3.2: How Much Should You Weigh?

The question really is, How fat should you be?, because weight and fatness aren’t the same. True, weight is one indicator of the amount of fat we store. But it can be a deceptive indicator. Consider the illusion wrought by water loss in some reducing diets. Remember, too, the wide variation in body shape and composition. Bone and muscle weigh more than fat. A stocky, burly person can weigh half again as much as the thin ectomorph of the same height.

Does this mean that the burly person is overweight? Does it mean that the thin person is underweight? In one perspective, the answer to both questions is yes. For if we measure these people against the charts of height and weight, one is above and the other below “normal weight.” But relative body weight isn’t a reliable index of fatness except in the extreme. Someone who is 5 feet tall and weighs 300 pounds is indeed likely to be fat.

As early as World War II, interest in standards for physical fitness led to studies that compared overweight to fatness. Football players, for example, averaged well above U.S. Army height-weight standards. But they proved to have low body fat. They were overweight, but not overfat.

But in practice, height and weight are easily measured whereas body fat isn’t. Body Mass Index (BMI) is commonly used to assess body weight.¹ Its main advantage is that it puts height and weight into a single number. BMI is your weight in kilograms divided by the square of your height in meters (kg/m²). A short-cut method is to multiply your weight in pounds by 703 and divide that number by the square of your height in inches:

Ht	Wt	Ht	Wt	Ht	Wt
4'10"	89-119	5'5"	111-150	6'0"	136-184
4'11"	92-123	5'6"	115-154	6'1"	140-189
5'0"	95-128	5'7"	118-159	6'2"	144-194
5'1"	98-132	5'8"	122-164	6'3"	148-199
5'2"	101-136	5'9"	125-169	6'4"	152-205
5'3"	104-141	5'10"	129-174	6'5"	156-210
5'4"	108-145	5'11"	133-179	6'6"	160-215

Table 3-1: Height, weight for BMI = 18.5-24.9

Your BMI presumes (correctly in most cases) that excess weight is mostly excess fat, but it doesn’t indicate how the fat is distributed. Having a lot of excess fat around the belly (abdominal fat, see Metabolic Syndrome in Chap. 9) increases the risk of disease (e.g., diabetes, high blood pressure, heart disease) even if one’s BMI is low. Also, the range in body weight for the BMI categories helps take into account that at a given BMI, body fat is higher in women than men, higher in Asians than whites, lower in blacks than whites, and lower in athletes than non-athletes.¹

How Fatness is Measured

Measures of weight, height, and waist circumference give a fair estimate of fatness, but more accurate measures are needed by research scientists. Others, such as athletes, also may want to have a more exact measure of body fat. The most inexpensive and easiest measure—especially in studies involving large numbers of people—is the “pinch test.”

Most of our fat stores can be found under our skin. The underlying fat adheres to the skin when it’s pinched, so measures of the width of “pinches” reflect the amount of body fat. Special calipers are used, and the measurements are made by trained personnel.

Typically, a person’s skinfold is measured at several sites, since people vary in where they deposit their fat stores. Three sites commonly measured are: the triceps (underside of the arm, midway between shoulder and elbow), the subscapular (below the shoulder blade), and the subcostal (just below the lowest rib).

Other measures of body fatness include measuring body density by underwater weighing (fatter bodies weigh less under water because fat “floats” in water whereas muscle and bone do not), and bioelectric impedance analysis (BIA), in which an electrode is attached to an arm and a leg and a mild electric current is passed between the electrodes (lean tissue facilitates the current, whereas fat tissue impedes it).

Realities of Losing Fat

In theory, tipping the balance of energy, so that the body loses some of its fat reserves, could hardly be simpler. You have only to achieve some mix of more energy expenditure and less caloric intake whereby more calories are used than taken in. However, “calories-out” and “calories-in” are not two separate “buckets;” There are dynamic interactions.

The laws of energy conservation tell us that energy is never really lost. Calories have to go somewhere, and add up to a neat balance at the end. This basic principle is often overlooked in judging popular weight-loss schemes. If ideas about weight control can’t account for an energy balance, they can’t be based on reality. You can’t have it both ways: you can’t “eat all you want,” avoid “tiresome exercise,” and expect to lose weight.

Most of us seem to settle in at a certain body weight. This weight is popularly referred to as a “set-point.” This phenomenon is thought to be part of the reason why it’s so easy to regain the weight we so painstakingly lose on a reducing diet. The intricacies of how this setpoint works are just beginning to be understood.²

Leptin, for example, plays a role as a hormone made by our fat cells in proportion to how much body fat we have stored—it sends a signal to stop eating when our “fat tank” has been replenished. There’s substantial evidence that increased exercise can lower the “set-point” in someone who is overweight. In any event, there are many good reasons for being physically active—fat or not.