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Questions and Answers
Which peripheral hormone primarily regulates meal-to-meal control systems through its short-term effects?
Which peripheral hormone primarily regulates meal-to-meal control systems through its short-term effects?
What is the effect of leptin injection in ob/ob mice?
What is the effect of leptin injection in ob/ob mice?
What is the role of insulin in hypothalamic orexigenic neurons?
What is the role of insulin in hypothalamic orexigenic neurons?
Which statement accurately describes the long-term regulatory functions of leptin and insulin?
Which statement accurately describes the long-term regulatory functions of leptin and insulin?
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How do ghrelin levels change in response to food intake?
How do ghrelin levels change in response to food intake?
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What is a primary function of glucagon-like peptide-1 (GLP-1)?
What is a primary function of glucagon-like peptide-1 (GLP-1)?
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What is the function of Cholecystokinin when produced in response to nutrient intake?
What is the function of Cholecystokinin when produced in response to nutrient intake?
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Which of the following hormones is measured for its levels after a meal and remains elevated for hours as a response to the food entering the stomach?
Which of the following hormones is measured for its levels after a meal and remains elevated for hours as a response to the food entering the stomach?
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Which condition is associated with the ob/ob genotype?
Which condition is associated with the ob/ob genotype?
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What initiates the production of ghrelin in the body?
What initiates the production of ghrelin in the body?
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What is the primary source of vitamin B12?
What is the primary source of vitamin B12?
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Which minerals are classified as macrominerals?
Which minerals are classified as macrominerals?
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What is a significant factor affecting mineral absorption from plant foods?
What is a significant factor affecting mineral absorption from plant foods?
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How much energy does fat provide per gram?
How much energy does fat provide per gram?
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Which of the following statements about minerals is false?
Which of the following statements about minerals is false?
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Which vitamins enhance the absorption of minerals?
Which vitamins enhance the absorption of minerals?
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What percentage of energy in a diet typically comes from fat?
What percentage of energy in a diet typically comes from fat?
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Which of the following ultrastrace elements is correctly matched?
Which of the following ultrastrace elements is correctly matched?
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What is the effect of Peptide YY (PYY) on neuropeptide Y (NPY) release?
What is the effect of Peptide YY (PYY) on neuropeptide Y (NPY) release?
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How does leptin affect fatty acid metabolism in adipocytes?
How does leptin affect fatty acid metabolism in adipocytes?
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What is the primary function of the Basal Metabolic Rate (BMR)?
What is the primary function of the Basal Metabolic Rate (BMR)?
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What distinguishes the circulating concentrations of pancreatic polypeptide (PP) in obese individuals compared to those with anorexia nervosa?
What distinguishes the circulating concentrations of pancreatic polypeptide (PP) in obese individuals compared to those with anorexia nervosa?
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Which of the following factors is NOT known to affect BMR?
Which of the following factors is NOT known to affect BMR?
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What is the relationship between leptin levels and food intake during periods of 'starvation'?
What is the relationship between leptin levels and food intake during periods of 'starvation'?
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Which of the following hormones primarily communicates fat reserves to the central nervous system?
Which of the following hormones primarily communicates fat reserves to the central nervous system?
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How is BMR calculated?
How is BMR calculated?
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In terms of BMR, which population is likely to have a higher metabolic rate?
In terms of BMR, which population is likely to have a higher metabolic rate?
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What is one of the key roles of leptin binding to its receptors in the hypothalamus?
What is one of the key roles of leptin binding to its receptors in the hypothalamus?
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What effect does leptin have on growth hormone secretion?
What effect does leptin have on growth hormone secretion?
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Which hormone is known to increase BMR?
Which hormone is known to increase BMR?
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How does insulin affect leptin production in fat cells?
How does insulin affect leptin production in fat cells?
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What effect does cold exposure have on BMR?
What effect does cold exposure have on BMR?
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What is the approximate BMR for an adult man?
What is the approximate BMR for an adult man?
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Which of the following statements about BMR is incorrect?
Which of the following statements about BMR is incorrect?
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What is the primary function of Peptide YY (PYY) in the gastrointestinal system?
What is the primary function of Peptide YY (PYY) in the gastrointestinal system?
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How do short-chain fatty acids (SCFAs) affect insulin signaling in adipose tissue?
How do short-chain fatty acids (SCFAs) affect insulin signaling in adipose tissue?
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What is the role of trimethylamine N-oxide (TMAO) in metabolic health?
What is the role of trimethylamine N-oxide (TMAO) in metabolic health?
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What effect does a high-fat diet have on the gut microbiome?
What effect does a high-fat diet have on the gut microbiome?
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Which of the following statements about prebiotics is true?
Which of the following statements about prebiotics is true?
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What mechanism does SCFA utilize to activate intestinal gluconeogenesis (IGN)?
