Using percentages or ratios to calculate protein, carbohydrate and fat requirements is a popular method of dividing calories.
We even have diet books based on this concept.
For example, the zone diet recommends consuming 40% of calories from carbohydrate, 30% of calories from fat and 30% of calories from protein.
There are other diet books like 80/10/10 which present a more extreme approach to this idea.
However, there are a few problems associated with using this procedure to calculate macronutrient requirements.
To demonstrate this, let’s take the example of three individuals with three different goals.
Person A weighs 60 kg and is looking to gain weight on 2500 calories daily.
Person B weighs 70 kg and is looking to maintain weight on 2500 calories daily.
Person C weighs 80 kg and is looking to lose weight on 2500 calories daily.
Let’s assume that each of these individuals engage in some form of resistance exercise.
We know that protein intake for resistance trained athletes is determined by using the formula, 1.8-2.2 g/kg of body weight.
For the sake of simplicity, let’s use 2g/kg of body weight to calculate their protein requirements:
Person A requires 2×60 = 120 g of protein
Person B requires 2×70 = 140 g of protein
Person C requires 2×80 = 160 g of protein
However, using a 40/30/30 approach, each of them will end up consuming 190 g of protein daily.
For Person A, 190 g will be unnecessarily high.
Not only will he end up spending more money on protein, but he may also struggle to hit his goal of 2500 calories due to the increased satiating effect of protein.
Similarly, B and C will end up consuming an extra 30-50 g over their recommended protein intake.
To further drive my point, let’s take Person C again.
Initially, he will be consuming 2500 calories per day to initiate fat loss.
As his diet progresses, he will have to adjust to 2000 calories and depending on his goals, he may eventually have to drop all the way down to 1500 calories per day.
Using a 40/30/30 approach, at the start of his diet he will be consuming 190 g of protein and towards the end he’ll end up consuming just 110 g of protein daily.
As you can see, he’ll be over consuming protein at the start and under consuming protein towards the end of his diet.
This is suboptimal because decreasing protein intake (below 1.8 g/kg) will increase the chances of him losing hard earned muscle mass.
Protein, carbohydrate and fat requirements should be calculated by taking into consideration an individual’s body composition, goals and preferences.
They should not be determined by using arbitrary percentages or ratios.
In practice, it is much better to use a formula based on body weight to calculate macronutrient requirements.
Formulas give us more accurate and personalized numbers, and the chances of over consuming or under consuming a particular macronutrient is greatly reduced.