Mednotes

L24 Metabolism Sports _ exercise nutrition

Properties2
tagsmetabolism, sports-nutrition
aliasesSports Nutrition - In a Nutshell

16 min read

Overview

This lecture introduces sports nutrition as applied to the “everyday” athlete a GP might encounter, not only the elite competitor. It works up the sports nutrition pyramid from a basic diet, through sport-specific macronutrient and fluid needs (carbohydrate, protein, fat), to supplements and anti-doping considerations, then covers Relative Energy Deficiency in Sport (REDs) as the unifying concept linking inadequate intake, disordered eating, amenorrhea and stress-related illness. It closes with a case study of an adolescent triathlete with amenorrhea and micronutrient concerns, tying the macronutrient and REDs content together into a clinical scenario.

What Is Sports Nutrition?

Sports nutrition is the application of nutritional principles to enhance sports performance. Its aims are to:

  • Promote good health
  • Promote adaptations to training
  • Recover quickly after training sessions
  • Perform optimally in competition

Lecture objectives: gain a basic understanding of sports nutrition; understand how sports nutrition may come up in medical practice; understand common issues that may arise when working as a medical practitioner, particularly as a GP (illustrated through the case study).

Who is an “athlete”? Not only elite competitors — recreational exercisers may train as hard as elite athletes and could present to a GP for overtraining, feeling unwell, or injuries. Elite/competitive athletes are more likely to already have a sports nutritionist or dietitian.

There is no "one size fits all" approach to sports nutrition — body type and composition vary widely even within closely related disciplines. An example set of gymnastics/aerobics/high-jump athletes was shown with differing heights and weights (e.g. Jessica Howard, Rhythmic Gymnastics, 5'7" 100 lbs; Shannon Miller, Gymnastics, 5'0" 97 lbs; Erin Aldrich, High Jump, 6'1" 143 lbs) to illustrate this variability.

Slide 15: the small caption text under each athlete's photo was low resolution; names, sports, and measurements are transcribed as best legible.

Common Nutritional Issues in Athletes

  • Inadequate intakes: energy, macronutrients, iron deficiency, other micronutrients
  • Fatigue
  • Eating disorders, or disordered eating
  • Amenorrhea
  • Stress-related issues: GI upset, frequent illness
  • REDs (Relative Energy Deficiency in Sport) — shown as a related but separately-boxed concept, not explicitly linked by a line to the other categories on the source diagram

The Sports Nutrition Pyramid

A three-tier pyramid model, built up in stages across the lecture:

  1. Basic diet (base, largest tier) — general population dietary guidance (see below).
  2. Sports nutrition (middle tier) — sport-specific macronutrient/fluid adjustments.
  3. Supplements (top, smallest tier) — added last and used least.

Basic diet guidance was illustrated with two food-guide models:

  • Heart Foundation heart-shaped diagram, banded from largest to smallest recommended intake: eat most — vegetables & fruit; eat some — grain foods & starchy vegetables; legumes, fish, seafood, eggs, poultry & meat; milk, yoghurt & cheese; healthy oils, nuts & seeds. Footer: cut back on junk foods, takeaways, and foods/drinks high in sugar, salt, or saturated/trans fats.
  • Ministry of Health “Choose a balance of healthy food every day” plate: vegetables, fruit, grains, milk & milk products, and legumes/seafood/eggs/poultry/lean red meat, plus a water callout.

The Athlete’s Plate

Model from Reguant-Closa et al. (2019): a circular plate divided into whole grains, lean protein, and vegetables & fruits, with separate allowances for fats and flavours, alongside a beverages list (water, dairy/non-dairy beverages, diluted juice, flavoured beverages, coffee/tea). The fat allowance and portion sizes scale with training load:

Training levelFat allowance
Easy training / weight management1–3 teaspoons
Moderate training1–2 tablespoons
Hard training2–3 tablespoons (with larger grain/protein/vegetable portions)

Carbohydrate

Carbohydrate metabolism during exercise

  • Intake forms: starch, glycogen, disaccharides, monosaccharides (glucose, fructose, galactose)
  • Storage: as glycogen
  • Distribution and utilisation: as free glucose, delivered to and used by muscle

Daily carbohydrate targets

Activity levelDescriptionDaily target intake
LightLow intensity or skill-based activities3–5 g/kg/day
ModerateModerate exercise programme (e.g. 1 hr/day)5–7 g/kg/day
HighEndurance programme, 1–3 hr/day moderate–high intensity6–10 g/kg/day
Very highExtreme commitment, 4–5 hr/day moderate–high intensity8–12 g/kg/day

Worked example: 70 kg individual, 60 min/day moderate exercise → daily target 5–7 g/kg/day → 350–490 g carbohydrate per day. An example meal distribution spread this across breakfast, a snack, lunch (specifically noted as ~350 g), a further snack, and dinner.

