Tuesday, March 3, 2009

Net calories

We're teaching about metabolism and nutrition . . . then comes the perennial question for which we have no good answer:

"Well then, which diet is best?" Meaning, which of the popular weight-reduction diets du jour are most scientifically sound, based on what we've just learned?

This is a great question!

Not because I have a great answer--I don't.

It's a great questions because I don't have an easy answer. We (meaning "the science community") simply don't know enough yet to say for sure. So it's a great question to talk about that aspect of how science works.

It's also a great starting point to ask, "based on what we are learning now, which do you think would be best?" This opens up possibilities to apply concepts, such as
  • how nutrients are converted to different forms (lipids, carbs, proteins),
  • how nutrients are stored in the body,
  • how metabolism works,
  • what an energy budget is,
  • how metabolic imbalances can created pH imbalances and other problems,
  • the role of vitamins and minerals in the body,
  • the role of fiber in the digestive tract,
  • what metabolic rates are,
  • the role of hormones,
  • and . . . well . . . this list goes on and on . . .
One concept that I often emphasize in this context is the balance between how many calories come in to the body (food calories) and how many calories go out of the body (metabolic calories expended). Much of the difference is stored* . . . and the favorite way we store it is as body fat. This concept is emphasized in my textbooks as well.

But what about all these different approaches to weight-loss dieting. Or just having a healthy diet in general? What about:
  • low-fat vs. high-fat diets
  • good-fat vs. bad-fat diets
  • low-carb vs. high-carb diets
  • processed foods vs. unprocessed foods
  • high-sodium vs. low-sodium diets
  • high-fiber vs. low-fiber diets
  • and this list also goes on and on . . .
You've probably heard about the latest news on this topic . . . something that can inform your next discussion of this topic . . . and perhaps spark additional discussions, eh?

A study recently published in the New England Journal of Medicine suggests that the best weight-reduction diet is as simple as reducing calories in a diet that can include just about anything, as long as it's proportionally high in "heart-healthy" foods such as vegetables and fish.

So the "it's all about the calories" notion is pretty close to the mark, eh?

Want to know more? Check out these resources:

Weight-Loss Winner: A Diet High in Fiber, Low in Calories
by Coco Ballantyne
Scientific American online. 25 February 2009
[FREE article summarizes the recent study]

Stick to a Low-Calorie Diet and It Will Work

by Nathan Seppa
Science News online. 25 February 2009
[Another FREE summary of the recent study]

Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates.
Sacks, F.M., et al. 2009.
New England Journal of Medicine 360(Feb. 26):859-873.
[FREE full-text article about the latest research.]

The Science of Weight Loss
Scientific American online. Accessed 27 February 2009
[FREE set of online resources related to this topic.]

Calorie Calculator
freedieting.com Accessed 27 February 2009
[FREE online calculator estimates the daily calorie needs of an individual based on age, gender, size, exercise habits, etc. Has advanced options and links to additional calculators. Interesting class, lab, online, small-group, or homework activity.]

* some of the calories are lost in the feces

[photo by NatalieTraynor at Flickr.com]

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