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].
Women with a BMI of less than 18.5 are considered underweight. The average woman's height is 5 feet, 4 inches. If you weigh 107 pounds or less at this height, you are considered underweight with a BMI of 18.4. A healthy weight range for that woman would be 108 to 145 pounds.
The recommended ranges for healthy men are between 10-20% body fat, and for women, the ranges are 18-28%. If your body fat exceeds these ranges, but you have a normal weight when you stand on the scale, you may be skinny fat.
First, what is skinny fat? “Skinny fat” simply describes a state in which someone has too little muscle mass and too much body fat. People who are skinny fat often look normal or even skinny when wearing clothes, but look soft, weak, and flabby underneath. Hence the name, “skinny fat.”
Muscle is denser than fat, and as it is more compact within your body, as you gain muscle mass, you end up looking thinner, no matter your physical weight. So, if you've been doing a lot of strength training lately, it's likely this is the reason that you're looking fantastic but not dropping those numbers.
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].
If you are a female and in a 5′1 height your ideal weight for small frame is 106-118, and for the medium frame is 115-129. And if you are a male in a 5″1 height your ideal weight for small frame is 100 to 131 lbs, and for the medium frame is 132 to 157 lbs.
If your BMI is less than 18.5, it falls within the underweight range. If your BMI is 18.5 to <25, it falls within the healthy weight range. If your BMI is 25.0 to <30, it falls within the overweight range. If your BMI is 30.0 or higher, it falls within the obesity range.
Many people use low body weight to excuse unhealthy eating and physical inactivity. But body weight is not the best indicator of internal well-being. A much better indicator is your diet. When it comes to your health, it's what's on the inside that counts and you really are what you eat.
“Thinness is a heritable trait”
So thin people not only stay slim “by not having the obesity genes, but they also have different genes that protect them” from gaining weight, she said. The research concludes that “thinness, like obesity, is a heritable trait.”
Maintaining a healthy body weight is important, but it should not be confused with being physically fit. Simply being thin does not protect you from health conditions related to a sedentary lifestyle.
What should your waist measurement be? For men, a waist circumference below 94cm (37in) is 'low risk', 94–102cm (37-40in) is 'high risk' and more than 102cm (40in) is 'very high'. For women, below 80cm (31.5in) is low risk, 80–88cm (31.5-34.6in) is high risk and more than 88cm (34.6in) is very high.
For some people, the first noticeable change may be at the waistline. For others, the breasts or face are the first to show change. Where you gain or lose weight first is likely to change as you get older. Both middle-aged men and postmenopausal women tend to store weight around their midsections.
A BMI number is designed to give you an idea of how much body fat you have as a ratio of your weight to height. It's measured by taking your weight in kilograms and dividing it by your height in meters squared. A reading at or over 30 means you're obese. A reading at or over 40 is severe obesity.
Not eating won't directly lead to weight gain -- in fact, you may lose weight as you'll temporarily eat fewer calories than you burn. The problem is that fasting is unsustainable, so any weight-loss benefit will likely be short lived and your health will pay the price.
The lightest adult of all time is believed to be the Mexican woman Lucia Zarate who weighed only 4.7 pounds (2.13 kg) at the age of 17 (and was 21.5 inches tall). She had put on weight, and was up to 13 lb.
Shorter-statured women should ideally weigh less than taller women. Whether or not you're too skinny is a matter of preference. However, women who are 5 feet tall and weigh 100 pounds are not classified as underweight, according to the University of Washington.