A bit about fruit

This blog post is slightly more technical than I usually like to post. Here are the key points to have set in your mind before reading:

  • Fructose and glucose are monosaccharides
  • All carbohydrates are broken down into monosaccharides;  the most common being glucose
  • Glucose circulating in the blood is known as blood sugar
  • Blood sugar is tightly regulated, with insulin being the hormone responsible for taking blood sugar out of the blood stream and delivering it to any cell that needs it
  • If there is more glucose present than is needed by the body’s cells it will be stored as glycogen (in the muscles and liver) or as body fat
  • Fructose is metabolised in the liver where it replenishes liver glycogen, is converted to glucose or converted to fatty acids
  • Different fruits contain different amounts of sugar
  • Different fruits contain different types of sugar
  • Whether a fruit is good or bad depends on what type of fruit it is, and the body’s circumstances at the time of digestion
  • Very obese people may benefit from removing all fruit from their diet for certain periods
  • Other people with fat loss goals may do well limiting fruit consumption to the post workout window only

 

When it comes to fat loss, fruit is a tricky subject. On one hand fruit is labelled healthy as it is natural and rich in anti oxidants, phytochemicals and fibre. On the other hand it gets labelled as unhealthy due to its sugar content and the bad rep that sugar (especially fructose) currently has.

As with everything in health or fitness, disregarding context when forming an opinion on something such as fruit will only lead to confusion. Fruit is neither good nor bad. How, why and when you choose to consume fruit is the crux of making it good or bad for you. With this post I hope to arm you with the information you need to make the right choice when it comes to including (or not) fruit in your diet.

A quick note: I am going to try and keep this as simple as possible. If the following section leaves you lost, skip to How does this apply to fruit and read from there.

Fruit causes controversy because of its sugar content. Therefore, I thought I’d begin with a quick intro to sugar. Sugar is simply the simplest form of carbohydrate. When digested, all carbohydrates are broken down to one molecule – a monosaccharide (literally one sugar). The three most common monosaccharides are glucose, fructose and galactose. We also have disaccharides which consist of two monosaccharides bonded together. Common disaccahrides include sucrose (commonly known as table sugar) which is fructose + glucose, and lactose (the sugar in milk) which is galactose + glucose. Longer chains of sugar consisting of more than two molecules are known as polysaccharides. The longer the chain is, the more complex the carbohydrate.

When we eat any type of carbohydrate the body breaks it down into monosaccharides – the most common of which is glucose. Glucose is the body’s favoured source of energy. After digestion, glucose will enter the blood stream where it will remain (and potentially build up) until the hormone insulin is released by the pancreas which allows glucose to cross cell membranes and be used by whichever cell needs it. Blood sugar (the term for glucose circulating in the blood) is tightly regulated by the body so insulin will continue to be released until blood sugar levels are back to ‘normal’. If we ingest a large quantity of sugar, the resulting increase (or spike) in blood sugar will lead to a similar increase in insulin.

When it comes to fat loss (or in this case, gain) it must be understood that a spike in blood sugar (and therefore insulin) will lead to different cells of the body ‘asking’ to be given some of the available glucose. If there is a surplus of fuel, glucose will be stored as either glycogen or fat. Glycogen is a chain of glucose molecules – a polysaccharide made up entirely of glucose. Your body will store glycogen in either your muscles or your liver.  These stores are finite and vary depending on a number of factors. Once glycogen stores are full, glucose will be transported to fat cells to be converted to triglycerides – or body fat. The take home message here is that excess levels of blood sugar can potentially lead to body fat storage.

Fructose is processed differently to glucose. Once it enters the body it cannot be utilised by all the cells in the body like glucose would be. It must be metabolised by the liver. To get to the liver, it does NOT need insulin, so it does not directly cause an insulin response (you’ll see why I say this in a moment).

Once in the liver, fructose will do one of three things:

  • Replenish liver glycogen; but only if these stores need replenishing
  • Processed into glucose (to be used by the liver for energy or put back out into the blood stream) which is then processed through the insulin pathway discussed earlier. This is why I said fructose does not directly cause an insulin response.
  • Synthesized into fatty acids which are then released by the liver for storage by fat cells

Which of these three processes is undertaken is governed by the requirements of the body at the time of consumption and the amount that is consumed. This is where context is oh so important! A point worth noting is that despite glucose and fructose having different metabolic pathways, and excess of either can lead to body fat storage. Or simply just consuming either when your body doesn’t need them can lead to fat storage. For most people, simply treating the sugars in fruit as easily digestible carbohydrates would be a sensible strategy. Only at the point of fine tuning a diet to an extreme degree would the difference between the fructose and glucose start to become relevant; in my opinion.

How does this apply to fruit?

Fruit is a very broad term that encompasses a large amount of different foods. While there are some similarities between fruits, there are also some differences – in the context of this post, the most important of which is the sugar content.

