Fat adaptation for the long haul

Fat adaptation is often presented as a switch: eat fewer carbohydrates, become better at burning fat and race longer on little else. That story is tidy, but the reality of an ultramarathon is messier. The metabolic change can be useful, yet the runner still has to climb, descend, manage heat and make decisions while tired.

The role of fat adaptation in ultramarathon fueling is therefore best seen as a supporting strategy rather than a replacement for carbohydrate. It may change what happens on an easy long run; it does not remove the need to practise race nutrition. Strong preparation combines metabolic development, aerobic fitness and a fuelling system rehearsed under fatigue.

Carbohydrate still does the heavy lifting

Most ultramarathoners rely on fat to produce energy and conserve glycogen. Muscle glycogen remains the fastest available fuel, and hard efforts, steep climbs or late surges can drain it quickly. When stores fall, pace becomes uneven, the legs feel hollow and focus deteriorates even if the aerobic engine is strong.

Carbohydrate intake during an ultra commonly falls around 60–90 grams per hour, with athletes testing their tolerance and using glucose-fructose combinations when needed. That number is not a law. Terrain, duration, heat and gut practice alter what works; the useful target is the highest intake that remains comfortable and repeatable.

Australian conditions make this especially practical. In summer, a race in the Blue Mountains west of Sydney may combine humid air with exposed fire roads. Sweat losses and missed drinking can ruin a sound plan, while excessive fluid without sodium creates its own danger. Test a bottle schedule, sodium strategy and backup fluids before race day.

What fat adaptation actually changes

Fat adaptation describes increased capacity to use fatty acids and stored intramuscular triglyceride during exercise. With consistent endurance work, mitochondria become more efficient at oxidising fat, and some athletes shift more of their energy toward fat at lower intensities. The possible prize is lower glycogen use on steady terrain and a longer period of comfortable pacing.

The benefit has boundaries. Once intensity rises, carbohydrate oxidation usually becomes more important, and fatigue can still be strongly linked to depleted glycogen and central factors. A fat-adapted athlete may therefore conserve carbohydrate earlier in an ultra without gaining a magical ability to skip fuel. In some studies the performance advantage is small or absent, especially when compared with athletes already well trained in endurance.

This is why fat adaptation should not be confused with a high-fat diet at every meal. A fuelling strategy built around large amounts of fat can slow gastric emptying, cause discomfort and crowd out the carbohydrate needed for demanding sections. Periodising carbohydrate around training may be useful, but deliberately starting key sessions under-fuelled risks poor quality and teaches the gut to expect the wrong thing at racing intensity.

Build the aerobic foundation

Adaptation develops through patient training, not a nutritional shortcut. Easy running gives mitochondria time to increase capacity, while steady efforts near marathon pace teach the body to hold pace without borrowing heavily from glycogen. Long runs also improve fat oxidation, but need quality work to preserve running economy.

Local terrain makes this adaptable. Runners preparing for the rolling trails and granite ridges around Melbourne’s Macedon Ranges can use long hilly sessions to practise descending with control. The aim is not to suffer more; it is to make technical fatigue familiar. Video, strength work and patient downhill running can protect the muscles that carbohydrate cannot fully spare.

I also draw on the broader endurance-planning perspective at N Athletix when treating training as a long project. That means tracking workload, reviewing evidence and changing one variable at a time. For fat adaptation, watch energy on easy days, hunger, resting heart rate, body-mass change and performance on fast sessions. If aerobic fitness improves but the athlete feels depleted, adjust the plan rather than adding restriction.

Turn long runs into fuelling sessions

A long run should answer race-day questions, not merely accumulate kilometres. Decide how much fluid fits each bottle, how quickly it can be drunk, which carbohydrate sources stay palatable after three hours and how much solid food can be handled while moving. Use race-day products, because a familiar gel, drink or roll beats a theoretically superior option.

Start with a familiar breakfast such as oats, banana and white bread with jam, then add race carbohydrate during the first hour. Avoid suddenly trialling rich fats or high-fibre foods on the longest run. A small amount of fat in a pre-race meal may improve satiety, but fat is slow to digest and has little place as the main fuel for hard climbing or fast finishing.

During an Australian event, plan for thirst and heat separately from fuel. Some runners use a flavoured hydration mix, while others carry electrolyte tablets or a commercial sports drink. Powerade is easy to find in supermarkets, while chemists sell electrolyte sachets and powders. Test sodium concentrations against expected sweat loss, and make drinking part of each aid-station routine rather than waiting for a strong signal.

Use race days as experiments

Aid stations can become useful laboratories. Before an event, write down the target for each bottle, gel or solid item, then record what was actually consumed. A missed intake is more valuable when tagged with a cause: poor appetite, nausea, unexpected heat, an unplanned climb or simply running too fast. Patterns emerge over a season rather than from one race.

I keep returning to practical lessons captured in my Ultra Challenge 2014 notes, especially the value of simple decisions made while fatigued. White bread with jam, bananas, lollies, rice balls and malt-based drinks such as Milo are accessible options for many Australian runners, though each must be tested personally. Familiarity beats novelty when the legs are failing.

Support crew can help only if the plan is simple. Use colour-coded bottles or labels, agree on what needs replacing and define a non-negotiable intake at each major station. Volunteers often provide more water than expected, so leave room for extras without turning the aid station into a random eating stop. Record those choices as they happen.

Build a repeatable weekly system

A useful final block combines three sessions: an easy long run with fuelling practice, a moderate run with controlled carbohydrate intake, and a harder session where carbohydrate is deliberately well supported. Keep strength work for downhill resilience, add recovery on other days, and avoid making every run a test of low-carbohydrate operation.

Write the week as a workable routine. Begin with an easy fuelled run, follow with strength or rest, add a medium aerobic run, take another recovery day, complete a fast session and finish with a long run plus race breakfast and aid-station simulation. Details change with the event, but the rhythm should be sustainable before taper begins.

Review the last three long runs and compare planned intake, actual intake, energy, digestion and finish-time strength. If intake was comfortable and energy stayed steady, keep it; if intake caused gut trouble, simplify rather than adding more products. The practical takeaway is to treat fat adaptation as a patient metabolic project, keep carbohydrate practice central, and arrive with one boring, tested fuelling routine that can be repeated for the final hours.