February 06, 2006

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A High Fat Diet?

I've been asked, "Your recipes use a lot of high-fat ingredients. Are you just substituting fat for carbohydrate?" I have to ruthlessly suppress my natural wise-acre tendencies to resist responding, "You say that like it's a bad thing."

No piece of advice has been repeated more often in the past couple of decades than "limit fats to 30% of calories or less." In particular, we were told that this would help us stay slim, but we were also told that limiting fats would prevent heart disease, cancer, and a host of other ills. So it may shock you to know that there simply was never much in the way of scientific data to back up that 30% figure.

Worse, telling people to limit fats to 30% of calories or less discouraged people from eating some excellent foods - for example, nuts and seeds, avocados, olives and olive oil, and fatty fish like salmon, sardines, and mackerel, all of which have been shown to reduce your risk of disease. It also fails to distinguish between truly horrible fats, like the over-processed, over-heated, hydrogenated oils used to make cheap restaurant fried foods, and truly excellent fats, like fresh butter, coconut oil, fresh lard, and extra virgin olive oil.

(To air a pet peeve, I frequently see objection to a low carb diet phrased, "Any diet that omits a whole food group is a fad diet." Ignoring entirely the fact that a low carb diet is exactly what the name says - low carb, not no carb - where were these people when we were being pushed to eat a low fat diet? And where do they stand on veganism, which really does omit a whole huge category of foods?)

Often I do, indeed, replace carb calories with fat calories, especially in baking, where I tend to use ground nuts - a high-fat ingredient - to replace flour. By doing this I not only make the baked goods more filling, and prevent them from jacking blood sugar around, but I dramatically increase their nutritional value.

Let's take a hypothetical cookie recipe that includes:

1 cup sugar
2 cups flour
1/2 cup butter

(Note that this is not an actual cookie recipe - for real cookies, you'd need a few more ingredients! But these are the ingredients that matter to our comparison.)

Assuming this recipe makes 36 cookies (3 dozen), each will have 69 calories, with only 34% of those calories coming from fat. They'll have 11 grams of carbohydrate each, with no fiber. Each cookie will have just 1 gram of protein, and the vitamins the flour was "enriched" with - 4% of your daily requirement of thiamin, 2% of your riboflavin, 2% of your niacin, 2% of your iron - oh, plus 2% of your vitamin A, from the butter.

Let me make my usual substitutions. Now our hypothetical cookies will contain:

1 cup Splenda
1 cup homemade almond meal (made with the brown skins still on the almonds, for the fiber and minerals)
1 cup vanilla whey protein powder
1/2 cup butter

Once again, let's assume 36 cookies. The calorie count per cookie actually drops a tiny bit, to 67 calories apiece, with 58% of those calories coming from fat - a big jump. Each cookie will have 2 grams of carbohydrate, a tiny bit of fiber, and 5 grams of protein.

But all of a sudden, each cookie also has 24% of your B6, 22% of your riboflavin, 21% each of your thiamin and B12, 10% of your zinc, 4% of your calcium, 2% of your vitamin A, 1% of your iron, and 1% of your potassium.

Would anyone like to argue that the lower fat cookies are better for you? I didn't think so.

But there's something else to look at when we talk about low carb being a "high fat diet," and that's ratios. What do I mean?

There are only three sources of calories - energy - in the human diet: protein, carbohydrate, and fat. (Okay, four. Alcohol has calories. But we earnestly hope you're not replacing all of your carbohydrate calories with alcohol!)

This means that if you cut out carbohydrates, by definition a greater percentage of your diet will consist of protein and, yes, fat.

For a long time, the government and other authorities have been advocating getting no more than 30% of your calories from fat, no more than 15% of your calories from protein, and between 55 and 65% of your calories from carbohydrate. If you are eating 2500 calories per day, and following these guidelines, you'll get no more than 750 calories from fat. Since fat has 9 calories per gram, this means you'd get about 83 grams of fat per day.

But say that by eating 50% of your calories from fat, 30% from protein, and 20% from carbohydrates ( making sure they're nutritious, low impact carbs,) you are so much less hungry you spontaneously eat 700 fewer calories per day, for a total of 1800 calories? You'll be eating 90 grams of fat per day, or just 7 more grams than you did on your "low fat" diet. That's a difference of just a half a tablespoon of olive oil per day.

In this example, the diet would be fairly high in fat as a percentage, but not particularly high in total fat intake.

I've been keeping track of my diet recently - consciousness is a powerful tool - and I can tell you that I average 58% of my calories from fat. Since I'm eating an average of 1858 calories per day, that means I'm getting 120 grams of fat, or 37 grams more than our hypothetical low fat dieter. That's a difference of a couple of teaspoons of butter, a couple of teaspoons of olive or coconut oil, and a handful of nuts. Somehow that doesn't strike me as dire.

Your protein intake is essential - you need at least a half a gram of protein for each pound of body weight, every day. More protein - up to about twice that - seems to limit hunger and improve metabolism. (And if you're eating a very low carb, ketogenic diet, extra protein is essential. Your body will use it to make what little glucose your body actually needs.) So if you weigh 150 pounds, you need a minimum of 75 grams of protein per day, and 100 to 125 grams per day is quite reasonable. At 4 calories per gram, that will account for 400 to 500 calories per day.

The rest of your calories will be distributed between fats and carbohydrates. These two foods are what your body uses for energy. (Remember that "energy" and "calories" are the same thing. )

Even the lowest carbohydrate diets, like the two-week Atkins Induction, contain at least 20 grams of non-fiber carb per day, and most of us will eat a few more - I find 30-50 grams a day is about right for my body. Those carb grams are where your fruits and vegetables come in, so you don't want to cut them out completely. No-carb is a bad idea.

So if your protein intake is fixed, and so is your carbohydrate intake, it is the fat fraction of your diet that can be expanded and contracted to adjust your calorie intake. If you get less of your fuel from carbohydrates, you'll need to get more of your fuel from fats. If you eat less fat, you'll need more carbohydrate.

(And no, you shouldn't just eat lean protein, with no fat and no carbohydrate. As pioneers who sometimes had nothing to eat but very lean game like rabbit found out, an all-protein diet will make you sick.)

I suppose it's theoretically possible for someone to construct their low carb diet around nothing but fat, but it doesn't seem likely - who wants to sit down to a nice glass of olive oil? Dr. Atkins recommended a short-term fat fast - a few days of a 90% fat diet - for the metabolically resistant. However, the fat fast limited calories to just 1000 per day. That would limit the dieter to 100 grams of fat per day - just 17 grams more than our theoretical low fat dieter.

In short, any diet that limits carbohydrate will be a diet with a relatively high fat percentage. That's just the way ratios work.

Posted by HoldTheToast at February 6, 2006 08:45 PM