Calories per 100g Protein: The Purity Metric
Not all protein powders are pure protein. Many contain significant amounts of fats, carbohydrates, and fillers that add calories without adding protein. Calories per 100g of protein tells you how efficiently a powder delivers protein relative to its total caloric load.
What Are Calories per 100g Protein?
Calories per 100g protein measures protein powder purity. Pure protein contains 400 calories per 100g—anything above that comes from fats, carbs, or fillers. Lower is better.
Not all protein powders are pure protein. Many contain significant amounts of fats, carbohydrates, and fillers that add calories without adding protein.
Why This Metric Matters
Lower calories per 100g means more protein per calorie consumed. If you're maximizing protein while controlling total calories, this metric reveals the true efficiency of your powder.
If you're tracking macros or trying to maximize protein while minimizing overall calorie intake, this metric is essential. A powder with 400 calories per 100g protein means you're getting a lot of "extra" calories from fats and carbs. A powder with 400 calories per 100g is much more efficient.
The Science Behind It
Pure protein contains approximately 400 calories per 100g (4 calories per gram). Any calories above 400 per 100g of protein come from:
- Fats: 9 calories per gram (common in blends with added MCT oil or from milk fat in concentrates)
- Carbohydrates: 4 calories per gram (sugars, maltodextrin, or lactose in concentrates)
- Fillers: Added ingredients for texture, flavor, or bulk
How Do I Calculate Calories per 100g Protein?
Divide calories per serving by protein per serving, then multiply by 100. Example: (120 calories ÷ 25g protein) × 100 = 480 calories per 100g protein.
This calculation is straightforward since both values are listed per serving on the nutrition label:
Calories per 100g Protein = (Calories per Serving ÷ Protein per Serving) × 100
For example, if a serving has 120 calories and 25g of protein:
Calories per 100g = (120 ÷ 25) × 100 = 480 calories per 100g protein
This means 80 extra calories (480 - 400) come from fats, carbs, or fillers
What is a Good Calories per 100g Protein Score?
Pure protein is 400 calories per 100g. Under 420 is excellent (isolate purity), 420-450 is very good, 450-500 is average, and over 500 indicates significant non-protein calories.
We compare each product against our entire database of 108 products and assign a tier based on percentile ranking. Lower calories per 100g means more efficient protein:
- Best: Top 10% — extremely pure, minimal extra calories
- Great: Top 25% — very efficient protein delivery
- Good: Top 50% — above average efficiency
- Below Average: 50-75% — contains more fats/carbs than most
- Not Good: Bottom 25% — high caloric overhead from non-protein sources
Isolate vs. Concentrate
Whey Isolate typically scores better on this metric because the extra processing removes most fats and carbohydrates. Whey Concentrate retains more of the milk's natural fats and lactose, resulting in higher calories per 100g of protein.
Most Efficient Products
Here are the top 5 most calorie-efficient protein powders in our database: