CytoSport Muscle Milk: what the milk proteins inside it do

CytoSport makes Muscle Milk, and we found no trial of Muscle Milk itself, so this page rests on trials of the whey and milk proteins such drinks contain. The strongest result is a caution about those trials. A meta-analysis of 75 randomized trials in 1,206 athletes found pure protein supplements improved endurance (SMD 0.37, 95% CI 0.02 to 0.71) and strength (SMD 0.72, 0.18 to 1.27). Every significant result came from trials where the two groups did not eat the same calories, so the extra energy may explain the gain. In 261 young adults doing resistance training across 12 studies, whey raised bench press by a mean difference of 8.87 and squat by 9.60, in units the abstract does not state. Lean body mass did not change significantly.

How much is actually in it

• USDA lists 3.5 oz (100 g) of ready-to-drink Muscle Milk at 27.6 mg vitamin C, 0.69 mcg vitamin B12 and 0.143 mg copper. — one USDA SR Legacy record Evidence E source
  Vitamin C 31% DV, B12 29% DV, copper 16% DV per 3.5 oz (100 g)

What your body absorbs

• Pooled data from 18 RCTs with 602 people show 57% of whey protein phenylalanine reaches blood within 5 hours, versus 45% for casein and 65% for milk protein, and less in older adults. — 602 participants aged 53 +/- 23 y in 18 randomized trials, 5-hour postprandial period (n = 602) Evidence A source
  Whey 57% +/- 10%, casein 45% +/- 11%, milk 65% +/- 13%; older 45% vs young 51%

What it does to your health

• A meta-analysis of 12 trials in 261 young adults found whey protein with resistance training improved bench press (mean difference 8.87) but did not change lean mass. — 261 young adults aged 18-30 y doing resistance training, 12 studies (n = 261) Evidence A source
  Bench press MD 8.87 (95% CI 5.95-11.79); squat MD 9.60 (5.61-13.60); lean mass no significant effect
• A meta-analysis of 75 RCTs in 1,206 athletes found protein supplements helped performance only in trials where the control group got fewer calories. — 1,206 athletes in 75 randomized trials (n = 1206) Evidence A source
  Endurance SMD 0.37 (95% CI 0.02 to 0.71), strength SMD 0.72 (0.18 to 1.27), all in energy-unmatched trials
• A meta-analysis of 65 RCTs found milk protein supplements lowered systolic blood pressure by about 2 mmHg and triglycerides by about 6 mg/dL in adults. — adults in 65 randomized controlled trials (n = 65 RCTs) Evidence A source
  SBP WMD -1.99 mmHg (95% CI -3.16, -0.82); TG -6.11 mg/dL (-9.78, -2.44); TC -4.03 mg/dL (-7.91, -0.16)

Safety, limits and interactions

• A meta-analysis of RCTs found milk-derived protein supplements did not change bone density at any site, against the claim that dairy protein leaches calcium. — adults in randomized controlled trials (7 to 10 RCTs per bone site) (n = up to 13 RCTs per outcome) Evidence A source
  No significant BMD change at whole body, spine, hip, femoral neck; IGF-1 increased
• A single case report describes lower valproic acid blood levels when the drug was taken together with a protein supplement, which normalized once doses were spaced apart. — one 60-year-old patient on valproic acid (n = 1) Evidence D source
  Plasma valproate fell with co-ingestion, returned to therapeutic range when spaced

What people believe that the data does not support

• The EU did not authorize the claim that whey protein taken after resistance exercise supports muscle growth, and none of 22 whey claims in the register is authorized. — — Evidence E source
  Non-authorized

Who this works differently for

• In advanced chronic kidney disease, a meta-analysis of 17 RCTs found protein or amino acid supplements raised serum albumin by 1.76 g/L, with no shown gain in quality of life. — people with eGFR below 30 mL/min or on dialysis, 17 randomized trials, supplement above 5 g/day (n = 17 RCTs) Evidence A source
  Albumin MD 1.76 g/L (95% CI 0.67 to 2.84), BMI MD 0.29 kg/m2 (0.10 to 0.49)

The bottom line

Milk proteins reach the blood at different rates. In pooled data from 18 randomized trials with 602 people, 57 percent of the phenylalanine from whey appeared in the blood within five hours, against 45 percent for casein and 65 percent for milk protein. Older adults absorbed less than young ones, 45 against 51 percent, and the tracer studies come from one research group. Across 65 randomized trials in adults, milk protein supplements lowered systolic blood pressure by 1.99 mmHg (95% CI 0.82 to 3.16) and triglycerides by 6.11 mg/dL (2.44 to 9.78), small shifts. USDA has one record for ready-to-drink Muscle Milk. It lists 27.6 mg vitamin C, 0.69 mcg vitamin B12 and 0.143 mg copper per 3.5 oz (100 g), from a single entry with no spread, and the brand has changed its recipe over the years. We hold no card for its protein or sugar per bottle, so the label on your bottle is the source for those. A common worry is that dairy protein pulls calcium out of bone. This was tested, and milk-derived protein supplements made no significant change in bone density at the whole body, spine, hip or femoral neck, with 7 to 10 randomized trials per site. The EU has not authorized the claim that whey taken after resistance exercise supports muscle growth, meaning the evidence fell short when it was assessed. Who should be careful: one case report describes a 60-year-old whose valproic acid blood levels fell when the drug was taken with a protein supplement and returned to range once the two were spaced apart. It is a single patient, so it is a question for whoever prescribes the drug. In advanced kidney disease, with eGFR below 30 or on dialysis, 17 randomized trials found protein or amino acid supplements raised serum albumin by 1.76 g/L (95% CI 0.67 to 2.84) with high risk of bias, and four studies that measured quality of life found no improvement. Those were supervised trials in people already under kidney care, so they are not a reason to add a protein drink on your own. With kidney disease, protein intake is a question for the care team. We hold no card on milk allergy, pregnancy or children for this product.

