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  • Rachel Fletcher

How can nutrition improve your exercise performance ?

Do you exercise ?

Couch to 5K ? running a marathon ? competing in a triathlon ? CrossFit ? Lifting weights ? Playing football/hockey/tennis ?

No matter what kind of exercise you enjoy, nutrition can make a difference to your performance. Have you ever noticed that some days your training seems great; you're energised and hitting some PB's. Whereas other days, you just feel sluggish and can't do what you usually do ? Whilst there are lots of factors that could be impacting your performance, such as sleep, stress, menstrual cycle etc, nutrition plays an important part.

If you want to get the best out of your training, there are 6 areas you should look at:

energy, carbohydrates, fats, protein, hydration and (potentially) supplementation.


Many people don't eat enough to fuel their training. This is especially true when the goal is weight/fat loss. However, under fuelling can not only negatively impact your energy levels and performance, long-term it can lead to illness, injury and loss of muscle mass. Females in particular can be at risk of loss of periods (amenorrhea) when over training and under fuelling. The loss of your period is a red flag and needs professional help.


Carbs are king when it comes to performance nutrition as they are our bodies preferred fuel. Some people worry that carbs will make them gain weight (not true) or feel sluggish (not true) but to perform at your best, they're needed to provide energy to fuel your training.

Our bodies store glycogen in our muscles and liver and this is used for fuel. However, we don't have a limitless supply and need to top it up by eating carbs. This is particularly important for sports/training over 90 mins. It's also important for high intensity training such as sprints, football, power/Olympic lifting and CrossFit because glycogen is our bodies preferred energy source as its quickly released. Insufficient carb intake will lead to fatigue and inhibit performance.

For those competing at a high level, there are some nuances for carb intake such as 'Training Low', periodisation and carb loading. This is something that a performance nutritionist can advise on.


Our bodies can obtain a great amount of energy from stored fat (lipids) but it isn't released as quickly as from glycogen. We tend to use a mixture of carbs and fat for energy and the proportion of these varies based on factors such as; intensity, duration, fitness levels and overall diet. Generally speaking, lower intensity and longer duration exercise will use fat for fuel. Our bodies will use fat for energy once our glycogen stores are depleted. Again, there are potential adaptations through diet and training which may lead to increased utilisation of fat but studies suggest these don't necessarily enhance performance.


Unlike carbs and fat, protein isn't really used as a fuel source but is essential for muscle repair and growth through a process called muscle protein synthesis. Also unlike carbs and fat, our bodies don't store protein so it's important to eat it regularly, ideally in all meals and snacks. Those who strength train will have a greater protein requirement than endurance athletes, especially if seeking to lose weight but still retain muscle mass.

Most of us consume sufficient protein every day, including those on plant based diets. However, as most plant sources don't contain all the essential amino acids, it's important to eat a variety across the day. A spot of myth busting - you don't need to consume protein within a 20 min window of training. The anabolic window is around 24 hours, so as long as you regularly eat protein, you're good.


Ensuring you're hydrated is really important, as dehydration impairs performance and can make you ill. You should aim to minimise fluid loss when exercising by ensuring you're well hydrated before exercise, drinking adequate amounts, according to your thirst during exercise - especially if training over an hour, it's high intensity and/or hot weather. Replace lost fluids (through sweating) afterwards.

The easiest way to judge your hydration levels is with a pee check. it should be a light straw colour. If not, you need to drink more. Other signs of dehydration include headaches and feeling sluggish.


Supplements probably aren't necessary for most people, unless competing at an high level. As with general nutrition advice, it is recommended we get our nutrients from food where possible, because the nutrients are absorbed more effectively. Plus it saves you £££. However, those with allergies, intolerances, or plant-based diets may need fortified foods or supplements.

Depending on your diet and goals, studies have shown that some supplements may improve performance

Sports drinks/gels - great for endurance training (over an hour) as they provide easily transportable carbs and electrolytes to refuel and rehydrate. Be aware that some can cause gut issues, so always try before a race/competition.

Protein powder - helps with muscle repair and growth. Is really popular but often not necessary as we can get sufficient protein from food. However, it's convenient and quick, especially when on the go.

Caffeine - can enhance endurance and high intensity exercise.

Creatine - fuels muscles to sustain all out effort for longer and recover quicker between sets. Can be useful for power/Olympic lifting, sprints and high intensity training.

The timing of your meals and snacks before and after training is also an important nutrition factor. I'll cover this in a later post, so keep your eyes peeled.....

Please note, the information here is intended to be generic. A performance nutritionist can calculate your unique energy/carb/protein/hydration requirements based on your goals, training patterns, daily activity, dietary preferences and body weight to provide bespoke advice, including the timing of meals and snacks.

If this is something you'd like help with, get in touch for a free discovery call:

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