Weight gain occurs when a person consumes more calories than they burn through physical activity and regular bodily functions. There are many potential causes of weight gain including poor diet, lack of exercise, certain medications, underlying health conditions, genetics, and more. However, the biggest and most common cause of weight gain is consuming too many calories. Ultimately, weight gain boils down to an energy imbalance between calories consumed and calories expended. When more calories are consumed than are burned off, excess energy is stored in the body as fat, leading to weight gain over time.
What are calories?
Calories are units of energy found in food and drinks. The number of calories a food contains indicates the amount of potential energy it provides to fuel the body.
The key sources of calories are carbohydrates, proteins, fats, and alcohol:
- Carbohydrates: 4 calories per gram
- Protein: 4 calories per gram
- Fat: 9 calories per gram
- Alcohol: 7 calories per gram
When we consume calories, our body breaks down foods into these basic components during digestion and absorbs the energy. Carbohydrates, protein, fat, and alcohol all provide calories that can fuel the body and contribute to weight gain if consumed in excess.
How many calories does the body need?
The number of calories a person needs each day varies based on factors like age, sex, height, weight, activity level, and health status. The average sedentary adult man requires around 2,500 calories per day to maintain his weight, while the average sedentary adult woman needs 2,000 calories per day.
People trying to lose weight often aim to cut 500–1,000 calories per day from their maintenance level. Those looking to gain weight purposefully aim to consume 500–1,000 extra calories per day. Modifying calorie intake by a few hundred calories per day can lead to weight changes over time.
Here are some average daily calorie needs estimates based on age and activity level:
| Age | Sedentary | Moderately Active | Active |
|---|---|---|---|
| Child (ages 4–8) | 1,200–1,400 | 1,400–1,600 | 1,400–1,800 |
| Child (ages 9–13) | 1,400–1,600 | 1,600–2,000 | 1,800–2,200 |
| Teen Girl (ages 14-18) | 1,800 | 2,000 | 2,400 |
| Teen Boy (ages 14-18) | 2,000 | 2,400–2,800 | 2,800–3,200 |
| Adult Man (ages 19-30) | 2,400-2,600 | 2,600-2,800 | 3,000 |
| Adult Woman (ages 19-30) | 2,000-2,200 | 2,200-2,400 | 2,400 |
As this demonstrates, the number of calories needed varies widely based on age, sex, and physical activity level. Consuming more calories than needed will lead to energy imbalance and weight gain over time.
How do calories lead to weight gain?
Weight gain occurs when calorie intake exceeds calorie expenditure over an extended time period. Here is a look at the process:
- When you eat food, you consume calories (energy). Carbs, protein, fat, and alcohol in the diet all provide calories.
- As food is digested, calories are absorbed into the bloodstream and delivered to cells throughout the body to provide energy.
- Any excess calories that are not needed immediately are converted into triglycerides and stored in fat cells.
- When calorie intake consistently exceeds expenditure, these stored triglycerides accumulate and fat cells enlarge, leading to overall weight gain.
This energy imbalance and fat storage can happen quite easily over time, such as gaining 1 pound per week by consuming just 500 excess calories per day. Small habitual excesses in calorie intake compared to expenditure therefore accumulate and lead to weight gain.
What are the major sources of excess calories?
While any food item or beverage containing calories can contribute to weight gain if consumed in excess, some major sources of excess calories in the modern diet include:
Added sugars
Many processed foods and beverages like soft drinks, baked goods, candy, ice cream, and sugary cereal contain lots of added sugar. The average American consumes over 270 calories per day from added sugars alone. Consuming extra sugary foods and drinks can cause excess calories and lead to weight gain.
Refined grains
Refined grains like white bread, pasta, pastries, and white rice have had the fiber- and nutrient-rich bran and germ removed during processing, leaving mainly starchy endosperm. This makes refined grains higher in calories and faster digesting. Easy overconsumption can lead to excess calories.
Fried foods
Deep frying cooking method adds a lot of calories from oil. Fried items like french fries, chicken nuggets, and donuts have extra hidden calories thanks to being cooked in fat. The calories can add up fast when eating fried foods.
Fast food
Fast food meals tend to be high in calories, fat, added sugar, and refined grains. It’s easy to consume 1,000 calories or more in one fast food meal. Frequent fast food intake can drive excess calorie consumption.
Alcohol
Various alcoholic beverages like beer, wine, and mixed drinks all provide empty calories, meaning they supply calories but limited nutrition. Just a single beer, glass of wine, or cocktail can contain 100-300+ calories. Drinking alcohol frequently adds to overall calorie intake.
Lack of exercise
Leading a sedentary lifestyle with minimal physical activity causes the body to burn fewer calories each day. Without exercise, it’s much easier for calorie intake to surpass expenditure, leading to energy imbalance and weight gain in the long run.
In summary, all extra calories beyond what the body needs can lead to weight gain. But added sugars, refined grains, fried foods, fast food, alcohol, and lack of exercise tend to be major contributors to excess calorie intake for many people.
