Nutrition, Body Comp, and Obesity

obesity basics

an increasingly convenient lifestyle, characterized by environments that promote unhealthy food intake and physical inactivity

overweight

• body weight that exceeds some predetermined average for height

– A person who is overweight has usually experienced an increase in body fat but not always, as in the case of muscular athletes.

overfat

condition of having more than a healthy amount of body fat

obesity

overfat condition that is accompanied by a host of comorbidities

increased risk of chronic illness and diseases

– Greater than 32% in women

– Greater than 25% in men

normal reproductive function

• A range of 12% to 17% body fat is necessary for normal reproductive function.

• 3% in men

body comp models

1. Fat mass (FM)

2. Fat-Free mass (FFM)

• 73.8% water

• 19.4% protein

• 6.8% mineral

• Assumptions built into model about density of tissue

- Water, bone mass

BMI

• calculated as the ratio of one’s weight to height:

– BMI = Weight (kg)/Height² (m)

advantages: not invasive

disadvantages: inaccurate

use of BMI in clinical setting

– APPROXIMATE degree of body fat

– Measure against which progress can be compared

– Provides potential health-risk factors

– Starting point for discussion about the relationship between body fat and chronic disease

android pattern

storing fat in the abdominal area

• apple shape

• more common in men

• greater risk of heart diseases, hypertension, diabetes, and stroke

• high waist to hip ratio

gynoid pattern

storing fat in the hips, buttocks, and thighs

• pear shape

• more common in women

waist circumference: high risk

Men > 102 cm (40 inches)

Women > 88 cm (35 inches)

bioelectrical impedance analysis (BIA)

• measures the resistance to an electrical current as it travels through the body’s water pool.

– Total body water (TBW) contains electrolytes, which conduct electricity.

– Conductivity of an electrical impulse is greater through lean tissue, which contains water, than through fatty tissue.

assumptions of BIA

• Electricity flows when conducive elements present

• Flow of current through body will follow path of least resistance.

• Conductive elements (electrolytes) present in body water

• Adipose tissue = less water and FFM = more body water

Greater TBW → Greater FFM

ultimate assumption from BIA

less resistance to electric current (from start to finish of circuit) means more FFM, less fat mass

skinfold method

• Indirect measure of subcutaneous adipose tissue

• Various measures of subcutaneous adipose tissue are summed and put into a regression model

• Skinfold predictions estimate body density (subsequently %BF is estimated from density)

– Curvilinear relationship between SKF and density

assumptions of skinfold method

• SKF is a good measure of subcutaneous fat

• Fat distribution (subcutaneous vs. internal) is similar for all individuals within gender

• Σ SKF can be used to estimate total body fat

• Relationship between Σ SKF and body density

reference methods of body comp assessment

• Densitometry

– Hydrostatic weighing

– Air displacement plethysmography

Dual-energy X-ray absorptiometry

hydrostatic weighing

• In the past hydrostatic weighing was considered the “gold standard” for computing body composition.

– Estimates body composition using measures of body weight, body volume, and residual lung volume

Air plethysmography (Bod Pod)

– Another densitometry technique

– Air displacement (instead of water)

– Easy for subject, less upkeep than hydrostatic weighing, expensive

• Similar concept to hydrostatic weighing

- Estimates body composition using measures of body weight, body volume, and sometimes residual lung volume

- Replacing UWW as standard in labs

Dual energy x-ray absorptiometry (DEXA)

– Measures absorbance of x-rays at two different energies

– Fat, bone, and fat-free mass have different absorption properties

– Can also measure bone density

assessing body comp and athletes

–Height and weight not enough to know fitness status

– more percent body fat, less performance

weight standards

• Possibly misleading

– Elite athletes define optimal performance.

– But do they define the optimal body? Not always!

Fat-free mass (including muscle)

–Important variable for athletes to know

– ↑ good for power, strength, muscle endurance

–But bad for aerobic endurance (more mass to carry)

Relative body fat (percent body fat)

– Fat: dead weight but useful energy store

– Less fat usually = better performance

– Exceptions: sumo wrestlers, swimmers, weightlifters

inappropriate use of weight standards

– Standards ignored by many coaches, players

– Misconception that small weight loss good, large weight loss better

– Possibly ↓ performance, eating disorders

– Sports with subjective scoring problematic

Making weight: severe weight loss

– Examples: wrestling, boxing

– Weight classes → extreme weight loss

–Competing in class too low → injury, poor health

risks with severe weight loss

• Dehydration

– Fasting, extreme caloric restriction à water loss

– 2%-4% weight loss as water à impaired performance

– Risk of kidney/cardiovascular dysfunction, death

• Training deaths of wrestlers

• Chronic fatigue

– Underweight → fatigue → ↓ performance, injury

– Mimics overtraining and chronic fatigue syndromes

–Underweight → substrate depletion

appropriate weight standards

– Body composition, not total body weight

– Optimal range of percent body fat

– Recognition of sex differences

weight standards not always appropriate

– Technical measurement errors

– “Ideal” composition not always best for performance

• Individual variation

• Trial and error with training, find best balance of performance and weight for overall health

fasting and crash diets

– Cause more water and muscle loss, less fat loss.

– Ketosis accelerates water loss.

Optimal weight loss: ↓ fat mass, ↑ FFM

– Moderate caloric restriction + exercise

– Caloric deficit ~200-500 kcal/day

– Loss ≤ 0.5-1 kg/week

- Slowing of weight loss when near goal

increases; decreases

•With age, fat mass _ ; lean body mass _

obesity effects

– Earlier onset of obesity

– Increasing rates of obesity

– Earlier onset of obesity-related diseases

factors controlling body weight

– Hormones

• Including leptin, ghrelin, human growth hormone

– Appetite

– Energy expenditure (variable in response to weight loss or decreased energy intake)

RMR

– Body’s metabolic rate in the early morning

– 60%-75% of total energy expenditure

TEF

– Energy expended to digest and store nutrients.

– 10% of total energy expenditure

– Possibly defective in obese individuals

TEA

– Energy expended to accomplish activities

– 15%-30% of total energy expenditure

Balance of RMR, TEM, TEA

– Aid for adaptation to ↑ or ↓ kilocalorie intake

– Controlled by sympathetic nervous system

– Key for maintaining weight around set point

physiological factors for obesity

– Heredity (genetics)

– Hormonal imbalances

– Altered basic homeostatic mechanisms

lifestyle factors for obesity

– Cultural habits/factors

• SES (i.e., income, savings, education, property ownership, etc.)

– Inadequate physical activity

– Improper diet

5-10%

a weight loss of just _ can reduce the risk of many chronic conditions associated with obesity.

positive energy balance

Calories Consumed > Calories Used

negative energy balance

Calories Consumed < Calories Used

energy balance

Calories Consumed = Calories Used

total daily energy expenditure

the amount of energy (kcal) your body burns per day

components of TDEE

1. Basal metabolic rate (BMR): energy for. breathing, circulation, etc

2. Thermic effect of food

3. Physical activity

3500 kcals

1 pound body weight

• To lose 1 pound of weight per week: cut 3500 kcal/7 day = 500 kcal per day