HNU 467 ADVANCED NUTRITION

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HNU 467ADVANCED NUTRITION
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• http//www.stfx.ca/people/pmazier/

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WHY EAT?
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Energy

• 1/3 of the average persons energy expenditure
  is for voluntary work, but....
• 2/3 maintenance of the bodys functions,
  homeostasis of the internal environment, and
  metabolic integrity.
• All the energy that we need is called the energy
  expenditure (EE).

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Energy expenditure

• Basal metabolic rate (BMR) represents the rate at
  which the body expends energy to sustain basic
  life processes
• Heart beat and blood circulates
• Breathing and respiration
• Electrical activity in nerves and muscles.

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of energy expenditure at rest
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• Wide variety of biochemical reactions occurring
  all the time in the body
• laying down reserves of fat and carbohydrate
• turnover of tissue proteins
• transport of substrates into, and products out
  of, cell
• production in secretion of hormones and
  neurotransmitters

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• When BMR is converted to units of kcal/24 hrs,
  its called the basal energy expenditure (BEE).
• The expenditure can also be referred to as
  resting metabolic rate (RMR) or resting energy
  expenditure (REE).
• Difference between the two???

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BEE REE

• Subject is fasted for 10-12 hours
• Lying down
• Completely relaxed
• Thermoneutral

• Fasting for 2-4 hours
• Individual is at rest in a comfortable position
• Slightly higher (10)

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• REE accounts for 70-90 of total energy
  expenditure (TEE) the remainder is accounted for
  by
• thermogenesis of foodstuffs,
• physical activity,
• thermoregulation.

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1. Thermogenesis

• aka thermic effects of food, diet-induced
  thermogenesis, specific dynamic actions, or the
  specific effect of food.
• Represents the increase in energy expenditure
  associated with the bodys processing of food
  digestion, absorption, transport, metabolism and
  storage of energy from ingested foods.

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2. Physical activity

• Voluntary movement most variable AND most easily
  altered component.
• Average 20 40 of total energy expenditure.
• Factors affecting energy expenditure intensity,
  duration, frequency, body mass, efficiency, extra
  movement.
• Energy expenditure can remain elevated after the
  activity has stopped.

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Thermoregulation

• Refers to the alteration in metabolism that
  occurs in the bodys maintaining its core
  temperature.
• aka adaptive, nonshivering, facultative, or
  regulatory thermogenesis.
• Occurs with change in temperature, overfeeding,
  trauma, burns, emotional stress, futile cycles
  

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Fig. 15-5, p. 536
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Units of Energy

• Energy expenditure ? units of heat ? calorie.
• Correctly, the joule is used as the unit of
  energy. To convert between cal and joule
• 1 kcal4.186 kJ OR 1kJ0.239 kcal 1 MJ 106
• 7.5 10 MJ/d for women 8 12 MJ/d for men

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Metabolic Fuels

• Metabolic energy carbohydrates (CHO), fats,
  proteins, and alcohol.
• End-products carbon dioxide, water (and urea).
• The energy yield of foods can be determined by
  measuring the heat produced when they are burnt
  in air (fundamental law of chemistry).

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Energy Yield of Metabolic Fuels

• kcal/gram kJ/gram
• Carbohydrate 4 17
• Protein 4 16
• Fat 9 37

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Metabolic fuels carbohydrates
No requirement - can be made in the
body. Average diets provide 45 energy from
carbohydrate (CHO).
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• Cons diets 35-40 of energy from fats are
  associated with ? risk of CHD, some cancers
  diets gt20 of proteins are associated with health
  problems.
• So...average diets provide 45 energy from CHO
  ideally, this should be increased to 55.)

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Metabolic fuels fat
No requirement for fat, apart from small amounts
of two PUFAs. Fat lubricates food in the mouth,
making chewing and swallowing easier. Much of
flavour in foods is in the fat. Vitamins A, D, E
and K are present in dietary fat - require fat
for absorption.
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• In countries where undernutrition is a problem,
  its difficult to eat enough of a very low-fat
  diet to meet energy requirement - whereas in
  Western countries there's a high intake of fats,
  contributing to obesity.

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Metabolic Fuel Proteins

• There is a requirement for protein in the body
  continuous small loss of protein from the body.
• Example hair, shed skin cells, enzymes and other
  proteins secreted into the guts and not
  completely digested turnover of tissue proteins,
  which are continuously being broken down and
  replaced.

