Fuel 101: Fat

Fuel 101: Fat

Long-Haul Fuel.

Of the three macronutrients, fat has probably had the hardest time of it from a public perception standpoint. For decades it was framed as the dietary villain responsible for heart disease, obesity and everything in between. That view has shifted considerably, but the anxiety lingers, and a lot of athletes still treat fat as something to minimise rather than use.

The reality is that fat is an essential fuel source, a critical building block for hormones and cell membranes, and a carrier for fat-soluble vitamins your body cannot function without. Getting enough of the right kinds is as important as anything else in your diet.

How fat is used for energy

Your body stores fat in adipose tissue and, to a lesser extent, within muscle fibres themselves as intramuscular triglycerides. Unlike glycogen, fat storage is effectively unlimited. Even lean, highly trained athletes carry tens of thousands of calories worth of fat energy.

At low to moderate intensities, typically below around 65 to 70 percent of maximum heart rate, fat is your dominant fuel source. This is why long, easy rides and runs are often described as fat-burning sessions. Your aerobic system is highly efficient at converting fat to ATP (the energy currency your cells actually use) when there's plenty of oxygen available and no urgency to work fast.

As intensity rises, your body shifts progressively toward carbohydrate. Fat simply can't be broken down quickly enough to supply the energy that hard efforts demand. This is why carbohydrate is the priority around hard sessions while fat takes on a larger role during easy days and aerobic base work.

The types of fat and what they do

There are four main types of dietary fat, and they are not all created equal.

Saturated fats are mostly solid at room temperature and come primarily from animal products: red meat, butter, cheese, full-fat dairy, and also coconut and palm oil. Eating large amounts of saturated fat is consistently associated with raised LDL cholesterol and increased cardiovascular risk. This doesn't mean eliminating them, but they're worth keeping at moderate levels.

Monounsaturated fats (MUFAs) are found in olive oil, avocados, nuts and seeds. They're well-established as beneficial for cardiovascular health and make up the cornerstone of Mediterranean-style eating patterns, which have some of the strongest long-term health evidence around.

Polyunsaturated fats (PUFAs) include the omega-3 and omega-6 fatty acids. These are essential, meaning your body cannot make them and they must come from food. Omega-6 fats are easy to get in modern diets (they're found in most vegetable oils). Omega-3s are where most athletes are deficient.

Trans fats are largely synthetic, produced through industrial hydrogenation of vegetable oils. They are genuinely harmful and increasingly rare in food supplies due to regulatory restrictions. Avoid where possible.

Why omega-3s matter for athletes

Omega-3 fatty acids, particularly EPA and DHA (found primarily in oily fish like salmon, mackerel, sardines and herring), have a well-documented role in managing inflammation.

Training creates inflammation. That's not necessarily a problem — some inflammatory response is part of the adaptation process. But chronic, unresolved inflammation slows recovery, increases injury susceptibility and impairs immune function. Omega-3s help the body resolve inflammation more efficiently.

Beyond recovery, EPA and DHA support cardiovascular function, brain health and joint lubrication. For athletes doing high volumes of repetitive loading, that last point is relevant.

Plant-based sources of omega-3 include flaxseed, chia seeds and walnuts, but these contain ALA, which the body must convert to EPA and DHA at fairly low conversion rates. Algae-based supplements provide EPA and DHA directly and are a practical option for athletes who don't eat fish regularly.

Fat and fat-soluble vitamins

Vitamins A, D, E and K are fat-soluble, meaning they require dietary fat to be absorbed properly. A chronically low-fat diet impairs the uptake of all four, with particular implications for vitamin D (bone health, immune function) and vitamin K (bone density, blood clotting).

This is one reason very low-fat dietary approaches often create problems even when calorie intake looks adequate on paper.

How much fat do athletes need?

A reasonable target for most endurance athletes is 20 to 35 percent of total calories from fat, with an emphasis on unsaturated sources. On a 3,000 calorie day, that's roughly 67 to 117 grams of fat.

Exact numbers matter less than source quality. Prioritising olive oil, oily fish, nuts, seeds and avocados, while keeping processed foods and high saturated fat sources at reasonable levels, covers most of what you need without requiring detailed tracking.

On easy days and rest days, when carbohydrate intake is a little lower, fat naturally makes up a slightly larger proportion of your energy intake. This is fine and appropriate.

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