BMI + Body Fat

Approx how many calories to consume per day

• males (16-50 yrs old): 2400-2800 calories/day, assuming a moderate activity level

• Females (16-50yrs old) 2000-2200 calories/day, assuming a moderate activity level

Maintaining a balance between….

• Energy intake (caloric intake)

→ you have (some) control over your dietary choices

→ prioritize nutrient dense, natural foods as much as possible

→ avoid sodium, saturated fat, and added sugar (in any form) as much as possible

Energy output or expenditure (caloric output)

• Basal/resting metabolic rate

→ accounts for ~60% of your caloric expenditure

• Thermic effect of digestion

→ aka the “specific dynamic action” or “diet induced thermogenesis”

→ accounts for ~8% of your caloric expenditure

• your lifestyle/activity choices

→ accounts for ~32%

→ you can modulate this too!

If you can maintain caloric balance (caloric intake = caloric output)

you will maintain body fat levels and your current health status (for better or worse)

• if body weight does not change over the course of several weeks, caloric balance has been achieved

if caloric intake > caloric output…

• that is called “positive caloric balance”

• you will gain abdominal fat and that leads to higher likelihood of negative physical and mental health outcomes

if caloric output > caloric intake…

• that is called “negative caloric balance”

• you will lose abdominal fat and that promotes physical and mental wellness

Body Mass Index (BMI)

• BMI = Body mass (kg)/Height² (m²)

• most common measurement of body condition in clinical and research settings

→ can be collected easily and lends itself well to LARGE population-based studies of body condition and health risks (w/ some caveats)

Multiple studies from the early 2000s have found that it is NOT unhealthy to have a BMI in the overweight category…

Providing some energy reserves for stressful times

• however, being in the underweight and obese categories does lead to significant health risks

Important limitations of BMI measurements

• it does not actually measure body fat, which is the main factor that determines negative health outcomes

• it is inaccurate for very muscular individuals, bc they weigh more than their height would predict

→ there are much better ways of actually measuring body fat, but they are more difficult to deploy to large populations

— muscle man vs chubby man

~using body roundness index

The best way to measure body fat

• calculating body fat requires a measure of body density, as shown in this equation

Hydrostatic weighing allows for a VERY accurate measurement of body volume

• therefore, it is the gold standard for measuring body fat percent

• subjects re weighed on dry land AND while submerged in a water tank and with all air pushed out of their longs

• These two weights are used to calculate body volume

→ the difference between these two weights is small for muscular individuals, bc muscle mass is denser than water

→ the opposite holds for ppl with high body fat, which is less dense than water

Air displacement plethysmography (The “Bod Pod” can also determine body volume and fat percent

• the volume and pressure inside the chamber are known

• placing a person in the chamber decreases the volume of air

→ therefore it will increase the pressure

• this change of pressure is used to measure the subject’s volume and therefore calculate their body fat

Skin fold analysis

• measuring the thickness of four skin folds at specific sites around the body

• sum those values and compare to a table to determine body fat percentage

Bioelectrical impedance

• measures the resistance of body tissues to the flow of a small electrical signal

• more body fat leads to more resistance

• less body fat leads to less resistance

• some small smart scales can do this or you can find devices to do this at your local heath club or some health food stores