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Sept 17 - Energy Balance part 2.doc

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Physical Education and Sport
Scott Forbes

Energy Balance part 2 identify peripheral and central signals associated with appetite regulation • No perceptible differences in total daily energy expenditures over a range of diets containing 10% fat to 80% fat (energy balance maintained) • When excess energy consumed differences emerge. .... generate a slightly higher dissipation of excess energy yielding higher .... storage • Note slide 4 • Fat has poor autoregulation Appetite Regulation • Over long period of time, energy balance (and body weight) remain quite stable • Daily food intake is highly variable combined with continual energy expenditure. Some days you may eat more than usual or you may do more PA. • How are appetite and food intake regulated by adipose tissue and GI tract (peripheral – from adipose tissue and GI tract) and relayed to areas of the brain (central)? How Do We Measure Appetite? Hunger – sensations that promote consumption and is a multidimensional attribute with metabolic, sensory, and cognitive facets Satiation – following initiation of a meal, eating proceeds, hunger subsides while satiation, the sensations that govern meal size and duration become increasingly dominant.. feelings of satiation will contribute to cessation of eating and begin a period of abstinence from eating Satiety – sensations that determine the intermeal period of fasting are termed satiety Appetite • All aspects of appetite have a physiological basis and are strongly influenced by environmental factors (food availability, sensory stimulation) or cognitive/behavioural issues (health beliefs, habitual meal times, social context) Common Measures 1.) Food intake 2.) Questionnaires – asking how hungry you are. There is some variability and use different scales 3.) Biomarkers – are expensive and aren’t perfectly sensitive. We would need to measure more than one biomarker to determine if someone was hungry or not All suffer from limitations Adipose tissue is from the GI tract and stomach Insulin is released from the pancreas Orexigenic stimulaes food intake Anorexigenic decreases food intake Ghrelin increases food intake White adipose tissue produces leptin Leptin decreases food intake Leptin activates a part of the hypothalamus called the arc Note slide 9 Peripheral hormones regulating appetite Insulin: • Rise in response to glucose load proportional to fat mass • Insulin crosses blood brain barrier and reduces appetite • Less effective in obese or type 2 diabetes (insulin – resistant) Leptin • 1994 obese (ob) gene identified..Protein synthesized from adipose tissue • Concentration of leptin is proportional to fat mass • Leads to decrease in food intake (anorexigenic) and weight loss • Tracks food intake and fasting (increases/falls) • Most obese people are leptin resistant, not leptin deficient • Obese people have higher levels of leptin Leptin: Acute and Chronic Indicator of Energy Status • Increase in concentration of leptin with high carb, low fat meals vs. Low carb high fat meals • 5 day high fat diet reduces concentration of leptin and promotes leptin resistance GI Tract Peptides Ghrelin • 1999: synthesized Predominantly in stomach • Stimulates growth hormone (GH), levels rise with fasting and fall with feeding • Growth hormone is involved with reducing carb oxidation and increasing fat oxidation • When fasting, you are usually deficient in carbs • Increases food intake (orexigenic) • Involved with meal initiation • Adipogenic properties • Carbs suppress ghrelin (high carb – low fat may help energy-reduced weight loss by mitigating (making less severe) increase in ghrelin with energy restriction) • Fibre effectively reduces ghrelin Peptide YY (PYY) • Secreted from small and large bowel (member of neuropeptide Y family; NPY) • Released after feeding and leads to reduced food intake • Unclear which macronutrient influences PY
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