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Minerals and Vitamins

• Small amounts of mineral salts and vitamins must
  be provided by the diets and losses must be
  replaced.
• Note they are extremely important in metabolic
  processes, but they have no fuel value

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Hunger and appetite

• Very elaborate systems
• Physiological mechanisms
• Psychological mechanisms
• Why??
• Bodys needs for metabolic fuels and nutrients
  are met AND
• Balance energy expenditure with food intake.

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Hunger and Satiety Short-term Control of Feeding

• There are hunger and satiety centers in the
  brain the hunger centers in the lateral
  hypothalamus, which stimulate us to begin eating,
  and the satiety centers in the ventromedial
  hypothalamus, which stimulate us to stop eating.

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Hypothalamic appetite control centres

• Short-term signals include
• Direct nerve input from gastro-intestinal tract
  and liver
• Plasma concentrations of metabolic fuels
• Relative concentrations of insulin and glucagon
• Peptide hormones secreted by gastro-intestinal
  tract during digestion

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• A variety of factors act on the hunger and
  satiety centres to initiate nerve impulses
• Neuronal input from the GI tract.
• Relative conc. of glucose (glu), triglycerides
  (TG), free fatty acids (FFA), and ketone bodies
  available in the fed and fasted state.

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• Relative conc. of hormones insulin or glucagon.
• Hormones secreted by the GI tract digestion
• Example Ghrelin. An orexigenic peptide hormone
  that the stomach and duodenum secrete into blood
  in response to several hours fasting stops
  promptly after eating.

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• Mechanisms that promote dietary intake are called
  orexigenic (or appetite stimulating). Example
  ghrelin.
• On the other hand, anorexia or anorexigenic is a
  state with suppressed intake behaviour (or the
  uncontrolled lack or loss of the appetite for
  food). Example leptin.

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• In other words...the appetite-promoting neurons
  are stimulated by ghrelin (signaling an empty
  stomach) and inhibited by leptin (signaling
  fat-filled adipose tissue).

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• Incidentally the diurnal variation in ghrelin
  release is thought to set meal patterns in
  humans.
• Trivia removal of a large part of
  ghrelin-producing tissues during gastric bypass
  surgery may be one of the reasons for sustained
  weight loss after surgery.

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Long-term Control of Food Intake and Energy
Expenditure

• In addition to the immediate control of feeding
  by hunger and satiety, there is also long-term
  control over food intake and energy expenditure.
• Largely a function of the hormone leptin
  secreted by the adipose tissue

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Once upon a time

• 1994 Zhang et al identified the gene that is
  defective in the ob/ob genetically obese mouse
  and showed that it was likely to code for a
  secreted protein. The gene was expressed only in
  adipose tissue.

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• Injecting the gene product into ob/ob mice causes
  them to lose weight, hence called leptin (Greek
  leptos lean).
• ob/ob mice do not secrete leptin.

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• Injecting leptin into genetically obese diabetic
  fa/fa rats does not cause weight loss already
  secrete lots of leptin.
• fa/fa rats have a defect in hypothalamic leptin
  receptors.

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So people?

• Leptin is secreted into the bloodstream and helps
  to regulate the amount of fat stored in the body.
  
• More leptin in the bloodstream increases energy
  expenditure and decreases food intake
• Less leptin decreases energy expenditure and
  increases food intake.

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Leptin resistance and obesity

• Obese people have an unusually high circulating
  concentration of leptin.
• Resistant to the effects of leptin (similar to
  people with type 2 diabetes, they are resistant
  to the effects of insulin).

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• ?leptin from the enlarged adipose stores result
  in leptin desensitization.
• Leptin control in obese people may be flawed the
  body doesn't adequately receive the satiety
  feeling subsequent to eating.

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What else?

• Cholecystokinin (CCK) plays a major role of
  appetite regulation by limiting meal size
  providing a sense of fullness.
• The hormone is secreted by endocrine cells of the
  small intestine in response to the presence of
  fat and other nutrients.

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Adiponectin Resistin

• Leptin, adiponectin, and resistin are all
  produced by the adipose tissue.
• Adiponectin protein hormone that modulates a
  number of metabolic processes, including glucose
  regulation and fatty acid catabolism.
• Secreted from adipose tissue into the
  bloodstream very abundant in plasma (relative to
  many hormones).

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• Levels of the hormone are inversely correlated
  with body mass index (BMI).
• In other words despite being produced in adipose
  tissue, adiponectin was found to be decreased in
  obesity.
• (MSlow adiponectin)

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• Resistin early studies suggested that there
  might be a correlation between blood glucose
  levels and resistin concentrations in mice
  however, did not show increase in blood resistin
  in obese humans with diabetes.
• Soresearch is still in progress as to the exact
  function of resistin.