The effort to get leaner—a worthy goal for all athletes—is essentially a game of energy partitioning. Also called nutrient partitioning, energy partitioning refers to what becomes of the calories that enter your body in food. There are three main destinations of food calories in your body. They are as follow:
- Protein calories are incorporated into muscle tissue.
- Fat calories are delivered to fat tissue for long-term storage, or carbohydrate or protein calories are converted to fat calories and delivered to fat tissue for long-term storage.
- Carbohydrate calories, and to a lesser extent fat and protein calories, are used to meet the body’s immediate and short-term energy needs.
If you want to become leaner, you need to shift the balance of energy partitioning in your body so that more protein calories are incorporated into your muscles, fewer calories are stored in your fat tissues, and more calories are used to supply your body’s immediate and short-term energy needs. This balance shift often can be achieved with little or no reduction in the total number of calories that enter your body. We’re really talking about sending calories to different destinations once they’ve entered your body, not about decreasing the number of calories that enter your body in the first place.
So then, how is this balance shift achieved? The most effective way to increase the number of protein calories that are incorporated into your muscles, to reduce the number of calories that are stored in your fat tissues, and to increase the number of calories that are used to supply your body’s immediate and short-term energy needs is exercise.
Exercise and Energy Partitioning
To see why, consider what happens to your body after a good workout. A good workout breaks down some of the proteins your muscles are made of as well as many of the carbohydrate molecules stored inside your muscles as a short-term fuel source. These effects of exercise trigger chemical changes that help your muscles rebuild their lost proteins and replenish their depleted carbohydrate fuel supply.
One set of chemical changes increases the level of insulin sensitivity in the muscles cells. Most people think of insulin as a hormone that facilitates fat storage. But insulin also facilitates storage of protein and carbohydrate in muscles. Whether insulin tends to store more fat in fat tissue or more protein and carbohydrate in muscle tissue depends in part on which tissue is more insulin sensitive. When a tissue is insulin sensitive, it has a big nutrient storage response to a small amount of insulin. When the muscle cells become more insulin sensitive after exercise, carbohydrate and protein calories from food are able to enter the muscle cells more easily.
A good workout also causes other chemical changes that affect the brain and fat tissues in important ways. For example, during exercise, the muscles and fat tissues release a special signaling molecule called IL-6. Increased levels of IL-6 in fat tissue during exercise causes stored fat molecules to be released and used for fuel. Increased levels of IL-6 in the brain after exercise causes the brain to direct food calories consumed in the post-workout period toward the muscles and away from fat tissue.
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 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.
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 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 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 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!
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.
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.