Presented as a balance tipped toward one side:

  • Avoidance of carbohydrate → low energy intake, possibly low nutrient intake.
  • Gastrointestinal upset → from limited carbohydrate intake (opposite side of the balance, less commonly the presenting problem).

Protein

  • Recommended intake: approximately 0.8–1.7 g/kg/day.
  • Worked example: 70 kg female → 119 g protein/day.
  • A glass of milk (~250 mL) ≈ 12 g protein.
  • Example logged breakfast (2 Vogel’s bread slices, ½ avocado, 3 eggs, ½ cup spaghetti) ≈ 34 g protein.

Fat and Fluid

  • Fat: same recommendation as the general population — 20–35% of total energy intake.
  • Fluid: higher needs with increased training volume and in hot climates. A sports drink (carbohydrate + electrolytes) is recommended when exercise exceeds 1 hour, or when food is not tolerated.

Weight-Loss Diets and REDs

Weight-loss “diets” remain common among athletes, including:

  • Very low energy diets
  • High fat and “train low” approaches
  • Manipulating the glycaemic index (GI)
  • Fad diets, e.g. ketogenic, lemon detox, intermittent fasting
  • ”& many more”

Relative Energy Deficiency in Sport (REDs)

Relative Energy Deficiency in Sport (REDs), per the Mountjoy et al. (2023) conceptual model, is driven by a central problem of low energy availability, from which multiple impairments radiate:

REDs — systems affected by low energy availability: impaired reproductive function, impaired bone health, impaired gastrointestinal function, impaired energy metabolism/regulation, impaired haematological function, urinary incontinence, impaired glucose & lipid metabolism, mental health issues, impaired neurocognitive function, sleep disturbances, impaired cardiovascular function, reduced skeletal muscle function, impaired growth & development, and reduced immunity.

Impact on performance (same low-energy-availability hub): decreased athlete availability, decreased training response, decreased recovery, decreased cognitive performance/skill, decreased motivation, decreased muscle strength, decreased endurance performance, decreased power performance.

Supplements

Ron Maughan’s Rules of Supplements

  1. If a supplement works, it’s probably illegal (for use in sports).
  2. If a supplement is legal, it probably doesn’t work.
  3. There may be exceptions.

Supplement use decision framework (Close et al. 2022 — “Food First but Not Always Food Only”, FFNFO)

What counts as a supplement:

  1. Functional foods — foods enriched with additional nutrients/components outside their typical composition.
  2. Formulated foods and sports drinks — products providing energy/nutrients in a more convenient form than normal food for general sport nutrition support.
  3. Single nutrients or other food components/herbal products, isolated or concentrated.
  4. Multi-ingredient products combining any of the above targeting similar outcomes.

Decision chain:

  1. Does the product fall into one of the supplement categories above (Maughan et al., 2018)? If no → likely not a supplement.
  2. If yes: is it proven to improve health or sport-specific performance?
  3. Is there a reason whole-food sources cannot supply the desired nutrient (consider the FFNFO guidance)?
  4. Have the ingredients been checked for prohibited substances?
  5. Has the product been batch-tested by a known third-party laboratory (e.g. LGC, NSF, BSCG) or registered/tested with Informed Sport? If yes → consider the product. If no → do not use.

FFNFO framework — reasons a tested supplement may be justified over whole food:

  1. Some nutrients are difficult to obtain in sufficient quantity from a regular diet without excessive intake of foods containing them.
  2. Some essential nutrients are abundant only in foods some athletes do not consume.
  3. The precise nutrient content of some performance/health-enhancing foods can be difficult to establish.
  4. Concentrated doses of some nutrients may be needed to improve health; exceeding the reference nutrient intake for some nutrients may have beneficial anti-inflammatory/ergogenic effects that reduce infection burden.
  5. Food sources for some nutrients may be difficult to consume close to, during, or soon after exercise.
  6. Tested supplements can be a convenient alternative, particularly where food contamination or hygiene is a concern.

Drug Testing in Practice

  • What is tested: supplements, recreational drugs, medication.
  • Who is tested: any athlete, at any time — but testing usually focuses on high-performance athletes and those tracking toward that level.

Clinical example

A 24-year-old 800 m runner presents with dermatitis. Before prescribing hydrocortisone, check its status via Global DRO (or call Drug Free Sport NZ: 0800 DRUGFREE / 378437).

Hydrocortisone status by route (per the Global DRO reference card shown):

  • In competition — prohibited: intramuscular injection, intravenous injection, local injection (joint/bursa/tendon), subcutaneous injection, oral, rectal.
  • Out of competition — not prohibited: the same six routes above.
  • In and out of competition — not prohibited: dental-intracanal, inhalation (metered-dose device), nasal, ophthalmic, otic, topical-dermatological.

