Ask Dr Adam: Does It Matter What You Eat Before a Workout?

Walk into any gym and you will find strong opinions on pre-workout nutrition. Some people swear by a bowl of oats an hour beforehand. Others train fasted and would not have it any other way. The supplement aisle adds another layer of noise: powders, gels, and energy drinks all competing to be the thing that unlocks your best session.

The truth, as ever, is more nuanced. What you eat before a workout does matter, but how much it matters, and what the optimal strategy actually looks like, depends on the type of workout you are doing and what you are trying to achieve. Dr Adam Collins, Form’s Head of Nutrition and researcher in exercise metabolism at the University of Surrey, breaks it down.

Are carbohydrates really key for exercise?

Any workout involves burning fuel, and the body’s preferred fuel during exercise is carbohydrate. On that basis, topping up with carbs before a session is a sensible strategy, and the research supports it.

Sports nutrition has been built on this premise since its research origins in the early 1980s. Studies consistently show that starting exercise with well-stocked glycogen stores (the form in which carbohydrate is stored in the liver and muscles) allows you to sustain effort for longer, or work harder over the same period before fatigue sets in.

The practical recommendation is to eat a carbohydrate-containing meal in the roughly four-hour window before exercise, aiming for around 50g or more of carbs, ideally from lower to moderate glycemic index (GI) sources. Lower GI foods release glucose more steadily into the bloodstream, providing a sustained supply of fuel rather than a spike and crash. A mixed meal with some protein and fat alongside the carbs works well, both for fuel delivery and because it simply makes the meal more palatable.

That said, this ideal is not always achievable. If you are training early in the morning, eating a full meal at 5am is neither practical nor appealing. In that case, your pre-exercise nutrition is effectively the dinner you had the night before, which can serve the same glycogen-topping purpose if it contained adequate carbohydrate.

A useful additional tactic, particularly for morning sessions, is a small, fast-digesting carbohydrate source in the 30 to 60 minutes before your workout. High GI options such as a banana, rice cakes, or a sports drink can help top up blood glucose and prime the muscles to take up carbohydrate for energy. This is the legitimate use case for sports gels and drinks, rather than relying on them as a substitute for proper pre-exercise fuelling.

Does caffeine actually make a difference?

The evidence on caffeine is unusually robust for the world of sports nutrition. It has been studied extensively since the 1970s and consistently shown to improve performance across a wide range of activities.

Caffeine works primarily by acting on the central nervous system, reducing the perception of effort and fatigue. This means you can work harder, for longer, before you feel like stopping. Beyond that, it has been shown to improve power output, speed, and cognitive function during exercise, and may also raise your pain threshold, which helps with strength-based efforts.

Research suggests a dose of between 3 and 6mg per kilogram of body weight is optimal, equivalent to up to four double espressos. More recently, lower doses of under 3mg per kilogram (around 200mg or less) have been shown to be effective with fewer side effects such as jitters, headaches, or disrupted sleep. Even a single cup of coffee can provide a meaningful boost. Form’s Boost supplement contains 100mg of caffeine, alongside L-theanine, which research suggests can blunt some of caffeine’s less desirable effects.

What about beetroot?

Beetroot has been a fixture of endurance nutrition since the early 2000s, when researchers first identified its high nitrate content as performance-relevant. Those nitrates are converted in the body, first to nitrites, and then to nitric oxide, a molecule that causes blood vessels to widen and improves blood flow to working muscles. The result is improved oxygen delivery and greater exercise efficiency.

The effect typically kicks in within around four hours of consuming a nitrate dose, which is why concentrated beetroot shots are timed accordingly before competition or a hard session.

The performance benefits are real but modest, and they come with caveats. Beetroot works best for sustained, continuous exercise rather than intervals or team sports. It also tends to show more pronounced effects in people who are not already well-trained endurance athletes. And to get a meaningful dose from whole beetroot, you would need to eat a considerable amount, which is why concentrated shots or nitrate supplements have become the practical delivery method.

