Monday, July 20, 2009

Good Calories, Bad Calories

"Good Calories, Bad Calories by Gary Taubes is held up to be something of a bible by those on the low-carb diet bandwagon. From what I've read about it, it:
  • attempts to destroy the conventional wisdom that low-fat diets are good for you
  • explains how not all calories are created equally, due to the different ways carbs, fats and protein get metabolised
  • explains how carbohydrates cause havoc with insulin and blood sugar, and how this leads to appetite problems
  • explains how carbs cause heart disease
How solid is the science? The book seems to be painstakingly detailed - unusually so for a mainstream diet book. And it has certainly gotten a mixed response, with many lay-folk latching on to it with enthusiasm, and those in the research community pooh-poohing it. I won't link to all the various critiques and discussions that are out there, but a good starting point is here. It seems to at least mark a turning point in our understanding of nutrition.

Taubes' position is that obesity is caused by consumption of carbs, whereas the conventional view is that is is an energy balance problem. From what I've read, it sounds like no diet has been shown to be particularly effective in the long term, and that any diet can provide short-term weight loss.

But I'm not particularly interested in weight loss. It is the other health effects of carbohydrates that interest me more. There appears to be less argument over the way carbs cause heart disease - but perhaps I wasn't looking hard enough. Carbs are also a cause of inflammation, which some hold to be a source of many diseases. But this seems to be more hypothetical.

I'm going to have a crack at this low-carb malarky and see how my body responds. The only experiment that counts is the self-experiment!

1 comment:

  1. Hi Garth,

    Energy apportionment is an issue Taubes was not able to address in GC,BC. It's estimated that the digestive tract of the average human hosts about 2 kilograms of gut microbes. Since they eat what the host eats, how quickly they multiply and how many of them end up in the feces is determined by the quantity of food consumed and the mixture of nutrients consumed at each meal.

    On the fifth page of a document entitled "Basics of Fermentation" http://rothfus.cheme.cmu.edu/tlab/ferm/projects/t6_s99/t6_s99_manuel.PDF we learn that "A universal product of microbial growth is heat. The heat of combustion of microorganisms is fairly constant with a typical value of 5 kcal/g."

    To determine the total heat generated by gut microbes each day one needs to know the dry weight of feces. 50 to 60 percent of dry feces consists of gut microbes. On page 15 of "The Truth About Poop" by Susan E. Goodman the author writes, "Each day, on average, people produce one ounce of poop for each 12 pounds of their body weight. Since an ounce is 28.41 grams, I calculate that a 160 pound person will produce about 379 grams of feces per day. If feces is 75% water, the dry weight of feces would be 95 grams and the dry weight of microbes would be 48 grams. This yields 240 kcal of energy that didn't get absorbed into the bloodstream.

    This figure can vary either way depending upon the quality of food intake and variations in physiological and biochemical makeup. Consequently, determining the apportionment of calories to gut microbes is crucial to understanding what happens in overfeeding studies where subjects do not gain as much weight as expected. Likewise, when people underfeed themselves as in dieting to lose weight, the effect on gut microbes may partly explain why yo yo dieting results in greater weight gain (rebound effect) after each effort to lose.

    For more on this I suggest you visit Gary Tivendale's collection of documents on gut microbes and obesity at http://www.scribd.com/people/view/3737769-gary-tiv

    Regards,
    David Brown
    Nutrition Education Project

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