All fruits contain sugar. That’s why we like them – they are nature’s dessert. The amount of sugar and type of sugar varies from fruit to fruit.  The sugars in fruit are glucose, fructose or sucrose (fructose and glucose bonded). The misconception around fruit is that they contain only fructose; they don’t. Different fruits have different ratios of glucose to fructose and different amounts of sucrose, and this is important when appreciating how fruit will be used by the body. Fruit with more glucose than fructose (plums for example) will cause effect your insulin levels more directly than fruit that has more fructose than glucose (apples for example). Remember what I said earlier though, fructose still has the potential to spike insulin; it just depends on the body’s circumstance at the time of digestion.

Let’s put the amount of sugar into context first. For most, just appreciating the overall sugar content in a fruit is enough. This list shows the amount of total sugars per 100g of fruit (in alphabetical order)

Fruits

The more sugar a fruit has in it (per portion size, or per 100g), the more body will have to deal with this digested sugar, either via the insulin pathway or the liver. Regardless of the pathway, if your body has no use for this influx of sugar, it will be stored as fat. Simply put, the more sugar a fruit has in it, the more likely it is to be stored as fat – unless you have given your body a need for energy (recovery after a weights session for example). To aid recovery, the fruits higher in the list would be ideal. As a post dinner snack, the lower fruits would probably be a better choice. It should be noted at this point that the sugar content of each fruit is simply an average figure. Different varieties of the same fruit could have differing sugar levels if one was bred to be sweeter. Ripened fruit will be sweeter, and the levels of glucose, fructose and sucrose can all vary on how ripe the fruit is.

Here is the same list, this ordered from highest to lowest in sugar content:

Fruits sorted by sugar

 

The sugar profile information can be useful if you are using fruit in a more fine tuned diet. Knowing that some fruits will have a more immediate insulemic effect compared to others, or that some fruits have far more fructose than others may be beneficial in the context of your goals. It is also worth noting that fruit portions will vary between different fruit. A portion of berries will be a different weight to a portion of banana. For the scope of this article however, the total sugar content is all I wanted to discuss.

When it comes to fat loss, your specific requirements need to be taken into account. Someone who is metabolically very ‘sick’ (i.e. very obese) may not deal with carbohydrate very well generally, and therefore fruit would be a no-go regardless of glucose or fructose content.

For others, who may not be obese but may be aggressively trying to shed some body fat, fruit may only be appropriate at certain times of the day (after training for example) and then only certain fruits would be appropriate. Again, it’s worth repeating; context is everything. Understanding what and how much you are eating can be a key factor in making consistent and sustainable progress in your fat loss.

As a final thought, the role of fruit in the diet should be considered carefully. Not only is the type of fruit important, so too is the individual eating it.

A repeat of the summary of take home points:

  • Fructose and glucose are monosaccharides
  • All carbohydrates are broken down into monosaccharides;  the most common being glucose
  • Glucose circulating in the blood is known as blood sugar
  • Blood sugar is tightly regulated, with insulin being the hormone responsible for taking blood sugar out of the blood stream and delivering it to any cell that needs it
  • If there is more glucose present than is needed by the body’s cells it will be stored as glycogen (in the muscles and liver) or as body fat
  • Fructose is metabolised in the liver where it replenishes liver glycogen, is converted to glucose or converted to fatty acids
  • Different fruits contain different amounts of sugar
  • Different fruits contain different types of sugar
  • Whether a fruit is good or bad depends on what type of fruit it is, and the body’s circumstances at the time of digestion
  • Very obese people may benefit from removing all fruit from their diet for certain periods
  • Other people with fat loss goals may do well limiting fruit consumption to the post workout window only

Feel free to leave any Qs in the comments section! Thanks for reading.

2 thoughts on “A bit about fruit

  • Thank you Fran, a very helpful blog post!!!!!

    What would you suggest having an hour or two before a workout to give me a quick boost before going to the gym?

    Id be coming back from work.. I eat enough good stuff during the day but need a boost! Someone suggested a banana helps before a workout too.

    (I also eat my dinner after the gym).

    Thanks

    Sharan

    • Thanks for the comment Sharan.

      My suggestion would depend on what your hope to achieve from your workout and what you plan to do in the gym.

      A banana may be fine to give you a quick boost of energy, but it may also slow the mobilisation of fat from fat cells due to its effect on insulin. If you feel you absolutely need a boost before training it may be worth looking at the rest of the diet to see if there are any flaws. You should also focus more on post workout recovery rather than pre workout preparatory eating. Recovering from a workout will help your performance in the next session, and this is a a factor a lot of people miss out on. Typically, when I see someone who straggles with energy to train, it’s because their food leading up to the session (from 2-3 days out) isn’t conducive to what they hope the achieve from exercising.

      Think of ancestral humans. They wouldn’t have needed to eat food prior to any strenuous exercise (hunting food or avoiding predators for example) or else suffer from a lack of energy. After their bout of exercise they would have refed and recovered. Your body should be set up to perform exercise without the need for an injection of sugar.

      However, if the intensity of your workout dictates that cabs would be a useful energy source, you could consider having them as you train. A banana would suffice here, or something like dextrose powder which can be added to a workout drink may be more convenient.

      Personally, I have some form of easily digested protein (either whey or BCAAs) before I train, a black coffee if I need a kick, and possibly some easily digested fats (MCT oil or coconut oil).

      Having said all this, context is key. So, if a banana helps you train harder and you still see results then it is fine.

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