There's no such thing as "instant energy" when it comes to food.

What you may be referring to is an energy boost, which is a quick spike in blood sugar with little to no burden on your digestive system.

Eating 500kcal worth of steak would make you feel sleepy, while eating 500kcal of watermelon would not. 

If the blood is not redirected to the digestive system for extended periods of time, we experience less of the sensation of being tired upon a meal.

It's the reason, after a big feast, all you want to do is lay down and die.

But, you eat a small snack before hitting the gym.

Hence, generally, for snacking you should choose fruits which take the least effort to digest. 

However, it is important to remember, that in case of fruits, we are not dealing with "normal" sugar.

Most juicy, sweet fruits are rich in fructose rather than glucose.

Glucose being the primary fuel of all human cells.

Fructose need to be converted into glucose before can be utilized by the human body. 

Which happens in the liver.

That extra step is the reason why, even if you didn't know it, you need to avoid corn syrup in your diet.

Because the liver need to convert extra sugar, it will not be available for the rest of the body, and usually will be converted into fatty acids, and stored away instead.

Now, this is not a kin to saying "don't eat fruits, you'll get fat".

It's a kin to say "don't look for energy boosters, eat regularly but in small portions"

Blood Sugar boosting wise, there's virtually no difference between eating a banana and eating bread.

But if you must choose.

Eat Banana, Kiwi, Apple, and Pomelo.

The best fruit one should it if he is looking to get an energy boost is definitely banana!

Why? 

Because it is packed full of important nutrients, fibers, natural sugar, vitamins, carbohydrates, potassium, vitamin B6,  and  essential amino acid tyrosine. 

Energy boosting benefits of eating bananas include:

1. Researchers concluded, eating bananas before, or during periods of prolonged and intensive exercise is an effective way to keep your body fueled and to maintain good performance throughout your workout. 
2. Each banana contains about 12 milligrams of tyrosine which is an essential amino acid that helps your brain produce norepinephrine. When the norepinephrine system is activate, it exerts effects on large areas of your brain, influencing your levels of alertness and your internal reward system. Tyrosine also creates new neurotransmitters that promote alertness,  strengthens memory, motivation, and ability to focus.
3.  A large banana has 16  grams of sugar. The sugar in a banana is different from refined sugars in sodas and candy, however. Your body needs the natural sugar in bananas, fructose, to produce glucose, which fuels your brain and gives you energy.  Unlike refined sugars, which can cause all sorts of health issues, most known of which is diabetes. Natural sugars, like those found in bananas, are perfectly healthy to consume and actually help promote our health, instead of destroying it, like refined sugars do.
4.  One banana contains about .5 milligrams of vitamin B6, a nutrient that may lower your risk of cardiovascular disease and even some kinds of cancer, according to the National Institutes of Health.  Vitamin B6 also helps your body produce hemoglobin, which is in charge for carrying the oxygen from your lungs to every cell in your body.

That's why you will often see athletes, especially tennis players, eat a banana before and during the match to keep their body fueled, boost their energy levels and improe both their performance and endurance.

Hi there,

If we are talking about the fruit which give you instant energy then I have a list of top 5 fruits that will help you to boost your energy level instant-

1- Banana- As we all know that Banana is a rich source of  Potassium.  carbohydrates ,Fructose and Glucose that will give you instant energy and help you to be charged It is also good for heart and  very helpful when you want to gain weight. 

2-  Yogurt - If do workout then Yogurt is the best option for you boost your energy after the workout as it has good % of magnesium and it can be used a snacks and it helps to reload glycogen sources. 

3- Apples- It is also a good option to charge your body but it is quite slow but it is good source of  vitamin C and B and potassium. 

4- Orange & Sweet Lemon- It is good source of Vitamin C and Sweet lemon helps to make our immunity system strong and increase our blood. 

5- Watermelon  & Papaya-It is a good option to boost energy in summer specially and it has Vitamin C & Glucose that refresh your body. Papaya has some  anti-inflammatory benefits that help you improve your immunity level and it also help you to keep your eyes healthy..

The over utilization of anything could be harmful so be responsible. 

Be Healthy, Be Safe

Thank you :-)

The best fruits for energy are the most calorie dense.

Also there is no such thing as instant energy.

Bananas and dates are a good choice. Dates are fantastic due to their small size and decent calorie density for fruit. Grapes are also another good choice.

There is a reason why bananas are so popular at professional sporting events. If you go to any event where there is time to eat you will find the pro's eating bananas. When people must eat on the go like with ultra marathons they may prefer dates or gels, again because of the size and calories offered.

The reason I also like grapes is because they are also really hydrating.