When you’re training for a triathlon, the mantra “fuel for the work required” couldn’t be more true. Carbohydrates (CHO) are the key fuel for moderate to high intensity work — but the how, when and how much matter just as much as the what. You want to avoid under-fueling (you’ll suffer performance, recovery and adaptation) and over-fueling (you’ll carry excess weight or blunt fat burning when desired). Let’s break it down.

1. Nutrition Prioritisation / Nutrition Periodisation

Often referred to in sports science as periodised nutrition, this is the strategic alignment of your nutrition (especially carbs) with training phases, session demands and adaptation goals. Biomedres+3NSCA+3worldathletics.org+3

In practice for a triathlete this means:

• On high-intensity or key sessions: you prioritise high carbohydrate availability (to support performance and stress adaptation).
• On lower-intensity or easy sessions: you might choose reduced carbohydrate availability (to promote metabolic flexibility, fat adaptation or recovery without excess CHO).
• Across days/weeks: you vary carbohydrate intake in line with training load (micro-, meso- and macro-cycles). worldathletics.org+1

Why do this? Because your body responds differently depending on fuel availability. Training with low glycogen or reduced CHO can trigger adaptations (e.g., increased mitochondrial signalling) but it may compromise performance if used at the wrong time. BioMed Central

So your goal: match your carb availability to the work required — neither all high, nor all low.

2. Exogenous vs Endogenous Carbohydrates

• Endogenous carbs = glycogen stored in your muscle and liver, plus circulating blood glucose. These are your internal carbohydrate stores.
• Exogenous carbs = the carbohydrates you consume during exercise (or immediately before) via drinks, gels, bars, etc.

Why make the distinction? Because during training (especially long or high intensity), you’ll tap into endogenous stores and you can supplement with exogenous carbs to maintain blood glucose, spare muscle/liver glycogen and delay fatigue. Recent work has shown that exogenous carb oxidation (how fast the carbs you ingest are used) varies considerably between athletes. BioMed Central+2MDPI+2

For example: a 2025 proof-of-concept study found that some athletes could achieve peak exogenous oxidation with ~65 g/h of glucose rather than 90 g/h, without impairing performance—suggesting more isn’t always better for everyone. BioMed Central

3. How Much Carbohydrate Can You Oxidise?

Many athletes consume 120 g+ per hour, but the evidence suggests oxidation peaks around 90 g/h (for mixed carbs). The literature supports this: guidelines for prolonged exercise (>2.5 h) often cite up to ~90 g CHO/h as a “ceiling” for maximal exogenous oxidation in many athletes. NSCA+2BioMed Central+2

What does “extra” carbohydrate do (i.e., above what you oxidise)? Some plausible benefits:

• It may support central nervous system (CNS) / brain fuel (glucose for brain activity, delaying central fatigue).
• It may signal to the body “fuel is available” which may permit you to sustain higher output or delay fatigue.
• It may help recovery post‐session by providing substrate for glycogen re-plenishment.

The evidence is still emerging: for instance a recent review described how carbohydrate supplementation influences glycogen storage, blood glucose and performance, and noted that the “extra” may not always yield proportional oxidation gains—it depends on individual capacity, gastrointestinal tolerance and session demands. MDPI

Therefore: consume enough carbs to match the work demand, train your gut to tolerate higher intakes if needed (e.g., for long rides/races), but recognise that blindly hitting super high numbers (e.g., 120 g/h) may not yield extra oxidation and may increase GI risk.

4. “Go Slow – Go Fast Fuel” Framework

A practical approach you use: match your type of fuel to session intensity and substrate-use.

• Go Slow (Zones 1 & 2 / easy endurance): These sessions rely largely on the oxidative system—fat and low-intensity carb use. Carbohydrate intake during these sessions can be relatively modest. Example: you aim for ~40 g CHO/h on a long endurance ride (16 weeks out from race) and you might use slower‐releasing sources (oat bars, bananas) rather than fast sugar hits.
• In Between (Zone 3 / moderate‐high tempo): This is a blend — carb requirement starts to increase, and you may shift from slow to a mix of slow + fast release carbs.
• Go Fast (Zone 4+ / high intensity, interval, race work): These sessions are highly glycogen-dependent. Fast releasing carbs per hour (gels, sports drink, lollies) are appropriate to support high exertion and maintain intensity.

Putting the example in context: If your goal is 40 g CHO/h on an easy ride and an oat bar has ~20 g CHO, you could eat one every 30 min. On a high intensity session you may target 60-90 g CHO/h (or whatever your personalised max is), via faster carbs.

