A single cup of whole cow’s milk (240 ml) delivers a broad package of nutrients: 7.5 grams of protein, 4.5 grams of fat, 12 grams of natural sugar (lactose), and roughly 150 calories. But the macronutrients are only part of the picture. Milk is unusually dense in minerals and B vitamins, which is why it remains one of the most nutrient-complete single foods available.
Protein: Two Types Working Together
The 7.5 grams of protein in a cup of whole milk come from two distinct protein families. About 80% is casein, a slow-digesting protein that forms curds in your stomach and releases amino acids gradually. The remaining 20% is whey, which digests quickly and spikes amino acid levels in your blood faster. Together, they supply all nine essential amino acids your body can’t make on its own, making milk a complete protein source comparable to meat or eggs.
This combination matters for muscle repair and growth. The fast whey fraction kickstarts the process, while the slow casein fraction sustains it over several hours. It’s the reason milk has long been popular as a post-exercise recovery drink, not just because of the protein quantity but because of how the two types complement each other.
Fat Composition
Milk fat is more complex than most people realize. It contains roughly 400 different fatty acids. About 70 to 75% of milk fat is saturated, with palmitic acid (28% of total fat) and stearic acid (nearly 13%) being the dominant types. The remaining quarter is split between monounsaturated and polyunsaturated fats. Oleic acid, the same monounsaturated fat found in olive oil, makes up over 20% of total milk fatty acids.
Milk also contains small amounts of short-chain fatty acids, which are relatively rare in the diet. These contribute to milk’s distinctive flavor and are thought to serve as a quick energy source for cells lining the gut. The fat in milk also plays a practical role: it helps your body absorb the fat-soluble vitamins A and D that milk contains.
Calcium and Other Minerals
Calcium is milk’s signature mineral. One cup provides around 290 mg, which covers roughly 20% of the daily value for adults. What makes milk’s calcium particularly valuable is how well your body absorbs it. Studies using isotope-labeled calcium show a fractional absorption rate of about 22%, which is higher than most plant-based calcium sources like spinach or beans, where compounds like oxalates and phytates interfere with uptake.
Potassium is the other mineral present in large quantities, at about 375 mg per cup. That’s comparable to a small banana. Most adults fall short of the recommended potassium intake, so milk can meaningfully close that gap. Phosphorus works alongside calcium to build and maintain bone tissue, and milk is one of the richest dietary sources of it.
On the trace element side, milk provides smaller but meaningful amounts of zinc, selenium, and iodine. Typical values in conventional milk run around 350 to 390 micrograms of zinc per 100 grams, roughly 1.5 to 2 micrograms of selenium per 100 grams, and 20 to 26 micrograms of iodine per 100 grams. Iodine is especially worth noting: many people get a significant share of their daily iodine from dairy, and iodine is essential for thyroid function.
B Vitamins
Milk is one of the best natural sources of several B vitamins. A single cup of whole milk delivers about 1.16 micrograms of vitamin B12, which is close to half the daily recommendation for adults. B12 is critical for nerve function and red blood cell production, and it’s found almost exclusively in animal foods, making milk an important source for people who eat little meat.
Riboflavin (B2) comes in at about 0.44 mg per cup, covering roughly a third of daily needs. Your body uses riboflavin to convert food into energy and to maintain healthy skin and eyes. Pantothenic acid (B5) is also present in generous amounts at nearly 1 mg per cup, supporting your body’s ability to metabolize fats and carbohydrates.
Vitamins A and D
Whole milk naturally contains vitamin A, which supports immune function and vision. When milk is reduced to lower fat levels (2%, 1%, or skim), much of the naturally occurring vitamin A is removed along with the fat. U.S. regulations require manufacturers to add it back, which is why you’ll see vitamin A listed on the labels of reduced-fat and skim milk.
Vitamin D is a different story. Milk doesn’t naturally contain much of it. Virtually all commercial milk in the United States is voluntarily fortified with vitamin D3, at levels up to 84 IU per 100 grams. A full cup typically provides around 100 to 120 IU, contributing roughly 15 to 20% of the daily value. This fortification, which began in the 1930s to combat rickets, remains one of the primary ways Americans get vitamin D from food.
Carbohydrates: Lactose
Nearly all of the 12 grams of sugar in a cup of milk come from lactose, a naturally occurring sugar made of glucose and galactose bonded together. None of it is added sugar. Lactose gives milk its mildly sweet taste and also appears to enhance calcium absorption in the gut.
About 68% of the global population has some degree of reduced ability to digest lactose after childhood, though severity varies widely. Many people with low lactase activity can still tolerate a cup of milk at a time without symptoms, especially when consumed with food. Fermented dairy products like yogurt and aged cheeses contain less lactose because bacteria break it down during processing.
How Pasteurization Affects Nutrients
Standard pasteurization (heating milk to 72°C for 15 seconds) has minimal impact on milk’s nutritional value. Research on heat treatment shows losses of less than 15% for heat-sensitive nutrients like thiamine (B1), copper, and calcium. Macronutrients, most B vitamins, and minerals remain essentially unchanged. The protein structure shifts slightly with heat, but this doesn’t reduce its nutritional quality or amino acid availability. In practical terms, pasteurized milk and raw milk are nutritionally very similar.
Comparing Whole, Reduced-Fat, and Skim
The main nutritional difference across milk types is fat and calorie content. Skim milk has almost no fat and about 80 to 90 calories per cup, while whole milk has 4.5 grams of fat and around 150 calories. Protein stays consistent at roughly 7 to 8 grams across all types. Calcium, potassium, and B vitamins are also largely the same regardless of fat level.
Where the types diverge beyond calories is in fat-soluble vitamins. Whole milk delivers more naturally occurring vitamin A and retains small amounts of vitamin K. Reduced-fat and skim versions compensate through fortification but don’t contain the same spectrum of fat-soluble compounds found in full-fat milk. The fat in whole milk also slows digestion, which can help you feel full longer after drinking it.