Why don’t we gain weight no matter what we eat? 15 reasons why we don’t get fat. How to gain weight and gain it faster? Is there a way to increase weight quickly but healthily?

Sunday, March 09, 2025  Read time5 min

If you are underweight and want to gain weight, there are simple methods to gain weight quickly but naturally, which we will explain in this article.

Why don’t we gain weight no matter what we eat? 15 reasons why we don’t get fat. How to gain weight and gain it faster? Is there a way to increase weight quickly but healthily?

Obesity is one of the problems of modern societies, but there are also people who suffer from excessive thinness. Just as obesity causes many problems, being underweight and lacking weight is also dangerous, as it leads to malnutrition, a weakened immune system, osteoporosis, reduced energy levels, weakness, fatigue, anemia, childbirth complications, menstrual disorders, etc. However, if this thinness is not excessive and does not cause malnutrition-related problems, it is not problematic. On the other hand, there are many women who are unfamiliar with weight gain and even return to their pre-pregnancy size a few months after giving birth. Generally, there are many indicators used to identify thinness in individuals, but the BMI index is one of the most reliable. If the BMI (Body Mass Index), which is calculated by dividing weight in kilograms by the square of height in meters, is below 18.5, the person is considered underweight and should view this thinness as a health condition that needs to be treated.

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Is being underweight dangerous?

Before we explain the reasons for not gaining weight, it's good to know the potential dangers of being underweight. Just as obesity causes many problems, being underweight and lacking weight is also dangerous because it leads to malnutrition, a weakened immune system, osteoporosis, reduced energy levels, weakness and fatigue, anemia, childbirth complications, menstrual disorders, etc. However, if this thinness is not excessive and does not cause malnutrition-related problems, it is not problematic.

How to know how much weight you are lacking?

There are many indicators used to identify thinness in individuals, but the BMI index is one of the most reliable. If the BMI (Body Mass Index), which is calculated by dividing weight in kilograms by the square of height in meters, is below 18.5, the person is considered underweight and should treat this thinness as a disease and seek treatment.

Are you in a hurry to gain weight?

The best way to gain weight is to eat six calorie-rich meals daily. Foods like cheese, olive oil, nuts, and pasta can be added to your meals to increase their calorie content.

Additionally, instead of drinking only water, add high-calorie drinks like milk and whey protein shakes to your diet. If you want your extra weight to turn into muscle, be sure to perform stretching and jumping exercises at least twice a week. Keep in mind that in order to gain weight naturally, it is necessary to sleep enough, eat properly in suitable conditions, and exercise.

Why don’t some people gain weight?

If you are underweight and want to reach an appropriate weight, you should know that underweight, just like overweight, can be caused by poor eating habits or certain health issues that threaten our well-being. Below are 15 common reasons why some people don’t gain weight:

  1. Loss of appetite and insufficient food intake
    Loss of appetite is often caused by mental issues and stress. To gain weight, you need to eat food, and if you have no appetite, it is better to write down what you eat each day, and you will realize that you are not eating as much as you thought.

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  2. Eating slowly
    Some thin individuals eat very slowly. Eating slowly gives the brain enough time to receive fullness signals. Eating quickly can lead to overeating because the brain receives the "full" signal too late.

  3. Neglecting meal plans
    Thin individuals may have a nutritious meal only 1 or 2 days a week. Some may feel full quickly by eating very little or not-so-nutritious food.

  4. Skipping breakfast
    Eating all meals is essential for this group. However, they may easily skip some meals, especially breakfast.

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  5. Choosing the wrong foods
    Foods like salads and spinach are very healthy, but they do not help with weight gain. We need calories, so we should focus on calorie-dense foods like pasta or nuts.

  6. Genetic factors
    Another cause of being thin is genetic reasons. Some people may eat a lot but still not gain weight. There isn’t much to do for such individuals except engage in muscle-building exercises to make their body more muscular and less bony.

  7. High physical activity
    If a person’s job involves a lot of physical activity and they burn a lot of calories, the amount of food they eat may only be enough to meet their body's energy needs, preventing weight gain.

  8. Incorrect exercise routines
    Exercise, along with a proper weight-gain diet, is helpful, but not all exercises are suitable. Muscle-building exercises can help.

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  9. Fear of adding fat
    Many of us want to gain weight without adding fat. This is an impossible goal. The right approach is to accept the inclusion of some fats in the weight-gain process and then focus on converting them to muscle once the goal is achieved.

  10. Inconsistent diet
    No method will work if it is not followed consistently. If you follow a diet for a few days and then ignore it for a few more days, don’t expect to see results.

  11. Wrong beliefs about gaining weight
    One of the obstacles to gaining weight is our belief system. We believe that because our family members are thin, we too will remain thin.

  12. Losing hope of gaining weight
    Some people expect results as soon as they start their diet, constantly checking the scale without realizing that seeing results might take at least a month. This leads to discouragement and giving up.

  13. Metabolism
    People who are underweight typically have a high metabolism. Metabolism refers to the amount of energy the body needs for daily activities like heartbeat, breathing, maintaining body temperature, etc.

  14. Stress and emotional tension
    These factors can cause some people to lose weight, a condition often referred to as "drying up." Stress can cause weight gain in some individuals and varies from person to person.

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  15. Certain medical conditions
    Parasitic diseases, digestive disorders, and hyperthyroidism can prevent weight gain. However, these conditions can be controlled and treated with medical intervention.

Unhealthy weight gain for underweight individuals can lead to diseases like high blood pressure, high cholesterol, and diabetes. Therefore, be sure to consult a nutrition specialist to reach your ideal weight.

How to have successful weight gain?

If you have tried multiple times but have not succeeded in gaining weight, the first recommendation is to consult a nutritionist or seek help from a dietitian. There are also some general tips for successful weight gain, which are listed below:

  • Go to bed on time and wake up on time.

  • Drink water after waking up.

  • Avoid stress, anger, and pressure.

  • Control or eliminate caffeine and coffee consumption.

  • Never exercise on an empty stomach.

  • Drink beverages containing carbohydrates and proteins during exercise.

  • Eat calorie-dense, nutritious foods.

  • Never skip meals to save calories.

  • Eat small meals frequently.

  • Never skip breakfast.

Final Thoughts

To reach an appropriate weight, follow a healthy diet program specifically designed for weight gain and keep eating. With healthy nutrition and bodybuilding exercises, you can increase muscle mass and boost your metabolism.