What mechanism does SCFA utilize to activate intestinal gluconeogenesis (IGN)?
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Which peptide is known to increase insulin sensitivity?
Which peptide is known to increase insulin sensitivity?
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What is a significant consequence of fasting-induced adipose factor (Fiaf) inhibition by SCFAs?
What is a significant consequence of fasting-induced adipose factor (Fiaf) inhibition by SCFAs?
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Study Notes
Biochemical Aspects of Nutrition
- Biochemical aspects of nutrition are a subject of study.
- There are questions about inhibiting factors and absorption.
Nutrients in Foods
- Essential nutrients include water, carbohydrates, proteins, and lipids.
- Regulatory nutrients include vitamins and minerals.
Carbohydrates in Nutrition
-
Monosaccharides are the major part of carbohydrates.
- Glucose
- Fructose
- Galactose
-
Disaccharides include:
- Sucrose (table sugar)
- Lactose (milk sugar)
- Maltose
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Oligosaccharides are prebiotic, partially indigestible.
- Raffinose
- Stachyose
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Carbohydrates are needed daily in the diet at least 50-100 grams/day.
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Most diets contain more than enough carbohydrates.
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Dietary Fiber:
- Structural parts of plant foods not digestible by the body.
- Lack of necessary enzymes
- Polysaccharide
- Essential nutrient
- Two types:
- Insoluble fiber: does not dissolve in water or gastrointestinal fluids, provides bulk (cellulose, hemicelluloses), prevents constipation, and helps with weight management.
- Soluble fiber: dissolves in water, turns to a gel-like substance, slows down digestion, promotes fullness, and accelerates the exit of harmful substances in food (e.g., gums, pectins).
- Insoluble fiber is found in cereals, whole-wheat bread, and lentils. Soluble fiber is found in oats, beans, and sweet potatoes.
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Importance of Carbohydrates in the Diet: preventing constipation, improving bowel-related health problems like constipation, hemorrhoids, and fecal incontinence, and colorectal cancer, helping in weight management.
Maintenance of Blood Glucose
- Discussed in two states:
-
Absorptive state (lasts about 4 hrs after a meal)
- Blood glucose readily available for ATP synthesis.
- Excess glucose stored as glycogen in liver and muscles or as body fat.
- Fats taken by tissues mainly adipose and muscular tissue.
- Amino acids utilized for protein synthesis.
- Regulated largely by insulin, which stimulates nearly all cells to absorb glucose.
-
Postabsorptive state (fasting)
- Prevails hours after meals and overnight.
- Regulates blood glucose levels, critical for the brain.
- Glucose drawn from body's glycogen reserves in the liver and muscles.
- Synthesized from fats (gluconeogenesis).
- After 4-5 days of fasting, the brain uses ketone bodies as supplemental fuel extracted from fats
- If glycogen and fat reserves are depleted, the body burns proteins (skeletal muscle proteins are first).
- Regulated by the sympathetic nervous system and glucagon.
- Glucagon promotes glycogenolysis (glycogen to glucose), gluconeogenesis (AA/FFA to glucose), and lipolysis (triglyceride to FFA).
-
Lipids in Nutrition
- Lipids: Major lipids include TAGs, fatty acids, glycerides
- Saturated fatty acids
- Unsaturated fatty acids
- Neutral glycerides
- Phosphoglycerides
- Non-glyceride lipids, waxes
- Sphingolipids, steroids
- Complex lipids, lipoproteins
- Examples of fatty acids: stearic acid, oleic acid, linoleic acid, arachidonic acid.
- Fats and oils usually contain mixtures of fatty acids.
- Butter and other animal fats: saturated.
- Olive and canola oils: monounsaturated.
- Fish, corn, safflower, soybean, and sunflower oil: polyunsaturated. -Essential fatty acids:
- Alpha-linolenic acid (omega-3 fatty acid)
- Linoleic acid (omega-6 fatty acid)
- Need in small amounts for cell membranes, hormone-like compounds, blood pressure, blood clotting, and immune response.
- Sources: vegetable oils (safflower or corn), grains, nuts, and seeds, vegetables, fish
- Hydrogenation in food industry for better stability, resistance to rancidity, and a solid and spreadable form, however, conversion from cis form to trans fats poses health risks.
Microbiota
- Complex, diverse, and vast microbial community in human intestines.
- Composed of approximately 1,100 prevalent species.
- Four main bacterial phyla in a healthy human gut: Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria
- Produce various kinds of metabolites (beneficial and harmful for the host):
- Short-chain fatty acids (SCFAs)
- Trimethylamine N-oxide (TMAO)
- Bile acids
- Branched-chain amino acids
- SCFAs (e.g., acetate, propionate, butyrate) are produced by anaerobic fermentation of undigested nutrients and are absorbed in the intestines.
