4.1: Introduction to Weight Management

Weight Management

You have likely seen weight loss ads in the newspaper, magazines, or in your social media feed. With about 50% of the U.S. population saying they tried to lose weight in the last 12 months^[1], it is not surprising that the weight loss industry is estimated to be a $3 billion dollar industry.

Although this chapter will address those who are underweight, the predominance of information will relate to persons who are overweight or obese. Overweight and obesity are linked to more deaths worldwide than underweight. In the U.S., an estimated 1.5% of adults aged 20 and over are underweight^[2], compared to about 42% of adults who are considered obese. The goal is to strive for a healthy weight since persons who are underweight or overweight have negative health implications.

This chapter focuses on body weight and body composition. Both body weight and body composition are important measurements to understand your health. Body weight is typically measured in pounds or kilograms and is simply your body’s total mass. Body composition is what your weight is made of (muscle, bone, water, and fat) and is typically measured as a percentage of body fat. For example, a person might have a body weight of 200 lbs and a percentage body fat of 30%, in this example, 60 lbs of their body weight comes from fat, while another person also weighing 200 lbs with a body fat of 15% will only have 30 lbs of their body weight come from fat. Although body weight is the measurement most commonly used to assess the health of our body size, body composition is a more accurate look at our body size by understanding what the body is made up of. It is quick and easy to step on a scale and measure your body weight, but measuring body composition is much more challenging, thus body weight is the standard used to address overweight and obesity.

Fat is not bad, we need fat for healthy cellular function, energy, cushioning for vital organs, insulation, long-term energy storage, and absorption of fat-soluble vitamins. The minimum amount of body fat needed by males is about 3% and females is about 12%. It is generally accepted that an overall range of 10-22 percent for men and 20-32 percent for women is considered satisfactory for good health. This necessary body fat for health is considered essential body fat. When the body stores additional body fat above the essential amount it is called non-essential body fat. A woman’s essential fat range is naturally greater than a man’s because of fat deposits in breasts, uterus, and sex-specific sites.

The Calorie Balance Equation and Metabolism

The energy (Calorie) balance equation, simply compares the energy you take in from your diet to the energy you expend. If a person consumes an excess of 3,500 Calories that is the equivalent of gaining one pound of weight. That means if you reduce your daily calorie intake by 500 calories or burn 500 more calories each day than you consume, you may be able to lose a pound a week. Caloric expenditure is most often associated with exercise, however, most of our daily caloric expenditure is to maintain bodily functions, like breathing, circulating our blood, and digesting food.

The term used to describe the chemical processes in the body that convert Calories into energy is Metabolism. Your body needs a minimum number of Calories to sustain these functions. Basal Metabolic Rate (BMR) and Resting Metabolic Rate (RMR) are measurements used to estimate how many calories your body burns when you’re not exercising. These two measurements are often used interchangeably, however they do have a slight difference. A BMR measurement is slightly more accurate because it is measured when you are doing nothing, just upon waking up, while lying down in a dark room after sleeping for at least eight hours, and fasting for 12 hours. RMR is taken without the strict conditions of the BMR; BMR is usually slightly lower than your RMR. Both Basal metabolic rate (BMR) and resting metabolic rate (RMR) measures the amount of energy (Calories) that your body needs to stay alive and function properly. It is helpful to understand your BMR/RMR since it accounts for about 60-80% of your total energy expenditure each day. Your BMR/RMR is affected by your weight, height, age, gender, and genetics. A key component of your weight that impacts BMR/RMR is the amount of muscle you have; muscle mass increases BMR/RMR.

Defining Overweight and Obese

One commonly used measurement to identify if a person is overweight or obese is called the Body Mass Index (BMI), which is based on a person's weight versus their height. BMI is used because it is an inexpensive and easy screening method to identify weight categories (underweight, healthy weight, overweight, and obesity). It is important to recognize that BMI does not assess body composition or body fatness, it is simply a measurement of body size and is used as a screening tool. Although it may not be accurate for some of the population, for example, athletes with high muscle mass, it is correlated to other more accurate measures of body fatness and various weight-related diseases.

BMI is a person’s weight in kilograms divided by the square of height in meters:

BMI= weight (kg) / [height (m)]2

Table (\PageIndex{1}\): BMI Indicators

BMI	Weight Status
Below 18.5	Underweight
18.5 – 24.9	Healthy Weight
25.0 – 29.9	Overweight
30.0 and Above	Obesity

As noted previously, BMI is the most commonly used tool to assess health weight, but for many people, it is not an accurate measurement because it does not assess your body composition. For example, two people can have the same height and weight, thus the same BMI, but one could be a professional athlete who is very active with low body fat and the other could be sedentary with high body fat.