When we want to get into shape, it can be tempting to focus our diet on low calorie foods in the hope that they'll aid weight loss.
But these foods can cause our energy to dip and in turn, have a negative impact on our ability to exercise.
In order to both look and feel strong, we really need to consume foods that help us to be fit, not thin.
"Food is fuel, and the more you work out the more you tend to need," nutritionist Alice Mackintosh tells HuffPost UK Lifestyle.
"But like a car, the type and quality of fuel is incredibly important and can have big impacts on the way we function.
"Get what you eat and when right and you can improve performance, reduce injury and improve recovery time."
What To Eat Before A Workout
Jo Travers, of The London Nutritionist, recommends eating a low GI meal 2-4hrs before training.
"This will mean that by the time you are starting your session those carbs are being digested and you will have a continuous gradual release of glucose to the blood throughout training," she says.
Low GI meals Travers recommends include porridge, brown rice and wholemeal pasta.
"A light snack (20g carbohydrate) should be eaten an hour before training begins to top-up the glucose supply," she adds.
"If training begins without any carbohydrate, say if you are exercising first thing in the morning, eat snacks, such as cereal bars, dried fruit, a banana or a sports drink throughout the session."
Mackintosh agrees that carbs are important to eat before a workout. She advises to avoid any snacks that are "unnaturally high in sugar" and instead, go for something easily digestible such as berries, banana, avocado, spinach or almond butter.
Her top food to eat before training is beetroot.
"A good source of a compound called nitric oxide that naturally helps to increase blood flow by causing blood vessels to dilate, beetroot is a good food to support endurance, helping you go that extra mile," she says.
"It also contains iron which is vital for red blood cell production, muscle cell health and energy, the demand for which increases when we work out."
It's also important rehydrate before you dehydrate.
"Have a good drink of water (250-500ml) before the session depending on how much feels comfortable in your stomach," Travers says.
"Isotonic drinks offer quick hydration at 2-3 times that of water and also supply energy in the form of glucose. They are best used when a combination of fluid and energy are required such as in the gym."
What To Eat After A Workout
Exercise causes muscle fibres to break down - replacing them is essential to avoid deficiency and help you get back in the gym, faster.
Because of this, protein is key post-exercise.
"Your mood, liver function, immunity, kidney health, hormone balance and adrenal function are all things that can become compromised if they don’t get the amino acids they need," Mackintosh explains.
"Don’t think that eating protein post exercise will bulk you up - just as fat doesn’t equate to fat gain, protein doesn’t necessarily lead to muscle gain.
"The type of exercise will determine that more, but either way you need to ensure enough protein from the diet whatever the workout."
Opt for eggs, chicken or salmon for a meal or snack on nuts post workout for the ideal protein fix.
As well as considering carbs before a workout, Travers says it's important to think about them afterwards.
"If glycogen (carbohydrate stored in the muscles) stores are not replenished after training, initial levels will be too low and may ‘run out’ at the start of the next session," she says.
"A high carbohydrate diet will increase glycogen stores and therefore improve performance. Conversely the reverse is true for a low-carbohydrate diet."
She recommends eating high GI foods such as white bread, jacket potato, white rice and white pasta when you finish exercising.
Mackintosh adds that berries help muscles to repair because they are rich in antioxidants, while green leafy veg are beneficial due to their high magnesium content.
Magnesium helps to maintain muscle, nerves and bone health.
But the most important thing to remember when aiming to be fit not thin, is to eat a balanced diet.
"Exercise puts extra strain on many of the metabolic pathways that rely on vitamins and minerals putting athletes at a greater risk of deficiency," Mackintosh says.
"Vitamin D, iron, zinc and magnesium have been shown to be deficient in many athletes and consuming a nutritionally dense diet with colourful veg, wholegrains, protein and healthy fats should deliver these."