Causes and Risk Factors
Weight gain happens when the body stores more energy than it uses, but many forces influence that balance:- Energy imbalance: Calorie intake that consistently exceeds calories burned, though the drivers of that imbalance differ greatly from person to person.
- Genetics: Body weight and fat distribution run strongly in families.
- Medical conditions: An underactive thyroid (hypothyroidism), polycystic ovary syndrome, and other hormonal disorders can promote weight gain.
- Medications: Some antidepressants, steroids, insulin, and seizure medicines are associated with weight gain.
- Sleep and stress: Short sleep and chronic stress alter appetite hormones and increase cravings.
- Environment and habits: Calorie-dense foods, large portions, and sedentary work and leisure time all contribute.
Health Risks
Excess body fat is metabolically active and affects nearly every organ system. Losing even a modest amount of weight lowers the risk of nearly all of the following conditions:- Type 2 diabetes: Obesity is the strongest modifiable risk factor for diabetes.
- Heart and vascular disease: High blood pressure, abnormal cholesterol, heart attack, and stroke are all more common.
- Fatty liver: Fat accumulation in the liver can progress to inflammation and scarring (fatty liver disease).
- Sleep apnea: Interrupted breathing during sleep causes daytime fatigue and strains the heart.
- Joint disease: Extra load on the knees and hips accelerates osteoarthritis.
- Certain cancers: Obesity raises the risk of several cancers, including colon and uterine cancer.
Diagnosis
Diagnosis starts with BMI: 25 to 29.9 is classified as overweight, and 30 or above as obesity, though BMI is a screening tool rather than a perfect measure of health. A good evaluation goes further: waist circumference, blood pressure, blood sugar, cholesterol, thyroid testing, and a review of medications and sleep habits. The goal is to understand why weight has changed and what health problems are already present so treatment can be targeted.Treatment
Effective treatment is long-term and usually combines several approaches:- Nutrition changes: A sustainable, reduced-calorie eating pattern matters more than any specific named diet.
- Physical activity: Roughly 150 minutes of moderate activity per week, plus strength training, helps keep weight off.
- Behavioral support: Regular follow-up, self-monitoring, and realistic goal-setting improve results.
- Medications: GLP-1 receptor agonists such as semaglutide and liraglutide reduce appetite and produce substantial weight loss; metformin is sometimes used when insulin resistance is prominent.
- Bariatric surgery: For severe obesity, surgery is the most effective durable treatment and can put type 2 diabetes into remission.
Making Obesity Treatment Work Long Term
Obesity is treated the way any chronic disease is: with a plan that is measured, adjusted, and continued, rather than a diet that ends. What follows is how the medical options play out over months, what to protect during weight loss, and what to check along the way.
How GLP-1 treatment actually goes
Semaglutide and liraglutide are started at a low dose and raised in steps over several months, and most nausea happens in the week after each step; smaller meals, stopping when full, and avoiding fatty food get most people through it, as our GLP-1 side effects guide describes. Tirzepatide, which acts on two gut hormones, produces somewhat greater weight loss on average. Weight falls fastest in the first six months and then plateaus at a new set point; the plateau is the treatment working, not failing. Stopping returns most of the weight within a year for most people, so it is planned as ongoing treatment, using only FDA-approved products from a pharmacy; the compounded semaglutide article explains why.
Who qualifies, and what else is on the list
Prescription weight medication is indicated at a body mass index of 30, or 27 with a weight-related condition such as high blood pressure or prediabetes. Metformin produces modest loss and suits people with insulin resistance; bupropion combined with naltrexone, and topiramate combined with phentermine, are older options that fit some people better. Our maximizing success on GLP-1 medications article covers what to do alongside the injection.
Protect the muscle you are losing
A substantial share of weight lost on any program is lean tissue unless it is defended, and losing muscle after 60 is the difference between weight loss that improves function and weight loss that causes frailty. Protein at every meal, on the order of what our protein by age guide recommends, and two or three sessions of strength training a week preserve most of it. Walking early or late and in shade is how activity survives the Florida summer; our exercising in the Florida heat article sets out the rules.
The conditions that ride along, and the medications that add weight
Sleep apnea, fatty liver disease, and metabolic syndrome are looked for at the outset because each improves with weight loss and each undermines it when untreated. A medication review comes first as well: certain antidepressants, antipsychotics, insulin, sulfonylureas, beta-blockers, and steroids promote gain, and a weight-neutral alternative often exists. Hypothyroidism is checked but is rarely the whole explanation.
When surgery is the right tool
Bariatric surgery is considered at a body mass index of 35 or higher, and at lower levels when type 2 diabetes or another metabolic disease is poorly controlled, and it remains the most durable treatment for severe obesity. It is one option weighed alongside medication, not a last resort. Our endocrine team manages weight medication and coordinates surgical referral. NIDDK and the CDC publish patient guidance.
If you have lost and regained the same weight more than once, schedule a visit; the plan needs a different structure, not more effort.