How much of a calorie surplus causes weight gain?
It does not take a massive calorie surplus to gain weight. A subtle imbalance between calories consumed and calories burned over time is all it takes. Here are some estimates on how calorie surpluses can lead to weight gain:
- 100 extra calories per day could lead to about 10 pounds of weight gain per year.
- 200 extra calories per day could lead to about 20 pounds of weight gain per year.
- 500 extra calories per day could lead to about 50 pounds of weight gain per year.
This shows that even an extra 100-200 calories per day, which is easy to consume from small portion size increases, extra snacks, or bigger beverage sizes, can easily pack on 10-20 pounds over 12 months. The little things add up over time.
To put it another way, cutting out or burning just 100-200 calories per day more than you consume could prevent up to 20 pounds of weight gain per year. Small calorie deficits and surpluses make a big difference long-term.
What are other causes of weight gain?
While excessive calorie intake is the main driver of weight gain, some other factors can also contribute by promoting fat storage and making weight loss more difficult:
Lack of sleep
Not getting 7-9 hours of sleep per night has been associated with increased hunger and appetite, higher calorie intake, and elevated fat storage hormones. Lack of sleep appears to disrupt appetite regulation.
Stress
Chronic stress exposure activates the body’s “fight-or-flight” response which triggers several hormonal changes that increase appetite and encourage fat storage in the abdomen. Stress makes weight loss more difficult.
Medications
Some prescription drugs used to treat mood disorders, diabetes, seizures, migraines, and high blood pressure can cause weight gain as a side effect. Birth control pills, antidepressants, and antipsychotics are linked to modest weight gain.
Aging
As we age, hormonal changes lead to a gradual loss of muscle mass and a slower metabolic rate. Both of these make it easier to gain fat as we get older. Calorie needs decrease with age due to lowered metabolic rate.
Pregnancy
During pregnancy, women naturally gain weight to support fetal growth and development. Weight gain of 25-35 pounds is expected. Some women find this pregnancy weight difficult to lose entirely postpartum.
Medical conditions
Some conditions like polycystic ovary syndrome (PCOS), underactive thyroid (hypothyroidism), and Cushing’s disease involve hormonal imbalances that can increase appetite and promote fat storage.
While these factors can contribute, consuming too many calories still ultimately drives weight gain in most cases. Key strategies for preventing excessive weight gain include limiting portion sizes, choosing lower calorie foods, decreasing stress, getting enough sleep, and exercising regularly. But regulating calorie intake is most vital.
How can you determine your daily calorie needs?
Here are some simple steps to determine your approximate calorie needs per day:
- Calculate your basal metabolic rate (BMR) using an online calculator. This estimates the minimum calories you burn through basic functions.
- Factor in your activity level:
- Sedentary: Multiply BMR by 1.2
- Moderately active: Multiply BMR by 1.35-1.55
- Very active: Multiply BMR by 1.6-1.8
- Make adjustments based on individual factors like pregnancy, age over 60 years old, etc.
- Aim for a calorie intake around your estimated needs for maintenance or below for weight loss.
Using online TDEE (total daily energy expenditure) calculator can simplify this process and provide an estimate of your total calorie needs per day.
Tracking your food intake and weight over time can also help gauge your personal calorie needs for maintenance and loss. Make adjustments as needed based on your unique results.
How can you maintain or lose weight?
To avoid excessive weight gain or promote weight loss, focus on achieving a calorie deficit by:
Monitoring calorie intake
Track your food and beverage calories daily using a journal, app, or other tool. This helps ensure you stay within your target intake.
Controlling portions
Use smaller plates, weigh and measure foods, and avoid oversized servings to control calorie consumption.
Choosing lower calorie foods
Focus on non-starchy veggies, whole fruits, lean proteins, high-fiber whole grains, and healthy fats. Limit added sugars, salty snacks, and fried items.
Exercising more
Aim for 150-300 minutes of moderate exercise per week to maximize calorie burn. Combine aerobic activity and strength training.
Reducing stress
Use relaxation techniques like yoga, meditation, massage, or counseling to minimize stress hormones that promote weight gain.
Getting enough sleep
Aim for 7-9 hours per night. Maintain a consistent sleep-wake cycle and limit light exposure before bed.
Sustaining an energy deficit of about 500 calories per day through diet and exercise modifications can lead to 1 pound of weight loss per week on average. This gradual loss promotes fat burning while preserving muscle mass.
Conclusion
In summary, excessive calorie intake is by far the biggest cause of weight gain over time. Consuming more calories than the body expends through metabolism and activity consistently leads to energy imbalance and fat storage. Just small daily excesses of 100-200 calories can pack on 10-20 pounds yearly. While lack of sleep, stress, aging, genetics, and some medications play a role, managing calories ultimately controls weight. Carefully monitoring intake, reducing portion sizes, lowering stress, exercising, and getting enough sleep can help maintain a calorie deficit for weight management.