Low Carb? Low Fat? What is a Runner to Do?
The latest and greatest on the low carb diet craze
by Carolyn McClanahan

           Well into February, long after all New Year's resolutions should have been broken, I walk into the bookstore and encounter rows and rows of diet books. I think back to my days of being large (30 pounds and 14 years ago) before I saw the light. I want to cry out, "Stop spending your money. Eat healthy. Exercise. That is the answer."

          But the problem is: What does it mean to eat healthy? 

          The medical establishment (which includes me) has preached the gospel of low-fat diet and exercise to thousands of patients. And Americans followed. Fat consumption in this country has greatly decreased in the past decade. But what has happened? Are we our normal weight? No. We are fatter. So is eating healthy still equal to eating low-fat?

          Much of what we are learning about nutrition is rocking the rules of the low-fat mantra. There is quite a bit of new information to cover, so I will "feed" you in three installments. But before we start, just so you know, the answer at the end is "Eat healthy."

Physiology of metabolism (or how we use our energy)

          No matter how you slice it, a calorie is a calorie. Consume more calories than you burn, you gain weight. One pound of body fat is equal to eating 3,500 calories of food. A Whopper, large fries and medium milk shake for lunch two days in a row would add an extra pound of glorious adipose to your sexy waistline. Easy to gain, so hard to lose, because to take off that pound, you would have to run 30 to 40 miles (can you say ultramarathon?). 

Daily caloric need

          To figure out your daily caloric need, multiply your ideal weight by the following:

          Couch potatoes and desk jockeys use 12.

          Hardworking doctors, mail handlers and other "active" people use 13.

          Landscapers, construction types and heavy-duty laborers use 14.

          That will calculate your basic metabolic need; then add the calories you burn from running (or other exercise). A 150-pound person will burn about 100 calories a mile. A 100-pound person burns about 80 calories a mile. A great website to calculate how many calories you burn exercising is:

http://www.changingshape.com/resources/calculators/caloriesburnedcalculator.asp

          As an example, my ideal weight is 110 pounds and I have an "active" job. My daily caloric need is 1,430 calories (110 x 13). If I run 3 miles, I need another 240 calories to maintain weight that day.

          It seems simple. If I want to lose half a pound a week, I have to cut 250 calories a day. It doesn't matter what I cut out -- fats, protein, carbs. I just have to do it, but still maintain a healthy, balanced diet to get all the vitamins and minerals that I need.

          Here is where the controversy kicks in: Low-fat/high-carb diets leave some people feeling hungry, which makes a diet miserable and hard to stick to. These diets have been the mantra of the American Heart Association and The Amercian Diabetes Association (but their support is wavering).  Supposedly, low-carb diets don't do this (I'll explain how later), but long- term effects on health haven't been tested. What will the answer be? Let's go through what happens when we eat to help us arrive at what I think is the answer (which is also the current thinking of researchers at Harvard).

What happens when we eat:

Carbohydrates are broken down by enzymes in our stomach to simple sugars.  They hit the small intestine and are taken up by the liver. In the liver, the sugars are released as glucose into the blood or stored as glycogen. Sugar not used as energy is packaged into a very bad thing called VLDL, which goes through the bloodstream to your fat cells to drop off triglycerides. These make your fat cells fatter.

          The only purpose of carbohydrates is to provide a quick, efficient energy source. Great for people who need it, like runners. But if you are sitting all day, too many carbohydrates will make you just as large as too much butter.

Protein is broken down into tiny building blocks called amino acids.  These are essential in our diet. Nothing else will do to provide the building blocks we need for muscles and other tissues. We need about 1 gram of protein per day per kilogram of body weight. Anything we take in over that gets turned into glucose or ketones (another source of energy) and used as energy, or it can be turned into fat for storage. So too much protein will make you just as large as too much butter.

Fat is broken down by bile acids in the intestine into monoglycerides and diglycerides. Believe it or not, fat is an essential part of our diet.  Essential fatty acids we cannot get from other sources are important building blocks of the hormones our body produces. However, most of the fat we eat is used as energy, or repackaged back into triglycerides and stored as fat. So too much fat can make us fat.

A word about insulin:

          How insulin works is the crux of the theory behind low-carb diets. The main function of insulin is to maintain normal glucose levels. It is also required for our cells to use glucose and protein. Finally, insulin stimulates fat production (lipogenesis) and discourages fat breakdown (lipolysis). 

          When we eat carbohydrates, a lot of insulin is released. Depending on the type of carbohydrate we eat (discussed next month), insulin levels may skyrocket. After all the sugar is cleared out of our bloodstream (used as energy or stored as fat), all that excess insulin is hanging out, reminding us that we need to eat again due to our low sugar. This is what makes high-carb diets less satisfying for some people, because they always feel hungry.

          Protein causes a small amount of insulin release and fats cause no insulin release. Therefore, a meal consisting of these energy sources theoretically leaves us feeling satisfied for a longer period of time. Your appetite is decreased and you eat less, unless of course you are like many people and eat just to eat.

          Carolyn McClanahan, M.D., is a family physician, runner and expert dieter.