The ultimate guide to protein in milk: choosing the best option for weight loss and muscle

Milk isn’t just “white liquid with calcium.” It’s one of the most complete protein sources in a typical diet and can play a real role in weight loss, muscle maintenance, and overall health.¹

A typical 250ml glass of cow’s milk gives you around 8-9g of high-quality protein, mostly from casein and whey. Plant drinks (milks) vary far more, from almost no protein (many almond drinks) to levels similar to cow’s milk (soya).*

What’s the protein in milk (casein vs. whey)?

Most of the protein in milk comes from two families:¹

• Casein: around 80% of the total protein

• Whey: around 20% 

They behave very differently in your body.

Casein

Casein forms tiny “micelles” in milk, which are little complexes that slow down digestion. That means:²

• Amino acids are released more gradually

• You get longer-lasting satiety

• It helps limit muscle breakdown between meals or overnight

Casein also carries minerals like calcium and phosphorus. It’s the source of several bioactive peptides that get released during digestion or fermentation and may influence blood pressure, immunity, and oral health.²

Whey

Whey is the clear liquid left when milk is curdled (think of the liquid in yoghurt). It’s:³

• Rapidly digested, making it ideal to fit around exercise.

• Naturally rich in branched-chain amino acids (BCAAs), especially leucine, which directly stimulates muscle protein synthesis.

• The source of well-known components like lactoferrin and immunoglobulins which have been studied for possible immune and antimicrobial benefits.

Together, casein and whey give milk protein its reputation as a “complete” protein. It contains all the essential amino acids in proportions that closely match human requirements.^1-3

How much protein is in your glass of milk?

If you’re Googling “how much protein in milk” or “how much protein in a glass of milk”, you’re usually looking for simple numbers you can plug into an app. Below are approximate values for a 250ml glass (about a standard mug), based on UK composition data.

Protein content by cow’s milk type (full fat, semi-skimmed, skimmed)

Per 100ml and per 250ml glass:⁴

So if you’re specifically wondering about protein in semi-skimmed milk, a 250ml glass of semi-skimmed gives you roughly 9g of protein. 

As shown, protein doesn’t change much between whole, semi-skimmed and skimmed. What really shifts is the fat and calorie content.

Plant-based ‘milk’ protein

Plant milks are completely different. Their protein in milk equivalent can vary hugely depending on the base ingredient and how it’s formulated.

Typical values per 100ml and 250ml (unsweetened versions):⁵

A few takeaways:

• Soya drink is the closest match to cow’s milk for protein, and also counts as a high-quality plant protein.

• Oat drink is much lower in protein unless fortified; it’s mainly chosen for taste, texture, or because it’s dairy-free.

• Almond drink is usually very low in protein unless specially enriched.

If you rely on plant milks and are conscious about weight loss or muscle maintenance, it’s worth checking the nutrition label, not just the front of the carton.

Which milk is best for weight loss and muscle gain?

Here’s where the numbers meet real-world goals. The big question isn’t just “how much protein in milk?” but “which milk is best for weight loss and muscle?”

Milk for weight loss: calorie density vs. satiety

For weight loss, you want an eating pattern that:

1. Keeps you in a calorie deficit

2. Still keeps you full, energised, and able to preserve muscle

Protein is the most satiating macronutrient. Several studies show milk proteins, especially whey, produce stronger short-term fullness signals and can reduce later calorie intake compared with some other protein sources or carbohydrate drinks.^2,6

Putting this into practice:

• Skimmed or semi-skimmed cow’s milk

  • Similar protein to whole milk

  • Fewer calories because most of the fat has been removed

  • Good option if you’re tracking calories closely and want the best milk to lose weight while still getting decent protein

• Whole milk

  • Slightly fewer grams of protein per 100ml than semi-skimmed

  • More calories from fat

  • Can still fit into a weight-loss plan, but easier to overshoot calories if you drink too much

• Soya drink

  • Protein similar to cow’s milk (if unsweetened)

  • Lower saturated fat

  • Solid option if you follow a plant-based diet but are conscious about protein and appetite control

If you’re asking “which milk is best for weight loss?”, a good default is semi-skimmed cow’s milk or unsweetened soya drink, as both give you useful protein with moderate calories, and help with satiety.

