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Pathway
Intermediate
68 min read

What becomes of what you eat

Eight steps following protein, carbohydrate, fat and water from the meal to the muscle. A pathway of mechanisms, with no amounts, no recommended foods and no timing.
Few subjects generate as many contradictory claims as this one. Part of the reason is the most common shortcut: imagining that a food eaten ends up unchanged where you expect it. A protein does not enter a muscle; a sugar does not directly become energy.
This pathway follows the real route, from digestion to use. At no point does it say what to eat.

What this pathway lets you understand

Three ideas hold it together. Nutrients are taken apart before being reused, and what reuses them is not only muscle. Stores are not interchangeable: glycogen and fat are not mobilised at the same rate or under the same conditions. And water does not accompany those stores, it is part of them.

Level, prerequisites and reading time

The Understanding muscle growth pathway is a useful prerequisite: it sets up the balance between building and breakdown that this one feeds.
Allow around seventy minutes.

The steps of the pathway

The eight steps, in order

0 of 8 steps completed
  • From meal to common pool
    A protein is taken apart into amino acids poured into a common pool, where muscle is only one of the recipients.
    9 min read
  • What muscle does with it
    Building and breakdown run continuously; growth comes from the repeated imbalance, not from a single intake.
    8 min read
  • The two flows in pictures
    The same balance, animated: the effect of a meal, of a session, and accumulation over several days.
    8 min read
  • The journey of a carbohydrate
    Digestion, absorption, the compulsory pass through the liver, then a sort into three destinations, two of which share a name.
    9 min read
  • The other fuel
    Muscle glycogen, its limited capacity, and the water it holds — what the scales show after a long effort.
    8 min read
  • The journey of a fat
    A nutrient that will not dissolve, takes the lymph and joins a store on a different scale from the others.
    9 min read
  • Who burns what, and when
    The aerobic pathway oxidises carbohydrate and fat; the proportion changes with intensity, without either switching off.
    9 min read
  • Water, the third part
    Blood volume, heat dissipation, water bound to glycogen: three roles that losing water touches at once.
    8 min read

What to take away

The amino acid pool is the idea that undoes the most shortcuts. It is fed as much by the turnover of the body's own proteins as by the last meal, and it is consumed by far more than muscle — enzymes, hormones, transporters, immune cells.
Certainty level · Established
Dietary proteins are broken down into amino acids that join a common pool before being reused.
This is a point of agreement across reviews of dietary protein. What remains debated is the relative share of food and internal recycling according to nutritional state and activity, which varies from one situation to another.
Phillips SM, Van Loon LJC (2011)
Second point: the effect of extra intake is real but modest compared with training itself, and it stops increasing beyond a certain point.
Certainty level · Probable
Additional protein intake improves the gains obtained from resistance training, with an effect that plateaus.
The meta-analysis covers healthy adults following supervised training. The average effect is small compared with that of training, and the plateau point varies between individuals and between the studies included. Body Lab does not convert that result into an amount.
Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM (2018)
Third point: the energy pathways do not take turns, they overlap. What changes with intensity is their relative contribution, never whether they are switched on.
Certainty level · Established
The energy pathways run simultaneously; intensity changes their relative contribution, not their activation.
Reviews of energy system interaction converge on this from gas exchange measurements and biopsies. The exact timing of the shifts and the proportions attributed vary with the estimation method and the protocol used.
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011) · Gastin PB (2001)
Limit
What this pathway does not do
None of these six pages recommends an amount, ranks foods or proposes a time to eat. Needs depend on age, body mass, activity, health status and the diet followed — none of which a page knows.
A question about a particular diet, an intolerance or a specific need belongs to a health professional, who has the context.

Checking what stuck

Check my understanding

What becomes of a dietary protein after a meal?
How do the energy pathways follow one another during effort?
Why does weight often drop after a long effort?
Choose an answer

Sources

Sources for this pathway

  • Phillips SM, Van Loon LJC (2011). Dietary protein for athletes: from requirements to optimum adaptation. Journal of Sports Sciences.
  • Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine.
  • Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences.
  • Gastin PB (2001). Energy system interaction and relative contribution during maximal exercise. Sports Medicine.

Read next

  • Energy and recovery
    A six-step reading pathway that follows muscle energy from the second to the night: the instant recharge of ATP, the glycogen stores and their water, then the role of sleep. A closing quiz lets you check what you have taken in.
    Described without a scene
  • Hydration and performance
    Water is not a side note to effort. It carries the blood, carries heat away and accompanies glycogen storage: three roles that explain what losing water changes.
    With a 3D scene
  • Glycogen and weight swings — the video
    An animation that explains why the number on a scale moves by several hundred grams from one day to the next: muscle glycogen is stored along with water, and that water changes in quantity far faster than tissue does.
    With a 3D scene
Put it into practice in Shapier

Everyday protein in Shapier

Choosing and spreading protein across meals is done in Shapier; Body Lab only explains what becomes of the protein from the last meal.
Everyday protein in Shapier
Body Lab explains; Shapier lets you act and track.

Available offline

Offline download is available in the mobile app.

Trust and method

Author
equipe-editoriale-shapier
Editorial review
Thanh Chau
Scientific review
Pending
Published on
August 2, 2026
Reviewed on August 2, 2026
Next review due August 2, 2027
Limits of this page
  • The pathway gives no amounts, no foods to favour and no timing: that would be personalised advice, outside Body Lab's scope.
  • The work cited concerns healthy adults. It does not transfer as it stands to children, older people, pregnant women or situations of illness.
  • Protein synthesis measurements follow an instantaneous rate over a few hours: on their own they do not predict the mass gained over months.
  • Any question about a particular diet, an intolerance or a specific need belongs to a health professional.
Sources
  • Phillips SM, Van Loon LJC (2011). Dietary protein for athletes: from requirements to optimum adaptation. Journal of Sports Sciences.
  • Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, Aragon AA, Devries MC, Banfield L, Krieger JW, Phillips SM (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine.
  • Burke LM, Hawley JA, Wong SHS, Jeukendrup AE (2011). Carbohydrates for training and competition. Journal of Sports Sciences.
  • Gastin PB (2001). Energy system interaction and relative contribution during maximal exercise. Sports Medicine.
Educational content. Body Lab does not diagnose and does not replace professional advice.
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