Part III – Hormones and Homeostasis
It’s lunch time, and once again you meet Janine and Mitchell at lunch. You notice that today Janine has chosen a turkey sandwich on whole wheat, a green salad, and a carton of milk instead of her usual burger, fries, and milk shake.
“Yeah,” Janine says, a little self-consciously. “With all this talk about diets, I’ve been reading up on nutrition and health. I figured that eating more veggies and fiber and a little less fat wouldn’t be a bad thing. I’m going to start taking walks, too. I’ve been eating a lot of fast foods this school year because it’s convenient. Between that and sitting around studying a lot more than I used to I’ve seen my weight go up a few pounds—well, okay, more than a few,” she adds, ruefully. “Switching to healthier habits just makes sense. I figure a few small changes at a time will be easier to manage than trying to change everything at once.”
Mitchell now arrives at the table with a large green salad, two hard boiled eggs—and a small muffin.
“Low-carb muffin?” Janine asks with a grin.
“Nooo,” Mitchell admits. “It’s just that, well, I get pretty hungry and tired and cranky eating nothing but the low-carb stuff I’m supposed to have. And I was getting headaches. Okay, so I’m cheating a little bit. But man, you can’t believe the cravings I’ve had for bread and cereal and stuff. So I started eating some, and I feel better.”
You give Janine a quick nudge before she can say, “I told you so.”
Janine changes her smug expression to a sympathetic one. “It’s a blood sugar issue,” she says. “If your blood sugar dips too low, you can get tired and cranky. And get headaches, too. It has to do with insulin, if I remember right.”
Mitchell looks surprised. “I’m not diabetic. I don’t take insulin.”
“No,” says Janine, “but insulin is a hormone we all have and it controls blood sugar. I forget how it works, but if you don’t get enough sugar in your blood, you have problems. And if you get too much sugar in your blood, you can get problems, too. It has something to do with the hormones, and the carbs and sugars you eat, and if the sugar is moving into the cells or not … oh, I forget how it works.”
“Oh,” Mitchell replies. “I thought blood just carried oxygen. I didn’t know it had any sugar in it.” He looks worried. “Sugar is unhealthy, right? What if I have sugar in my blood? Is that a bad thing?”
Janine has learned some empathy, you think, as this time she visibly restrains herself from laughing and puts on a serious look. “You have to have some sugar. It’s what your brain needs. It’s just that you don’t want to have too much or too little blood sugar, but the right amount.”
Mitchell looks a little quizzical. “How do I know if I’ve got the right amount?”
“Your doctor can do a glucose test at your next check-up. It’s pretty routine. Or you can ask about it at the student health center.”
“Oh.” He looks puzzled again. “So is that what’s making me hungry? Low blood sugar? I heard some guys in the gym saying something about low blood sugar.”
“Kind of,” Janine says, then stops to think about it. “I think low blood sugar can make you crave carbs or something. But appetite, being just plain hungry—well, there’s a bunch of hormones someone discovered that affect appetite. There’s an article in a magazine I ran across the other day. I’ll have to dig that out.”
Mitchell looks a little downcast. “The fact is I’m tired of this diet. It’s hard to stay on it, and after those first few pounds dropped, I haven’t lost any more. It’s frustrating.”
“Then let it go,” Janine urges him. “You’re fine just like you are. Stop worrying about counting carbs or protein or calories or grams of this or that or whatever. Just eat good food, not too much of it, and get some exercise. That’s what I’ve decided to do.” She gestures to her lunch selections. “Nothing extreme. I threw away the chips and stuff in my room, but if I want an ice cream bar once in a while, that’s okay. I figure if I eat sensibly most of the time, and start getting more active, like taking a walk every day, I’ll improve my health. That’s the important thing.”
“But still,” Mitchell insists, “the diet seems like it should work. It worked for other people. Why isn’t it working for me?” Mitchell now turns to you. “What do you think? How come I’m not losing weight on this low-carb diet? Am I doing something wrong?”
“Tell him to quit dieting,” Janine insists. “He doesn’t need to diet at all.”
Questions
What is meant by “sugar”? What is a “carbohydrate”? How are sugars and carbohydrates related?
Janine mentioned blood sugar levels, which puzzled Mitchell. What does blood have to do with sugar? How do endocrine hormones control blood sugar levels? Why is the homeostasis of sugar balance important for overall body health? Include a brief discussion of diabetes and hypoglycemia in your answer.
What other hormones could affect Mitchell’s appetite? Where do these hormones originate, and what are their effects? Use the textbook and the resources from the resource list (NOVA video, Science News article, NIH website) to answer this question. Note that this is a relatively new area of research and new information may arise at any time.
Why could a low-carb diet cause headaches, fatigue, and carbohydrate cravings?
Resources
- NOVA Science Now: Obesity
- http://www.pbs.org/wgbh/nova/sciencenow/3313/03.html
- Science News articles, “The Hunger Hormone?” (February 16, 2002; Vol.161 #7), and “Still Hungry?” (April 2, 2005; Vol 167 #14). Check the Science News website at http://www.sciencenews.org/ for this and the newest findings on appetite hormones. Also check your library to see if they carry print copies of this magazine.
- National Institutes of Health Weight Loss:
- http://health.nih.gov/topic/WeightLossDieting
Originally published at http://www.sciencecases.org/atkins/case3.asp
Copyright © 1999–2010 by the National Center for Case Study Teaching in Science. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.
