Mars used to have the advertising slogan “A Mars a day helps you work, rest and play” and was regularly recommended as a sports snack or even a meal replacement. Now advice given to junior sports teams almost always warns against eating chocolate bars, recommending “energy bars, flapjack, muesli bars or granola” instead. There are a huge array of this type of bar now on the market, many of which are designed specifically for sport. But is there a big difference between these bars and traditional chocolate snacks and how do you choose between them all?

CALORIE CONTENT

A calorie is a measure of the energy value of food. Calorie content is marked on all foods sold in the UK and is worked out from the knowledge that 1 gram of fat = 9 calories, 1 gram of protein = 4 calories, 1 gram of carbohydrate = 4 calories and 1 gram fibre ~2 calories.  These values were originally set by burning the foods in a bomb calorimeter but are now generally extrapolated from the amounts of each macronutrient in the food.

I have a problem with calories. Firstly I don’t feel the way they are calculated is fair, as the value of different types of fat, carbohydrate or protein are not the same. Secondly the concept of ‘energy content’ makes us compare food to the fuel in a car, failing to take into account differences in the structure of meals, the timing of meals or differences between people. But in the calories favour it is a consistent measure of energy and it is written on the packet.

How much energy an individual burns during the day or during a specific session of exercise, is dependent on their age, weight and height, as well as the intensity of effort and it varies massively between different individuals and different sessions. Research in children and adolescents has found that during a group team-sport training session individuals can cover 4-6Km/hr, around 20% of which is at high intensity. During a match some individuals can cover up to 10km/hr (though 6-8km is more common), with 40% being at high or very high intensity. In my research a measured one-t0-one hockey training session for a 12yr old girl gave an estimated calorie burn of 250-350 calories and a similar training session for a taller heavier 15yr old gave a possible calorie burn of 500-600 calories, with both children giving maximal effort. The calorie content of the bars I bought locally varied from 296 calories for the Digestive slice to just 89 in the Special K Bar.

The problem with using calories as a measure of the value of a snack for sport, is that it tells you only how much energy is in the bar, and not how quickly or easily it is released. The quickest release form of energy is sugar and sugar content is also given on the pack.

CARBOHYDRATE AND SUGAR CONTENT

During training and competition, glycogen energy stores in the muscles get depleted. In order to restore them quickly individuals needs to consider the speed at which carbohydrate is converted into blood glucose and how quickly it can be transported to the muscles. Taking carbohydrate before or during exercise lasting over 1hr has been found to boost performance and endurance. For junior athletes this may be particularly important for swim or track events where there are a number of races consecutively or at tournaments where individuals will play multiple games. Junior athletes have lower glycogen stores than adults.

Not all carbohydrates are equal.

Carbohydrate can be divided into starch, sugar and fibre. Starch and sugar provide 4calories/g and fibre around 2calories/g depending on digestion. Fibre is very slow to digest, starch can also be slow to digest and the assumption is that sugar is all quickly digested, immediately raising blood sugar. In fact there are four main types of sugar, and they raise blood sugar levels at different rates. Foods with a high concentration of glucose need no conversion and raise blood sugar rapidly. Fructose (the sugar in fruit), however, needs to be converted in the liver and so is released more slowly; as is lactose which is the main sugar in dairy products. Sucrose (table sugar) is made up of glucose and fructose and is absorbed at a rate between the two.

This range of the snack bars, bought from a variety of local shops and supermarkets contain a wide range of different quantities of sugar. The amount of sugar varies from 29.5g in the Cadburys double decker to 8g in the Mars Tracker Bar. Some of the difference is due to the various sizes and weights of the bars but not all. The ingredient list may give an idea of the type of sugar included and listed as ‘sugar’ but this is not always clear.

The speed at which a food is absorbed and the effect it has on blood sugar, can be assessed by looking at its measured glycemic index (GI) or glycemic load (GL). The faster and higher the blood glucose rises after the food is eaten the higher its GI. GL gives an idea of not only how fast blood sugar rises but also how much carbohydrate is in the food, making it the slightly more useful measure. Sports gels and drinks are designed to be very quickly absorbed and will therefore have a very high GI / GL. They are often sweetened with maltodextrin which is a chain of glucose molecules and very easily absorbed.

