Any athlete concerned about performance has questioned, if not thoroughly investigated, whether they should eat more or fewer carbs to improve their fitness. Actually, with the current trend toward low-carb diets and a paleo lifestyle, and considering the world pandemic of obesity, you may be a conscientious carb-counter. This topic is much more involved than just cutting carbs and going gluten-free with hopes of improved health and athletic performance.
There are important questions to be explored here. In regard to training, when is the best time to eat carbs: before, during, or after exercise? Which type of carbs should you consume: sugary stuff like pure sucrose or honey, or complex carbs such as pasta and potatoes? And, of course, how many carbs should you be eating? Ultimately, the amount, type, and timing of carbohydrates doesn’t come down to who The New York Times asked for an interview or what is making headlines as the superior diet or performance enhancement. It’s about what works for you with respect to your health, fitness level, activity level, and how you perform with any given food.
Fuel Your Athletic Body
Our bodies primarily run off of carbohydrates (glucose) and fat for energy. Though fat is the preferred fuel source in most instances (unless you’re sprinting), most people burn more sugar (glucose) for fuel even when they train aerobically. Many burn more than ideal glucose to get them through daily tasks, even if that includes sitting at a desk for most of the day. Relying on sugar as a primary fuel source results in a host of health and performance problems, both mental and physical.
You need to burn sugar at certain times—it’s essential for health and, to some extent, athletic performance. For the most part, you’re always using a combination of fat and sugar for energy. Less glucose isn’t always better, but you want to spare your sugar reserves and rely on them only when necessary. In other words, you want to use fat for fuel as much and as long as you can, so the glucose is there when you need it—perhaps for a longer duration workout, a race, high-intensity training, or just to keep you from being stupid. Yeah, that’s right—adequate glucose getting to your brain will keep you from being stupid. When your glucose levels are depleted (you’re close to or have already hit the wall or “bonked”), your brain will be starved of its preferred fuel source, so you won’t think straight, and maybe you’ll just be a moody pain in the ass. This is why so many athletes participating in endurance events (which I define as at least a one-hour duration), especially ultras or Ironman events, don’t stick to their race plan when it comes to eating, drinking, and pacing. When glucose levels in the blood drop, the body focuses on the muscles, including the heart, rather than the brain.
Insulin, Stress Hormones, and Blood Sugar
Let’s learn a bit of biochemistry relative to the subject, as well as you, a hopefully efficient or soon-to-be efficient athlete.
Simply put, when you eat something containing sugar, whether it’s fruit, bread, or a sweet treat, your body releases a hormone called insulin from your pancreas. This insulin causes your liver and muscles to take in glucose from the blood. If your liver and muscles don’t need to store this sugar, then the insulin will assist in delivering the sugar to your adipose tissue, so you store it as fat.
Hormones never work alone in the body; it’s never that simple. Although there are many complex biochemical pathways involved, one thing to understand is the relationship between the major stress hormone, cortisol, and insulin. When blood sugar goes up (you just ate some carbs), insulin goes up, which helps bring the blood sugar back down. But when you need more blood sugar, your body often does so at the expense of cortisol, which is released from the adrenal glands. Glucagon from the pancreas also plays a role in helping to elevate blood sugar. However, for athletes training hard and the average person often under considerable daily stress, there is a constant tug-of-war between the pancreas (which releases insulin) and the adrenal glands (which release cortisol) to stabilize their blood sugar.
We need insulin to survive; it’s not the bad hormone that many have made it out to be. But most people make too much, too often, and then their body stops paying attention to the high levels. The receptors that deal with insulin eventually get tired of dealing with the hormone, and like the fable “The Boy Who Cried Wolf,” these receptors stop paying attention to the high insulin levels. This is known as insulin resistance. With insulin resistance, the body has lost its sensitivity to insulin; it’s not paying attention to it as well as it once did. Now, the body has to produce more and more of the hormone to achieve what it once required a little of to accomplish the job. It’s inefficient, and linked to pretty much all inflammatory diseases and a host of health problems, from obesity to cardiovascular disease to cancer. Aside from diagnosable health problems, insulin resistance will give you a slew of other problems, such as a low sex drive, premature aging, poor mental and physical concentration, and overall not feeling as good as you should be feeling.
When your body stores this glucose (sugar), it does so in the form of glycogen, which is stored in your liver and muscles. If it’s in the muscles, as most of it is, then it is going to be used by those muscles for energy. The liver will convert its stored glycogen to glucose to keep your blood sugar stable (or as stable as possible), using it for energy and metabolic processes, as well as for your brain to function efficiently (hopefully).
The process of converting stored glycogen to glucose is called glycogenolysis (breaking down glycogen). Again, it’s not a bad thing to pull from the stores, as long as you don’t do it too much and deplete your stored sugar. This process is promoted primarily by epinephrine (adrenaline), which is one of the stress hormones secreted by your adrenal glands in response to stress. This is why when you’re under stress, you make stress hormones and your body burns more sugar—it’s the preferred pathway to get your body out of trouble, out of that “fight-or-flight” system.
The average 150-pound endurance athlete can store roughly 400–450 grams of glycogen. This stored sugar is divided between the liver (100–125g) and the muscles (300–350g) for when it is needed. Whether you need to pull from those stored glycogen levels depends on your exercise intensity, your exercise duration, and your overall health and fitness. It’s not a cut-and-dry number, and it doesn’t necessarily always depend on your heart rate when training or racing. Though heart rate can often be one of the best measurements of exercise intensity, you may still be burning more glucose than is appropriate, even if you feel you are training aerobically. Yeah, this is why some people don’t make gains when they train easy—their body is still burning too much glucose.
If your body is running too low in blood glucose and glycogen, then it will want to make more. So it calls on a different part of your adrenal glands to secrete another stress hormone, this time cortisol, to help make glucose from another source. This process is called gluconeogenesis, and it occurs in the liver too. But this time, the body is making sugar (-genesis), and most often, it is doing so from amino acids, which are coming from protein, which is often coming from breaking down valuable muscle tissue. And no, that’s not a good thing.
Even if you’re burning mostly fat during training, after some time, you will be pulling protein for fuel. Many say this occurs around three hours in a well-conditioned athlete, and therefore, for those not so well-conditioned, it will occur much sooner.
Aside from breaking down muscle tissue and not using fat for energy, those stress hormones (which are created to help provide the “necessary” glucose levels) will wreak havoc on your health over time. Obviously, chronic stress is not a good thing. So if you’re always training hard and depleting your tanks, then you’re a great candidate for illness, injury, and a variety of health problems.
Part II is here where I discuss how to train your body to burn fat as fuel, not just during training, but throughout the entire day.