Sources

1. cyto-daily-r7-01 · USDA FoodData Central SR Legacy, dataset
   Beverages, CYTOSPORT, Muscle Milk, ready-to-drink (FDC 174814, SR Legacy, Beverages): vitamin C 27.6 mg per 100 g = 31% DV; vitamin B12 0.69 ug = 29% DV; copper 0.143 mg = 16% DV; Foundation samples 0, CoFID match none
   USDA FoodData Central, SR Legacy, FDC 174814 · checked 2026-10-02
2. cyto-daily-r7-02 · meta-analysis
   We included data from 18 randomized controlled trials with a total of 602 participants ... Casein ingestion resulted in a smaller (45% ± 11%), whey protein ingestion in an intermediate (57% ± 10%), and milk protein ingestion in a greater (65% ± 13%) fraction of dietary protein-derived phenylalanine appearing in the circulation (P < 0.001).
   J Nutr, 2020 · checked 2026-10-02
3. cyto-daily-r7-03 · meta-analysis
   A total of 12 studies with 261 participants were included after full-text screening with the main reason for exclusion being wrong population. The analysis found no significant effect of either whey or soy protein supplementation on LBM. However, protein supplement increased peak plasma total EAA with whey protein significantly improved bench press (mean difference [MD] 8.87; 95% CI: 5.95-11.79) and squat performance (MD 9.60; 95% CI: 5.61-13.60), with low to no heterogeneity.
   J Diet Suppl, 2026 · checked 2026-10-02
4. cyto-daily-r7-04 · meta-analysis
   Pure protein supplements demonstrated statistically significant effects compared to the placebo group in both endurance performance [μ(SMD): 0.37, 95% CI: 0.02 to 0.71] and muscle strength [μ(SMD): 0.72, 95% CI: 0.18 to 1.27]. ... However, all statistically significant results were derived from studies in which energy intake was not matched between groups.
   J Int Soc Sports Nutr, 2026 · checked 2026-10-02
5. cyto-daily-r7-05 · meta-analysis
   The pooled analysis of 65 RCTs revealed that MP supplementation significantly reduced levels of total cholesterol (TC) (weighted mean difference [WMD]: -4.03 mg/dL; 95% CI: -7.91, -0.16; P = .042), systolic blood pressure (SBP) (WMD: -1.99 mmHg; 95% CI: -3.16, -0.82; P < .001), and triglycerides (TG) (WMD: -6.11 mg/dL; 95% CI: -9.78, -2.44; P = .001) in the MP group compared with the untreated group.
   Nutr Rev, 2026 · checked 2026-10-02
6. cyto-daily-r7-06 · meta-analysis
   Milk-derived protein supplementation did not significantly affect whole-body BMD (n = 7 RCTs) and BMD at the lumbar spine (n = 10), hip (n = 8), femoral neck (n = 9), trochanter (n = 5), intertrochanter (n = 2), and ultradistal radius (n = 2). ... Our findings do not support the claim that proteins of dairy origin are detrimental to bone health.
   Osteoporos Int, 2023 · checked 2026-10-02
7. cyto-daily-r7-08 · case report
   we present a clinical case of a 60-year-old patient under treatment with VPA, whose plasma VPA concentrations were analyzed and a decrease in these concentrations was detected when administrated with protein supplement. When the intake was spaced out, VPA serum concentrations returned to the therapeutic range.
   Nutr Hosp, 2025 · checked 2026-10-02
8. cyto-daily-r7-09 · EU register
   POL-HC-8187 Whey Protein Taken after resistance exercise, whey protein supports muscle growth Non-authorised
   EU Register on nutrition and health claims, claim POL-HC-8187, snapshot 2026-09-21 · checked 2026-10-02
9. cyto-daily-r7-07 · meta-analysis
   Of 5,699 articles, 17 were included for analysis. We found no improvement in HRQOL in qualitative synthesis of four studies. Protein and/or amino acid supplementation was associated with an improvement in serum albumin (mean difference (MD) = 1.76 g/L, 95% confidence interval (CI) [0.67, 2.84], P = .002, I2 = 88%)
   J Ren Nutr, 2026 · checked 2026-10-02