The Only Plant-Based Milk That Matches Dairy Milk's Protein Level
Unsweetened soy milk provides 3.55g protein per 100g — virtually identical to dairy milk's 3.3-3.4g. No other widely available plant milk comes close: almond has 0.4g, oat has 0.8g, rice has 0.03g, and coconut beverage has 0g per 100g. A cup (240g) of soy milk delivers 8.5g protein [1].
Soy protein has a PDCAAS (Protein Digestibility Corrected Amino Acid Score) of 1.0 — the maximum possible, shared only with dairy, egg, and a few other protein sources. This means soy milk's protein quality is not just high in quantity but also complete in essential amino acids: all nine are present in adequate amounts [2].
At 39 kcal per 100g, unsweetened soy milk provides 9.1g protein per 100 kcal — better than whole milk's 5.4g/100kcal and comparable to skim milk's 10g/100kcal. This protein-to-calorie efficiency makes it a standout for plant-based tracking [1].
Why Soy Milk Has the Lowest Sugar of Any Milk
Unsweetened soy milk contains just 1.29g total carbohydrates per 100g, with only 0.56g sugars. Compare this to dairy milks (4.6-5.0g carbs), oat milk (5.1g), and even unsweetened almond milk (1.3g). Soy milk edges out almond by the slimmest of margins for the lowest-carb milk title [1].
Per cup (240g), unsweetened soy delivers 3.1g carbs — compared to dairy milk's ~12g and oat milk's ~12.2g. For anyone tracking net carbs, soy milk is the most favorable milk option by a wide margin: roughly 75% fewer carbs than any dairy milk [1].
However, sweetened soy milk changes the equation dramatically: original sweetened jumps to 6.3g carbs per 100g (4.8g sugars), and chocolate to 10.5g carbs per 100g (9.0g sugars). The difference between unsweetened and chocolate soy milk is 16x more sugar per serving — always check which version you're logging [1].
How Soy Milk's Mineral and Vitamin Profile Compares When Both
The USDA profile for unsweetened soy milk (FDC 1999630) shows: 101mg calcium, 158mg potassium, 69mg phosphorus, 22mg magnesium, and 0.54mg iron per 100g. These represent a mix of natural soy minerals and fortification. The calcium is largely fortified (natural soybeans contain ~25mg/100g in milk form) [1].
B12 at 0.39mcg per 100g is entirely from fortification — soybeans contain no natural B12. Per cup, that's 0.94mcg (39% DV). Vitamin D at 0.68mcg per 100g is also added, providing 1.6mcg per cup (8% DV). Sweetened versions are often fortified more heavily: original sweetened has 1.08mcg B12 per 100g [1].
Soy milk's natural mineral advantages over dairy include higher magnesium (22mg vs 12mg per 100g), higher iron (0.54mg vs 0mg), higher manganese (0.21mg vs 0mg), and notably higher copper (0.11mg, 12% DV per 100g). These come from the soybeans themselves, not fortification [1].
Unsweetened vs. Original vs. Chocolate
The calorie progression: unsweetened (39 kcal), original sweetened (54 kcal), vanilla (57 kcal), chocolate (66 kcal) per 100g. The increase maps directly to added sugar: from 0.56g to 4.8g to 5.8g to 9.0g per 100g. The protein decreases as sugar increases because sugar and water replace some soy base [1].
Per cup comparison: unsweetened delivers 8.5g protein at 94 kcal, while chocolate delivers 5.9g protein at 158 kcal. The protein-to-calorie ratio drops from 9.1g/100kcal (unsweetened) to 3.7g/100kcal (chocolate) — a 59% efficiency loss [1].
The extra protein variant reverses this trend by adding soy protein isolate: 5.0g protein per 100g at 46 kcal, yielding 10.9g protein per 100 kcal — the most protein-efficient milk of any kind. Per cup: approximately 12g protein at 110 kcal, rivaling Greek yogurt for protein density [2].
