Fast and slow carbohydrates: timing is everything for athletes

As a sports nutrition coach, I regularly get asked about carbohydrates. “Should I eat fast or slow carbohydrates?” and “When should I eat which?” are common questions. The answer lies not so much in what you eat, but primarily in when You eat it. In this blog post, I will explain how to strategically time your carbohydrate intake around your training for optimal performance and recovery.

What are fast and slow carbohydrates, really?

The distinction between fast and slow carbohydrates is about how quickly your body can digest and convert them into glucose (blood sugar). This is expressed by the glycaemic index (GI). Products with a high GI cause a rapid rise in your blood sugar, while products with a low GI cause a gradual rise.

Fast carbohydrates are found in sports drinks, energy gels, white bread, white rice, bananas, dates, rice cakes, and products with honey or jam. Slow carbohydrates are found in whole grain products, legumes such as lentils and chickpeas, sweet potato, porridge, and most vegetables.

But note: there is also a category of easily digestible carbohydrates that are not necessarily fast in terms of GI, but are easy to digest because they contain little fibre. Think of white rice, regular pasta, or white bread. These are crucial in your timing around workouts, as they provide sufficient energy without burdening your digestion.

The 24-hour timeline: when to eat what?

3+ hours for training: Slow carbohydrates as a base

At this time of day, you can safely eat full meals with slow-release carbohydrates. Your body has enough time to digest the food and convert it into energy. Whole grain products are ideal now precisely because they provide energy over a longer period, keep your blood sugar stable, and also contain more fibre, vitamins, and minerals than refined products.

This is the time for your wholemeal bread with savoury toppings, wholemeal pasta or couscous, brown rice, porridge with fruit and nuts, or pulses with vegetables. You can now opt for your most nutritious, fibre-rich meals without worrying about how your digestion will feel during training.

2-3 hours before training: Switch to easily digestible

Timing really becomes important now. Wholegrain products that are high in fibre can still be sitting in your stomach during your workout, which can lead to a feeling of fullness, cramps, or an upset stomach. This is the time to switch to easily digestible carbohydrates that still provide plenty of energy but won't burden your digestive system.

Your best choices right now are white rice with chicken or tofu, regular pasta instead of wholewheat, white bread or a white roll with toppings, or potatoes and sweet potato which are relatively easy to digest. Porridge is in between wholewheat and white in terms of digestion and may still work well for many people at this time.

Avoid wholemeal bread or pasta, large amounts of legumes, fatty meals, and too many raw vegetables for now. You want to start your training feeling light and energetic, not with a full stomach.

30-60 minutes before training: The danger zone

This is a crucial moment to understand. Between 30 and 60 minutes before your workout, you're best off eat nothing at all, and certainly not fast carbohydrates. This might seem strange, but there's an important physiological reason behind it.

If you eat fast carbohydrates at the moment, your blood sugar will rise quickly. Your body responds to this by producing insulin to lower that blood sugar. The problem is that this insulin response can cause your blood sugar to drop too much, precisely at the moment you start training. This is called reactive hypoglycaemia, and you'll experience it as an energy dip, feeling heavy, or even slight dizziness. Exactly what you don't want when you're just starting your training.

Allow your body to rest during this phase. If you've eaten well 2 to 3 hours beforehand, you'll have enough energy available. This is the ideal moment to warm up and mentally prepare yourself, not to quickly eat something.

0-15 minutes before training: Last opportunity for quick energy

If you really feel you need one last boost, you can have some fast-acting carbohydrates in the final 15 minutes before you start. At this point, you'll be starting to move almost immediately, meaning the glucose will be used straight away for your exertion and you'll avoid that unpleasant dip.

A small banana, a couple of dates or a sip of sports drink can help here. Keep it small and simple, though. For most recreational athletes, however, this isn't necessary. It's more for competitive athletes who want to squeeze out every last bit of performance.

During training lasting longer than 90 minutes: Continuous replenishment

For training sessions or matches lasting longer than 90 minutes, you need a continuous supply of fast-acting carbohydrates. Sports drinks with 30-60 grams of carbohydrates per hour, energy gels, sports bars, or natural options like bananas and dates are ideal for this.

However, for most recreational athletes who train for 60-90 minutes, water is sufficient. Only during truly long endurance efforts does supplementation during training become relevant. Do experiment with this during training sessions, not during your most important competition.

