Friday, March 09, 2007

Nutrition Expert Lyle McDonald

Recevied the following information from Lyle Mcdonald's great nutrition newsletter.

Feature Article - Dieting by Percentages Part 3

Last week, I looked at some problems with using percentages to set up diets, you can read it in the archive. This week I want to finish up by looking at several other ways that focusing only on the percentages of nutrients in the diet (or in a meal) can be misleading and inaccurate.
It's quite common to see statements of "Such and such is a high-fat diet and hence bad." or "High-protein diets are bad", things of that nature. Most commonly, those statements are based on the percentages of a given nutrient in a diet. For example, diets containing 30% or less total calories from fat are generally considered 'low-fat' while, by definition, higher fat intakes are considered high-fat. But this can be terribly misleading as well as misused. Here's an example.

Let's say we have a person who's currently eating 2000 calories of which 150 grams (600 calories) are protein, 176 grams (707 calories) are carbs, and 77 grams (693 calories) of fat. Using the math from the last chapter, this yields a diet that is 30% protein, 35% carbohydrate, and 35% fat. Most would refer to this as a high-fat diet and deem it bad because it contains 35% fat calories. They would probably also call it 'low-carbohydrate' and 'high-protein' based on the percentages.

Ok, so let's say we add 200 grams (800 calories) of carbohydrates (let's use table sugar just because) to the diet without changing anything else. Total calories now go to 2800 and the percentage of calories from fat drops 35% to 25% (protein drops from 30% to 21%, carbs increase from 35% to 53%), even though the total fat intake in grams hasn't changed. By typical naming conventions a 'high-fat' diet has now magically become a 'low-fat' diet and nobody will have a problem with the protein or carbohydrate intake, based on the percentages. Of course, total fat intake in grams didn't change. Neither has protein intake in grams. All we did was skew the percentages by adding 200 grams of table sugar to the diet. And I don't think anybody would argue that adding 200 grams of table sugar to this diet is particularly healthy. Yet many clueless folks would automatically assume or claim that the second diet (25% fat) is healthier than the first (35% fat) because it's a 'low-fat' diet even though both diets contain the same number of grams of fat.

On a related note, many food companies will use this strategy as well. By simply adding table sugar to a food, to increase the caloric content, they can drive the percentage of calories from fat downwards below 30% and call it a low-fat food. You can make vegetable oil (100% fat calories at 14 grams fat/140 calories) a low-fat food if you add enough table sugar to it. Does that make it healthy because it's now 'low-fat'? Obviously not. Or perhaps not so obviously because some folks fixate so hard on the percentages that they miss the forest for the trees. Using the same starting diet from last week, say we decide to take all of the carbohydrates out of the same diet. Now it contains 150 grams of protein (600 calories), zero grams of carbs, and 77 grams of fat (693 calories) and 1293 total calories. Now it contains 46% protein and 54% fat. Most would call this a high-protein, high-fat diet and go into an apoplectic fit even though it contains the exact same number of grams of protein and fat as the previous diet. By simply changing the total carb and caloric content, we can skew the percentages. But we haven't changed a damn thing in terms of absolute protein or fat intake.

Or an even more extreme example, let's say we decide to move this guy to nothing but protein (an approach called a protein-sparing modified fast or PSMF). Now he's eating nothing but 150 grams of protein per day. That's a 100% protein diet, which most would call 'high-protein'. First they'd freak out, then they'd tell you that his kidneys are going to fall out of his ass. Except that it contains no more and no less protein than the previously two described diets; once again, by manipulating the total caloric content of the diets we've changed the percentages even if we really haven't changed the gram intake. On that note, this is a common criticism of 'low-carbohydrate' and/or 'ketogenic diets'. Most will call them high-protein and/or high-fat because the percentage of total calories from protein and fat is very high. But this can be misleading because ketogenic diets are also commonly low in total calories. Studies typically show that total protein and fat intake change very little when people move to ketogenic diets. Rather, total calorie and carbohydrate content come down, and the percentage from fat and protein go up. Nitwit diet critics will look at the high fat percentage and condemn the diet, without looking at the actual gram intake.

Another example: one of the popularly referenced studies by lower-carbohydrate diet advocates refers to a group of athletes given only 40% of total calories from carbohydrates, who are able to maintain performance. This is frequently used (by low-carbohydrate diet proponents) to argue that a diet of 40% carbs is sufficient and/or that 'high-carb' diets are unnecessary. Here's the problem: because of the extremely high total caloric intake in these athletes, 40% of total calories still yielded in excess of 400 grams of carbohydrates per day (a far cry from the 150-200 grams/day you might get on a typical lowered-carb diet). So even though it was 'low-carbohydrate' by percentage standards, it was still high-carbohydrate relative to their bodyweight needs. Even at only 40% total calories, they still got close to the 5 g/kg value listed above needed to sustain glycogen stores. Once again, the percentage had absolutely no relevance to the actual gram intake.

And, finally, here's a rather humorous example from my college days. At some point or another, during a nutrition class, a professor of mine had made the rather common statement that "As long as you don't eat foods with more than 30% total fat calories, you will be fine" something to that effect. It seemed like a logical extension of trying to get total fat intake below 30%: make sure no individual food contains more than 30% fat calories and you should be safe. At some later date, I took him a cookie recipe of mine that contained approximately 20 calories/cookie and 1 gram of fat (the cookies were mostly air, with a little sugar and some chocolate chips). My professor bristled, because these cookies contained nearly 50% of calories from fat (9 calories out of a total 20). Well, yeah, but they still only contained 1 gram of fat/cookie. ONE GRAM. A cookie that was 200 calories and 30% fat (70 calories) would contain 8 grams of fat even though it's below the magical 30% cutoff point. Yet he would have considered the second a better food choice based on just the percentage even though it had 10 times as many calories and 8 grams of fat vs. 1. Go figure.

Making my point

Looking simply at the percentages of a given nutrient contained within a diet or food can lead people down entirely incorrect paths. Whether it's in setting up a diet, on interpreting a given diet, looking at the percentages alone is a mistake. A 15% protein diet might contain too much protein if calories are absurdly high, and far too little protein if the calories are very low. And a diet which contains 'only' 40% carbohydrate may contain more than enough actual carbohydrates by grams as long as the total caloric intake is high enough. A diet which was considered 'high-fat' by percentage can be made 'low-fat' by simply adding carbohydrates/calories/sugar to the diet but that's not necessarily improving anything.

As I pointed out last week, daily nutrient requirements are (generally) based on bodyweight, not the percentage of that nutrient in a diet. If someone requires, say, 1 gram of protein per pound of bodyweight, they need 1 gram per pound whether it represents 10%, 50% or 100% of their total calories. If someone needs 5 g/kg of carbs to maintain performance, that's what they need whether it's 40% of their total calories or 60% of their total calories. If they need X grams of fat (X not really having been established at this point except for minimal essential fatty acid requirements), they need X grams no matter the percentage. Are we clear now on the different between percentages and total grams? I certainly hope so.

My Training


Tempo Running 8 x 100 yards @ 65% intensity


A-1 Reverse Lunges
2 x 16kg's 4 x 6/6

B-1 Snatches
20kg 5/5
24kg 4 x 10/10 = 80 reps

Felt good.


Bikram's Yoga

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