Fuel to Burn
Empty calories, like low-grade gas, can bring your engine a sputtering stop.
But nutrient-rich foods can help you run lean and clean.
When it comes to the body’s survival requirements, water tops the list—humans can’t live much more than five days without it. But while water is immediately necessary for our mere existence, food maintains that existence by being transformed into the energy that keeps the body functioning. As Michele Wilbur, RD, CDN, a personal chef and nutritionist based in Ithaca, New York, puts it, “Food is fuel.”
Wilbur compares our fuel requirements to those of the vehicles we drive. “It’s no more than basic gas in a car,” she says. This analogy is refreshingly straightforward. How the body processes biological fuel, however, is anything but simple.
Energy All the Time
Metabolism sets the stage for our fuel usage. Each person has their own basal metabolic rate (BMR). BMR is the energy your body expends at rest to maintain normal bodily functions—the amount of energy you would burn if you weren’t active all day.
This minimal energy usage largely dictates what will happen to nutrients as they break down. “A primary role of metabolism is to convert food into energy,” explains Douglas Mashek, PhD, assistant professor in the Department of Food Science and Nutrition at the University of Minnesota. “After consuming food, the carbohydrates, fats and proteins are broken down into metabolites on the path to producing energy. The metabolic pathways that a specific nutrient goes through largely determine if it will produce energy immediately or be stored so that it can produce energy later when needed.”
Energy production is such a vital function that the body likes to store fuel, also known as calories, in several different forms. The most common (and bemoaned) form is fat, known technically as adipose tissue. This serves as long-term storage to protect the body against potential calorie shortages in the future.
Being practical, the body also likes to store energy in a more readily available format. “We store carbohydrates in our liver and our muscles, and the way that we store it is known as glycogen—in the liver as liver glycogen, and in the muscles as muscle glycogen,” explains Lisa Sasson, MS, RD, clinical associate professor of nutrition and food studies at New York University in Manhattan. (Some glycogen is also stored in the brain, which has high energy requirements.)
Related to glycogen is glucose. Commonly referred to as blood sugar, glucose needs to be maintained at steady levels throughout the day or fatigue and dizziness can set in. To prevent that from happening, the liver breaks down glycogen and releases it into the bloodstream as glucose as directed by the pancreas, the organ responsible for monitoring blood-sugar levels.
But there’s a catch. “The glycogen that we store in our muscle is exclusively for the muscle’s use,” Sasson says. “If I’m starving and I haven’t eaten for hours and hours, and I have glycogen stored in muscle, it won’t give it up. It’s only for that particular muscle.” What would seem like a disadvantage is actually a survival mechanism; this feature allowed early humans to either fight danger or flee from it even if they hadn’t consumed anything substantial in days. “If our bodies had relinquished that kind of stored energy, then we wouldn’t have survived as a species,” Sasson explains.
The liver is another matter. Sasson says this organ “is very generous” with its glycogen supply, but “you can’t store that much liver glycogen.” Despite its limitations, this form of glycogen is what the body often uses when you first get up in the morning. Having gone without food for hours, the body draws upon liver glycogen, but its finite nature tends to offer only enough energy to get the body minimally moving—not enough for you to feel fully energized.
This is where breakfast comes into play, a meal that Sasson, Wilbur and Mashek all resoundingly emphasize is crucial to balanced energy. As Sasson notes, “It literally means ‘breaking your fast.’”
That concept can get lost in the morning rush to get going, which means that all-important morning meal is often overlooked. Wilbur compares skipping breakfast to “kind of like starting the car and driving cross-country without filling up the tank.” Mashek notes that not eating in the morning, a common strategy among many would-be dieters, is eventually self-defeating. “It will likely cause you to be more hungry at the next meal, which may change your metabolism, and lead to over-consuming calories, only to store those extra calories as fat,” he explains.
Energy or Fat
Just as the storage of glycogen in muscles enabled our ancestors to make quick getaways when needed, the storage of fat in adipose tissue let them cart around extra energy as a defense against calorie shortages. “In times of famine, people were able to store this fat as a fuel source, and that’s how they survived,” notes Sasson. As a result, in sharp contrast to today’s societal standards, carrying some degree of excess fat on your body was once considered a virtue—it was a sign that you had the means to afford extra calories.
