Tuesday, June 8, 2010


My generation has identified ourselves as the low-carb dieters. From high school, I remember carbohydrates (or carbs) being bad, and protein and fat being good. This was supposed to trick our bodies into believing that it was being starved and thus, burning our fat stores. The most extreme example I can remember is when my grandmother decided to go on the Mayo Clinic diet to try to outsmart her diabetes. She would eat piles and piles of meat and fat: bacon and eggs, chicken breast, steaks, hamburger without the bun. But before she ate it, she had to drink a glass of unsweetened grapefruit juice to more efficiently burn calories. Even at 12, I thought this was a little ridiculous. However, the trend has kept on: Atkins, South Beach, and Zone Diets all contain low-carb components.

I think much of the reason people decide to go on these silly diets is a lack of understanding about what they are eating and how their body uses the food to make energy. So let’s start with some basic facts. (I’m not going to reference these because they are commonly found in biology and biochemistry textbooks. )

1)      Sugars are the body’s preferred source of energy. 

2)      Glucose is the only energy source for the brain.

3)      Glucose is converted into glycogen and stored in the liver or muscle for later use.

4)      There is a limit to how much glycogen any body can store. When your store is full, excess carbohydrates are converted to fat. 

 Sugars are broken down differently dependent on their chemical structure. We’ll talk about the common dietary sugars first: Sucrose (table sugar), lactose (milk sugar), starch (bread sugar), fructose (fruit sugar), and glucose. We’ll also include cellulose (fiber) because it’s commonly part of your diet.

Sucrose is table sugar. It’s what you might put in your coffee. In its more refined state, it’s white and crystalline. Brown sugar is sucrose with molasses, ‘raw’ sugar isn’t truly raw in the US, but it does contain trace elements and molasses. Calorically, they aren’t much different, but the darker varieties will have different flavors, minerals, and possibly trace vitamins.

Sucrose is one part glucose and one part fructose linked together in a specific chain. Inherently, sucrose is 50% glucose and 50% sucrose. To your body, fructose is >70% sweeter than sucrose or glucose, but glucose is the preferred energy and the only one used in the brain. Furthermore, glucose is a potent signaling molecule, telling your body when it has enough of the glucose it needs to do the job.
High fructose corn syrup (HFCS) is 55% fructose to 45% glucose. It has more free fructose than normal table sugar. Some people claim it is the cause of the obesity epidemic in America. I’ll talk more about my thoughts on that when I get to fructose. 

Lactose is milk sugar. It is 50% glucose and 50% galactose linked together. The interesting thing is that lactose is specifically broken down by an enzyme called lactase (-ase usually means it breaks down whatever the first half of the word contains. Lactase = breaks down lactose). Lactase isn’t made by your body unless it needs to break down lactase. In fact, if you eat other foods that are not rich in lactose, sugars in those foods prevent your body from making much lactase because it’s energetically wasteful. Very few people are actually born without the gene for making lactase, making them genetically lactose intolerant. When people eat very little lactose, their body can stop making lactase, making digestion of milk sugars very uncomfortable. However, if the milk products are re-introduced into the diet slowly, discomfort is limited and can be overcome.

Cheese and yogurt contain microorganisms that digest much of the lactose for us. This is the reason some people are very sensitive to milk and ice cream, but can eat most cheese with no problem. 

Starch is all glucose linked together very specificially. We get most of our starch from plants that store these in large seeds or pools. Wheat, corn, and potato are three plants with high starch content. Rice and cassava are commonly eaten outside the US.  Starch is your body’s premiere source of sugar because it’s easy to break down and contains only your body’s favorite simple sugar, glucose. Starch is also the culprit behind skyrocketing blood sugar and being hungry shortly after a meal. Are you familiar with ‘Chinese Takeout Syndrome’? That is when you eat Chinese food and are stuffed to the gills, but an hour later you are hungry again. People try to pin that on MSG, but really it’s high amounts of sugars (sweet sauce), starches (breading, rice), and protein (General Tso’s Chicken, anyone?) than you are consuming. Your body puts on the brakes because it senses that your blood sugar is high and you are having trouble storing your glucose. The fat also signals to your body that you are full. Those things break down fairly quickly, though, and an hour later you have nothing in your tummy. A little bit of fiber would fix this deal….

