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By Elena Voropay
 The average metabolic rate depends on who you are and what you do. One interesting phenomenon of the differences in the overall caloric burn is linked to age. It sets up a stage for many parameters such as size, activity level, body composition and overall growth rate.
To explore this I would like you to refresh your memory as far back as childhood. I bet you can remember the times when you were a kid and could eat just about anything you wanted and stayed slim and trim. Now it seems that no matter how little you eat, every single calorie goes straight to your “spare tire”. This shouldn't be a surprise - children burn more calories. Not only they are more physically active, but their resting metabolism is a lot higher, in fact two times higher than resting metabolism of an average adult. How come not fully developed children, who don't have nearly as much muscles as their parents, burn so much energy? Because they are growing! A very important note here is that kids don't grow because they eat voraciously. It actually is the other way around – they eat a lot because they are growing! And guess what? When you work out in the gym to add lean body mass, you are going against your natural biology somewhat, except in a good way. Asking your body to lift weights heavier than it is normally accustomed to, you stimulate every tissue to grow bigger and stronger, and this induced catabolism demands energy. So, you have to get more fuel into your system to grow. Don't get me wrong – kids don't need to eat huge servings of food like adults as their bodies don't need as many calories. The Basal Metabolic Rate of a child is less than that of an adult, because, of course, there is less of the body size to support. However, the Basal Metabolic Rate per gram of body weight of a kid is greater than that of an adult. This is the basic concept of physiology which can be applied to all living creatures. For example, a mouse burns 25 times more energy than an elephant, but not in the absolute terms. Each gram of a bodyweight of a mouse metabolises 25 times more energy than one gram of elephant flesh. So, why do smaller bodies have to work so hard? One of the most important reasons is that a small body demands more heat to maintain body temperature. Plus, children have faster heart and breathing rates and have more energy-burning mitochondria and brown fat which increases heat production. This is probably part of the reason kids are more “energetic” than adults – they can't sit still for long periods of time and move faster and more spontaneous. Observe kids' behavior for a day – their moods change every few minutes, topics of conversation jump from one to another in a matter of seconds, they get more into their energetic “highs” and “lows” than grown-ups. The link to such behaviors can be traced to hormones and growth rates. The little monsters are growing rapidly. Every single cell in their bodies multiplies constantly and a great part of their body weight is metabolically active tissue - heart, lungs, brain, liver, kidneys. To maintain growth and cell replication, children need to eat more and sleep more. Rest is especially important for growth - only during sleep the body is able to regenerate itself; you may know that the levels of the most important anabolic growth hormones are usually at the peak at night. Hence, many bodybuilders worship their nourishing recovery of sleep and rest as the only way to completely restore all cells from the catabolic activities of the day. Gracefully Fading Bodies Between the ages of 6 and 18, most people have a 25% drop in Resting or Basal Metabolic Rate, and then an additional drop of 2% -3 % in BMR each decade. The reason? There is a continuos cellular change in the body which slows down as you age - cells become larger and their capacity to divide, reproduce and repair tends to decrease. Membranes, enzymes, chromosomes, organelles such as the mitochondria (the powerhouse of all energy production) and lysosomes sense the damaging effects of time on DNA causing cells to function less efficiently. When the mitochondria looses its function, metabolism is decreased to about 95% of capacity by age 50, and to 85% by age 70. When you turn 85, lung capacity goes down by 50%; muscle strength by 45%; and kidney function by 30%. Heart muscle becomes less efficient, less pliant and less able to pump large quantities of blood. Blood vessels lose elasticity and hard fatty deposits may form resulting in high blood pressure or heart disease. Mitochondrial function in muscles decreases, especially in muscles not regularly exercised leading to a gradual reduction in motor neurons. Right around your middle age, your muscle mass drops naturally, even if you haven't changed your diet or exercise. This effect also ties in with a decrease in hormonal secretions. As youth fades, the raging hormones slowly but surely take their toll and the body naturally stops its growth. The decrease is mostly due to loss of muscle and changes in hormonal balance. Growth Hormone and Testosterone circulate in our blood in abundant amounts during the first 20 years of our lives. Their levels then slowly decline as we get older, around 14% - 50% every 10 years after the age of 31. The decline in muscle-building hormones makes putting on lean tissue a lot more challenging. By age 75, the percentage of lean tissue is typically half of what it was during young adulthood. In addition, tissue atrophy does cause a drop in the mass of most organs, which ultimately affects muscle strength and the slowing of reflexes. Muscles cannot contract as quickly because more fast-contracting (Fast-twitch) muscle fibers are lost than slow-contracting (Slow-twitch) muscle fibers. Fast-twitch fibers are the ones used in strength and power activities, they give you size, shape and density. Without sufficient nutrition and exercise, by the 7th decade some people get to the point of extreme muscle wasting, a condition known as sarcopenia (from the Greek, meaning “poverty of flesh”). Blood and tissue concentrations of many other hormones (Thyroid Stimulating Hormone, thyroid hormone Thyroxin, Anti-Diuretic Hormone or ADH, Prolactin, and Glucocorticoids such as Cortisol) remain unchanged, however some endocrine tissues become less responsive to stimulation. For example, there is less GH (Growth Hormone) and Insulin secreted after a carbohydrate-rich meal or during a glucose tolerance test. Peripheral tissues also become less responsive to some hormones, particularly glucocorticoids and ADH which can affect metabolism and the inability to deal with stress. Tolerance for exercise decreases, partly from the tendency for rapid fatigue and a reduction in thermoregulatory ability, which leads to overheating. Not only previously successful training and diet stop 'working', just keeping the existing muscle mass is hard enough already, not to mention how terribly impossible it is to put more on. In addition, a decline in hormonal production will also reduce the anti-inflammatory and immuno-suppressive qualities that they give. This means that the elderly people are more prone to have pains, get sick more often and recover slowly. Collagen