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Nutrition 3 - Energy Balance
Humans ingest energy as food, which is then converted to:
chemical energy --> ultimately converted to heat (thermogenesis) & work
Energy is required for:
- 1. Maintenance of structural integrity (eg. growth or repair of muscle & bone)
- 2. Maintenance of chemical integrity (eg. ion gradients across cell membranes)
- 3. Internal work (eg. circulation, respiration, & gut motility
- 4. External work (eg. contraction of skeletal muscle)
- 5. Maintenance of body temperature (thermoregulation)
Energy stores are typically _____ while carbohydrate stores are comparatively _____
- energy stores: LARGE; of macronutrients of protein (muscle + organs) & fat (adipose tissue + organs)
- CHO stores: SMALL; glycogen
Respiratory Quotient (RQ)
- the ratio of vCO2/vO2 -> tells you what a certain tissue is using for Energy
- different RQs correspond to the oxidation of different macronutrients
- when macronutrients are oxidized, oxygen is consumed (vO2) & carbon dioxide is produced (vCO2)
What are the 3 components of total energy expenditure (TEE)?
- 1. BEE (basal energy expenditure): accounts for ~2/3 of TEE
- 2. TEF (thermic effect of feeding): accounts for ~10-15% of TEE
- 3. EEPA (energy expenditure for physical activity): highly variable, depends on exercise and other lifestyle factors (high levels of activity will reduce the % contribution to TEE from BEE & TEF)
Basal energy expenditure (BEE)
BEE or basal metabolic rate (BMR) is the energy required in a 24-hour period to maintain cellular, tissue, system metabolism'
How is BEE or BMR measured?
after a 12-hour fast in a resting supine position & in a thermoneutral (comfortable) environment, usually over 30 to 60 minutes
Resting energy expenditure (REE)
- or resting metabolic rate (RMR)
- similar but may be measured after a shorter fast & under less controlled conditions
- BEE, REE, BMR,or RMR can be used interchangeably to indicate the energy required at rest over 24 hours
What is the most important determinant of BEE?
- Fat free mass (FFM) - the most metabolically active tissues in the body
- *the major TISSUE determinant of BEE
Do men or women tend to have a higher BEE?
- males have more FFM and less fat than females after puberty so they expend more energy per body weight
- in women BEE tends to decrease further after menopause
What is the primary hormonal determinant of BEE?
- thyroid hormone
- Hypothyroidism --> low BEE
- Hyperthyroidism --> high BEE
What is the relationship between aging & BEE?
- aging is associated with decreased BEE
- mostly due to the age-related loss of muscle mass
- it decreases over the adult lifespan by about 1-2% per year
What effect does illness have on a person's BEE?
Illness, both acute and chronic, can INCREASE BEE due to the effects of fever, inflammatory cytokines, & catecholamines
What types of medications can increase BEE? Decrease BEE?
- increase: amphetamines, tobacco)
- decrease: beta adrenergic blockers, sedatives, anesthetics
What else affects a person's BEE?
catecholamines + the sympathetic nervous system
What does indirect calorimetry usually measure?
- BEE: it's the measurement of vO2 and vCO2 by devices that capture expired air, such as facemasks, canopies, or mouthpieces
- it may be done in ill patients to guide feeding or in obese patients to demonstrate that BEE is normal
Thermic effect of feeding (TEF)
- the increase above BEE due to food intake
- is proportional to the amount of energy ingested & to the macronutrient composition of food
- represents the energy cost of digestion, absorption, & assimilation or storage of macronutrients
- Protein > CHO > Fat
When is TEF a significant contributor to body weight?
when we consume macronutrients at extremes outside our usual range
Energy expenditure for physical activity (EEPA)
- comprised of two highly variable components
- 1. exercise
- 2. non-exercise activity thermogenesis (NEAT)
- the energy expended on volitional physical activity
- just after aerobic exercise, the excess post-exercise oxygen consumption (EPOC) consumes approximately an additional 15% of the energy associated with exercise
NEAT (non-exercise activity thermogenesis)
- energy spent on activities of daily living: posture, fidgeting, chewing gum, etc.
- may consume 100-700 kcal/day
- in some studies of overfeeding, subjects who increased NEAT gained less weight
How can energy expenditure can be quantified?
- 1. by measurement of oxygen utilized and carbon dioxide produced
- 2. by heat production
- 3. by indicators of motion or work
How is physical activity most often measured?
