What Are 12 Surprising and Unexplained Causes of Weight Gain?

  • Medical Reviewer: Dany Paul Baby, MD
Medically Reviewed on 8/11/2022

What causes weight gain?

Overweight and obesity develop if you're not careful about controlling your weight. Surprising and unexplained causes of weight gain include genetics, stress, depression, and other causes.
Overweight and obesity develop if you're not careful about controlling your weight. Surprising and unexplained causes of weight gain include genetics, stress, depression, and other causes.

Weight gain is a problem for many people. Overweight and obesity develop if you're not careful about controlling your weight. Obesity increases your risk of heart disease, diabetes, high blood pressure (hypertension), cancer, and other conditions. Overeating and lack of exercise are well-known causes of weight gain, but several other causes may be underlying your weight gain. These unsuspected reasons may cause your healthy eating and weight control plans to fail.

You will gain weight if your calorie intake is more than you burn through activity. This imbalance of calories eaten and spent is a basic part of weight gain. 

Your body digests the food you eat and converts it to energy for your activities and bodily functions. Surplus food is converted to stored energy. Sugars are stored as glycogen, mostly in the muscles and liver. Fat is stored in fatty tissue as triglycerides. If you regularly consume more than your body needs, this storage will build up, causing weight gain.

Any circumstance or disorder that reduces your activity or makes you consume more food (and calories) will increase your weight. Beyond this simple mathematical fact, many factors can contribute to weight gain. 

1. Genetics

Genes control your metabolism, digestion, energy production, and fat storage. Some genetic diseases, like Prader-Willi syndrome, cause obesity from childhood, along with other problems. Your genes may predispose you to store fat or make it difficult for you to be active. Unsuspected genetic factors may underlie your weight gain. 

2. Stress

Your body produces cortisol, an adrenal hormone, when you're under stress. This hormone has several effects on the body, including the deposition of fat around the waist. This is called abdominal or visceral obesity. 

Cortisol also increases hunger. You're more likely to eat unwisely when you're under stress — high-calorie foods packed with saturated foods that add pounds quickly. 

Stress can have many reasons, both at home and at work. Progressive muscle relaxation, relaxation techniques, meditation, diaphragmatic breathing, yoga, and other methods can help you to reduce stress. Stress management methods can help in reducing weight as well as stress.

3. Depression

Your emotions and mental state affect your physical health in many ways. If you're depressed, you're at high risk for unintentional weight gain. Depression often causes increased appetite, increased sleepiness (hypersomnia), and a poor metabolic profile. All of these things can cause you to gain weight.

The relationship between obesity and depression is bidirectional — it works both ways. People with depression are more likely to be sedentary and overeat, leading to weight gain. People who become obese are also more likely to be depressed.

4. Poor sleep

Sleep is an essential component of good health, physical and mental. Not sleeping well causes your body to accumulate fats. You also feel more hungry when you aren't sleeping well.

Hormones released during sleep control the body's use of energy and regulate appetite. If you're not sleeping well, these hormones are disturbed, which can lead to weight gain. You're also more likely to overeat if you're not sleeping well. People who don't sleep enough are more likely to have a high body mass index (BMI). 

5. Medications

Prescription medications you might take for some conditions can interrupt the chemical signals that control hunger and satiety. Such medications can cause you to gain weight. Among them are:

If you notice your weight increasing while on long-term treatment, talk to your doctor about it. They may be able to switch you to a drug that is also effective but doesn't make you put on weight.

6. Sugar

Sugar creeps up on you in various ways. Each gram of sugar is metabolized to give 4 calories to the body. You should consume 10% or less of your total calories as sugar. For an average adult, the recommended limit is 12 teaspoons (200 calories).

Sugars that increase your weight include sucrose (table sugar), dextrose (glucose), honey, syrups, and the sugars in concentrated fruit or vegetable juices. You may not be adding sugar to your coffee but may still be consuming sugars pre-added to various foods and drinks. If you're concerned about weight gain, look at your consumption of sugar-sweetened beverages (sodas, fruit drinks, frappes, etc.) and sweet snacks like brownies, cookies, ice cream, frozen desserts, cakes, pastries, and sweet rolls. 

Sugar-sweetened beverages are a major cause of weight gain in children as well as adults. Regular consumption of such beverages is associated with significant weight gain. You may be surprised by the amount of sugar you're consuming without knowing it.