- SCFAs are associated with energy, regulating food intake, increasing satiety, improving glucose tolerance, and suppressing fasting-induced adipose factor (Fiaf) expression.
- TMAO is a metabolite of gut microbes and is associated with the development of atherosclerosis.
- Generated through metabolism of choline, phosphatidylcholine, L-carnitine, and betaine, via TMA lyases.
- Oxidized into TMAO by hepatic flavin monooxygenases (FMO3).
- Prebiotics are non-digestible but fermentable polysaccharides
- Probiotics are live microorganisms
Proteins in Nutrition
-
Basic structural material of the body (in cell membranes and blood)
-
Enzymes
-
Antibodies
-
Collagen in connective tissue
-
Many hormones (e.g., insulin)
-
Food contains approximately 20 common amino acids
- Essential amino acids for humans
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
- Essential amino acids for humans
-
Indispensable amino acids
- Arginine
- Cysteine
- Tyrosine
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Protein sources include foods of animal origin (meat, fish, eggs, dairy products) and plant origin (soybeans).
-
Vegetarian diets have high lysine and low methionine.
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Grains have complementary strengths and weaknesses.
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The recommended daily protein intake for adults of both sexes is 0.75 gram of protein per kilogram of body weight.
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additional protein needs for endurance athletes, infants, children, pregnant, and lactating women.
Vitamins in Nutrition
- Vitamin A for embryonic development, growth, reproduction, immune function, integrity of cells, and vision
- B Vitamins (coenzymes assisting in energy metabolism)
- Folic acid (Vitamin B9) helps protect against birth defects
- Vitamin C building connective tissue, antioxidant
- Vitamin D calcium and phosphorus homeostasis, bone metabolism
- Vitamin E antioxidant, heme synthesis
- Vitamin K blood clotting
- Humans can synthesize certain vitamins to some extent (Vitamin D, Niacin, Vitamin K, Biotin)
- Humans need vitamins from their diet (specific deficiency often irreversible)
- Some vitamins are found in precursor forms in food that must be activated by the body (eg. beta-carotene converted to Vitamin A)
- Water-soluble vitamins are more easily destroyed by cooking, and water-soluble vitamins are synthesized by both plants and animals.
- Vitamin B12 is supplied by foods of animal origin, vegetarians at risk of deficiency
Minerals in Nutrition
- Simple inorganic elements (4-6% of body weight) in the body as salts
- Not metabolized themselves
- Not a source of energy
- Function broadly in metabolism & controlling water movement, fluid balance, osmotic pressure, and acid-base balance
- Components of enzyme systems
- Macrominerals (in amounts of 100 mg or more daily) include calcium, phosphorus, magnesium, sulfur, sodium, chloride, and potassium.
- Microminerals (required in amounts of 15mg or less per day) include iron, zinc, copper, manganese, iodine, selenium, fluoride, molybdenum, chromium, and cobalt.
- Ultratrace elements (in micrograms daily) include arsenic, boron, nickel, silicon, and vanadium.
- Levels of different minerals in foods can be influenced by growing conditions (soil and water composition).
- Minerals are not destroyed during food preparation, and better absorbed from animal foods than plant foods.
- Fibres in plants interfere with absorption of certain minerals, especially phytates.
- Some minerals (especially iron and copper) can compete for absorption if present at high levels.
Energy
- Human body is an engine that releases energy present in food.
- Energy utilized for mechanical work (muscles, secretory processes), maintains body structure and functions.
- Food is the fuel source of the body
- Carbohydrates: 4 kcal/gram (17 kJ/gram)
- Proteins: 4 kcal/gram (17 kJ/gram)
- Fats: 9 kcal/gram (38 kJ/gram)
- Energy from diet: Protein (12-15%), fat (30-40%), carbohydrate (50-60%).
- Basal metabolic rate (BMR): minimum energy required by the body maintaining life at physical and mental rest in the post-absorptive state.
- BMR is influenced by age, sex, body surface area, environmental conditions (cold), body temperature, and exercise.
- Other factors influencing BMR: drugs, pregnancy, racial variations, barometric pressure, state of nutrition, and hormones (thyroid hormone, adrenaline, catecholamines, growth hormone, male sex hormone)
Appetite
- Hunger and satiety are regulated by complex interactions involving multiple brain centers, hormones, and sensory/motor pathways.
- Central appetite control:
- Hypothalamus (ventromedial hypothalamus: satiety center; lateral hypothalamus: feeding/hunger center)
- Hypothalamic messengers
- Peripheral signals of appetite (hormones)
- Peripheral signals of appetite (hormones): Insulin, cholecystokinin, peptide YY, pancreatic polypeptide, leptin, ghrelin, glucagon-like peptide-1
- Two types of neurons in the arcuate nucleus: -1. Orexigenic NPY/AgRP neurons (stimulate appetite) -2. Anorectic POMC neurons (inhibit appetite)
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