Tuesday, July 29, 2008

Calories and energy (once again)

The other day I was offered an energy drink sample "without calories." It happened at the expo for a major race. I was in a good mood, the drink tasted fine and the sales person was upbeat. So I decided to ask a stupid question: how can the drink have energy without calories? The friendly sales person did not get the joke. He seriously tried to help me by talking about carbohydrates, fats, and the like. It fell short.

Desperate, and suspecting he missed something important, he referred me to his expert colleague who pondered the same question. We had a bit of a back and forth and the "expert" finally agreed there was a minor problem "in my way of looking at things."

Well, he said, look at it this way, the drink does not contain energy, it releases your energy. There you go. My energy was trapped in my body. It could even make me fat if I was not careful. My body was good at storing energy, yet when it came to using it, it underperformed. No wonder we have so many obese people?

My energy was screaming to be released, apparently in vain. And that is why his company had developed this miraculous drink. So I could use the energy stored in my body. It is amazing what one can hear at health expos. Athletes must be very gullible indeed.

Energy and no calories. The trick? Caffeine.

At the risk of spoiling the fun, I want to just clarify a few issues.  A calorie is a unit of energy, much like a inch (or a meter) is a unit of length and a pound (or a kilogram) is a unit of weight. When you say a food contains energy but no calories you make no sense. It is like saying my arm is long but has no inches, or my backpack is heavy but has no pounds. If a drink has zero calories it has no energy. Ergo, it is not an energy drink.

Nobody requires special stuff to burn energy. We do it continuously. It is essential to life. If you cut off my energy supply I die. Right away. Every cell in a body needs a continuous energy supply. You cut it off and it's game over. Not all cells are equally demanding however, and some can use energy anaerobically (i.e. without oxygen). Ironically enough, the cells that transport oxygen (the red blood cells) are anaerobic cells. No fair stealing the cargo!

Here is another trick question that is often asked in physiology exams: how long does it take for your brain to die when there is no glucose? Hint: Brains are very energy intensive and they can only use glucose under normal conditions.

Most people think it takes a while. A few hours maybe? So, let's ask the question a different way, how long does it take for your brain to die without oxygen? That is better you say, everyone knows it takes only a few minutes (three minutes is often used). 

Have you ever wondered what your brain does with the oxygen? It oxidizes sugar (glucose). No sugar is equivalent to no oxygen. 

What throws people off is that everyone knows you have to breathe all the time to stay alive, but you don't have to eat nearly as frequently -although some seem to have missed the latter rule. The reason you don't need to eat all the time is because you can store substrate (fuel) but not oxygen.

There is glucose floating around in your blood all the time. The level of glucose is constant and your liver keeps it that way. It is a tightly regulated system and only your brain can use glucose at any time. The rest of your body has to do with fatty acids.

To keep glucose levels constant, your liver has access to plenty of stored glucose in the form of glycogen. If the glycogen runs out, the liver can regenerate sugar from protein. It can keep going like that for a day or two. Fortunately, that is rarely called for and most people eat 3-4 meals a day to replenish the stores.

Should trouble arise, there is another fallback mechanism. The liver can produce ketones from fat. Although you can and do make fat from sugar there is no way back.

During times of starvation, your brain can switch to ketones and stay alive. At the same time, your metabolism is throttled back too. All these combined give you several weeks to months worth of survival if needed. 

However, as any diabetic can tell you, if your blood sugar (glucose) level drops by even a small amount, you can go in coma and die rather quickly. The reason diabetics know this is because they have access to a rather powerful drug called insulin. And they have to measure their insulin carefully because insulin can play havoc with your glucose levels in a heartbeat. All diabetics experience hypoglycemia at least once in their lives. It is a rather unpleasant and potentially deadly experience that requires quick intervention lest it be fatal.

The latter also explains why so-called "hypoglycemic" attacks in otherwise normal individuals who do not inject insulin, are nonsense. Nonsense too are the prescriptions not to eat sugars before exercise lest you suffer from a bout hypoglycemia minutes later. Some extend this to simple sugars (versus the "healthier" complex carbohydrates) or to sugars and coffee. All of it is nonsense.

It is often explained in the following way: you eat too much sugar so you get an insulin response with an overshoot and then you start shaking and feel weak because of hypoglycemia. Unfortunately, there is no evidence for it whatsoever. Although it may sound plausible, it is not. Blood glucose levels are not to be messed with. Remember, no glucose is equivalent to no oxygen. No room for sloppy behavior here. No room for "a bit of an overshoot."

Not convinced? Ever seen evidence of people going in coma with convulsions after eating too much candy?  It does not happen. If it did, the US population would decrease rather quickly.

As for the complex carbs, it is another popular myth. Complex carbs are absorbed as simple sugars. It takes marginally longer to do, but the difference is irrelevant.  Carbohydrate breakdown in the gut is incredibly fast. Furthermore, as far as the blood is concerned, the only "visible" sugar here is glucose.

No evidence for fiber either. Absorption with or without fiber appears equally quick. Some have shown evidence that the presence of fiber may accelerate uptake instead of slowing it down.

In short, all the talk about glycemic index is pseudoscience. It is not even clear that the stated glycemic index of a particular food item is accurate.

There is only one thing to remember about carbohydrate. Too much makes you fat. And it does so because it is easy to eat carbs and to keep eating them. If you only eat carbs you are very likely to over-eat. And that is not good. Put some cream cheese on your bagel !

1 comment:

Anonymous said...

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Feel it fast.
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Elle Davis
Brand Ambassador