Therapeutic Use Exemption (TUE)

  1. Medication recommended — inform your medical professional you are an athlete who could be tested at any time.
  2. Check status of the medication/method (drugfreesport.org.nz).
  3. Consider a permitted alternative if prohibited; if none exists, check whether in-advance TUE criteria are met.
  4. Apply for a Therapeutic Use Exemption — download the application form and submit with supporting medical evidence (checklists available on the website).
  5. Submit application to TUE@drugfreesport.org.nz, or to the athlete’s International Federation if competing internationally.
  6. Application review by the TUE Committee, who may request further information.
  7. Application result — if approved, a certificate of approval with an expiry date is issued.
  8. Next steps — for an ongoing condition, monitor the expiry date; if tested, inform the Doping Control Officer (DCO) of the approved TUE.

Case Study: Adolescent Triathlete

Presentation: female, 17 years old, 52 kg, 169 cm.

Training load: swim 2 hr × 3/week; run 1 hr × 3–4/week; cycle 1.5–2 hr × 6/week; gym 1 hr × 2–3/week — approximately 15–17 hours of training per week.

Findings: low iron, borderline vitamin D; menarche at age 16, followed by 3 menstrual cycles before menstruation stopped (secondary amenorrhea).

Reason for presentation: wants advice on eating for sport performance and on her amenorrhea.

Nutritional concerns raised (four linked areas)

  • Other micronutrients (calcium): intake 1000–1600 mg vs. recommended 1500 mg; 1–2 vegetable portions, 2–3 fruit portions.
  • Iron: low iron is common in adolescent athletes; endurance sport increases iron losses — assess intake of iron-rich foods and dietary iron inhibitors/enhancers.
  • Energy intake: negative energy balance, due to excessive exercise and/or reduced intake — assess with a food diary and dietary analysis; the key question posed is what her energy requirements actually are.
  • Amenorrhea: linked to the negative energy balance (i.e. the REDs picture above).

Slide 40: the "2–3 fruit portions" bullet was partly obscured behind the central diagram in the rendered slide; wording was confirmed via the extracted text layer.

Goals set

  • Food: increase vegetable intake; high-nutrient snacks; smoothies for extra “hidden” vegetables.
  • Other: label reading; consider fortified breakfast cereal.

Useful Resources

  • Factsheets: sportsdietitians.com.au
  • Infographics: mysportscience.com
  • Drug Free Sport free e-learning courses: drugfreesport.org.nz

Slide 42: the acknowledgement line ("Thanks to Dr Lisa Daniels and Dr. Katherine Black for some of the slides") was very low-contrast against the slide background and barely legible visually; wording was confirmed via the extracted text layer.

Slides skipped as decorative/non-informational: 2–6, 8, 9, 11, 12 (title slide, lecturer-origin map, Vevox join instructions, and live-poll question/results slides carrying no static data or content).

Self-test

  1. Define sports nutrition and list its four stated aims.
  2. Why might a GP encounter a patient who trains as hard as an elite athlete but has no sports nutritionist?
  3. List the six categories of common nutritional issues in athletes shown on the overview diagram.
  4. Describe the three tiers of the sports nutrition pyramid, from base to top.
  5. What are the two food-guide models used to illustrate the “basic diet” tier, and what do they broadly emphasise?
  6. Describe the athlete’s plate model: what three main food groups does it divide into, and how does the fat allowance change with training load?
  7. Trace carbohydrate from intake to use in the carbohydrate metabolism diagram: what forms are ingested, how is it stored, and in what form is it used by muscle?
  8. What is the daily carbohydrate target range (g/kg/day) for light, moderate, high, and very high activity levels?
  9. A 70 kg athlete does 60 minutes of moderate exercise daily. Using the moderate-activity target, what is their daily carbohydrate range in grams?
  10. On the carbohydrate “balance” diagram, what two problems sit on either side, and what drives each?
  11. What is the recommended daily protein intake range for athletes, and what does this equal in grams per day for a 70 kg female?
  12. What is the fat recommendation for athletes, and how does it compare to the general population?
  13. When is a sports drink (carbohydrate + electrolytes) recommended over plain fluid?
  14. List the weight-loss “diet” approaches still commonly seen in athletes.
  15. What is the central driver in the REDs conceptual model, and name at least five body systems it can impair.
  16. List four ways REDs (via low energy availability) can impair athletic performance.
  17. State Ron Maughan’s three rules of supplements.
  18. In the supplement decision flow, what must be true before a tested supplement should be “considered” for use?
  19. Give two reasons from the FFNFO framework for why a tested supplement might be justified over a whole-food source.
  20. What three broad categories of substance are checked in athlete drug testing, and who can be tested?
  21. A 24-year-old runner with dermatitis needs treatment — what should be checked before prescribing hydrocortisone, and by what route(s) is hydrocortisone prohibited in competition?
  22. List the eight steps of the Therapeutic Use Exemption process, in order.
  23. Summarise the triathlete case: her training load, key clinical findings, and the two things she wants advice on.
  24. For the triathlete case, what four nutritional concern areas were identified, and what was the key question raised under “energy intake”?
  25. Integrative: explain how the triathlete’s training load, negative energy balance, and amenorrhea connect to the REDs model described earlier in the lecture.

Answers

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