Thursday, May 08, 2008

percentage according to whom?

Okay, following up on the percentage of fat question.

I was reading "Spontaneous Healing" by Andrew Weil a couple weeks ago. The SP had acquired a copy of it from somewhere and, well, I've always been a little suspicious of Weil because he seemed so mainstream crunchy. Too slick, too well-marketed. But I'm a lot more crunchy myself these days, and I thought I'd see what he had to say.

For the most part I think his advice is sound. But I was startled when I was reading his chapters on diet and he recommended no more than 30% of calories from fat. That actually sounded high to me--I figured a low-fat diet such as Weil advocated would be more like 15 or 20% fat calories.

And then I realized, with all the reading I've done about diet and low-fat/low-carb, I didn't have any hard numbers in my head. Atkins' book isn't real precise about numbers; in fact a selling point of his diet is that you didn't have to count, except for the magical 20-grams-a-day during induction, and then figuring out your carb threshold later. (Mine's around 65. Below that and I start dropping.)

So, I went researching. Turns out that the 30% of fat calories is the American Dietary Association's recommendation, which is based on the AMA and the America Heart Association's assumption that fat and cholesterol in the diet cause heart disease. Which is, as I and others have mentioned, a pretty shaky assumption.

Here are some quotes and reference links. Most of the articles I found were written in the mid-nineties. The science and diet climate has changed somewhat since then.

The New York Times:
"In 1990, a recommended low-fat diet for adults should be no more than 30% fat calories."

The San Diego Earth Times:
"In the average American diet, 34.3 percent of the calories came from total fat and 15 percent from saturated fat."

The Weston A. Price Foundation:
"By analyzing menus from turn-of-the-century cookbooks, we can estimate that the fat content of the diets at that time was about 35-40 percent of energy as fat."

"...the American Dietetic Association (ADA) recommends that "diets should provide moderate amounts of energy from fat (20 percent to 25 percent of energy)" and noted that the more restrictive level of 15 percent offered no advantage. However, since typical diets have been found to be closer to 35 percent of energy as fat, even their recommendation of 20-25 percent represents a lowfat approach."

"The USDA food consumption survey revealed the percent of fat in American's diet continues to go down: 33% in 1994, 34% in 1990, and 40% in the 1970s."

The American Academy of Family Physicians (detailed report on clinical studies):
"Under current recommended guidelines set by the National Academies of Sciences, Americans are advised to take in 45 percent to 65 percent of calories from carbohydrates, 20 percent to 35 percent from fat, and 10 percent to 35 percent from protein."

So, here are the answers to the questions I asked you:

The average American diet in the mid-nineties appears to have consisted of approximately 33% fat calories.

The Powers That Be recommend consuming no more than 30% of your calories from fat, although more and more often nutrition gurus are making the distinction between poly/mono and saturates and unsaturates. I think these distinctions are just the gurus scrabbling to take back the lines in the sand which they drew before the latest data was in.

An Atkins-type low-carb diet, at its most extreme, may consist of up to 60% of calories from fat. At this point, however, you'd be consuming at most 1200 calories a day, because you'd be living off your body's fat reserves.

As for how what percentage of calories "should" be coming from fat? I say go back to the 40% that was common in cookbooks in the early part of the 20th century. But they have to be the natural fats that people were eating back then--butter, olive oil, lard and schmaltz (chicken fat).

Bottom line is, your body needs a certain amount of dietary fat, not only to run smoothly but also to process certain vitamins. I think if you're not eating enough good-quality fat, your body thinks it is being malnourished, possibly because it can't make good use of the nutrients that are coming in (and probably because the cheap starches that we eat instead of those good fats are not, in fact, very nutritious). So we feel hungrier--but it's not hunger per se, it's malnourishment. So we eat more cheap starchy crap, because it's low in fat and supposedly harmless. And we get fat.

That's what I think, anyway.

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