A fast metabolism is not the only reason behind it. The answer to this question is quite complex as several factors are at play. Genetics, nutrition, and even behavioural factors are involved which help slim people to maintain their body weight.
What causes being underweight? People become underweight for many different reasons. Some may be born naturally small and their low BMI is due to their genes. Some may have a very high metabolism and find it hard to put on weight, even if they eat foods that have a lot of calories.
Some common reasons why a person may find it hard to gain weight include: genetics. not eating enough. having a very physically active lifestyle or job.
It may be that you have a fast metabolism (meaning your body burns energy from food at a fast rate than the people around you) or you're just naturally slender. For some people, underlying health conditions and certain medications and treatments can make it difficult to reach and/or maintain a healthy weight.
Malabsorption. In some cases, an inability to gain weight effectively could indicate that a person can't absorb the calories and nutrients they consume – a condition called malabsorption.
The Complications of Being Too Thin
Registered dietitian Katherine Basbaum shares, “It's a jumping-off point to determine a healthy weight, but definitely not one-size-fits-all of healthy body factors." To get a rough idea, if your BMI is less than 18.5, you're considered underweight.
Eat more for weight gain – quality first, quantity second
You should also try and eat at least three good meals every day, with slightly larger serves if you can. If you're finding it hard to feel hungry, have five to six smaller meals instead so you're still getting the calories and nutrients your body needs.
Skinny fat people are often a normal weight (or underweight!) but because of their sedentariness, lack of muscle, or poor diet, they have a high percentage of body fat. Often, skinny fat people are at risk of certain medical issues as listed: Raised blood sugar, leading to insulin resistance or diabetes.
If you are losing weight rapidly or having trouble gaining weight, it may be time to contact your provider for help. A natural thin-build is OK, and if you maintain a healthy diet and exercise regularly – it's not a health concern.
People who are clinically underweight face an even higher risk for dying than obese individuals, the study shows. Compared to normal-weight folks, the excessively thin have nearly twice the risk of death, researchers concluded after reviewing more than 50 prior studies.
Too Skinny: What BMI is Considered Underweight? From a clinical perspective, an individual is considered “too skinny” if they are deemed underweight. According to the Centers for Disease Control, an individual is underweight if their Body Mass Index (BMI) is below 18.5 [1].
Malabsorption. In some cases, an inability to gain weight effectively could indicate that a person can't absorb the calories and nutrients they consume – a condition called malabsorption.
The higher your metabolism, the more calories you will burn and the harder it will be to gain weight. Having a fast metabolism is often genetics – if your parents or grandparents were thin, chances are you will be too. This can also mean that you have to eat more calories than the average person to gain weight.
For a 3,000-calorie diet, you may want to think about each meal consisting of 700 to 800 calories and snacks providing about 200 to 300 calories. Including adequate balances of protein, fat, and carbohydrates at each meal and for each snack will keep you fuller for longer.
BMI values of less than 18.5 kg/m2 are considered underweight. BMI values between 18.5 kg/m2 to 24.9 kg/m2 are healthy. BMI values between 25 kg/m2 to 30 kg/m2 are overweight. BMI values greater than 40 kg/m2 are considered obese.
If your BMI is: under 18.5kg/m2 – you are considered underweight and possibly malnourished. 18.5 to 24.9kg/m2 – you are within a healthy weight range for young and middle-aged adults. 25.0 to 29.9kg/m2 – you are considered overweight.
Muscle mass: It takes more energy (calories) to build and maintain muscle than fat. People with more muscle mass often have faster metabolisms that burn more calories. Age: You lose muscle as you get older, which slows down the metabolism. Sex: Males tend to have faster metabolisms than females.