View Full Version : Science of feeding

02-12-2006, 07:50 PM
There's a blog that I read daily called "Mind (Collective) of Iron" which is written by a very knowledgeable woman. Today's post is about nutrition and I though it would be a good idea to share it with you, since I found it very interesting.


Sunday, February 12, 2006

Sports Nutrition 101

Somebody (not saying who) thought that working out for 3.5 hours with no calories going in would encourage more fat burning. Uh-huh.

DOH! Here's how I lay it down. This is part (mostly) science, and part (also mostly) experience. I've been at this awhile, and think I carry some street cred. If you don't believe the science part, get yourself 2 books: Physiology of Sport and Exercise by Jack H. Wilmore and David L. Costill, and Complete Guide to Sports Nutrition by Monique Ryan (although there are other good sports nutrition books out there, but I will stand by Monique all the way). Read them cover to cover and then check back with me if you think I'm full of it. If you don't know what glycogen is, Google it and read all about it.

When you are exercising, your body needs to burn carbohydrates. It can get those carbs from 3 places:

1. Glycogen stored in your liver (about 400 calories worth)
2. Glycogen stored in your muscles (1400-1800 calories worth)
3. Circulating glucose (sugar) in your bloodstream (depends on how much is there)

Exercising at less than 60% of Max HR (WHO DOES THAT???) will burn almost 100% fat.

When you exercise at 60-80% of your Max HR, about 50% of the energy comes from muscle glycogen and blood glucose, about 50% from fat, and a small amount from protein (muscle breakdown). The percentages of carbs vs. fats depends on the intensity.

When you exercise at over 80% of your Max HR, about 75% of the energy comes from muscle glycogen and blood glucose (fat can't be utilized effectively at this intensity).

Stay with me here, I'm getting to the point.

As a person becomes more fit, their body is able to burn a little more fat during aerobic exercise. This is accomplished by spending the bulk of the training time at 60-80% of Max HR.

A couple of things should stick out to you, but in case they don't, let me point them out (they are subtle but true):

1. If you spend too much time exercising at over 80% Max HR, you are teaching your body to burn glycogen preferentially for fuel. Your body just gets used to it. This is why I preach DO YOUR EASY STUFF EASY. There's a "dead zone" that is 80-85% of Max HR (depending on your fitness) that can be a waste of time to spend any of your training time in. Better to go easy or hard. And if you are going to go hard, GO HARDCORE AGGRO while you're at it!
2. If you put sugar into your bloodstream WHILE YOU EXERCISE, your body can use it pretty effectively.
3. If you don't put sugar into your bloodstream WHILE YOU EXERCISE, your body is going to exhaust its glycogen stores faster, which won't make you a better fat burner--it will just use up your glycogen faster, and if you exercise long enough, it will make you bonk faster!!!!

See if by not feeding yourself while you exercise you could make your body burn lots of fat, then why would someone eat during an Ironman? We all have TONS of potential fat calories (I, little Yard Gnome that I am, have over 43,000 potential fat calories) available. But like it or not, our bodies are going to go through that glycogen and whatever is in our blood before it starts tapping on those mega-fat stores. Our bodies need to preserve a few things: our brains, which live off of pure glucose (see this is why the first sign of impending bonk is that your judgment gets weird, or you get dizzy) and our internal organs. Our brains would rather shut down our muscles (i.e., make you stop moving) than risk injury to the internal organs. This is the extreme form of bonk.

Bonking occurs when your body cannot meet its carbohydrate needs during exercise from a combination of glycogen and blood glucose. But it's a little trickier than that. Let's say you exhaust your glycogen stores and then dump sugar into your bloodstream. It may be too late! You need to put so much in at a constant rate (generally to tolerance--my rule of thumb is to try and take in 50% of the calories I am burning, a little more while biking) so that your GI tract is able to process it and your metabolism keeps the "switch" turned on so that you keep using that circulating blood glucose for energy. You've all read or heard about athletes whose digestion shuts down, and that inevitably leads to a bonk or else they need to stop and wait it out until their GI tract recovers.

I ALWAYS take in sugars while exercising, even for as little as a 30-minute workout. Why? Because then I am always training my gut to process those sugars and send them to my working muscles. EVERY DAY. Now, of course that means that the stuff I take in during exercise counts towards my daily calorie needs, and of course it does, and maybe that means I get to eat less "food" than otherwise, but the tradeoff to me is clear. My body is trained to utilize fuel, and a side bonus is that I am not starving once I finish a workout (well, except when it's 2 or more hours, then pretty much I'm hungry).

