NATS1560 Lecture 4.1 - Energy PDF

NATS1560: Understanding Food Angela Cope [email protected] Week 2: Energy Part 1  LEARNING OBJECTIVES To explain the equivalence between energy and heat, and the primary function of food as “fuel” for the body To...

NATS1560: Understanding Food Angela Cope [email protected] Week 2: Energy Part 1  LEARNING OBJECTIVES To explain the equivalence between energy and heat, and the primary function of food as “fuel” for the body To define the measurement units of food energy, the kilocalories, and their moniker, “calories” To explain the difference between the gross energy and the metabolizable energy of food To define the standard metabolizable energy values of the macronutrients, also know as the Atwater Values, and to apply the “4-9-4” rule to estimate the metabolizable energy of a food To assess critically the accuracy of the Atwater Values, and to define and apply the USDA Modified Atwater Values To define and use the Acceptable Distribution Ranges, or Dietary Reference Intakes for macronutrients 2  Human Nutritional Needs (Review): Humans are omnivores and need a variety of different foods to survive. Nutrients: pure substances that scientists have identified as capable of providing nourishment to our organisms. Nutrition science currently recognizes six categories of nutrients needed for human nutrition: 1. Proteins 2. Carbohydrates 3. Fats Together, these are the Macronutrients. These are the nutrients needed in the largest quantities. 3  Human Nutritional Needs (Review): Water Minerals Vitamins (A seventh category, phytochemicals, is currently under study.) These are the micronutrients. Minerals and Vitamins. These are needed in far smaller amounts than macronutrients. Water is something we need in macro-quantities but provides neither macro nor micronutrients (for the most part). 4  WHY DO WE NEED FOOD? Our body needs food for  matter (atoms), needed for the growth, repair, and functioning of organs and tissues  energy (capacity to do work), needed for all physiological From the NBC show, Parks and Recreation processes Food does not “become” Food is the source of matter and energy for the organism energy In all physiological processes, matter and energy are not created, destroyed, or transformed into each other, but are separately conserved Metabolism: all the physical and chemical processes that take place inside an organism ‒ a flow of matter and energy (from food) in, through, and out the body 5 Metabolism: … IS INCREDIBLY COMPLEX – WHAT IS PRESENTED IN THE NEXT SLIDES IS A MASSIVE SIMPLIFICATION.  FOOD ENERGY Energy exists in different forms that can transform into one another: kinetic energy (motion), thermal energy or heat (motions of molecules), chemical energy (potential energy of chemical bonds), and others The cells of living organisms are able to extract chemical energy from food molecules through the complex process called cellular respiration In cellular respiration, monomers from food molecules are oxidized, producing many ATP (adenosine triphosphate) molecules and heat in the process, and carbon dioxide and water as waste products monomers cellular respiration food from + CO2 + H2O O2 chemic al energy ATP molecules heat The heat keeps the body warm ATP molecules pack energy and take it to where it is needed for physiological functions and muscle motion The body stores unused food energy as chemical energy in glycogen and fat molecules The body uses its glycogen and fat molecules for energy when food is insufficient 7 KILOCALORIES AND “CALORIES” Energy for body’s use is extracted from food when food molecules are oxidized inside body cells a process similar to burning fuel to produce kilocalories heat In nutrition, food energy is commonly measured in units of heat: kilocalories, or food calories, or large calories (kcal or Cal) familiarly but inaccurately called “calories” kilocalorie = amount of energy required to raise the temperature of 1 kg of water 1°C at standard atmospheric pressure – kilo = 1000 – calorie = energy required to raise the temperature of 1 g of water 1°C at standard atmospheric pressure  HOW MUCH ENERGY DO WE NEED? Estimated Energy Requirement (EER): energy intake needed to maintain body weight An individual’s EER depends on many factors - height ‒health condition - weight ‒being pregnant or lactating - body composition ‒nutritional state (proportion of muscle ‒stress mass and fat) ‒hormones - age ‒environmental temperature - physical activity level HOW MUCH ENERGY DO WE NEED? kilocalories per day  DOES FOOD “BECOME” Food does not ENERGY? become energy. Food is the source mass of of matter and exhaled CO2 + energy for the body excreted H2O body! mass mass in = mass stored + Food = = energy mass out stored + = energy in energy out = chemical heat and energy in motion physiologic al molecules, and in body fat and glycogen  DOES BODY WEIGHT “BECOME” ENERGY? Weight (= gravity) is No Metabolic processes cannot proportional to mass. transform mass into energy. ! You could lose weight When the body’s demand for moving to a place energy exceeds the food with lower energy intake, the body gravitational resorts to its energy store: attraction. glycogen and adipose fat molecules. On Earth, losing The process of cellular weight commonly respiration extracts energy means losing mass. from body glycogen and fat molecules and converts them into ATP, CO2 and H2O molecules CO2 and H2O are expelled.  