Milk for muscle building: whey, casein, and timing

For muscle building or maintenance, especially if you’re lifting weights:^2,6,7

• You need enough total protein across the day

• You benefit from leucine-rich proteins (like dairy) that stimulate muscle protein synthesis

• You want both fast (whey) and slow (casein) proteins for different times of day

Cow’s milk naturally provides:

• Whey: handy around training or in a shake

• Casein: slowly digested, useful in meals or as an evening snack to support overnight recovery

That combination is one reason dairy protein is often used as the “reference” against which other proteins are judged.

If you’re in a muscle-gain or “lean bulk” phase:

• Whole milk can be useful if you struggle to get enough calories

• Semi-skimmed gives a middle ground: good protein, some fat, but not too energy-dense

If you’re cutting body fat but want to hold onto muscle, skimmed or semi-skimmed milk, or unsweetened soy gives you protein with fewer calories so you can keep your deficit without dropping protein.

Separating fact from fiction: oat milk, fat, and calories

Oat drink has exploded in popularity, so it’s no surprise people search things like:

• “Is oat milk good for weight loss?”

• “Is oat milk better than cow’s milk for weight loss?”

• “Does oat milk make you gain weight?”

Here’s the reality:⁵

• Protein: Oat milk generally has far less protein than cow’s milk or soya (around 1–1.3g per 100ml vs ~3.3g).

• Calories: Standard oat drinks often have a similar or slightly lower calorie content per 100ml than semi-skimmed milk, but you lose the satiety punch that comes from higher protein.

• Fat: Fat content varies by brand; some “barista” formulations are higher in fat to improve foam and texture.

So, is oat milk good for weight loss? It can be, if your overall calorie intake is controlled, but it’s not inherently better than cow’s milk, and the lower protein may make it less filling.

If you swap a high-protein, moderate-calorie drink (semi-skimmed or soya) for a low-protein oat drink, you may feel less full and snack more later. For some people, that makes weight loss harder.

But no single milk choice “makes” you gain weight. Weight change depends on total daily calories over time. But it’s easier to drift into a surplus if you drink large lattes made with oat milk that’s relatively high in calories and low in protein.

Choose oat milk if you like the taste, are dairy-free, or find it easier on your stomach, just be aware of the lower protein and watch the portion size.

The numan take

Semi-skimmed cow’s milk is the best all-round choice for weight management, while unsweetened soya is the closest plant-based match. Oat and almond milks are fine in a balanced diet but low in protein unless fortified. 

Early research suggests milk proteins may also support immunity, metabolic health, and blood pressure, though evidence is still developing. Whatever your goal, focus on overall protein intake, calorie balance, and how satisfying your meals feel, and speak to a clinician if you have underlying health concerns.

References

*Do note that this article is for general information only and isn’t a substitute for personalised medical or nutrition advice. Always speak to a healthcare professional before making big changes to your diet.

1. ^{Davoodi SH, Shahbazi R, Esmaeili S, Sohrabvandi S, Mortazavian A, Jazayeri S, et al. Health-related aspects of milk proteins. Iran J Pharm Res. 2016;15(3):573–91.}

2. ^{Kay S-IS, Delgado S, Mittal J, Eshraghi RS, Mittal R, Eshraghi AA. Beneficial effects of milk having A2 β-casein protein: Myth or reality? J Nutr. 2021;151(5):1061–72.}

3. ^{Marshall K. Therapeutic applications of whey protein. Altern Med Rev. 2004;9(2):136–56.}

4. ^{Milk. THE NUTRITIONAL COMPOSITION OF DAIRY PRODUCTS. 2021. [accessed 27 Nov 2025] Available from: https://milk.co.uk/nutritional-composition-of-dairy/milk/}

5. ^{Nowson GK, Fallaize R, Earl KE. Exploring the nutritional profile and cost of plant-based milk alternatives compared with dairy milk in the UK with consideration of environmental impact data. Curr Dev Nutr. 2025;9(6):107436.}

6. ^{Bendtsen LQ, Lorenzen JK, Bendsen NT, Rasmussen C, Astrup A. Effect of dairy proteins on appetite, energy expenditure, body weight, and composition: a review of the evidence from controlled clinical trials. Adv Nutr. 2013;4(4):418–38.}

7. ^{Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.}