By Michael F. Filosa & Anthony M. Ocana We depend on energy to sustain life and to function, and derive this energy from food. Food energy is stored in the form of a high-energy compound, adenosine triphosphate (ATP), which is produced by body metabolism. Energy use is at the lowest rate when we are at rest, and this is referred to as the resting metabolic rate. When the resting metabolic rate is measured at rest in bed, immediately after 8 hours of sleep in a fasted state, it is referred to as a basal metabolic rate (BMR). Energy is consumed throughout life, day and night, even in the basal state. Any activity above the basal level results in increased consumption or expenditure of energy. Our total physical energy needs include energy to maintain the basal state, as well as energy expended for activities. Different animals have different basal energy requirements, and they also expend energy at different rates. Physical energy needs vary among people, and are dependent on the types of activities. Measure energy consumption Only about 40% of energy from food metabolism is used to produce ATP. The remaining 60% produces heat. A unit of heat is a calorie, which is the amount of heat needed to raise one gram of water one degree centigrade. Nutritionists use Calories (with capital C) to mean 1000 calories. So 154 Calories means 154,000 calories or 154 kilocalories. The BMR of an adult female is about 1,300-1,500, and for a male about 600-1,800 Calories per day. One way to measure body energy expenditure is to measure heat production. Another easy way is to measure respiratory gases. Carbohydrate and fat metabolism use oxygen and produce carbon dioxide and water. Gases exchanged in the lung normally equal energy expended by the body. Increased activity leads to increased metabolic rate, which is reflected and measured in increased oxygen consumption. Eating for energy In order to obtain adequate fuel energy, we need a balanced diet with a variety of foods in the appropriate amounts. Foods are composed mainly of carbon, hydrogen, oxygen, and in the case of protein, nitrogen as well. When at rest, the body derives energy almost equally from carbohydrate and fats. During short-term physical activities, energy is generated almost exclusively from carbohydrate, which is converted to glucose and distributed to body tissues, or stored as glycogen in muscles and the liver. Liver and muscle glycogen reserves are limited and can be depleted unless the diet contains appropriate amounts of carbohydrate. Fat provides energy for prolonged physical activities. The fat reserve for energy is much larger than carbohydrate, but fat is less accessible for metabolism because it must be reduced from the complex form of triglyceride to simpler forms to generate ATP. Protein is the building block for the body and are not metabolized until much of the fat reserves have been metabolized. When metabolism uses proteins for energy the body is starting to take itself apart in an attempt to survive. Carbohydrates as fuel Carbohydrates are fuel for the muscles and the brain, and comprise of energy that is used first. Carbohydrates are broken down by enzymes during digestion and converted to glucose (blood sugar). Assisted by the hormone insulin, blood glucose is transported into cells throughout the body where it is either metabolized to supply energy, or stored. The body mobilizes muscle glycogen for energy during physical activities. When muscles run low on glycogen for fuel, they use blood glucose. As blood glucose drops, fatigue hits. The more intense and prolonged the activity, the sooner glycogen is depleted and fatigue sets in. Ideally, about two thirds of the daily caloric intake should come from carbohydrates. They are found in grain products, fruits, vegetables, and sugars. Protein Protein is also essential for energy. The body breaks down dietary protein into amino acid building blocks to make enzymes and cells. They are essential for building and repairing muscles, red blood cells, hair, and other tissues. Proteins also keep the immune system functioning, assist in transporting nutrients around the body, and are important in the synthesis of hormones. Most dietary animal proteins contain all 20 essential amino acids, but plants do not. A vegetarian diet needs to combine foods such as tofu with vegetables, or rice with yams to achieve complete proteins. Complementary amino acids in the form of different vegetables and fruits do not have to be taken in the same meal. As long as they are consumed within the same 24 hours, they will be converted into complete proteins. Although excess protein can be converted into fat, this is actually unlikely. Most dietary proteins are accompanied by large amounts of fat, such as in meat, and whole fat diary products. It is not the protein, but the accompanying fat that leads to weight gain. The body needs about 50-100g of protein per day. For people who are fairly inactive, the recommended dietary allowance (RDA) is 0.36 grams per pound of body weight per day. Protein should amount to about one sixth of total calorie intake. Proteins are found in animal products such as meat, fish, egg, nuts, seeds, and beans. Fat Fat is an important fuel and energy source. It provides about twice as many calories as carbohydrates and protein. It is essential for insulation, assists in the transportation of some vitamins, and helps regulate hormones. We have come to fear this nutrient, most likely because of an almost universal preference for the lean body image and the health risks, such as heart disease, cancer, and stroke, that are associated with a high fat diet. Actually, not only is a certain amount of fat required for health, there are some types of fat that can help maintain heart health. Health Canada recommends that fat intake should be limited to no more than 30% of total daily calories, including no more than 10% saturated fat. Saturated fats are usually solid at room temperature and include butter, lard, coconut, and palm oil. These fats increase bad cholesterol levels and decrease good cholesterol. Polyunsaturated fats are found in oils that are liquid at room temperature and include corn, sunflower, and other vegetable oils. They can reduce total cholesterol levels when used as a replacement for saturated fats. Omega-3 fatty acids are polyunsaturated fats found in fish, nuts, and seeds and are heart healthy. Monounsaturated fats are preferred because they lower bad cholesterol levels and increase good cholesterol levels. They include olive, peanut, and canola oil. In addition, fats can either be hydrogenated or non-hydrogenated. Hydrogenation changes liquid fat into solid fat at room temperature, such as canola oil into margarine. The process creates trans-fatty acids, which increase bad cholesterol. As fats in foods can be invisible, it is important to read nutrition or ingredient labels. Saturated, polyunsaturated, and monounsaturated fats are listed on food labels. Trans-fatty acids are not listed, but are identified as “partially hydrogenated” vegetable oil on food labels. Water Of the over 50 nutrients that we require daily, water is the most important. Most people do not think of water as a nutrient, and as a result, it is often forgotten. It is essential to life. We can only live for 3 or 4 days without water, but we can survive for several weeks without food. Water carries nutrients throughout the body, maintains body temperature, and helps rid the body of waste products. When the body is low on fluid, both physical and mental performance are impaired. Lack of water can result in fatigue, dizziness, headache, weakness, dry skin and lack of concentration. As a rule of thumb, daily water intake for adults should be 8 glasses of 250 ml (2 litres) of fluid. Note: Please refer to articles in the Body and Gourmet sections of this issue for more details on eating and drinking for performance and energy. References: Wilmore JH, Costill DL. The physiology of sport and exercise, Champaign, Il> Human Kinetics,1999 115-151 Nutrition review, Vol. 59 S13 – 16 www.healthsmith.com www.americanheart.org

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