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The Problem with Dieting by Percentages

Commonly, when you see diet plans laid out, the intake of the various macronutrients (protein, carbohydrate, fat) is presented in terms of percentages of total caloric intake. So you might see a diet which was 60% carbohydrates, 30% protein and 10% fat or some other set of percentages. Or you’ll see recommendations that ‘…athletes only need 15% of their calories from protein.’ or ‘don’t eat more than 30% of your total calories from fat’, that sort of thing.

In this article, I want to teach readers what these percentages mean and how to use them (if you so desire) either analyze a given diet, set up a diet, or figure out what a food label means.

A Quick Recap on Calories

In a previous chapter I gave you the caloric content of the various macronutrients. To save you needless paging, I’ll review them here.

  • Protein: 4 calories/gram
  • Carbohydrate: 4 calories/gram
  • Fat: 9 calories/gram
  • Alcohol: 7 calories per gram

Calculating Diet Percentages

With the above values in hand, and using some basic math, we can do several different operations in terms of diet and food analysis. Let’s look at each one in turn. I’ll give examples but don’t read too much into the numbers. They are only examples.

Setting Diets up Based on Percentages

Probably the most common use of methods is to do actual diet set up, to determine how many grams of each nutrient someone will be consuming. Let’s say we have a 170 pound male with a maintenance calorie level of roughly 2700 calories per day and let’s say we wanted to put him on a diet that was 60% carbohydrate, 20% protein and 20% fat (again, don’t read too much into these values, I’m using them for example only). We want to find out how many grams of each nutrient he will be consuming per day.

Step 1: Calculate total calories of each macronutrient

The first thing we’d do is multiply his total caloric intake (2700 cal/day) by the percentages of each macronutrient as this will tell us how many calories will be coming from each nutrient. To convert percentages, just divide by 100 so 20% becomes 0.20, 60% becomes 0.60, etc.

The calculations appear below

  • Carbohydrate: 2700 * 0.60 = 1620 calories from carbohydrate
  • Protein: 2700 * 0.20 = 540 calories from protein
  • Fat: 2700 * 0.20 = 540 calories from fat
  • Note: It should be obvious that the percentages need to total 100% (or 1.0).

Step 2: Determine total grams from each macronutrient

Now we simply divide the total calories from each macronutrient by the caloric content of each macronutrient. This tells us how many grams of each food our guy will be eating each day.

  • Carbohydrate: 1620 calories / 4 cal/gram =405 grams carbohydrate
  • Protein: 540 cal / 4 cal/gram = 135 grams protein
  • Fat = 540 calories / 9 cal/gram = 60 grams fat per day

So this particular diet, with 2700 calories and 60% carbs, 20% protein and 20% fat yields a diet of 405 grams of carbohydate, 135 grams of protein and 60 grams of fat per day. For the remainder of the diet setup, you’d divide that up across some number of meals including pre- and post-workout, all that jazz.

Working Backwards to Determine Diet Composition: Part 1

You can just as easily work the math backwards, to determine what percentage of each nutrient a given diet is. Let’s say someone was eating 150 grams of protein, 200 grams of carbohydrate, and 50 grams of fat and we want to find out how many total calories they are eating and what the percentages of the diet are.

Step 1: Determine caloric intake

First you simply multiply the total grams of each nutrient by the caloric content of that nutrient. That tells you how many calories they are eating each day

  • Protein: 150 grams * 4 cal/gram = 600 calories from protein
  • Carbs: 200 grams * 4 cal/gram = 800 calories from carbs
  • Fat: 50 grams * 9 cal/gram = 450 calories from fat
  • From those values, you can calculate total daily caloric intake by simply adding up the numbers.
  • Total calories = 600 + 800 + 450 = 1850 calories per day.

Step 2: Determine percentage from each nutrient

Now simply divide the calories from each nutrient by the total number of calories being consumed to determine the percentage each nutrient is providing. Multiply the decimal amount by 100 to get the percentage

  • Protein: 600 calories/1850 calories = 0.32 * 100 = 32%
  • Carbs: 800/1850 = 0.43 * 100 = 43%
  • Fat: 450/1850 = 0.24 * 100 = 24%.

So our example person is consuming 1850 calories per day with 32% from protein, 43% from carbs and 24% from fat.

