Energy Gels for Running: When and How Many?

An energy gel is not a magic potion. It is a tool that only works when quantity, timing and tolerance line up. Most recreational runners don't fail because of the sport itself — they fail because they use gels too late, too rarely or untested, and then hit the wall with an empty tank at the decisive moment.

Why gels work at all

Your body stores glycogen in the liver and muscles — around 1,800 to 2,200 kilocalories in a trained marathon runner. At a moderate pace that lasts roughly two to two and a half hours. After that, the body increasingly falls back on fat as fuel, but it can only convert fat into energy at a limited rate per minute. From that point on, pace drops while effort rises: the famous wall.

Carbohydrates from outside push exactly that point further back. Every gram of carbohydrate that reaches the muscle stays available as fast energy. Taking in 240 to 320 grams of carbs during a marathon covers roughly 40 to 60 percent of your energy demand — that is the difference between finishing evenly and grinding through a tough final 10 kilometres. How much more you can absorb depends less on willpower than on your gut's uptake capacity (see Gut training for runners).

The 60-gram limit — and how to break it

The gut absorbs glucose through a specific transport pathway, and that pathway is limited: about 60 grams of glucose per hour get through, after which the rest backs up in the stomach and causes pressure, cramps or nausea. That is why "more gel = more performance" is simply wrong.

Fructose is absorbed through a second, independent pathway. Combined gels with a glucose-to-fructose ratio of 2:1 — two thirds glucose, one third fructose — bypass the limit and allow 90 to 120 grams of carbs per hour with a trained gut. That is exactly why such labels appear on almost every gel wrapper today: anyone using plain glucose gels stays stuck at 60 grams per hour.

The order matters when switching up: higher intake has to be built up over weeks of training. Increase by roughly 10 to 15 grams per hour each week — not from zero to 100 on race day.

Guidelines by race duration

• Short runs under 60 minutes: No gel needed. Water is enough, unless you are heading out fasted in the morning.
• 60 to 90 minutes: 30 to 60 grams of carbs per hour, in practice usually one gel. For most tempo runs without race pressure, optional.
• Half marathon (1:20–2:00): 60 to 90 grams per hour, spread across two to three gels plus carbohydrate drink at the aid stations.
• Marathon (3:00–4:30): 60 to 90 grams per hour, 240 to 320 grams in total. With a trained gut, up to 120 grams per hour — that is six to eight gels across the race.
• Ultra and gran fondo beyond five hours: 60 to 100 grams per hour, mixed from gels, bars and drink. Pure gels become hard work for taste and stomach at this duration.

All values apply at normal temperatures and moderate intensity. In heat, fluid needs rise far more than carbohydrate needs — the bottleneck then tends to be drinking rather than gels (see Hydration for runners).

Timing: the first gel comes early

The most common race mistake is the latest one: you start, feel great, only reach for a gel after two hours — and wonder why it barely helps. A gel takes about 10 to 20 minutes to arrive in the blood as glucose. If you take it only once your legs get heavy, you are already running those 20 minutes on reserve.

• Start: In races over two hours, take the first gel after 30 to 45 minutes, not at the halfway point.
• After that: one gel every 20 to 30 minutes, or an equivalent carbohydrate drink, aligned with the aid station order.
• Two thirds of intake before the finish: The final 30 minutes add little performance because the carbs no longer arrive before the race is over.

As a rough rule for the marathon: the total amount of carbohydrates you take during the race should ideally match what your stomach tolerates in the three to four hours afterwards — not what you can swallow in ten minutes.

Dosing caffeine gels correctly

Caffeine is one of the few legal, well-established performance aids in endurance sport: 3 to 6 milligrams per kilogram of body weight measurably improve endurance performance. A gel typically contains 50 to 100 milligrams — so one to two gels at 75 kilograms of body weight. Placing a caffeine gel about an hour before the finish hits the point where concentration would otherwise fade.

The limits: more than 200 to 300 milligrams spread across the race adds no extra benefit, just more side effects — heart palpitations, stomach irritation, restlessness. Anyone who doesn't drink coffee normally reacts strongly to low doses. The key test remains the training run: caffeine and high intensity are not a good combination to try out for the first time on race day.

Tolerance: the gut has to be trained

Stomach problems are the most common reason for abandoned marathons. The reason is anatomical: at high intensity, blood flow is redirected from the digestive tract to the muscles, and the stomach empties more slowly. A gel tolerated perfectly at rest can sit there at 4:30 min/km.

• Always with water: A gel belongs with a cup of water, not with drinks containing extra sugar or, worse, carbonation.
• Test a fixed setup: Best done on the long runs of the build phase — same brand, same flavour, same drink volume as on race day.
• Not on an empty stomach: The first gel at a half marathon without breakfast is a classic mistake. Better: half a gel plus a piece of banana beforehand.
• When problems arise, dose earlier: Not less gel, but smaller and more often — half a gel every 20 minutes instead of a whole one every 40. That is far easier on a sensitive stomach.

Gels, bars, drink — what goes together?

Three sources, three jobs. Gels deliver fast, concentrated carbohydrates, but they are intense in flavour and follow the 60- or 90-gram limit. Carbohydrate drinks are the simplest source because they arrive with fluid automatically. Bars are practical for long sessions — easier to dose piece by piece and more filling — but harder on the stomach at high intensity.

The proven standard for the marathon: a carbohydrate drink at every aid station plus a gel between stations as total intake accumulates. Athletes following a vegan diet now have a wide range of plant-based gels without gelatine or dairy — the uptake capacity is identical.

Questions and answers

How Peakora plans your fuelling

Peakora builds the fuelling calculator into training planning itself: for every long session and every race it computes carbohydrates, sodium and fluid per hour — matched to duration, intensity and race day. Instead of guessing mid-race, you know in advance how many gels to take and when. Because the long runs of the build phase rehearse the fuelling plan week after week, the timing becomes second nature before it counts. More on building your carb stores before the start in Tapering: the final 14 days before a race.