Energy Balance, Body Mass and Health

Energy

The ability to do work (W=Fd)

Form of energy

• chemical (form stored in chemical bonds between atoms)

• thermal (form which releases heat)

• electromagnetic (form which travels in waves)

• mechanical (form involved with movement)

• electrical (form resulting from movement of charged particles)

Potential energy

form of stored energy

has the ‘potential’ to do work

Kinetic energy

form of energy in motion

kinetic = relating to motion

Units of energy

Kilojoules (kJ)

Kilocalories (Kcal)

Note:

• Calories (Cal) x 4.186 = kilojoules (kJ)

• Kilojoules (kJ) / 4.186 = Calories (Cal)

Metabolic processes in the body that require energy

• Muscle contraction

• nerve impulse conduction

• Active transport

• Digestion

• Biosynthesis

• Storage of nutrients

• Maintenance of body temperature

Metabolic rate

the rate of energy output by the body

Resting metabolic rate (RMR)

Energy cost at rest (energy body needs to perform only essential activities)

Basal Metabolic Rate (BMR)

standardized measure of metabolic rate during complete rest (more restrictive: individual is fasted (12hr), rested (8hr) and inactive but awake)

Total Metabolic Rate (TMR)

BMR/ RMR + energy from output from physical activity (taken over a 24 hour period)

• gives us a guide to how much energy to consume to regulate a healthy weight

Determinants of Basal Metabolic Rate

• weight

• height

• surface area (greater SA:vol means more heat loss)

• age (younger = more growth + muscle mass)

• gender (males = more muscle)

• Muscle mass

• hormones (thyroid, progesterone)

• pregnancy + lactation

• stress (increased cortisol = prolonged behavioural response not always immediate)

• food-induced thermogenesis (increases rate)

• health state

• ambient temp

• sleep (reduces by 10-15% when you sleep)

Mechanisms to spot the patterns between physical activity levels and total metabolic rate and energy need of the body

PAL trends: numbers how that the person who is less physically active requires less energy

how to measure metabolism

• direct calorimetry (calorimetric chamber)

• indirect calorimetry (measures oxygen use/ gas exchange)

• “foodworks”

Energy storage

Visceral fat

fat stored between organs that have the most substantial impact on the development on non-communicable diseases

Energy balance

Control of food intake:
➢ Complex homeostatic mechanism with many players
➢ Key role for hypothalamus for controlling feeding behaviour (i.e., the ability to recognise satiety vs. hunger)
➢ Neural signals from digestive tract
➢ Blood borne signals related to body energy stores (e.g., blood glucose)
➢ Other peripheral signals inside the body such as hormones (e.g., insulin, glucagon, leptin and ghrelin)
➢ Body temperature (heat suppresses appetite)
➢ Psychological factors (e.g., stress)
➢ Environmental cues
➢ Health
➢ Ageing

Key objective: to maintain adequate energy stores in the body to
ensure survival

Causes of obesity

• genetics

• diet composition (increased food intake)

• decreased energy expenditure (sedentary lifestyle)

• stress/ mental health (eating behaviors)

• hormonal effects

• psychological factors

• metabolic rate

• environmental cues (culture and body image)

• smoking (cravings often substituted with food)

• genetics (the choices that people make can imprint on their future offspring)

Obesity related health issues

• Type II diabetes Mellitus

• Dyslipidemia

• CHD

• Cancer

• Osteoarthritis

• Sleep Apnoea

• Physiological factors

• joint/ mobility issues

• Gall bladder disease

• stroke

• hypertension

pros and Cons of BMI

Pros:

• does not require a skilled healthcare professional

Cons:

• does not consider someone’s body composition (they migt have high skeletal muscle but are denoated as obese)

Measurement of BMI

Body composition measured by:

• dual energy X-ray absoptiometry (DEXA)

• BodPod (air displacement Plethsmograph)

• Skinfolds

• Bioelectrical Impedance Analysis (BIA)

Metabolic Syndrome

(An increased risk of diseases)

There is a clustering of metabolic abnormalities that increase the risk of a person developing these diseases:

• insulin resistance

• abdominal obesity

• dyslipidemia

• hypertension

If we know somebody is at elevated risk of these diseases, we can. prevent/ intervene. Lifestyle modification is important in reversing the pathway of the disease progression

Adipogensis

Surplus energy converted into triglycerides + stored as adipose cells

Energy stores are important during periods of increased demands:

1. prior to pregnancy

2. prior to birth

3. prior to weaning

Influenced by:

• neurohormonal factors

• genetics

• environment

Individual differences

Hormonal Differences:
― Peripheral Adipose: Leptin; Adiponectin; Resistin
― GI Tract: Ghrelin; CCK
― Pancreatic: Insulin
― Central Hypothalamus
➢ Lack of adiposity feedback signal / receptor (in mice)
➢ Leptin → ‘The Lipostat’

Diets

Types: are you trying to reduce overall energy or only certain food groups (and their specific nutrients)

• Yo-Yo dieting not effective because they are very restrictive (because it is so far removed from your regular lifestyle that after your motivation wears off, you slip back into old habits). can change body composition (lose weight as lean muscle mass)

• Low kilojoule diet cf. low fat / low CHO diet
  ➢ May not be sustained long-term → Yo-Yo Dieting
  ➢ ↑ risk of Eating Disorders
  ➢ ↑ risk of Obesity long-term
  ➢ Nutritionally deficient in Vitamins & Minerals
  ➢ High Protein diets → ↑ workload on liver & kidneys
  ➢ Preoccupation with Weight & not Health

Relationship between fitness, obsesity and risk of non-communicable disease

Normal weight, overweight and obese but still fit all have similar risk to non-communicable disease