Working Backwards to Determine Diet Composition: Part 2

You can use the identical math above to determine the composition of a given food (based on the food label) or a given meal.

So say you wanted to determine the macronutrient percentages on a food or a meal that contained 10 grams of protein, 20 grams of carbohydrates, and 9 grams of fat.

Step 1: Determine calories from each nutrient

First you’d simply multiply the total grams of each nutrient by the caloric content of that nutrient.

  • Protein: 10 grams * 4 cal/gram = 40 calories
  • Carbohydrate: 20 grams * 4 cal/gram = 80 calories
  • Fat: 9 grams * 9 cal/gram = 81 cal

Although most food labels list the total caloric content, even if they don’t, you can easy figure it out by adding up the totals above. This food/meal would contain 201 calories (40 cal + 80 cal + 81 cal)

Step 2: Determine percentages from each nutrient

Now you simply divide the total calories from each nutrient by the total calories in the food.

  • Protein: 40 calories/201 calories = 0.2 * 100 = 20% calories from protein
  • Carbohydrate: 80 calories/201 calories = 0.4 * 100 = 40% calories from carbohydrate
  • Fat: 81 calories/201 calories = 0.4 * 100 = 40% calories from fat

So this food or meal would contain 201 calories, with 20% protein, 40% carbs and 40% fat. Whether those percentages mean anything is the topic of the next chapter

A Note on Food Labels

Many people become perplexed when they do the math above on food labels and find that the caloric content listed isn’t the same as what they calculate. So you might see a food that was listed as containing 212 calories with 10 grams protein, 20 grams of carbs and 9 grams of fat (which, as above, only yields 201 calories). There are a couple of reasons that this happens.

The first is that determining the caloric content of a given food isn’t doesn’t give perfect values, there is always a little bit of slop. As well, the 4, 9 and 4 cal/g values are rounded values in the first place. Finally, food labels almost always round off the values for protein, carbs and fat grams (for example, a food containing less than 0.5 g of fat can list it as 0 grams of fat). If the food listed above actually contained 10.5 grams of protein (44 calories), 20.5 grams of carbs (84 calories) and 9.5 grams of fat (85 calories), that would make up for the difference in values.

Ultimately, these types of tiny differences are no big deal. Even under the best circumstances, caloric estimates are only estimates and there’s always going to be a little bit of slop either direction. We’re not doing clinical nutrition here and, as long as it’s not excessive, small discrepancies in calore values are nothing worth worrying about.

The Problems with Diet Percentages

With the above information as background, let me now look at the problem I have with setting up or even analyzing diets by percentages.

Basic Nutrient Metabolism

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 utilizing 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, 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? Obviously 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 day.  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 Usage

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.

Tricks of the Food Companies

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 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.

An Extreme Example

Or an even more extreme example, let’s say we decide to move this guy to nothing but protein (as in my Rapid Fat Loss Handbook). 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.

A Commonly (Mis)Cited Study

One of the popularly referenced studies by lower-carbohydrate diet advocates refers to a group of swimmers 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.  This is 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%.  If you 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.

Finally Making my Point about Diet Percentages

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 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.

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3 thoughts on “The Problem with Dieting by Percentages

  1. Having trouble trying to get help from here its not working the question i need is multiply your total grams of fat by 9 and total grams carbs by 4 separtate calculations) this give you your total calories from fat and carbs, then divide the results by your total calorie intake and multiply by 100 this is the percentage of calories you consumed of fat and carbs, my carbs is 268 fat is 82 my isnt comming out right can you help.. Analze your protein intake by first calculating your personal RDA based on your body weight. convert pounds to kilograms by dividing your in pounds by 2.2 then multipy your body weight in kg by 0.8 grams protein/kg of body weight.

  2. Hi Lyle,

    Just wondering and please correct me if I am wrong but wouldn’t the last figure spit out at just under 212 calories also seeing 10.5 grams of protein and 20.5 grams of carbohydrate nets 42 calories and 82 calories respectively given it isn’t below .5?

    I know it’s minutia here as you said not to sweat the small stuff but the last paragraph has my numbers mixed up and I am happy to be incorrect.

    Thanks for your site, it’s awesomeness personified.

  3. It wouldn’t surprise me if my math was screwy. I’m a physiologist.

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