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De Sedentário a Maratonista

A motivação também se treina!

08.Jun.12

Emagrecer com a Partição de Energia

Já não são nem uma nem duas as pessoas que me dizem como estou magro. Na verdade estou magro, sim. Mas a questão é que nunca me senti tão em forma e com saúde como atualmente. Bom, talvez tirando os dias em que o esforço dos treinos bi-diários acusa e se faz notar no corpo. Enquanto tento perceber se estou ou não magro (em demasia, claro), procurei alguma informação na net sobre nutrição e exercício, dietas para controle de peso, quer seja para baixo como para cima. Seja para ganhar peso ou perder peso emagrecendo - um objectivo para alguns atletas - o esforço reside essencialmente no que se chama de partição de energia, ou seja, assegurar que o número de calorias que se consomem são utilizadas para desenvolver e alimentar os músculos. Este fenómeno, que também se pode chamar de partição de nutrientes, refere-se ao que acontece às calorias que entram no nosso corpo em forma de alimento. Há três principais destinos para estas calorias e funcionam mais ou menos da seguinte forma:
  1. As calorias das proteínas são incorporadas nos tecidos musculares.
  2. As calorias das gorduras são entregues aos tecidos gordos para armazenamento a longo prazo.
  3. As calorias dos carbohidratos são usadas para fornecer as necessidades imediatas (a curto prazo) de energia.
Se o objectivo é emagrecer, então é necessário ajustar o equilíbrio da partição de energia no corpo, por forma a que mais calorias de proteínas sejam incorporadas nos músculos, menos calorias sejam armazenadas nos tecidos gordos e mais calorias sejam usadas para fornecer as necessidades de energia imediatas (e de curto prazo) que o corpo precisa. Este ajuste pode muitas vezes ser conseguido com pouca ou nenhuma redução do número de calorias que entram no nosso corpo. O que se trata é mesmo de enviar estas calorias para destinos diferentes assim que entram no corpo e não em diminuir o número de calorias que entram no corpo. Mas então como é que esta alteração é conseguida? A forma mais eficaz é através de exercício.

