Now that you know how to do the calculations from last chapter, I want to talk about some of the problems inherent in setting up diets based on percentages. In the next chapter, I'll talk about what I consider a better method and solution to them.
Reviewing basic physiology
On a day to day basis, your body has certain nutrient requirements, a topic which is discussed in detail elsewhere in this book. As described in those chapters, those nutrient requirements are generally related to how much you weigh (or how much lean body mass you have). There are a few exceptions, places where the requirements for a given nutrient are absolute which I'll mention when necessary.
For example, at any given moment, nearly all of the tissues in your body are utilizating some amount of protein for various processes. Your liver, your kidneys, your muscles, your fat cells, your gut are all using protein for protein synthesis and energy needs. Meaning that the more of those tissues you have, the more protein you need; the less of those tissues you have the less protein that you need.
The same goes for carbohydrate and fat. Your body is using energy at some rate (set by your metabolic rate which is fundamentally related to your body mass but also determined by factors such as hormones, the temperature and other factors) and that means providing energy at some level related to bodyweight. Since carbohydrate and fat are your body's primary energy yielding nutrients, that means that they are required in some amount related to bodyweight. In addition, fat is being used for other structural processes and is going to be required in some amounts relative to bodyweight as well. And although those values may change (based on activity and other factors such as genetics, age, etc.), they are still going to change relative to your bodyweight. Some numerical examples:
The RDA for protein is set at 0.8 g protein/kg body weight (0.36 g/lb) while dieters may need as much as 1.5 g/kg (0.68 g/lb) to avoid excessive protein loss. Endurance athletes need protein at roughly 1.2-1.4 g protein/kg (0.54-0.63 g/lb) and weight trainers may need 1.6-1.8 g protein/kg (0.72-0.81 g/lb). Most bodybuilders use 1 g/lb as a rough estimate and this isn't too far off from the value of 0.8 g/lb.
So someone who weighs 200 lbs and is sedentary needs about 72 grams of protein per day; if they were dieting, they'd need at least 136 g/day; if they are an endurance athlete, they need between 108-126 grams of protein per day; if they are weight training, they may need 144-164 grams of protein per day. Note, at this point, that I've said nothing about percentages.
And while there's no true requirement for carbohydrates (refer back to chapter XXX), studies show that maintaining daily endurance performance may take 5 g carbohydrates/kg (2.2 g/lb); glycogen supercompensation requires amounts on the order of 10 g carbohydrates/kg (4.5 g/lb).
For the most part, fat intakes in relation to bodyweight haven't really been determined, and most research still simplistically talks in terms of percentages. A minimal intake of 3-6 grams of linolenic acid, and 1-2 grams of linoleic acid has been suggested to avoid deficiency syndromes. As discussed elsewhere, whether this represents an optimal amount in terms of health or body recomposition is debatable. Even then, it seems impossible that some fixed amount of either linoleic acid or alpha-linolenic acid would apply to everyone regardless of bodyweight.
But this is all sort of tangential to my point which is that nutrient requirements are related to your bodyweight or lean body mass.
Why is this a problem?
So why is this a problem? When someone puts protein, carb, or fat requirements in terms of percentages only for a diet setup, it doesn't necessarily have any relevance to what that person actually needs. For example, it's not uncommon to see diets for bodybuilders set up with 25-30% protein. Others take a more conservative 15% and use that across the board for athletes or general intake. But what do those percentages actually mean? Obivously nothing unless you also know how many calories that person is eating.
Let's use our 200 lb example individual above and look at his protein intake. Let's split the middle value for weight training and say he actually needs 150 g/day of protein and put him at two different caloric extremes: 1000 cal/day (a starvation diet) vs. 10,000 calories/day (Parillo style). Let's set protein at 30% which most would say is sufficient (or excessive depending on who you're talking to).
1000 cal/day at 30% yields 300 calories from protein, or 75 grams of protein. He'd need 60% protein on 1000 cal/day to get 150 grams of protein per dya. 10,000 cal/day at 30% yields 3000 calories from protein, or 750 grams of protein. Although both diets are 30% protein, the first is half of what our guy actually needs (75 g/day vs. 150 g/day); the second diet has 5 times as much protein as he actually needs. Yes, these are extreme examples and deliberately chosen that way. But they point out that the percentage itself has no relevance whatsoever to what our guy's actual requirements are.
Now, the typical counter-response to what I wrote above is that the percentage values are assumed to be based on some fairly average caloric intake. That is, if we were to put our 200 lb guy (150 g/protein required per day) on a more 'average' 2400 cal/day (12 cal/lb) and 30% protein, he will come out with a protein intake of 2400 * 0.3 = 800 cal from protein yielding 200 grams/day or 1 gram per pound. Yes, a little higher than the 150 g/day but not excessively so. And that's fine, percentage based diets are going to be roughly valid within a certain caloric range. The problem is that isn't always how they are applied and that's certainly not how the percentages are typically interpreted.
More problems: interpretation and useage
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 becuase some folks fixate so hard on the percentages that they miss the forest for the trees.
Using the same starting diet from above, 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 intrepreting 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 early in this chapter and elsewhere, 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.