How many people do you know who swear by "I just drink water when I train" and then watch them after a workout and they just undid all their hard work by pigging out? Not only that, but while they were busy exercising with no fuel, their brains figured, "Hey, we're being starved here," so the body went into fat preservation mode, NOT fat burning mode.

Even if a person is trying to lose weight or lean out, I would NOT recommend that they cut back on their training nutrition. Face it, if you are trying to be smaller, then you are going to need to get used to eating less across the board. Eventually, the calories you take in during training will need to drop as well, but initially the last thing you want to do is deprive your body of calories while training, which even MORE convinces it that you are starving it, and will slow your metabolism even further!

So if I were to state "Crackhead's Basic Nutrition Rules" they would be:

1. Eat frequently. 6 or more times a day.
2. Don't eat a lot of food, by volume, at any one sitting
3. Always be sipping Gatorade or your favorite training beverage during workouts, even if they are short. Do some math. Make sure you achieve proper fluid volume (4-6 oz. every 15-20 min., or 16-24 oz. per hour, adjust up depending on your sweat rate and heat), and that you are replacing 50% or better of your calories
4. Don't forget to include your training nutrition calories in your daily totals
5. Don't be afraid to be a little hungry when you aren't training.
6. You should NOT be hungry while you are training! If you are, pop a gel or something.
7. So that you teach your body to burn fat effectively, complete your workouts at the proper intensity. Don't be tempted to turn an easy workout into a hard one--it will do a number on your glycogen stores
8. Be sure to replenish after workouts. I use Endurox R4 on days when I train 1.5 hours or more, which is pretty much daily now. I drink it after my last workout of the day. You can also drink sports drink, but I think it's important to have some protein right away, too.
9. If you are trying to lose weight or just lean out, go a little higher on your protein calories and slightly lower on your carbs (but NOT DURING TRAINING!).
10. If you want to jump start leaning out, you probably should do some strength training. Lots of cardio has a way of making you want to eat to replace the calories you burned; whereas strength training helps you manufacture muscle and just burns more calories at rest.

Train (and NOURISH) on!

Running Mommy
02-12-2006, 09:20 PM
VERY COOL! Thanks! I love how she describes herself as a "garden gnome" thats IS ME!!! :p
I'm also trying to lose a few lb's, but MAN this Ironman training has been making me eat like a linebacker! And I'm not one to let myself starve... Which is obviously how I got myself into this in the first place! lol
Thanks, it was a great read.

02-13-2006, 07:51 AM
I'm glad you found it useful. If you go to her blog, she talks about the first time she trained for IM and how she ate so much she gained weight (pretty crazy!). She has learned a lot since then and her knowledge of nutrition and exercise physiology is impressive. She is certainly an inspiration . I am training for an oly and trying to loose the weight I gained while applying to grad school. I absolutely get you about the linebacker appetite...I just got back from a swim/weights workout and its 8 am and I am HUNGRY!

02-13-2006, 11:01 AM
I'm glad you found it useful. If you go to her blog, she talks about the first time she trained for IM and how she ate so much she gained weight (pretty crazy!).
Thank you so much for posting this. I will have to read up more on this, because for me training = pigging out = gaining weight. Every time I have embarked on a major training effort I have ended up gaining about 15 pounds, probably half muscle half fat. :o

02-13-2006, 11:58 AM
I'm glad you liked it. I agree with you; I have the same mentality of pigging' out is OK if I train... I am slowly changing the bad habit.

04-10-2006, 10:03 AM
I know this post is a little older but I only just found it. I have been gone from the boards for quite some time, but lurking frequently.

This nutrition post has been very helpful. My riding this year so far could cheerfully be described as dismal, with a trip in the SAG yesterday. Ugh! I am mortified. I know, I know, so much worse happen but...sigh. :mad:

I am selling my home, b/f and I had a fight, and I get nervous anyway before group rides. I just couldn't eat much, but am training for an event and don't have enough time in the saddle so I felt I had to go.:rolleyes:

Anyway, love this information. Am trying to focus so I won't have this happen next weekend...and this is going to help, I just know it.

Thanks :D