- accelerometers detect body motion
- heart rate is proportional to energy expenditure but is affected by factors that aren't due to activity
- self monitoring by diaries of physical activity (over- & under-reporting are issues)
What does a clinician need to know in order to estimate a patient's energy needs?
knowledge of that patient’s expected energy requirements
- a behavior that occurs in response to multiple biochemical, physiologic, psychological, & environmental stimuli
- there are basically two types of control systems
- 1. Homeostatic
- 2. Non-homeostatic
Homeostatic (Physiological) Control System
- short term (to signal the need to eat); include availability of glucose or free FAs in the brain, gastric distention, & hunger and satiety hormones
- long term (to indicate amount of body energy stored as fat): LEPTIN & INSULIN
Non-homeostatic Control System
- those that result in reward and reinforcement of intake
- reinforcement results from the metabolic consequences of eating, like increased glucose availability
- sensory properties of food are paired with the reward that it stimulates --> we learn to like that particular food
What stimuli lead to the initiation of eating?
- Cravings (the desire to eat specific foods)
- Availability of food in the immediate environment even without hunger or cravings
- Cognition (knowing it is lunchtime)
- Reduced availability of glucose or fatty acids in the brain may enhance desire to eat
- a peptide hormone secreted primarily by the stomach that results in hunger and food intake by action in the hypothalamus
- it appears to stimulate the vagus nerve afferents from the gut, & also through serotonin or something…
- blood concentrations of ghrelin increase between meals & fall after meals
What happens after after weight loss by dieting?
- ghrelin INCREASES, in part explaining why weight is regained after weight loss
- however after some types of surgery for obesity, ghrelin does not increase & may decrease, which may in part explain superior weight loss that occurs from GI surgery
- Gastric distention
- Detection of nutrients in the GI system -> subsequent neural or hormonal communication with the brain
- Cognitive factors
- Substrate availability in the brain
- Hedonic/reward values of food
the processes that collectively determine the inter-meal interval
Glucagon-like peptide 1 (GLP-1) & cholecystokinin (CCK)
satiation/satiety hormones released from the gut & act via the circulation or the vagus nerve on hypothalamic centers
GLP-1 (Glucagon-like peptide 1)
- causes gastric emptying to slow down (“ileal brake”)
- secreted by the small intestine in response to the presence of macronutrients in the ileum
- promotes satiety via the hypothalamus
- is an incretin hormone: accentuates the pancreas' insulin response to blood glucose
- stimulating gallbladder contraction in response to protein & fat in the duodenum
- also contributes to cessation of eating by action on hypothalamic centers and by delaying gastric emptying
Where are sensory properties before and during food ingestion integrated in the brain?
the orbitofrontal cortex
What role does the midbrain play in the non-homeostatic way food Intake is controlled?
the midbrain is where the metabolic properties of the food, including its ability to provide energy substrates & the hormonal response to intake (as transduced via the hypothalamus) are translated into reward
What kinds of food appear to be superior in inducing reward?
- 1. foods that provide larger amounts of energy (i.e. more energy dense foods)
- 2. foods that lead to rapid rises in blood glucose
- non-homeostatic regulation of intake can overcome homeostatic control for ingestion of food with high reward value --> why high fat or high sugar foods are consumed beyond energy needs
- protein produced in fat cells (in proportion to amount of fat stored) secreted into the circulation where it travels to the brain, crosses the blood brain barrier, & acts on the hypothalamus to DECREASE food intake
- higher amounts of body fat are associated w/ higher blood concentrations of leptin
- in RODENTS (not humans) leptin stimulates energy expenditure
What affect does leptin have on someone who's obese?
while leptin concentrations in obese persons are appropriate for the amount of body fat, the action of leptin is impaired, suggesting resistance to leptin action in the brain
What is the effect of a leptin deficiency due to genetic mutations?
- such cases result in severe obesity at a young age
- occur very rarely in humans
- leptin injections in deficient individuals reverses obesity, however for those who are NOT leptin deficient, leptin injections have only a very modest and inconsistent effect on reducing weight
A defect in what receptor is associated with binge eating in obese people?
- the melanocortin 4 receptor, which is involved in leptin signaling in the hypothalamus
- this defect is present in approximately 5% of severely obese persons
- reduces blood glucose in the periphery (body tissues outside of the central nervous system)
- if glucose concentrations dip too low one of the responses is hunger
What happens when insulin is injected into the cerebral ventricles?