Soy Milk in a Latte, on Cereal, or in a Protein Shake: Tracking
A soy milk latte using 300g of steamed unsweetened soy milk contains approximately 117 kcal with 10.7g protein — nearly matching a dairy milk latte (180 kcal, 9.8g protein from whole milk) in protein at 35% fewer calories. The texture and foam quality depend on the brand's fat content and emulsifiers [1].
On cereal (1 cup soy milk + 30g cereal): 204 kcal, 11.5g protein. With dairy 2% milk: 232 kcal, 11.2g protein. The calorie saving is modest (28 kcal) but the protein is actually slightly higher from the soy milk combination — a rare win for plant milk in the cereal context [1].
In a protein shake (1 cup unsweetened soy milk + 1 scoop whey protein powder): 214 kcal and 32.5g protein. The soy milk base contributes meaningful protein (8.5g) unlike almond milk (1g). For someone tracking post-workout nutrition, soy milk provides the best plant-milk base by a wide margin [2].
Soy Milk vs. Other Milks (per 100g)
| Nutrient | Soy Milk (unsweetened) | Cow's Milk (whole) | Almond Milk | Oat Milk | Pea Milk |
|---|---|---|---|---|---|
| Calories (kcal) | 39 | 60 | 15 | 48 | 35 |
| Protein (g) | 3.55 | 3.27 | 0.4 | 0.8 | 3.3 |
| Total Fat (g) | 2.13 | 3.2 | 0.96 | 2.75 | 1.5 |
| Calcium (mg) | 101 | 123 | 184 | 148 | 120 |
| Carbs (g) | 1.29 | 4.6 | 1.31 | 5.1 | 0 |
| Iron (mg) | 0.54 | 0 | 0.28 | 0 | 0 |
Practical Tips for Soy Milk
- 1
Soy milk is the only plant milk matching dairy's protein — 3.55g per 100g with a perfect PDCAAS of 1.0. Almond has 0.4g, oat has 0.8g [1].
- 2
Lowest carbs of any milk at 1.29g per 100g — 75% fewer than dairy milk (4.6g) and less than even almond milk (1.31g) [1].
- 3
Watch for sugar in flavored versions: chocolate soy milk has 16x more sugar (9.0g) than unsweetened (0.56g) per 100g [1].
- 4
Natural mineral advantages over dairy: higher magnesium (22 vs 12mg), iron (0.54 vs 0mg), and copper (0.11mg, 12% DV) per 100g [1].
- 5
A soy milk latte has 35% fewer calories than a whole milk latte (117 vs 180 kcal for 300g) with comparable protein (10.7 vs 9.8g) [1].
Frequently Asked Questions — Soy Milk
How many calories in a cup of soy milk?
Is soy milk a complete protein?
Does soy milk have as much protein as cow's milk?
Is the calcium in soy milk naturally occurring?
How does soy milk compare to almond milk?
Important Notice
Nutritional values are based on USDA FoodData Central data for soy milk, unsweetened, plain, shelf stable (FDC 1999630). Sweetened, vanilla, chocolate, and extra protein variants are estimated from comparable USDA entries and manufacturer data. Fortification levels vary by brand. This tool is for informational and nutrition journaling purposes only — it is not a substitute for guidance from a qualified nutrition professional.
About the Author
Certified fitness professional and nutrition researcher with over 10 years of experience in the fitness and wellness industry. Founder of Food Nutrify, dedicated to making accurate, science-backed nutrition data accessible to everyone through free, easy-to-use calculators.
References & Sources
- [1] USDA FoodData Central (2024). Soy milk, unsweetened, plain, shelf stable (FDC 1999630). U.S. Department of Agriculture, Agricultural Research Service.
- [2] Various Authors (2022). Soy beverages: nutritional composition, processing, and health-promoting properties. ScienceDirect — Food Chemistry Advances.
- [3] Various Authors (2023). Plant-based milk alternatives: a comprehensive review of composition, processing, and nutritional aspects. PMC — Foods.