SWIMMING AND DIET

.One of the things I used to tell people when they asked me why I swim, is that swimming allows me to eat anything I want. And I 

.love to eat. I have heard many athletes express similar sentiments.

In a way it was true. I made sure to get all the basic nutrients in my diet, but on top of that I piled on the high-carbohydrate foods I loved, particularly frozen yogurt. Sure enough, as long as I was working out, I could eat just about anything and never put on weight. But as I learned several years ago, I was fooling myself, and in the process cheating myself of a valuable training tool and a key to long-term health.

For years nutritionists have told us that it is important to eat a balanced diet, one high in carbohydrates and low in both protein and fat, and one containing the basic vitamins and minerals and a high level of fiber. But in recent years a new discipline has emerged that offers a powerful and compelling challenge to the conventional wisdom about the ideal diet.

Dietary Endocrinology

Dietary endocrinology, a new area of nutrition, studies our bodies’ hormonal responses to the foods we eat. One of the leaders in this field is Barry Sears, a former research instructor at the Boston University School of Medicine and the Massachusetts Institute of Technology, and now president of Surfactant Technologies, Inc.

Although dietary endocrinology originally was developed for the treatment of cardiovascular patients, it appears to be applicable both to the enhancement of athletic performance and to the maintenance of ideal levels of body fat. Since 1989 research in this area has been conducted with the Stanford University men’s and women’s swim teams, and dietary endocrinology played an important role in the impressive success of the Stanford swimmers who participated in the 1992 Olympics.

New Attitudes about the High-Carbohydrate Diet

Contrary to sports nutrition gospel, it appears that high-carbohydrate diets may limit athletic performance. This statement is based on thirty years of endocrinological studies which indicate that the food you eat generates a powerful hormonal response. According to this new theory, you have a choice: either you control these biochemical responses or they control you. Athletes, particularly endurance athletes, often believe that their bodies do not obey the laws of biochemistry and endocrinology that govern everybody else. As I used to do, they treat their stomachs like blast furnaces; they believe that because they are athletes they can digest anything. Nothing could be further from the truth.

Several basic biochemical facts govern athletic performance. First and foremost, the primary source of muscle energy is fatty acids—that is, fats. The problem is that muscle cells contain very limited amounts of fat. Fatty acids must be released from the fat in your body into the bloodstream to be used as an energy source by the muscle cells. If the muscles cannot access fatty acids, they are forced to use a secondary and inferior source for energy: carbohydrates. Although the muscle cells contain much of the body’s stored carbohydrates, only the carbohydrates in the liver can be mobilized to maintain the blood-sugar levels your brain needs to function. The task becomes to mobilize the stored carbohydrates from the liver into the bloodstream at levels the brain can access.

An athlete’s body has a virtually unlimited supply of stored fat, but it has limited supplies of stored carbohydrates. For example, a world-class marathon runner or a long-distance swimmer can store twenty to forty times more energy as fat in his or her body than as carbohydrate, so carbo loading makes absolutely no sense at all. What we should be discussing is how best to utilize the fat in our bodies.

It is important to note that the brain can use only carbohydrates as an energy source. As long as the muscles can access fatty acids and the brain has its carbohydrates, the body works smoothly during exercise. The trouble begins when the muscles and brain start to compete for carbohydrates. This is the worst possible dilemma for an athlete, because if the brain is deprived of its carbohydrate supply, the athlete will simply lose concentration.

According to Sears, the problem with nutrition in general, and sports nutrition in particular, is that the conventional wisdom has people looking at the trees and ignoring the forest. Nutrition, he points out, is far more complex than counting the calories you eat or calculating how much fat or carbohydrates are in a serving. “Every time you put a piece of food in your mouth,” he points out, “you trigger a hormonal response. This response ultimately dictates how our bodies perform.”

With this background, we can look at the effects that high-carbohydrate diets have on hormonal response. Initially there is a rise in blood sugar, which causes the secretion of the hormone insulin. As insulin levels increase in the bloodstream, blood-sugar levels begin to fall. Once blood sugar drops below a critical threshold, the brain begins to demand more of it. This starts the cycle over again, and it accounts for the constant hunger and carbo cravings experienced by many athletes, as well as people on high-carbohydrate weight-loss diets.

Several additional facts must be explained. First, the rate of the rise in blood sugar determines insulin levels in the bloodstream. However, not all carbohydrates have the same effect on insulin secretion. In fact, some complex carbohydrates actually increase insulin levels faster than simple sugars. The faster that insulin rises, the more rapidly blood-sugar levels drop. For example, pasta increases insulin levels much faster than a Snickers candy bar. This is why many people, including athletes, become hungry only two to three hours after eating a high-carbohydrate meal.

Second, the human body has a limited capacity to store carbohydrates as glycogen. Once the glycogen pools are full, the rest of the carbohydrates are stored as fat. So high levels of insulin, which are a direct consequence of a high-carbohydrate diet, lead in a roundabout way to an increase in body fat.

Third, elevated insulin prevents the release of free fatty acids from the fat stores. The end result is that a high-carbohydrate diet actually cuts off the primary energy source for your muscles.

The Benefits of Balancing Hormones

Just as carbohydrates affect insulin, protein affects other hormonal responses. In particular, protein in the diet drives up the blood levels of the hormone glucagon. It is the dynamic balance between insulin and glucagon that ultimately determines an athlete’s endurance.

Glucagon has the opposite physiological effect of insulin. For example, whereas insulin prevents the release of fatty acids from your fat stores, glucagon mobilizes these fatty acids. Likewise, glucagon mobilizes carbohydrates from the liver to maintain blood-sugar levels while insulin lowers blood sugar. So it is important to keep a favorable ratio between insulin and glucagon in order to maintain the flow of energy to your muscle cells. The key point to remember is that the glucagon-to-insulin ratio is determined totally by the food you put in your mouth.

There are a number of immediate and profound benefits for anyone who follows a glucagon-favorable diet, but athletes in particular can gain by these advantages:

• Hunger is eliminated because blood-sugar levels are maintained for up to six hours.

• Muscular endurance is increased because fatty acids are being released from your fat stores.

• You stay more mentally alert since blood-sugar levels are stabilized.

• Finally, your body fat decreases because you are utilizing stored fat.

The Ideal Diet

How can you establish a balanced, glucagon-favorable diet? The key is the ratio of carbohydrates to proteins that you eat. This determines the ratio of insulin to glucagon in your bloodstream.

The typical athlete’s diet contains 60 to 70 percent carbohydrates, 15 percent protein, and 15 to 25 percent fat. In addition, the carbohydrates often have a high glycemic index, causing blood sugar to rise rapidly. High-glycemic carbohydrates include pasta, bread, and starches. This type of diet is guaranteed to promote high insulin levels and ultimately limit your performance.

The diet of the typical American is even worse: 50 percent carbohydrate, 13 percent protein, and 37 percent fat. This is a tailor-made prescription for developing heart disease, diabetes, and several forms of cancer.

Research has shown that a favorable glucagon balance can be achieved with a diet consisting of 40 percent carbohydrates, 30 percent protein, and 30 percent fat. What is most important is maintaining the 4-to-3 ratio between carbohydrates and protein.

It is interesting that recent research by anthropologists indicates that this 4-to-3-to-3 ratio closely approximates the diet eaten by our prehistoric ancestors.

Thirty percent fat is the level recommended by the American Heart Association. For good health, your diet must include at least some fat, but this poses no health risk because most people, as a result of well-established diet preferences, find it difficult to get fat levels much below 30 percent. However, if you are one of the few who can get your fat intake below 30 percent, you can still maintain the essential 4-to-3 carbohydrate-to-protein ratio. For example, with a diet containing only 22 percent fat, you can have a 4-to-3-to-2 ratio between carbohydrates, proteins, and fats, yielding the same 4-to-3 ratio in carbohydrate-to-protein intake.

To further complicate things, you must try to maintain the 4-to-3 ratio at every meal, and you must also eat about a third of the vitamins and minerals you need at every meal. At one time medical authorities believed vitamins’ only role in health was preventing or curing diseases specifically caused by vitamin deficiencies. But recent studies have shown many vitamins to be useful in protecting overall health. Among these are vitamin C, and the antioxidants, vitamin E and vitamin A, especially in the form of beta carotene.

Some may protest that this diet appears to be just what they have long been told is not conducive to weight loss. But you will lose weight, because using your stored body fat as a primary source of energy means that you will not have to put as many calories in your mouth to maintain your energy level. In fact, people on a glucagon-favorable diet eat only about half the total calories of a typical American diet because of better appetite control as well as the diet’s ability to provide better access to stored fat.

Once you calculate the number of grams of protein and carbohydrates you will need in a glucagon-favorable diet, it quickly becomes apparent that this is a low-calorie, low-fat, protein-adequate, and high-nutrient diet. It is precisely this kind of diet that geneticist Roy Walford has shown experimentally can lead to a significant increase in life expectancy.

Why are scientists only now beginning to understand the powerful hormonal effects of diet? The reason is that there is a very narrow target zone of protein to carbohydrate that generates the favorable glucagon-to-insulin ratio. If an athlete eats too much carbohydrate (relative to protein), excess insulin is released. If he eats too much protein and not enough carbohydrate, he will develop a physiological state known as ketosis. Ketosis is actually far worse for an athlete than excess insulin production because it inhibits the release of glucagon and promotes the loss of muscle mass.

Therefore, it is essential to eat just the right balance of protein and carbohydrate at every meal—not an easy task. Appendix H provides examples of meals with the proper protein-to-carbohydrate balance.

How do you know if you are in the target zone? Your lack of appetite. If your blood-sugar levels are stabilized, your brain will be satisfied and not send out any hunger signals for four to six hours. If you are out of the target zone, you will constantly be hungry. It’s as simple as that.