 Type of Drink    Sugar (Spoons)       Calories       
 Sports Drink   5    97
 Brewed Sweet Tea    7    115
 Energy Drink    9    162
 Regular Soda   10    155
 Fruit Juice Drink   10    186
 Regular Orange Soda    13    195


Weight loss occurs in the belly before anywhere else. See Answer

7. Saturated fats

You should consume no more than 10% of your daily calories as saturated fats. A diet with 2,000 calories a day should contain no more than 22 grams of fats since each gram of fat provides 9 calories. 

Processed foods contain a lot of fats. Read the labels carefully to know which foods will add weight to your body. You shouldn't aim to remove fats from your diet completely because that would be unhealthy. Apart from the amount, the type of fat is also important for good health. Plan to consume more healthy fats (monounsaturated and polyunsaturated fats) and avoid unhealthy fats (saturated and trans fats). Saturated fats are mainly found in meat and dairy.

8. Hypothyroidism

This hormonal disorder often goes unrecognized for a long time. The thyroid gland produces thyroid hormones necessary for your body's metabolism. If your thyroid doesn't produce enough hormones, you could gain weight even though you're still eating the same diet as before. Other symptoms of hypothyroidism include:

Your doctor will ask for blood tests to diagnose this condition. Treatment is simple but usually lifelong.

9. Polycystic ovary syndrome (PCOS)

Your ovaries produce not only eggs (ova) but also hormones that regulate your menstrual cycle and fertility. PCOS is a disorder that affects the ovaries and upsets your body's hormone balance and reproductive function. This condition is not well known but affects 1 in 10 women. The symptoms of this disorder are:

  • Irregular periods or no periods
  • Excessive hair growth on the body (hirsutism)
  • Weight gain
  • Acne and oily skin
  • Infertility

Your doctor will treat you with medication to keep PCOS under control.

10. Where you live

The place where you live can have a surprising effect on your health and weight. If your residential area doesn't have affordable gyms, parks, and sidewalks, it's difficult to stay physically active. Though you may be eating only the recommended number of calories, your lack of activity could cause you to gain weight.

Another factor is the distance from supermarkets that sell healthy food like vegetables and fruits. You're more likely to consume calorie-rich and fattening foods if healthy food is hard to get.

11. A sedentary lifestyle

Your lifestyle may not have enough activity, though you may feel you stay busy all day. Adults should get 150 minutes of physical activity a week and do muscle-strengthening activities at least twice a week. Routine activities at your work or home that don't increase your heart rate don't count toward this activity recommendation. Spending a lot of time sitting down at work, watching television, or playing video games contributes to weight gain and increases the body mass index (BMI).

12. Too many calories

This is a primary cause of weight gain, of course. You know it, but it can still take you by surprise. You believe you have a healthy diet plan and stick to it. But snacking, cheat days, and occasional treats all add up. Most such treats are calorie-rich and can increase your intake without your realizing it. 

Some food labels can deceive you too. You may be careful about buying low-fat biscuits and fat-free desserts, but you may not notice that these are packed with sugars. A low-fat muffin with lots of sugar can give you more calories than the currant bun you so carefully avoid. Always read the label carefully, with special attention to the calories in each portion. 

Portion sizes are important, too. Though you choose healthy foods for your diet, the ever-increasing portion sizes in restaurants and supermarkets can nullify your good intentions. Larger portions and serving sizes encourage you to eat more. At restaurants, ask for small sizes, choosing from a junior menu if necessary. At home, serve yourself smaller portions and think carefully before reaching for a second helping. 


The Best Diet Tips: How to Lose Weight the Healthy Way See Slideshow

Health Solutions From Our Sponsors

Medically Reviewed on 8/11/2022

Ashford & St Peter's Hospital: "Hidden causes of weight gain."

Centers for Disease Control and Prevention: "Fats - Saturated, Unsaturated, and Trans Fat," "Get the Facts: Added Sugars," "Rethink Your Drink."

Journal of Molecular Biochemistry: "Impact of a stress management program on weight loss, mental health and lifestyle in adults with obesity: a randomized controlled trial."

Journal of Personalized Medicine: "Diet, Obesity, and Depression: A Systematic Review."

National Health Service: "Polycystic ovary syndrome (PCOS)," "Underactive thyroid (hypothyroidism) - Symptoms."

National Heart, Lung, and Blood Institute: "Overweight and Obesity: Causes and Risk Factors."

NICHD: "What causes obesity & overweight?"

Obesity Facts: "Sugar-Sweetened Beverages and Weight Gain in Children and Adults: A Systematic Review from 2013 to 2015 and a Comparison with Previous Studies."