What about protein, creatine, and other pre-workout ingredients?

Including protein in your pre-workout meal is worthwhile, not primarily because it helps during the session itself, but because it begins loading the system with amino acids ahead of the recovery window that opens after exercise. Getting those building blocks into circulation early means the body can take advantage of them as soon as training ends.

Branched-chain amino acids (BCAAs) have attracted particular interest in the pre-workout context. Some evidence suggests they can be taken up and used directly in muscle during exercise, and certain BCAAs, particularly leucine, independently stimulate insulin release, which supports carbohydrate uptake. Some earlier studies also suggested BCAAs could reduce perceived exertion, though those findings were later questioned and the evidence remains mixed.

Creatine is a common ingredient in pre-workout products, but it is worth being clear about what it can and cannot do in this context. Creatine does not work acutely, that is, a single dose before training will not enhance today’s session. Its benefits accumulate over days and weeks of consistent supplementation as muscle creatine stores gradually rise. The reason it appears in pre-workout products is largely because people use them regularly, which means creatine builds up in the muscle over time whether they think of it that way or not. For a full breakdown of how creatine works and whether it is right for you, see my series: What does creatine actually do in your body?, What are the benefits of taking creatine?, The most common creatine myths, answered, and Creatine for women.

Sodium bicarbonate is an acid-base buffer that can help manage the build-up of lactic acid during high-intensity exercise. It works acutely, unlike some other buffering agents, but results are mixed and gastrointestinal side effects are common and often severe enough to put people off. Beta-alanine is now the more widely used buffering option. It works by increasing levels of carnosine inside the muscle, which acts as an internal buffer during intense effort. Like creatine, it only works cumulatively: regular supplementation over weeks is required to see a benefit.

Do you always need to eat carbs before training?

Not necessarily, and this is where it gets interesting. There is now good evidence that certain training sessions may actually benefit from deliberately restricting carbohydrate beforehand.

The concept is called “training low”: exercising with limited carbohydrate availability, either by training in a fasted state (first thing in the morning before eating) or in a glycogen-depleted state (after a previous session has already drawn down your stores). The rationale is that exercising with limited fuel amplifies the cellular signals associated with energy stress, which drives stronger adaptive responses in the muscle.

These adaptations include the creation of new mitochondria (the structures that generate energy in cells), the formation of new blood capillaries, and other changes that improve the muscle’s capacity to burn fat as fuel. In practical terms, you become more efficient at using fat as an energy source, which matters because fat stores are effectively limitless compared to carbohydrate stores.

Training low is particularly relevant in the early phases of a training block, when intensity is lower and the goal is building a stronger aerobic base, improving fitness, or reducing body fat. It can also be a useful approach for anyone whose primary goal is metabolic health rather than peak performance. There are, however, important caveats.

Longer sessions (around 60 minutes or more) or high-intensity efforts may be compromised if carbohydrate availability is very low, because some fuel supply becomes necessary to complete the work. The benefits of training low also appear to differ between men and women, with the research suggesting that for women, restricting carbohydrate after rather than before exercise may be the more effective approach. For more on these nuances, see my Carbs & Exercise series.

So what should you actually eat before a workout?

The honest answer is: it depends.

If your session is long, intense, or performance-focused, pre-workout carbohydrates matters and is worth planning around. A balanced meal three to four hours before, with a small, fast-digesting carbohydrate top-up closer to the session, is a well-evidenced approach. Add caffeine if you tolerate it well.

If your session is moderate in intensity and your goal is general health or metabolic conditioning, the case for aggressive pre-workout fuelling is weaker. Training in a lightly fasted state may even serve you better.

The bigger picture is this: pre-workout nutrition is one input among many, and its importance scales with the demands of the session. Be sceptical of the marketing that surrounds pre-workout products. The ingredients that actually work are well-researched and relatively simple. Everything else is largely noise.