carbgrrl · 2009-03-22

343,000 reasons to be annoyed

The positive reaction to this new series has really encouraged me, and given that my dear readers tend to be smarties who like to know the logic behind how a thing works, it seems like a good time to lay down some basic information. (Sean, this one’s for you!) So that means this post is going to be somewhat dense.

In GCBC, Gary Taubes reviews the fat-cholesterol hypothesis of overweight, heart disease, etc. that’s been the default position among diet scientists for some decades now, and contrasts its explanatory power with that of the carbohydrate hypothesis. The basic story in making the case for the latter is that insulin and its close hormonal cousins are housekeepers, cleaning up and putting away for later any sugars that flood your bloodstream when you eat.

But there’s more. GCBC goes into exhaustive detail about related impacts of this activity on cholesterol itself, the lipoproteins that convey it, and their various types and subtypes. You may think you know about “good” and “bad” cholesterol and heart attack risk factors and such; I learned just how much was wrong about what I thought I knew. Here’s a tiny sample.

On a diet that [Ronald] Krauss calls the “average American diet,” with 35 percent of the calories from fat, one in three men will have the atherogenic pattern B profile. On a diet of 46 percent fat, this proportion drops: only one man in every five manifests the atherogenic profile. On a diet of only 10 percent fat, of the kind advocated by diet doctors Nathan Pritikin and Dean Ornish, two out of every three men will have small, dense LDL and, as a result, a predicted threefold higher risk of heart disease. …. Krauss and his colleagues even tested the effect of types of fat on these lipoproteins, and reported that, the more saturated fat in the diet, the larger and fluffier the LDL — a beneficial effect. [GCBC, Ch. 9, p. 173; emphasis in original; footnote elided]

Bizarrely, when it comes to scientific study results rather than public-health pronouncements and diet books, there isn’t much that’s particularly controversial about how all this works. (By the way, the cholesterol/lipoprotein discussions were the biggest of the reading “slogs” I mentioned in my first post, but if you really want to know, you’ll really want to read it.)

But fructose is one of those “good” sugars that’s okay to have in your diet, right? You know, ’cause it’s from fruit? Not so much.

As Peter Mayes has explained, our bodies will gradually adapt to long-term consumption of high-fructose diets, and so the “pattern of fructose metabolism” with change over time. This is why, the more fructose in the diet and the longer the period of consumption, the greater the secretion of triglycerides by the liver. [Ibid., Ch. 12, p. 200; footnote elided]

Seen one of those ads on American TV touting the wonderfulness and safety of high-fructose corn syrup? Yeesh.

Because sucrose and high-fructose corn syrup (HFCS-55) are both effectively half glucose and half fructose, they offer the worst of both sugars. The fructose will stimulate the liver to produce triglycerides, while the glucose will stimulate insulin secretion. [Ibid., Ch. 12, p. 201]

The really frustrating part is that these feedback mechanisms in our bodies can lead to a vicious circle of starvation in the land of plenty, so to speak.

[I]nsulin renders the fat deposits temporarily invisible to the rest of the body by shutting down the flow of fatty acids out of the fat cells, while signaling the cells to continue burning glucose instead. As long as insulin levels remain elevated and the fat cells remain sensitive to the insulin, the use of fat for fuel is suppressed. We store more calories in this fat reserve than we should, and we hold on to these calories even when they’re required to supply energy to the cells. We can’t use this fat to forestall the return of hunger. [Ibid., Ch. 24, p. 436]

Well. That’s encouraging, isn’t it?

Not to pick on anyone specifically, but in the first dozen (out of 343,054) diet books that happened to be listed on Amazon at the moment, I found a lot of reasons for frustration:

  • Advice on how to “think like a thin person”, from someone who believes that any calorie-controlled diet will work
  • Instructions on how to lose belly fat by eating things like English muffins (at least they’re whole-wheat ones)
  • How to swap items at your local fast-food place to choose lower-calorie ones
  • A book about getting a flat belly that insists low-carb foods make you fat
  • A popular and not entirely clueless diet that nonetheless lists low-fat (vs. high-fat) dairy as an inherently good thing
  • One book on “eating clean” that seems to have a clue about the actual science of metabolism

All of the above — the science and the largely contradictory diet advice — explains a lot, if you’re a long-time low-fat dieter: you’ve probably been doing it the hard way (and the unhealthy way), assuming it’s even been working for you at all.

While I acknowledge that different diet approaches really do seem to work for different people (another future post or three), increasing the knowledge and awareness of metabolism-science facts is a great Step 1.

Can we agree that a good Step 2 is starting to ignore stuff like this?