O exercício e a partição de energia

Para entender como isto acontece, temos que perceber também o que acontece com o nosso corpo. Uma boa sessão de treino quebra algumas das proteínas que compõem os nossos músculos, bem como alguns dos carbohidratos que aí estão armazenados como fonte de combustível de curto prazo. O exercício despoleta alterações químicas que ajudam o corpo a reconstruir as proteínas perdidas e recuperar as fontes perdidas de carbohidratos. Um dos conjuntos de alterações químicas aumenta o nível de sensibilidade à insulina nas células dos músculos. Muitas pessoas pensam na insulina como uma hormona que facilita o armazenamento de gordura. Mas a insulina também facilita o armazenamento de proteína e carbohidratos nos músculos. Quando um tecido é sensível à insulina, tem uma maior capacidade de armazenagem de nutrientes. Quando, depois de um exercício, as células dos músculos se tornam mais sensíveis à insulina, os carbohidratos e as calorias das proteínas que provêem da alimentação conseguem penetrar mais facilmente nas células musculares. Um bom treino também provoca outras alterações químicas que afectam o cérebro e os tecidos gordos de forma importante. Por exemplo, durante um exercício, os músculos e os tecidos gordos libertam uma espécie de sinalizador molecular chamado IL-6. Níveis mais elevados de IL-6 nos tecidos gordos durante os exercícios fazem com que as moléculas gordas sejam libertadas e utilizadas como combustível. Níveis elevados de IL-6 também fazem com que o cérebro direccione as calorias consumidas depois do exercício para os músculos e não para os tecidos gordos.     These crucial metabolic effects of exercise last for hours, and also lead to long-term changes in the body that enhance their effects even further. As a result, those who exercise every day, or almost every day, achieve an almost constant body state in which their muscles are hogging calories and their fat tissues are sacrificing “old” calories and being denied “new” calories. Nutrition and Energy Partitioning Winning the game of energy partitioning means creating a competition for calories in which your muscles always win and your fat tissues always lose. While exercise is the most powerful way to favorably control energy partitioning, nutrition also makes a major contribution. Certain nutrients tend to promote muscle tissue growth, while others tend to inhibit or reduce body fat storage, and some even do both. By combining regular exercise with a diet that is based on these nutrients, you will maximize improvements in your body composition. We could write a whole book on the effects of various nutrients on muscle and fat tissue, but for our purposes it will suffice to highlight a few. Nutrients That Promote Muscle Growth There are three key nutrients that promote muscle growth: protein, essential fats, and simple carbohydrates (when consumed at the right times). Protein Protein is the main structural component of muscle tissue. It accounts for roughly 20 percent of muscle mass; the rest is mainly water. Muscles grow when protein is added to them. (When protein is added, water follows automatically.) Protein is the only macronutrient that contains nitrogen. Carbohydrate and fat do not. Therefore, eating protein is the only way to make more protein available to the muscles so they can grow. Essential Fats Ten years ago the average person did not know much about essential fats. These days, essential fats are all over the news and commercial advertising. There’s good reason for all of this attention. The essential fats DHA and EPA cannot be synthesized from other fats inside the body, so they must be obtained in the diet. But the typical diet contains only a fraction of the amount of DHA and EPA that are needed for optimal health. The essential fats are best known for improving heart health, in part by increasing the elasticity of blood vessels. A lesser known benefit of the essential fats is that they increase insulin sensitivity. When higher levels of essential fats are consumed, more essential fats are incorporated into cell membranes. Cell membranes containing more essential fats are more permeable, enabling nutrients and other materials to enter and exit the cell more easily. Increased consumption of essential fats improves insulin sensitivity by making insulin receptors in the cell membrane more responsive and by allowing the nutrients that insulin transports to enter the cell more easily. When a diet providing optimal amounts of essential fats is combined with other healthy eating habits and regular exercise, insulin sensitivity in the muscle cells is maximized. This helps muscles grow and eat more body fat. Unfortunately, it is very difficult to obtain optimal amounts of DHA and EPA from regular foods every day. For this reason we recommend that you take a daily fish oil supplement. Simple Carbohydrates Simple carbohydrates are sugars and starches that have relatively small molecular sizes. Most of them are digested and absorbed into the bloodstream as glucose quickly compared to complex carbohydrates. The fast absorption of simple carbohydrates can be a good thing or a bad thing, depending on when you consume them. It’s best not to consume a lot of simple carbohydrates with your regular meals and snacks. If large amounts of quickly absorbed carbohydrates are consumed when they body does not need a lot of energy, the resulting spike in blood glucose will trigger the pancreas to release a large amount of insulin, which will transport much of the excess glucose to the liver for conversion to fat. But if simple carbohydrates are consumed when the body needs quick energy, this does not occur. The best time to consume simple carbs is within an hour after exercise, when the muscles are insulin sensitive and need glucose to replenish depleted fuel stores. At this special time, the release of insulin caused by the rapid influx of glucose into the blood stream will create a nutrient stampede straight to the muscles. If you consume protein along with simple carbs at this time, the amino acid building blocks of these proteins will get caught up in the stampede, resulting in rapid muscle protein synthesis. Research has shown that the muscles build new proteins much faster after exercise when protein is consumed along with simple carbs than when protein is consumed alone, or with slower, complex carbs. Nutrients That Inhibit or Reduce Fat Storage There are four key nutrients that inhibit and reduce fat storage: protein, complex carbohydrates, fiber and calcium. Protein Protein does double duty in the energy partitioning game: it promotes muscle growth and reduces fat storage. Due to its nitrogen content, protein is not as easy for the body to convert into stored fat as carbohydrate or fat itself. The body prefers to use protein to support the muscles and other protein-containing tissues, especially when there is a high demand for protein in the body, which is the case when you exercise regularly or eat fewer calories than your body burns in a day. Studies have shown that dieters lose more fat and retain more muscle on a high-protein low-calorie diet than they do on a moderate-protein low-calorie diet. Protein is also the most satiating macronutrient, so when you include enough protein in your meals and snacks you feel full faster, stay full longer, and consequently eat less throughout the day. And when you eat less, you store less fat. Research has found that men and women voluntarily eat fewer total calories each day on a high-protein diet than they do on a moderate-protein diet. Complex Carbohydrates Complex carbohydrates are starches with a large chemical structure. All carbohydrates, simple and complex, are broken down to the simplest carbohydrate of all, glucose, through the digestive process. But complex carbohydrates are typically digested and absorbed into the liver and bloodstream as glucose more slowly than simple carbohydrates (although there are notable exceptions). The faster a carbohydrate consumed in food is absorbed as glucose, the more likely it is to be converted to, and stored as, fat. Complex carbohydrates are therefore less likely to add to your body fat stores. Research has shown that men and women who get most of their dietary carbohydrate from complex carbs (found mainly in vegetables and whole grains) are leaner than those who get most of their carbohydrates from simple carbs (found mainly in refined grains and sugary foods). A recent study involving mice (whose diets can be controlled much more thoroughly than those of human subjects) makes the point very powerfully. For six months, one group of mice was fed a diet based on complex carbs, while the other was fed a diet based on simple carbs. At the end of six months, both groups of mice weighed the same, but those on the diet of simple carbs had twice as much body fat! Fiber Dietary fiber helps you win the game of energy partitioning by literally getting in the way of fat storage. Fiber is an indigestible component of plant foods. (There are actually two major types of fiber: soluble fiber, which is partially digestible, and insoluble fiber, which is totally indigestible.) When you consume fiber, it takes up space in your stomach, providing a feeling of fullness that encourages you to stop eating, but unlike other nutrients that create fullness (specifically, protein, fat, and carbohydrate), fiber does so without contributing any calories to your body. It passes straight through your digestible system and is eliminated without ever becoming part of your body. In addition to not being absorbed into your body, fiber also slows down the absorption of other nutrients. This effect also reduces fat storage, because food calories are most likely to be stored as fat when they are absorbed quickly. The best sources of fiber are fruits and vegetables. Whole grains are also a good source of fiber, but they contain more calories and less overall nutrition than fruits and vegetables. Calcium When you think of calcium, you think of bones, not body fat. After all, 99 percent of the calcium in the body is stored in bone tissue. But fat tissue contains calcium, too, and research has shown that the amount of calcium present in fat tissue is an important regulator of fat storage. Simply put, the higher the calcium level in your fat cells, the less fat they store. The lower the calcium level in your fat cells, the more fat they store. The reason is that calcium reduces the activity of a hormone called calcitriol, which promotes fat storage Studies have found that when overweight individuals who consume substantially less than the recommended daily calcium intake of 1,300 mg increase their calcium intake to the recommended level, the lose significant amounts of body fat. The best source of dietary calcium is, of course, dairy foods.