Monday, January 23, 2012

How Do I Calculate the Percentage of Carbohydrates in my Diet?

I've been trying to do a nutritional breakdown of my diet to establish the percentage Protein, Carbohydrate (complex and sugar),and Fat (especially Saturated Fat) I consume. I've been keeping a detailed food diary and nutritional details of each food I eat including the weight.
By my calculations, which I checked and rechecked, on an average day I consumed approximately 2600 kcals and 1700 grams of food and calorie-containing drinks.
What is the most accurate way of extrapolating my weekly % consumption of each food group please?
My previous calculations have fallen short in that when totalled the percentages didn't add up to 100%.

Thanks for your help--Mike S.

Dear Mike,
I can certainly help you with this!
The percentage you are trying to calculate is the fraction of calories contributed by each of the macronutrients: carbohydrates, protein, and fat.
The reason your numbers aren't coming up right is you are using the weight of the food instead of the calories. So here's how to calculate the percentage you are looking for:

Let's take an example and say you ate 2100 calories yesterday, including 320 grams of carbohydrates and 80 grams of protein. First, you multiply the grams of carbohydrate by 4, since there are 4 calories in a gram of carbs. This gives you 1280 calories from carbs. Now divide 1280/2100 and multiply by 100 to get percentage: 61 percent is the answer, and a good contribution of carbs to your diet.

Now let's move on to protein. First, multiply 80 x 4 because there are also 4 calories in a gram of protein. Then take 320/2100 x 100 to get the percentage of calories from protein: 15% of your calories are from protein.

We can assume the remainder is fat (unless the 4th source of calories--alcoholic beverages--contributed to your intake). Fat has 9 calories per gram (which is why it is fattening!) and alcohol has 7 calories per gram (and the calculations of that are more complex, as you have to figure the alcohol content by the 'proof' of the liquor).

I encourage people to practice this using the food labels you see on the box panel of cereals, milk, and other packages.  Multiply the number of calories in each energy-yielding nutrient by the number of grams contained in the serving of food. Then add up the total and see if you get something real close to the calories-per-serving on the label. It's a good way to check your work.


  1. Thank you for making it so easy!!!!!!!!

  2. Also found it useful. Thanks. Have question. Assuming that the rest is fat, from the example if the percentage of the fat is known and the 9 cals per gram is known, how best to work out calories of fat and total grams of fat to make up the 100%?

    1. OK, the remaining calories are 500 (If I subtract 1280 and 320 from 2100) or 24% (If I subtract 61% and 15% from 100%). 24% of 2100 kcal are close (504). Then take 504 Calories and divide by 9 (calories per gram of fat) and you get 56 grams of fat.