Fiber is also known as cellulose (or it’s relative hemicelluloses). It is the nondigestable part of plants. Celery is famous for being mostly cellulose, but many veggies and fruits are high in it too. Whole wheat bread is higher in fiber than white bread because the hull of the wheat is left in the mix, which allows for higher fiber. Though now, many commercial wheat bread are supplemented with fiber from other plant sources as well.
A single bond between two atoms is the only difference between starch and cellulose, but that linkage determines whether your body can break the sugar down. Starch is easily broken down, but cellulose is not. Cellulose is not a source of calories for your body, but it can act to flush all of your degrading food through your digestive tract.
How does this all affect your body? Your body breaks these things down differently. All of the more complicated sugars are broken down into their single parts. For the examples I gave, these are glucose, fructose, and galactose. These are then converted into energy for your body. I’m going to show you these pathways, but don’t be scared. There are just a few things I want you to take away from this picture:
1)      Glucose is the preferred energy source and dictates the main pathway in the picture (in the white box).
3)      All the other sugars need to be converted into something within the white box or back into glucose.
4)      Your muscle contains an enzyme that can convert fructose into fructose-6-phosphate, which is in the white box.
5)      Your muscle fills up its glucose stores faster than your liver, where more glucose is stored and used long-term. Your liver doesn’t have the ability and has to use the more complicated pathway shown to break down fructose. 
  image source Now, high fructose corn syrup (HFCS) is a touchy subject. I live in Iowa, corn capitol of the nation, and I dare say that I don’t like how HFCS is used and I am skeptical that your body uses it ‘just like sucrose’. In fact, many medical experts agree that HFCS are metabolized differently than table sugar, being more likely to convert to fat, and less likely to signal your brain you’re full. However, scientists disagree on the relationship between HFCS consumption and obesity in humans. In fact, I know another Ph.D who disagrees with me on this point. But you know what, that is a good thing. That means we are both actively analyzing the problem and learning from eachother. Sometimes having scientists disagree on a problem makes everyone learn more.
In the meantime, if you want to try this out on your own, try a simple experiment. Commercially available soda is sweetened with HFCS, though some are now being marketed with cane sugar (sucrose) as public backlash at HFCS has been mounting. You can buy Regular Mt. Dew and ‘Throwback’ Mt Dew (with cane sugar). Or, you can get some Coca-Cola and get some Coca-Cola at a Chinese, Indian, or Mexican speciality store. Many times they carry cane-sugar sweetened varieties. Just check the label. If all else fails, Coca-Cola makes cane-sugar sweetened varieties for Passover. 
Drink the entire can/bottle regular soda. Record how you feel. Could you drink another soda? How long until you feel you can drink another soda?
Drink the entire can/bottle cane-sugar sweetened soda. Record how you feel. Answer the same questions as above.
To be truly experimental, do this, alternating the order that you drink the sodas. Try to do it at the same time everyday. This isn’t a completely controlled experiment, but I think you get the idea.
Now, tell me your results. I’ll tell you my fiance’s story on the next Carb post: Carb II.
We’ll talk about no-calorie sweeteners then, too.


  1. Frannie, your blog is infinitely interesting to me. Also, I think you would be proud of my high levels of vegetable consumption today.

    I really dislike regular soda. I don't buy soda to keep at home, and if I get it out it's usually diet (which I know has its own health issues, but meh). I don't like how regular soda makes my teeth feel fuzzy, and I always feel THIRSTIER when I'm done with one than when I started. Is there a reason for that, or am I just picky and imagining things?

  2. I'll get to the diet soda, and I'm definitely an addict there...As for regular, basically, caffiene and high amounts of sugar are dehydrating, but I think your mouth is probably just reacting to having moisture pulled out of the cells. Salt and sugar effect the 'osmolarity' in your mouth - that means that the high amounts of salt and sugar actually pull the water from your mouth in order to make the water content on both sides equal. Same concept applies to eating salty food or licking icing off a cake.

    I am always proud of vegetable consumption. We ate pasta last night! We collaborated on a red clam sauce on angel hair. I definitely got alllllllllll my carbs yesterday ;)

  3. I like your website.
    I'm in a precarious health situation now myself and need to gain weight..I'm suffering severe constipation and trapped wind, and am at an all-time low. I don't even exercise anymore (except for a walk a day)...I"m confused!
    I like your blog much.

  4. Oh no! Don't despair because it WILL get better. I am not an expert, but avoiding bananas, coconut, and cheese has helped with constipation. Also, for a quick fix, you could take some senekot. It's natural and we give it to my little brothers when they can't poop. You should be able to find it in the drug store or grocery store.

    Hope you feel better!