- food intake DECREASES
- high insulin levels are an indicator that body fat stores are adequate --> no need for anymore eating
What are high levels leptin or insulin levels indicative of?
- that body fat stores are adequate
- in this state mechanisms that control food intake in the short term are accentuated
- Leptin and insulin act by modulating short term hunger & satiation/satiety signals
- especially soluble fibers, increase stomach distention, which activates afferent vagal nerve signals of fullness to the brain
- soluble & insoluble fibers also act as a physical impediment to digestion
- delayed carbohydrate digestion and absorption blunts blood sugar rise with intake, leading to a blunted insulin response
- undigested nutrients trigger secretion of the gut hormones like GLP-1 and thus cause slowed gastric emptying and prolongation of sensations of fullness
High protein, low carbohydrate Diets
- protein has been shown to be more satiating and slow the return of hunger in comparison to other macronutrients
- protein seems to be better at satisfying hunger than refined carbs partly b/c it doesn’t induce large fluctuations of blood glucose
- proteins are digested more slowly, sending nutrients into the blood stream over hours
What is likely to be a factor that contributes to satiation after high protein intake?
Stimulation of CCK
Glycemic index (GI)
- the increase in blood glucose following consumption of a standardized amount of carbohydrate in comparison to the increase observed with consumption of white bread or glucose (set at 100)
- foods with a lower glycemic index reflect slower digestion & absorption of glucose from food; lower GI foods result in a lower insulin response
Glycemic Load (GL)
a calculation of the total GI of the diet with consideration of the amount of each food eaten and the total carbohydrate of the diet
What are some determinants of a food's glycemic index?
- Carbohydrate content + type
- Higher GI: sucrose, glucose, amylopectin
- Lower GI: fructose, amylose
- Food structure and form
- Degree of cooking
- Presence of other substances that influence gastric emptying, digestion or absorption (eg. fiber or fat)
High fat diets tend to be ____ energy dense
- high fat = MORE energy dense diet since fat has over twice the energy
- per gram in comparison to other macronutrients
- when diets of higher and lower fat have the same energy density, equal volumes of each diet are consumed
What may now be one of the biggest challenges to our weight control?
- Continuously available food
- Large portion sizes can be viewed as a type of increased food availability; larger portions lead to greater intake regardless of hunger or desire to eat
Eating a higher variety of low energy foods such as vegetables is associated with ________, whereas eating a high variety of high-energy foods such as sweets, snacks, entrees is associated with _______
- more variety of low E foods: LEANNESS (presumably through reduction in energy intake)
- more variety of high E foods: FATNESS
Post Ingestive Conditioning
- there is a direct relationship between preferences for common foods & kcal/gram
- rat studies showed that digestion and absorption impact food preferences more than food taste
- if rats are given food tasting of vanilla that has few calories & it is allowed to pass into the stomach and then be absorbed in the intestine, they may eat SOME of the food at future occasions
- if the vanilla food is fed but is then removed from the esophagus via the cannula & replaced by a higher calorie food w/out vanilla that is placed the stomach via the cannula, rats will eat MORE of the vanilla food than in the 1st condition
- if rats eat the vanilla food & it is removed so that no food reaches the stomach, the rat will soon eat LITTLE vanilla food
- the gain in fat & fat free mass due to positive energy balance, energy intake in excess of energy expenditure
- generally w/ positive energy balance, about 3/4 of gained weight will be fat, while the remainder will be fat free mass including structural protein & water weight
What is the effect of obesity on basal energy expenditure (BEE)?
- it slightly increases in response to excess intake, but only by 5-10% of the excess energy intake
- therefore BEE will not dissipate most of the excess intake
- TEF: the thermic effect of feeding increases only in proportion to ingested energy so is NOT considered adaptive
- NEAT: non-exercise activity thermogenesis may increase substantially & appears to limit weight gain
How can obesity cause disease?
- Insulin resistance
- Promotion of pro-thrombotic state (increased coagulation of blood)
- Physical stress on joints & tissues
- Increased blood volume
- Psychosocial issues and discrimination
What often improves weight-related morbidities?
- a loss of 5-10% of initial weight
- weight loss beyond this range is difficult, therefore an initial goal of 5-10% of weight over 3-6 months is reasonable
What do some fad diets & weight loss supplements claim?