0-2 hours after training: The recovery window

Immediately after intensive training, your recovery window opens, and this window remains open for about 2 hours. Previously, it was thought that you really had to eat within half an hour, but research has shown that you have a bit more leeway. This is good news, as it gives you time to have a shower and prepare a normal meal at your leisure.

Within these 2 hours, your muscles are extra sensitive to glucose uptake, and replenishing your glycogen stores works best. The combination of carbohydrates and proteins aids muscle recovery. Fast-acting carbohydrates are most efficient here, but if you simply eat a normal meal with enough carbohydrates and proteins within that 2-hour window, you'll be fine too.

Chocolate milk or a protein shake with banana are classic recovery drinks you can take immediately afterwards. Rice cakes with peanut butter and honey, white bread with savoury toppings, white rice with egg or tofu, or a banana with Greek yoghurt are all excellent choices. However, a normal meal with regular pasta, potatoes, or rice combined with a protein source also works well.

This recovery window is particularly important if you're going to train intensely again within 24 hours. But don't stress about it if you go slightly over that 2-hour mark; the main difference lies in whether or not you eat after your training.

2+ hours after training: Back to basics

Once the recovery window has passed, you will return to your normal diet of slow-release, whole carbohydrates. Your next meal can be whole grain, fibre-rich, and nutritious again. Now is the time for whole wheat pasta with plenty of vegetables, brown rice with pulses, a wholemeal wrap with chickpeas, or a quinoa bowl with assorted vegetables.

The main timing rules at a glance

More than 3 hours before your training, opt for whole grains and slow carbohydrates, prioritising nutrient density. Between 2 and 3 hours before your training, switch to easily digestible carbohydrates like white rice or plain pasta, to give your digestive system a break.

Between 30 and 60 minutes before your training, it's best to eat nothing at all to avoid that annoying energy slump. Only in the last 15 minutes before you start can you optionally opt for fast carbohydrates if you feel you really need them. During very long training sessions, you continuously refuel with only fast carbohydrates that are immediately available. Within 2 hours after intensive training, combine carbohydrates with protein for optimal recovery. And from about 2 hours after your training, you switch back to whole grain and slow carbohydrates as a nutritious base.

How important is this timing to you?

For competitive athletes or those who train twice a day, this timing is truly crucial. With such high training frequencies, small nutritional errors quickly accumulate and you really notice the difference in performance and recovery.

For recreational athletes who train 3 to 5 times a week for about 60 to 90 minutes, you can be a bit more relaxed with these rules. The basics are already covered if you eat enough carbohydrates spread throughout the day, don't plan heavy meals right before training, and eat something within a few hours after intensive training. But for recreational athletes too: try to keep that 30-60 minutes before your training free from eating.

Experiment to find out what works for you personally. Some people can still eat whole grains 2 hours before training without any problems, while others really need 3 to 4 hours. Pay particular attention to how you feel during training: do you have enough energy, do you feel light enough, are you recovering well?

Vegetarian sources throughout the day

Fortunately, as a vegetarian, you have plenty of choice from good carbohydrate sources for any time of day. For your slow-release carbohydrates as a daily staple, you can choose from all whole grain products, quinoa and buckwheat, various legumes, and sweet potato. These products are not only rich in carbohydrates, but also provide valuable protein and iron for vegetarians.

For the period 2 to 3 hours before training, when you want to eat something easily digestible, white rice and plain pasta are your friends, as are plain potatoes and porridge. And for your quick carbohydrates immediately after training or possibly in the last 15 minutes before starting, you can rely on bananas, dates and raisins, rice cakes with honey or just white bread with jam.

The core: timing makes the difference

All carbohydrates have their place in your diet, but when you eat them determines how effective they are for your performance and recovery. Whole grains are fantastic for your daily diet, but not ideal 2 hours before an important competition. Fast-acting carbohydrates are perfect immediately after training for quick recovery, but they don't form a good basis for the rest of your day. And perhaps most importantly: leave those 30-60 minutes before your training alone to avoid that annoying energy dip.

If you apply this timing, you will find that you suffer less from a feeling of fullness during training, have more stable energy without unpleasant dips, recover faster between training sessions, and perform better at important moments.

Do you have any questions about how best to apply this timing to your specific training schedule? Please feel free to get in touch for personalised advice tailored to your sport and goals.