The need to make energy portable is the reason fat is so energy-dense; this way “we can store a lot of energy in a relatively small space,” Mashek says. When the body needs fuel, this fat can be broken down and burned. “It’s analogous to storing extra coins in a piggy bank and cracking it open when you need some change,” Mashek explains. “The big difference is the having a full piggy bank is a good thing, whereas having too much fat tissue, or being overweight or obese, is not such a good thing.”
What happens to a particular meal as it goes through the metabolic process largely depends on the amount of energy already stored in the body, particularly in the adipose tissue. When a person eats something highly processed and relatively low in nutrition—for example, a large plain bagel topped with a slab of cream cheese—most of that bagel is going directly into fat tissue, especially if they had a big meal not long beforehand.
However, Sasson makes an important distinction. “Energy is always primary,” she says. “If that bagel is the first thing that I’ve eaten all day, and my last meal was at 7:00 pm the night before, then it’s not all going into my adipose tissue. I could eat three doughnuts, and if I haven’t eaten for 12 hours, every morsel of those doughnuts is going to be converted into some form of glucose or glycogen.”
Filling Up on Premium
Of course, just because that bagel might not be converted into fat does not make it a healthy choice. Some kinds of carbohydrates, often called simple carbs—white flour, white rice, cookies, cake, candy—are like cheap gas; they might burn quickly but aren’t always easy on your engine. “Things like that are very easily broken down into glucose, and rapidly absorbed,” Sasson says. “And when you absorb sugars very rapidly, the body secretes a lot of insulin [the hormone that facilitates the intake of glucose by cells], and the insulin will immediately take the energy source and convert it into either glycogen or fat.” That rapid response plays havoc with glucose levels. “You get that high and low,” explains Sasson. “About a half hour later, you feel lethargic and hungry again. That’s what happens when you eat a lot of simple carbohydrates.”
A healthier alternative to a bagel with cream cheese is a slice of whole wheat bread and a modest spread of peanut butter. Wilbur recommends this kind of snack to the clients of her company, Green Cuisine (www.grcuisine.com), noting that by eating “whole grains and then adding protein [in the form of the peanut butter], your blood sugar is much more stable.”
Sasson certainly agrees. “Whole wheat bread with peanut butter is much better than a bagel with cream cheese,” she says, explaining that the bagel is “not really protein, and it’s a simple carb. You’ve had a lot more calories consumed, but in an hour you’re hungry.” On the other hand, she says that the pairing of a complex carbohydrate such as whole wheat and a protein such as peanut butter helps sustain your energy.
In addition, the combination of peanut butter and whole grain makes it easier to maintain a healthy weight level. “Fat and fiber stay in your stomach longer,” Sasson says. “They have a higher satiety value, so you feel fuller longer. You don’t break down these foods as quickly, and they don’t get digested as quickly.”
That is why Sasson encourages making whole foods—the biological equivalent of high-grade gasoline—the centerpiece of your family’s meals. “The more complicated a food is, the more whole it is from nature, the longer it takes to digest,” she says. “Your body becomes a digesting machine. When we eat very highly processed food, in a way, industry has already digested it for us.” Foods that promote a sustained release of energy along with a fuller, more satisfied feeling include nuts, legumes (such as dried beans, lentils and peas), eggs and oatmeal, along with fresh fruit and vegetables.
How you eat is just as important as what you eat. “A real key is to try and avoid extremes,” Mashek advises. “If we consume and expend the same amount of calories every day, then we don't really store or break down much adipose tissue. The problem is when we overeat, skip a meal, or eat a very unbalanced diet. These things cause big changes in metabolism in order to maintain the proper energy supply.”
Taking a steady approach to nutrition is the best way to maintain a high-performance engine. As Mashek puts it, “If you eat three meals a day with balanced composition, and try to minimize foods that are very high in fat or sugar, then your metabolism will likely be your friend rather than your enemy.”
Additional Aids for Energy
Generation, Weight Loss