Weight management Flashcards
what is the energy balance equation?
Energy intake = energy expenditure +- energy stored
Energy expen doesn’t tend to change
Energy intake can be changed
Energy intake > expen = store energy
Intake < expen = wont store energy in body - lose energy and weight - fat stores
units of food energy
SI unit: joule (J)
- Energy used when mass 1kg moved through 1m by force 1N
Non-SI unit: calorie (cal)
- Energy required to raise temp of 1g water by 1 degree
- Kcal = energy required to raise temp 1kg water by 1 degree
1kcal = 4.2 kJ
the total (gross) energy value of food
Total energy value
- Estimation in bomb calorimeter
- (Oxidation to CO2, H20 and N02)
Bomb calorimeter:
- Food is ignited electrically in presence of oxygen
- Heat of combustion measured from rise in water temp
Works well for carb and fat
Protein not fully combusted in body – broken down to ammonia and urea
what is metabolisable energy?
energy actually supplied to tissue by each food
Fibre and plant sources passed through as faeces
Digestible energy left
Metabolisable energy – energy body actually uses – calories
metabolisable energy of macronutrients (Atwater factors)
table
Diff carbs have diff monomers – pure glucose doesn’t produce same energy as fructose – not all plant material combusted – not all carb equal
Same for fat – most fat digested – very energy dense – can be stored densely – not stored with water
HoC for protein variable – AAs have diff HoC – digest most but some not fully digested depending on source – not fully oxidised
Alcohol also has calories
components of energy expenditure
Basal/resting met rate (BMR/RMR)
- Accounts for 60-70% total energy expen – fuel body processes
Energy expen of PA (EEA)
- Accounts for 25-30% energy expen – greater if athletes – lots of training
- Non-ex activity thermogenesis (NEAT) – fidgeting, get up and move around, everyday activities
- Deliberate ex
Diet-induced thermogenesis (DIT)
- Increase in met rate after meal – accounts for 10% energy expen – takes energy to digest, break down and store food/meal
basal metabolic rate
Minimum level of energy to sustain vital functions in waking state – heart, breathing, protein turnover
Heart and resp functions = 10%
Protein turnover = 25%
- Related to FFM – larger amount = higher rate
Fat and carb turnover
Maintenance of ion gradients across membranes
Measurement
- In supine position – no muscle contraction
- Thermoneutral env – don’t want shivering
- After 8h sleep and 12h fasting
diet induced thermogenesis
Energy required to digest, absorb and assimilate food nutrients
Obligatory thermogenesis
- Protein – 20-25% - requires lots of energy
- CHO – 5-7% - don’t have major store
- Fat – 2-4% - doesn’t take much energy to store and not used to synthesise structure
Adaptive/facultative thermogenesis
- Due to increase in sympathetic NS activity in response to feeding
thermic effect of ex
(EEA)
Sedentary indv: 10% of EE, athlete: 15-30% EE
thermic effect of illness
Partial starvation – -10-40% RMR
Postabsorptive - +10
Multiple fractures - +10-30%
Severe infection - +30-60%
3rd degree burns (>20% BSA) - +50-100% - temp raised to body temp – maintain met rate
what is obesity?