and elastin decrease in connective tissue leading to stiffer, less elastic and less efficient joints. The ability to recover from an intense workout or from any muscular injuries also no as good. In fact, extreme exercise in the elderly may lead to problems with tendons, bones, and joints. When injuries occur, inflexible scar tissue forms at a faster rate than tissue repair, thus causing a further loss of mobility. As we age, the amount and distribution of fat, muscle tissue and water also changes. By age 75, the percentage of body fat typically doubles compared with what it was during young adulthood. Fat tissue may become increasingly deposited toward the center of the body around the abdominal organs. The illusive abdominal muscle wall, the 6-pack washboard core gets a soft coverage made up of fat cells. As fat increases, lean body mass decreases. Muscles, liver, kidney, bones, joints, skin, and other organs are effected by aging, too. People may become shorter and thus have less body surface. People typically lose about 1 cm (0.4 inches) in height every 10 years after age 40. When you hit 70, you may shrink down to 7.5 cm or 3 inches. These changes in body fat and water reduction are the main reasons why the elderly respond differently to drugs than the younger population. The thyroid gland which produces hormones that help control metabolism often becomes lumpy or nodular with aging, which also contributes to slower metabolism. An aging body can't stand cold temperatures as well as a young one; a tendency to gain weight increases; there is a decreased efficiency in the body’s use of glucose, fats and proteins. Lipid and fat content of tissues also changes. What happens then is quite obvious – less energy is needed to maintain the tissues than to develop them. Thus old people eat less, but tend to put on more weight. They sleep less and feel more tired at the end of the day. The less they sleep – the less rested they feel the next day. Fatigue translates into higher catabolism, which unfortunately breaks down everything else in the body but the fat cells. Then the entire scenario of slower metabolism is pretty much unavoidable. Less muscle mass, less energy, poor diet and recuperation, the pace of life in general gets into a slow-motion, thoughts and moods change less frequently and overall productivity drops down as fast as the heavy stack of iron plates on your last set. Note that sarcopenia or age-related muscle loss doesn't happen just due to increased catabolism or protein degradation, but due to reduced protein synthesis. If muscles are not working, the protein synthesis is even lower. And if you train too hard at age 80, your immune response may not catch up with all demands and degradation prevails. Feeling Like A Kid Again! Disappointed? Cheer up, my friend! You can change this age-related pitiful scenario, keep the muscle mass you have built years ago when you had the time, desire and energy to show up at the gym every day. You can, yes, you can speed up your metabolism, melt the fat, and burn a lot more calories than the entire kinder-garden bunch! I am not saying that anti-aging process is an easy ride, but you have a very powerful mind which can and will help you through the toughest times. What's the recipe? Good sound nutrition and training to start with. Some evidence for this comes from a research group based at the University of Colorado. They compared a group of young and older inactive men with physically active men of a similar age. Even when differences in muscle mass between young and old subjects were taken into account, Basal Metabolic Rate was lower with age in both the inactive and physically active subjects. The older men burned around 64 - 68 calories per hour, compared to 72 - 77 calories per hour in the younger subjects. However, when researchers compared older and younger subjects doing the same amount of exercise and/or eating the same number of calories, there was no difference in BMR. So, you have all the control over these two factors – physical activity and diet. Once the body-food connection is in sync, you will be able to sleep better, feel more powerful and energized the next day, and get your hormones in better shape. No matter what the age, extremely demanding exercise is not as important as regular exercise, especially resistance training. The researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (HNRCA) in Boston, Massachusetts, have shown that training with weights can reverse sarcopenia and frailty in the elderly. A great body of evidence has proven that older adults can in fact put on muscle mass, although the process may be a bit slower than it is in young individuals. In one study they found that a simple home-based exercise program improved functional performance and balance in participants over the age of 70. Forget Your Birthday - Check Your Biological Age These and many other studies agree on one thing – you don't have to be as old as the calendar tells you. If your birth certificate tells one thing, all systems inside of your body could be telling an entirely different story. This is the difference between chronological age, which is simply your age in years, and biological age which is your age at a cellular level. These two numbers are not necessarily the same. The premise is that there are certain biological markers such as blood pressure, heart rate and pulse, blood sugar levels, hormonal levels, cholesterol levels, bone density, kidney and liver function which can help identify your true biological age. For example if you 48 years old with a blood pressure of 117/ 76 you could be said to have the blood pressure of someone in their early 20s. Similarly if you are in your 30’s and have a blood pressure level of 140 / 90 you would be considered much older than your age in regards to blood pressure. There is an unusually high number of centenarians in longevity hot spots around the globe, such as Okinawa Japan, Nicoya Costa Rica, and Sardinia Italy. Researchers found that regardless of chronological age, most people in these places have very young bodies or low biological age. So, to find how old your body is you need to do a body age assessment. It will tell you where you are today and give you a benchmark to measure your progress. But that's only the beginning. A complete evaluation will also tell you how many years you can take off your chronological body age and recommendations for how to do it. Components involved in the body age assessment include: How does this relate to your overall metabolism? Well, by knowing where you are now and what risk factors you have, you can make tremendous changes. You can't cheat your biological age. If you don't take charge of your lifestyle, you may look and feel 10 years younger than you really are, but the inside of your body could be telling you something entirely different. Lifestyle factors such as exercise, diet, nutritional supplementation, antioxidant status, and stress among others impact biological age. In other words, how you manage your life and the choices you make on a daily basis can either accelerate or slow down your biological aging process. All this boils down to quality of life |
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