Can fruit make you fitter?

Bolster your body's response to hard training

“An apple a day keeps the doctor away.” It’s an old adage, but by the end of this article I hope to convince you that an apple a day will not only keep you healthy, it’ll improve your cycling performance, too.


More specifically, I’m going to show you the evidence that fruit and veg can improve performance, and that you can eat yourself fit. Well, almost! Nothing can replace training, of course, but it seems we can enhance our adaptation to training by eating the right foods.

As a nutritionist I’ve always used the idea that including fruit and veg in your diet is primarily about staying healthy, but that can sound boring to an athlete who’s more focused on performance improvement. However, research shows that some of the nutrients in fruit and veg can also help the adaptation to training. And that’s exciting news.

So let’s start at the beginning and look at one of the ways you get fitter by training. When you train, one of the adaptations is an increase in the number of mitochondria in your muscles. Mitochondria are the cellular power plants in your muscles, which produce a large proportion of the energy you use during endurance exercise. So the more, the better.

There are certain triggers in the muscle which tell your body to produce more mitochondria. The four most important ones in this context are called AMPK, SIRT-1, PGC1- and PPAR, and to put it simply, to make more mitochondria in the muscle these molecular triggers need to be increased. Training can do this, but what if food can too?

Help to train harder

Over the past decade or so there has been an increasing amount of research looking at exactly this question. The increase in research activity in this area has been generated by the rise in obesity and the search for a ‘magic pill’ to help combat the health problems caused by obesity. However, some of the research findings also have exciting implications for endurance performance.

The research has focused on the area of polyphenols and flavanoids. These are nutrients found particularly in fruit and vegetables and there are many different types, all of which function in a similar way within the body. Resveratrol is one such polyphenol which can be found in red grapes (and therefore, happily, in red wine too.

In a 2006 edition of the prestigious science journal Cell, Lagouge and colleagues published a study whereby mice underwent a 15-week diet and exercise programme where they were either supplemented with resveratrol or a placebo. After the supplementation period, the results were striking. The mice which had been supplemented with resveratrol had a 33 percent higher peak oxygen uptake, and a near 50 percent greater run time to exhaustion.

When the researchers took samples of the mice muscle and attempted to look further into the mechanisms behind these increases there was a 2.5 times greater area of mitochondria in the muscle. Citrate synthase (a key enzyme to produce energy in the muscle) was also increased, as were all the key molecular triggers like SIRT-1 and PGC1-telling the muscle to build more mitochondria.

Polyphenol intake may help you to train really hard without breaking down and getting ill

When the researchers looked back at the exercise the mice had undertaken, they saw that the mice supplemented with resveratrol were able to complete more exercise. This in all likelihood allowed them to essentially get ‘fitter’, by training harder. This has big implications for athletes, as often one of the limitations to making performance gains is one’s ability to train hard. It appears that polyphenol intake may help you to train really hard without breaking down and getting ill.

Another research group in the USA looked at a polyphenol called quercetin. When mice were supplemented with quercetin for seven days there was a significant increase in the molecular triggers PGC1- and SIRT-1 in their muscles, indicating that their bodies were preparing to produce more mitochondria. After the seven-day supplementation period the mice were able to run for approximately 40 percent longer in a time-to-exhaustion exercise test.

Now, two important questions spring to mind. Firstly, does this work in humans too? There is equal evidence that quercetin supplementation can improve performance and that it does nothing at all. The most conclusive positive evidence appears to be in less well-trained individuals.

The second obvious question is: what are the natural sources of quercetin? Well, it’s found primarily in onions and apples – so we’re back to my starting point of the benefits of an apple a day. There’s pretty convincing evidence that quercetin can help reduce the stress of training and support the immune system. So maybe when you are training hard an apple a day can keep the doctor away, and hopefully help you get fitter.

Get cooking

Fruit and veg aren’t the only source of polyphenols. Those who enjoy cooking will be pleased to hear that herbs and spices are also excellent polyphenol sources. The health effects of cinnamon are increasingly being discovered, and one of them is that it turns on the mitochondrial building trigger PPAR. This hasn’t yet been tested in the context of athletes and performance, but it looks plausible that cinnamon intake can lead to an increase in the mitochondria in the muscle.

It’s important to remember that all this research is at a developmental stage, so I certainly wouldn’t suggest rushing out and buying lots of supplements containing quercetin and resveratrol. However, actively trying to increase your polyphenol intake through eating lots of fruit and veg will certainly do you no harm, and the performance improving potential is there waiting to be found.

Here’s how to make some simple changes to your diet:

  • Increase your fruit and vegetable intake to 8-10 portions per day
  • Choose red and other darkly coloured fruits and vegetables
  • Add herbs and spices to your meals

Three simple ways to increase your polyphenol intake

1. Blueberries

Add blueberries to Greek yoghurt. Blueberries have one of the highest polyphenol contents of all foods. The benefits include improving cardiovascular health and helping to prevent the development of cancer.

Blueberries have one of the highest polyphenol contents of all foods
Riccardo Bruni / EyeEm / Getty

2. Cinnamon

Add a teaspoon of cinnamon to your porridge. Not only is cinnamon high in polyphenols, it can help reduce the insulin response to a carbohydrate meal, helping your body use the carbs more effectively.

Cinnamon helps your body use carbs more effectively
Matthew O’Shea / Getty

3. Dark chocolate

Take dark chocolate to work for a mid-afternoon snack. Chocolate with a cocoa content over 75 percent has a high polyphenol content, and research shows that it can increase blood flow, which is key for endurance performance.

Dark chocolate can help with endurance performance
Andrew Hounslow / Getty

Other high polyphenol-content foods

  • Red kidney beans
  • Acai berries
  • Olives
  • Spinach
  • Walnuts
  • Cherry juice
  • Green tea/coffee
  • Turmeric