- that on such plans little or no FFM is lost and all lost weight is fat; these claims have NOT been substantiated
- the average composition of tissue lost 65-75% fat mass & 25- 35% fat free mass
What is the most effective measure of weight loss?
- the % of initial weight that was lost
- other less effective measures include absolute terms (pounds or kgs) or change in BMI
- low cal diets: 5-10% of initial weight lost
- VERY low cal diets: 15% of initial weight
- exercise without diet change: 1-2%
- addition of exercise to diet change: additional 1-2%
- Behavior therapy added to diet & exercise: additional 2-5%
- Meds: about 3-5% more than diet and exercise, or 10-15% of initial weight
- Surgery: 15-35% of initial weight
- very low calorie (VLCD): < 800 kcal/day
- low calorie diets: > 800 kcal/day
- “Moderate” diets: deficits of 500 kcal/day below maintenance of energy needs
- generally a deficit of 500 kcal/day leads to a loss of 1 pound/week
Very low calorie diets (VLCD)
- consumed for 3-6 months
- are usually products such as shakes & bars that are consumed 5-6 times/day
- they require regular medical monitoring due to risks including: dehydration, electrolyte disturbances (eg. hypokalemia, low potassium), cardiac rhythm disturbances (rare but due to electrolyte
- disturbances), or Gallstones
What do all weight loss diets carry some risk of?
- the rate of weight loss is a primary determinant of gallstone formation
Low calorie diets (LCD)
- have an average weight loss is 8% of initial weight over 3-6 months
- to achieve weight loss there must be long-term adherence to a diet that promotes negative energy balance
The Zone Diet
- most often employed for weight loss but need not be limited to this
- it is based on a carbohydrate to protein to fat energy ratio of 40:30:30
- it's based on the idea that less insulin secretion is fundamental to weight loss & health benefits achieved by diet
What foods are recommended & discouraged on the Zone diet?
- recommended: whole grains, fish, nuts, olive oil
- discouraged: refined grains, meat are
The South Beach Diet
- based on restriction of carbohydrates & some fat types
- is usually employed for weight loss
- the initial phase restricts bread, pasta, potatoes, rice, fruit, & foods w/ added sugar; lean meat & some vegetables ARE consumed
- diet is later advanced to include lean protein, low fat dairy, & some whole-grain carbs & fruit
- the last phase includes whole grains, vegetables, & fruit
The Atkins Diet
- a low carb diet primarily employed for weight loss; it features intake of protein and fat
- it discourages intake of foods with saturated fat but healthier fats are encouraged (*in practice it can include a high intake of saturated fat)
- over time the amount of carbs is increased to a level consistent with weight maintenance
- *this diet can be insufficient in water soluble vitamins & some minerals
Increases in physical activity provide multiple benefits that complement diet changes:
- reduced risk of cardiovascular disease, diabetes, & mortality
- maintenance of FFM during weight loss (happens more w/ weights v. aerobics; BEE may not be maintained to the same extent)
- improved self-efficacy (the belief than one can change behavior) & mood
- are considered for those who do not meet weight loss goals & who have BMI > 30 kg/m2 or BMI > 27 kg/m2 WITH weight-related conditions (eg. dyslipidemia, hypertension, sleep apnea, or heart disease)
- meds + lifestyle change improves weight loss by 3-5% of initial weight + that achieved by only lifestyle change
- can also help maintenance of lost weight by preventing regain
- a drug that acts on the central nervous system to suppress appetite
- it influences brain neurotransmitters (like serotonin, norepinephrine)
There are no approved or safe drugs that act primarily by increasing what?
energy expenditure, or that increase thermogenesis
- medication that inhibits gastric and pancreatic lipase, which decreases hydrolysis of dietary fat by up to 30%
- fat that is not absorbed will be excreted
- inhibiting fat absorption may also decrease absorption of fat soluble vitamins
When would surgery be considered to combat obesity?
- for those with BMI > 40 kg/m2
- or 35 kg/m2 w/ weight-related comorbidities
- *surgery is the only option demonstrated to result in long-term weight loss, long-term improved weight-related comorbidity, & reductions in mortality*
- the stomach size is reduced by partitioning (stapling) or by creating
- restriction with an adjustable band
- by bypassing part of proximal small intestine, food does not meet
- digestive enzymes and does not become available for absorption until further downstream in the small intestine