Why do some people have difficulty gaining weight?

Why do some people gain weight easily, while others eat what they like and never seem to put on a pound? And still more people really struggle to add the kilos, despite their best calorie-intake efforts? 

The fact is supporting a normal healthy weight can be trickier for some people than for others. And there are many factors that affect a person’s ability to put on weight, or cause unintentional weight loss

10 reasons some people can’t gain weight

Whether a person has ‘lean genes’, high metabolism, or an underlying medical condition, we list 10 possible reasons a person may have difficulty gaining weight.

–        Genes: A naturally low Body Mass Index (BMI) can mean a slender body type for some people.

–        High metabolism: People with a faster metabolism burn more calories both exercising and resting. If you have a high metabolism you may need to consume more calories to maintain a stable weight.

–        Hyperthyroidism (overactive thyroid): Overproduction of the thyroid hormone causes accelerated metabolism, resulting in unintentional weight loss if not regulated with medication.

–        Diabetes: In type 1 diabetes insufficient insulin means the body doesn’t get enough glucose from the blood to use as energy. Consequently, the body burns fat and muscle for energy, leading to weight loss.    

–        Malabsorption syndrome: Crohn’s disease, ulcerative colitis, celiac disease, cystic fibrosis, small intestinal bacteria overgrowth (SIBO) all come under a range of disorders, gastrointestinal diseases and food intolerances that affect the body’s ability to absorb nutrients from the food we eat.

–        Prescription medication: Some medications used to treat cancer, depression, ADHD, thyroid and other conditions can cause unintentional weight loss.

–        Mental health: Poor mental health, depression and anxiety can affect a person’s appetite and therefore their nutrient intake.

–        Eating disorders: Anorexia nervosa is restricted eating that leads to a person being unable to maintain a normal and healthy weight. Bulimia nervosa is binge eating, followed by purging, or forced vomiting, and sometimes excessive exercise. 

–        Regular physical activity: If you consistently burn off more calories than you consume you will struggle to keep a stable weight. 

–        Insufficient calories: If your busy lifestyle means you regularly skip meals, or if you aren’t getting enough calories in your diet, you may find it difficult to gain weight.

How do you know if you need to gain weight?

According to the Centers for Disease Control and Protection (CDC) a person is underweight if their Body Mass Index (BMI) is less than 18.5. BMI uses a person’s height and weight, dividing their weight in kilograms with their height in metres squared to get an estimate of body fat.

Being underweight can cause health problems such as malnutrition, fragile bones, and osteoporosis. It can also lead to a weakened immune system, which increases the risk of developing infections, as well as making it harder to recover from illnesses.

See your doctor if you have difficulty gaining weight

If you’re having trouble gaining weight, or if you’re experiencing unexplained weight loss, talk to your healthcare team. They will assess you for underlying medical conditions, and if appropriate, work with you to develop a healthy weight gain plan. 

Remember, you want to focus on building lean muscle, not fat. So, any weight gain program should follow your doctor’s advice and include regular exercise to support lean muscle gain.