5. Practical Tips & Athlete-Wise Adjustments

• Train your gut: If you plan to use high CHO/h in races, you must practise tolerating that during training (so your stomach and gut handle the load).
• Match carbs to session length + intensity: Short easy spin → minimal carb. Long or intense session → higher carb.
• Periodise across training blocks: In heavy load blocks, you might favour higher carbohydrate availability. In adaptation blocks (where you want metabolic stress) you might intentionally reduce CHO on selected sessions. But only if you can maintain training quality. BioMed Central
• Use individualisation: As noted above, oxidation capacity varies. Start with guidelines (~30-60 g/h for 1-2.5 h sessions; up to ~90 g/h for >2.5 h) and adjust based on your performance, gut comfort, and how you feel. BioMed Central+1
• Recovery matters: The carbs you take during and immediately after key sessions help replenish glycogen, repair, and adapt.
• Be aware of fat vs carb trade-offs: At higher intensities your reliance shifts more toward carbs (“crossover effect”). NSCA

6. Common Mis-conceptions & Pitfalls

• “More carbs = always better” — not true. If you overshoot your oxidisable capacity, you risk GI issues or unused carbs sitting in your gut or blood but not being used.
• “Easy days don’t need any carbs” — you still need some carbs for recovery, brain fuel and training quality.
• “Train low all the time to burn fat” — unless your goal is specific metabolic adaptation and you’re under coach supervision, constant CHO-restriction can negatively affect performance and adaptation. A meta-analysis found no overall performance benefit from chronic CHO restriction in endurance-trained athletes. BioMed Central

When it comes to weight loss for triathlon, the goal isn’t just to see a smaller number on the scales — it’s to arrive at race day lighter, stronger, and performing at your best. The problem is, many athletes cut too hard, lose muscle mass, and end up slower, weaker, and fatigued.
Here’s how to get it right.

Over the coming weeks, I will release a number of articles on weight loss, fuel for training and give some day examples on diets. We will start off with weight loss.

1. Protect Your Muscle Mass at All Costs

Muscle is your performance engine. It drives your swim, bike, and run, and it’s what keeps your metabolism firing. Losing muscle while dieting is like taking cylinders out of a car engine — you’ll still move, but not as efficiently.

After 40, muscle becomes harder to gain. After 50, it’s difficult to rebuild, and by 70 it’s almost impossible. So protect it at all costs.
That means:

• Strength training consistently — even if it’s just 2–3 short sessions per week.
• Hitting your daily protein target (around 1.6–2.0g per kg of bodyweight is a good range).
• Avoiding crash diets — rapid loss means muscle loss.

2. Your Food Should Taste Nice — But Not Too Nice

Sustainability is key. You need meals you actually enjoy, but not ones that are so delicious you can’t stop eating.
If your food tastes too good, you’ll overconsume. If it tastes too bad, you’ll quit. Aim for satisfying, simple, balanced meals that support your goals, not sabotage them.

3. Don’t Burn Carbs When You Don’t Need To

Your body will always prioritise burning carbohydrates when they’re available. So if you’re constantly topping up on carbs, you’ll rarely tap into stored fat.
The goal: train your body to burn fat when it should, and carbs when it needs to.
That means:

• Save higher carb intake for around key sessions.
• Keep easy days lower in carbs and higher in protein and vegetables.
• Avoid snacking on carbs when sitting at a desk or watching TV.

4. Fix the Big Three Nutrition Mistakes

Most triathletes you’ll meet make the same three nutrition mistakes:

1. They get enough carbs overall, but the timing is all wrong.
2. They don’t get enough protein.
3. They eat too much fat.

When athletes fix these — especially by timing carbs around training — weight often starts to drop without forcing it. You recover faster, perform better, and create a natural calorie deficit.

5. Master the Diet–Maintenance Cycle

When you finish a diet phase, you’re not done — you’re entering maintenance.
Your body needs time to stabilise before cutting again.
A good rule of thumb:

Spend half as much time maintaining as you did dieting.
So if you diet for 6 weeks, spend 3 weeks maintaining before starting the next phase.

For athletes with a large amount of weight to lose, this cycle keeps fatigue and hunger manageable. For example:

• 6 weeks dieting → 3 weeks maintenance → repeat.
  Breaking it into blocks keeps you mentally fresh and physically stable.

6. Adjust Calories Based on Progress, Training, and Fatigue

Don’t set your calories once and forget them. Training load, fatigue, and adaptation all change your energy needs.
Apps like MyFitnessPal or Hexis can help track intake and identify whether you’re eating too much — or not enough to support recovery.

7. Use Caffeine Strategically

Caffeine is a powerful performance tool, but overuse dulls its effect.
Save it for when you really need it — especially toward the later stages of a diet, when fatigue is highest. A well-timed coffee before a key session or long ride can make all the difference.

8. Plan for Setbacks

You will mess up at some point. Everyone does. The key is how you respond.
If you eat something you shouldn’t, don’t say “bugger it” and spiral.
Just get straight back on track at the next meal. One bad choice doesn’t ruin progress — giving up does.

9. Decide Before

Know what you need before going to the shops, don’t walk around just looking. know what you will order before eating out. Look online at what the restaurant offers and make the decision before leaving the house.

Final Thoughts

Weight loss for triathletes is about consistency, not perfection. Protect your muscle, fuel your training, and be patient. If you manage the timing of carbs, hit your protein target, and stay disciplined without being extreme, you’ll not only look better — you’ll perform better too.