Some snack bars, particularly sports bars, do list their GL, if it is not on the packet it can sometime be found on the manufacturers website. The GL values for common foods can also be found on diabetic association websites or via independent nutrition analytics companies like http://nutritiondata.self.com. A GL of 20 or more is high, a GL of 11 to 19 is medium, and a GL of 10 or less is low.

PRE-EXERCISE it is recommended you eat low GL foods for sustained energy. DURING EXERCISE it is recommended you eat moderate-to-high GL foods or drinks. POST-EXERCISE it is recommended you eat some carbohydrates within two hours of exercising but the type is less important.

From this sample not all the glycemic loads are known but the GL of a Mars Bar is 18, A snickers bar 20, Natures Valley Granola Bar 18, Kellogs Nutri-grain cereal bar (mixed berry) 24 and a Mars Tracker Bar 17, which would suggest from this tiny sample, there is very little difference between the granola or flapjack style bars and traditional chocolate based snacks in the speed at which carbohydrate is absorbed.

FIBRE AND PROTEIN CONTENT

What else affects the speed food energy reaches the muscles ?

• Fibre slows the time it takes the body to break down a food, improves gut health and possibly nutrient absorption. Fibre content is listed on almost all of the bars I bought. The fibre content of all the granola / flapjack style bars is the same as or higher than the chocolate bars but the difference is not as large as you would think. The sports energy bars and protein meal bars contain more fibre than the standard bars. A high fibre content will be particularly important for bars eaten pre-exercise.
• Fat content of food drastically slows the speed at which it leaves the stomach, slowing energy absorption. Fat content may well be the reason why chocolate snacks have not been recommended as sports snacks, as traditionally they have been high fat. In my sample the highest fat content was in the Digestive Slice (15.9g) but the next highest was the Eat Natural Almond and Apricot flapjack (12.5g). All the chocolate snacks were high fat though averaging around 8-10g against the granola bar/flapjacks’ 5-6g.
• Acidity like fat slows down digestion. This is not such an issue in snack bars but maybe important if they have citrus flavouring.
• Protein has little effect on glucose absorption but increasing the protein content of bars may lower available carbohydrate. Protein rich foods are important during recovery after exercise, boosting muscle growth and repair. In my sample the specialist sports protein bars had the highest protein content, followed by the granola bars. The Mars, Twix and squares had very little protein but also surprisingly did the Mars Tracker, Special K bar and Nutrigrain breakfast bake.

THE VALUE OF NUTRIENTS

As there is not a massive difference between the energy delivery from a granola bar or flapjack and a traditional chocolate snack, does this mean we should eat chocolate bars during sport?

Not really – the thing that makes the big difference between a good nut, seed and fruit flapjack and a chocolate bar is nutrient content. Natural foods are full of minerals, vitamins and phytonutrients. Although they are sometimes mentioned on ingredients list, the number of nutrients a food contains is not covered in the nutritional information. As a generalisation flapjacks and granola bars should be far richer in nutrients than chocolate bars. See for example the differences between the composition of a Snickers Bar which is low nutrient even though it contains peanuts and a generic Oat Fruit and Nut Granola Bar.

The problem in choosing a snack bar, is that not all the bars posing as a healthy choice are in fact that healthy, manufacturers know that consumers are looking for healthy foods but that they are swayed by taste and like sugar. Weight for weight there is very little difference between the Snickers Bar and the Snickers Flapjack. For sports performance you would be far better off making your own snack foods (see recipes for Banana & Nut-butter Bars and Granola Bars on my website or recipes in Eating on the move or Eat Like a Cricketer). Making your own sports nutrition means that you will know exactly what you are eating.

IMPORTANCE OF TEXTURE

Another important consideration is, now easy a bar is to eat, particularly if you are using it to refuel during exercise. Very crumbly bars are tricky both to store in your sports bag, as they are easily damaged and actually eat. Very sticky or gloopy foods may be hard to swallow or difficult to wash down. Talking to one cyclist he admitted that although he loves a chocolate bar normally, he can’t see himself managing cope with it on the road with his heart rate above 140.

ADVICE – What should you buy?

The most important piece of advice is to always test something you are going to use during an important trail or competition when it doesn’t matter. The fuel you choose should be personal to you. Some athletes use specifically manufactured gels, bars or jelly, others prefer boiled potatoes or home made power balls. If anything what this research tells you is that you can’t really choose a bar from its ingredients, or the information on the pack. You really need to test it to see.

FURTHER READING

Please contact me if you would like references for this research. The nutrient information on a selection of UK snack bars is given below.