too much body fat
% body fat
- Men >30%
- Women >35%
Waist circumference
- Men >102cm
- Women >88cm
Waist:hip ratio
- Men >0.9
- Women >0.85
internal control of energy intake (homeostatic)
Evolved to be able to store fat well and energy
Body adapted to take in as much as possible to be stored
Hunger – need food
Satiety – have enough energy – stop eating
Desire of hypothalamus is to eat – protect from starvation
Melanocortin system – stops us eating
Neuropeptide Y – promotes eating – signals to give you the desire to eat
Peptide YY, GLP1 – incretin hormones – short peptides – used in treatment diabetes – anti-obesity drugs
Don’t get signal to stop eating if hypothalamus resistant to leptin
Reduced gut hormones – continued desire to eat
external factors influencing intake
Psych (non-homeostatic)
- Cortical and limbic system influences to overcome metabolic determinants of eating – related to reward/pleasure pathways – ‘always room for dessert’ – simulated most by sweet and fatty ratio
- Palatability
- Variety
Cost
- Cheaper foods often energy dense
Convenience/time of day
- Snacks often energy dense
Social and peer pressure – eating is a social activity – want to eat if you see others doing it
genetic causes - leptin deficiency
Female, at 9 years, weight nearly 100kg
Homozygous mutation in leptin gene
V. low blood leptin concentration despite body fat exceeding 50% body weight
Hyperphagia
Monogenic disease
Designed recombinant leptin – injected it – desire to eat reduced and body weight started to decrease
Didn’t work with others – hypothalamus becomes resistant
low PA
due to PA rather than energy intake
dietary components
Fat
- Many ‘fat foods’ and convenience products contain high levels fat
- Leads to passive overconsumption energy
- Some evidence that indvs with reduced ability to oxidise fat at risk of weight gain
Sugar
- ‘Hidden’ energy consumption
- Decreases fat oxidation and increases fat storage
- Fat/sugar combo
- Increase in insulin – prevents fat oxidation
Alcohol
- Decreases fat oxidation and increases fat storage
- 7 kcal/g
high fat/energy dense foods lead to passive overconsumption
In facility for 7 days – measured energy expen and intake – accurate
Meals had hidden fat – all looked and weighed the same
All ate same amount over 7 days
Lost weight in low fat
Medium and high put on weight
Easy to overconsume energy in form of fat – hidden in food
preventing obesity: ex v diet
1g fat = 9kcal
70kg indv running at 8min/mile pace would expend approx. 900kcal in 1h
How many g fat?
High-intensity exercise tasks are usually not feasible for individuals with very high BMI and body fat %.
Energy expenditure that can be achieved through more gentle physical activity is more typically <500 kcal/day
45 g of fat
Therefore, achievable increase in energy expenditure through exercise must be used in conjunction with reduced daily calorie intake.
dietary advice
600-700 kcal/day weight loss is manageable
- = 4500 kcal/week
- 1 kg of fat = 9000 kcal
- = 0.5 kg/week or 13 kg over 6 months
Most weight loss is 75-90% adipose tissue and 10-25% FFM
Requires change in lifestyle
- Commitment of patient to change
Diet
- Low fat, low energy density, low energy content, high fibre.
- Replace saturated with monounsaturated fat, high GI with low GI foods, and increase protein (20% or greater)
- Very low calorie diets (800 kcal/day for several weeks) also efficacious
bariatric surgery
Reduces energy intake to 1200 –1500 kcal/day
> 30% weight loss in first year which is maintained for many years
Protein malnutrition?
Iron deficiency and vitamin D deficiency
Increases gut hormone response patients feel full with reduce desire to eat
how do you prevent caloric disparity?
energy output = energy input
how much of the US popn are overweight/obese?
65%
30.5% obese
leads to increase in diabetes and CV disease
what % do genetic factors account for in excessive body fat accumulation?
25-30%
what happens with a defective gene for adipocyte leptin production and/hypothalamic leptin insensitivity?
causes brain to assess adipose tissue status improperly
creates chronic state of pos energy balance
how much does the standard dietary approach to weight loss lose?
0.5kg/week
5-20% actually lose weight
1-2/3 returns weight within a year and all within 5 years
why does reducing body fat improve perf?
directly increases relative muscular strength and power and aerobic capacity
reduced drag force
what 3 methods unbalance energy balance equation to produce weight loss
1) reduce energy intake below daily energy expen
2) maintain normal energy intake and increase energy output
3) decrease energy intake and increase energy expen
what are the disadvantages of extremes of semistarvation?
loss of FFM
lethargy
possible malnutrition
depressed resting metabolism
how can you increase body’s ability to conserve energy?
repeated cycles of weight loss-weight regain
makes weight loss with subsequent dieting less effective
what does daily energy expen consist of?
sum of resting met, thermogenic influences and energy generated during PA
PA affects variability among humans in daily energy expen
what do moderate increases in PA do?
blunt appetite and depress energy intake of previously sedentary, overweight person
what does ex do?
enhances fat mobilisation and catabolism
aerobic retards lean tissue loss
resistance increase FFM
what does rapid weight loss during first few days of caloric deficit reflect?
loss of body water and stored glycogen
greater fat loss occurs per unit weight lost as caloric restriction continues
