and healthy?

Some people with a higher BMI have normal blood pressure, blood sugar and cholesterol. BMI is a screening measure and can't tell muscle from fat. But the risk of many conditions rises with more body fat, especially around the waist. A check-up with your doctor gives a much clearer picture than BMI alone.

How much weight do you need to lose to lower your health risks?

Less than many people think. According to the NHS, a loss of 5% to 10% of body weight brings health gains. The NIH reports that losing 5% to 7% may prevent or delay type 2 diabetes in people at risk, and 3% to 5% may reduce fat in the liver.

Does obesity shorten life expectancy?

Yes, on average. The NHS estimates that living with obesity is likely to take 2 to 10 years off life expectancy. Risk depends on how much excess weight a person carries, where it's stored, and other factors such as smoking, activity and existing conditions. Losing weight and staying active can lower that risk.

To see which BMI category you're in, use the BMI calculator.