299 ‒ Optimizing muscle protein synthesis: protein quality and quantity, & the key role of training

KEYPOINTS

• 01

  Muscle stays responsive to training and protein at any age.

  Van Loon, a professor at Maastricht University in the Netherlands who has spent around 30 years and about €30 million in research funding on muscle and protein, says you don't need to start at 40 to have good muscle at 80—muscle remains responsive at 70 and even past 100, though starting earlier is better.

• 02

  Stable isotope tracers reveal what happens to the food we eat.

  Carbon-13 has an extra neutron and is stable. Feeding labeled carbohydrate shows its oxidation via exhaled 13CO2; labeled amino acids such as phenylalanine show incorporation into muscle. His lab even produced 'intrinsically labeled' milk and meat by infusing tracers into cows—one experiment cost more than €50,000 in tracer.

• 03

  Exogenous carbohydrate oxidation tops out around 60–70 g per hour from glucose.

  Glucose alone is oxidized at about 1–1.1 g/min; adding fructose, which uses a different transporter, can push it to 1.3–1.4 g/min in high-output athletes. Glycogen storage is roughly 100–200 g in the liver and 300–350 g or more in muscle, though trained athletes can store more.

• 04

  Your body recycles far more protein than you eat.

  You synthesize about 300 g of protein daily but eat perhaps 70–100 g, so roughly 230 g of amino acids are recycled from your own tissues each day. Muscle proteins are fully turned over in about 50–100 days—'in 50 to 100 days you have a new arm'.

• 05

  The '20 grams per meal' figure comes from whey studies—and may underestimate needs.

  Studies found 40 g of whey didn't stimulate muscle protein synthesis more than 20 g over about four hours, so 20 g became the standard on packages. Body size matters (more for 120 kg, less for 50 kg), and with mixed whole-food meals, 30–40 g per meal may be more appropriate.

• 06

  A 100 g protein dose showed the 'ceiling' isn't real over longer periods.

  In his study comparing 0, 25 and 100 g of intrinsically labeled protein (mostly casein—milk is about 80% casein, 20% whey), the 100 g dose produced a larger and much longer anabolic response over 12 hours, and oxidation of excess protein had been overestimated. Digestion of a full meal takes 2–3 hours, versus peak amino acids within 30–75 minutes from a shake.

• 07

  Typical intake is modest; targets for muscle gain are higher.

  Healthy Americans eat about 1.1–1.3 g/kg/day; Peter suggests 1.6 g/kg or more for building muscle. Spreading it—20 g at breakfast, lunch, dinner and an evening snack—reaches about 80 g for a typical person.

• 08

  Presleep protein uses the overnight fast.

  Dinner at 5–6 p.m. and breakfast at 8–9 a.m. leaves about 15 hours without food, a period of muscle loss risk—'that's stupid'. Protein ingested before sleep, even delivered via nasogastric tube at 2 a.m. in early studies, is digested and incorporated overnight. Evening exercise plus 40–60 g of protein boosted overnight synthesis.

• 09

  Disuse rapidly destroys muscle, and hospital nutrition makes it worse.

  Immobilizing a leg loses about 220 g of muscle in a week, with declines in oxidative capacity. Healthy elective-surgery patients ate only about 0.5 g/kg during four hospital days—a third of guidelines (ASPEN suggests 1.2–1.5)—and lost about 1.4 kg. Of people over 65 with hip fracture, 15–30% die within a year, and about half of survivors never regain prior function.

• 10

  Older muscle shows anabolic resistance.

  Michael Rennie's group coined 'anabolic resistance' around 2005; van Loon's lab took nearly 10 years to confirm it. Older adults need more protein per meal and resistance exercise to get the same response, though cross-sectional young-versus-old comparisons limit conclusions.

• 11

  Glycogen recovery and endurance fueling have been rethought.

  Van Loon notes that with adequate carbohydrate, glycogen can be fully restored after exercise, unlike the old beliefs Peter grew up with as an endurance athlete. For ultra-long events, aiming for over 1 g per minute for 20 hours would be punishing on the gut, so practical intake is lower. Endurance cyclists perform hundreds of thousands of low-force repetitions at 80–100 rpm, none as hard as a heavy lift—different stimuli with different protein needs.