REVIEW Why do we need to eat? Does the food we eat transform into energy? How is cellular respiration similar to combustion? What is the unit used to measure the energy of food? What is another name for the “food calorie”, and how is it related to the calorie? 13  Cellular Respiration: Three Processes, from food to energy: 1. Glycolysis 2. Krebs Cycle/Citric Acid Cycle 3. Electron Transport Chain (ETC)  Glycolysis: An anaerobic process – no oxygen involved. Occurs in the cytoplasm of the cell. Converts one glucose molecule to two pyruvate molecules. Actual process requires several steps, but you only have to know that glycolysis converts one glucose into two pyruvate and two ATP (the energy for the body).  Aerobic process, requires oxygen. (‘respiration” part of cellular respiration) Occurs in the mitochondria of the Citric Acid cell. Pyruvate enters into Krebs cycle, gets or Krebs converted through several steps (you don’t have to know those steps) into ATP Cycle: Along with the Electron Transport Chain, cellular respiration creates 34 ATP for every glucose molecule that enters the system, for a total of 36 ATP.  Measuring Energy in the Body: The chemical energy stored in food is released and made available via ATP, in a process called cellular respiration. The way we measure this energy is by the calorie. Calorie: a unit of measurement of heat, technically defined as the amount of energy required to raise the temperature of one gram of water by one degree. In food, however, we don’t use the calorie, even though we call it that. What we are measuring in food is actually the kilocalorie. (1000 calories).  HOW MUCH ENERGY DOES FOOD PROVIDE TO OUR BODY? The only food molecules from which our body can extract energy are those of the macronutrients: − carbohydrates, fats, proteins Energy from food = energy from carbs + energy from fats + energy from proteins Metabolizable energy of a food = energy in the food – energy losses due to incomplete digestion and excretion Standard values of metabolizable energy, or Atwater values: - from carbs = 4 kcal/g - from fats = 9 kcal/g - from proteins = 4 kcal/g - from alcohol = 7 kcal/g - from anything else = 0 kcal/g 18  THE 4-9-4 RULE The standard values of metabolizable energy give us a simple method to estimate, approximately and on average, how much energy a food or meal provides to the body, when the quantities in grams of macronutrients in the food or meal are known - Metabolizable energy from carbs (kcal) = grams of carbs x 4 kcal/g - Metabolizable energy from fats (kcal) = grams of fats x 9 kcal/g - Metabolizable energy from proteins (kcal) = grams of proteins x 4 kcal/g - Metabolizable energy from food = metabolizable energy from carbohydrates + metabolizable energy from fats + metabolizable energy from proteins 19  HOW ACCURATE ARE THE STANDARD ENERGY VALUES? Carbs, proteins, and fats from different foods have different metabolizable energy content The standard energy values are averages calculated after measuring macronutrient composition, gross energy and energy losses due to incomplete digestion and excretion of many different foods Originally estimated by American scientist, Wilbur O. Atwater around 1900 for an average diet of people of European descent in his time in the USA Modified Atwater Values, from kcalori newer experiments (USDA es 1955 and 1973) with a variety of diets have yielded - averages that differ little (typically no more than 5%) from Atwater’s standard values - but non-negligible differences between different foods Source: M. Nestle and M. Nesheim, Why Calories Count (2012), p. 37.  REVIEW What are the energy-giving nutrients? Approximately and on average, how much metabolizable energy is provided by each of the energy-giving nutrients? How much energy do the other nutrients (non- energy-giving nutrients) provide? What is the “4-9-4 rule”? 21 HOW MANY CALORIES IN A FOOD? EXERCISE USING THE 4-9-4 RULE One 12 g chocolate chip cookie contains - 8 g of carbohydrates - 3 g of fats - 1 g of proteins Metabolizable energy from the cookie: 8 g x 4 kcal/g = 32 kcal from carbs 3 g x 9 kcal/g = 27 kcal from fats 1 g x 4 kcal/g = 4 kcal from proteins Source: M. Nestle and M. Nesheim, Why Calories Count (2012), p. 73. Total = 32 + 27 + 4 = 63 kcal 22 MACRONUTRIENT DISTRIBUTION Also called Dietary Reference Intakes (DRIs) for macronutrients Carbohydrates are the body’s primary energy source. A healthy diet provides at least 45% energy from carbs In a healthy diet for adults, 20-35% of the energy comes from fat and 10-35% from proteins 23  MACRONUTRIENT DISTRIBUTIONS (USING THE STANDARD VALUES) One 12 g chocolate chip cookie − energy = 8 x 4 + 1 x 4 + 3 x 9 = 63 kcal − 32 kcal/63 kcal = 51% from carbs − 27 kcal/63 kcal = 43% from fats − 4 kcal/63 kcal = 6% from proteins One chocolate chip cookie and one 100 g banana: − (8 + 23) g x 4 kcal/g = 124 kcal from carbs − (1 + 1.1) g x 4 kcal/g = 8.4 kcal from proteins − (3+ 0.3) g x 9 kcal/g = 29.7 kcal from fats − Total energy = 124 + 8.4 + 29.7 = 162.1 kcal − 76.5% from carbs, 5.2% from proteins, 18.3% from fats 24  REVIEW Does a diet of chocolate-chip cookies and bananas provide an acceptable distribution of macronutrients? Is a very low-fat diet (less than 20% of calories from fat) associated with reduced risk of chronic diseases? Is a diet that provides less than 45% calories from carbohydrates associated with reduced risk of chronic diseases? Given that the amounts of carbs, proteins, and fats in coffee can be regarded as negligible, how much energy do you get from a cup of black coffee? What percentage of calories in your © Toby Bridson diet should come from vitamins and minerals? 25