Saturday 20 January 2018

'You can't ignore the sugar content' - This is how your body digests juices, smoothies and fruit


Thalia Heffernan enjoying a smoothie on Grafton Street, Dublin
Thalia Heffernan enjoying a smoothie on Grafton Street, Dublin
Dietitian Orla Walsh

Orla Walsh

An apple, a carrot, an orange and some strawberries - dietitian Orla Walsh explains how the body digests them when juiced, made into a smoothie or eaten whole.

What is the digestive system?

The simplest explanation is that the digestive system is a fancy muscular tube with fancy organs attached to it. The gut muscle is always contracting. It runs from our mouth all the way down to our bottom. It's extremely long - about five or so average humans in length. In fact, it's so long that it's quite amazing that it manages to fit inside of us!

Food is the tasty carrier bag containing the nutrients needed to keep us well. It provides us with large nutrients like carbohydrate, protein and fat, as well as smaller nutrients such as vitamins and minerals. Proper digestion of food needs to occur to break down the food we eat, to allow us access to the nutrients needed for optimal health and wellness. Food is more than just nutrients that keep the body ticking over: it's also the fuel for the continuous maintenance work that goes on.

Dietitian Orla Walsh
Dietitian Orla Walsh

Most people are surprised to hear that our digestive system is made up of more than just our mouth, stomach and intestines. It also includes the liver, pancreas and gallbladder. Food follows a path from our mouth to our stomach, into our small intestine, before making its way into our large intestine. It then exits our body through our rectum and anus. Each section is controlled by junctions and muscles, so that the food is moved along the gut in a controlled fashion. Along this route, food is mechanically and chemically broken down, so that nutrients can be absorbed into our body. When the leftovers of this hits the large intestine, the masses of 'good bacteria' take over and finish off digestion. The waste then exits!

The interesting thing is that the gut and the brain are so closely connected and communicate so readily with each other. For instance, the gut will tell the brain when someone's full and the brain will tell the gut what it's thinking - if you think about chocolate, you might start salivating. If you think of someone or something that is making you nervous, you may feel nauseated. What's more, the vast majority of serotonin - the hormone related to mood - is found in the gut, not the brain. (It's no wonder the gut is considered the second brain.)

Let's focus in on the journey carbohydrates take when they enter the body.

Carbohydrates provide us with sugars, starch and fibre. Carbohydrates are considered to be simple or complex, depending on how long they are. Simple carbohydrates include sugars found naturally in foods such as fruit, vegetables, milk, yoghurt and soft cheese. They also include the less healthy sugars called 'free sugars' that are found naturally in fruit juice and honey, as well as added to foods. Complex carbohydrates provide us with starch and fibre, which are found in the likes of oats, potatoes, rice and legumes.

Green smoothie
Green smoothie

We start to digest carbohydrates in our mouth. Our mouth and our stomach have similar roles: they both mechanically break down food in order to chemically break down food. First, we mechanically break down the carbohydrates with our teeth into small pieces to allow for adequate chemical breakdown. The digestive juices get to work and turn the large molecules of food into smaller molecules. When the food leaves our stomach, it enters the small intestine. Some more chemical digestion, including digestion of carbohydrates, occurs here. The digestive juices are provided by the organs such as the pancreas and liver, as well as by the intestine itself. Again, larger molecules of carbohydrate are digested into smaller molecules of carbohydrate, which are then absorbed into the body through the muscular walls of gut. The nutrients subsequently get relocated to other parts of the body for storage or further chemical change. Hormones and nerves control a lot of the digestive process. The smaller molecules of carbohydrate enter our bloodstream and end up in the cells of our body to be used as energy. If we eat more carbohydrate than we need to fuel our activity levels, the excess is stored as fat.

Although the smaller molecules of carbohydrate are absorbed into our body from the gut, the leftovers travel to our large intestine. It's within the large intestine that water from this waste is reabsorbed back into the body, to prevent diarrhoea. The large intestine is the home of kilogrammes worth of 'good bacteria'. They munch on some fermentable carbohydrates; they take some of the energy from this these carbohydrates and use it as food, while the rest is given to the cells of our gut and to our body as extra fuel. The diversity of our diet helps to encourage diversity of our gut bacteria. On the flip side, poor diets result in poor diversity and problems with gut function. The rectum then stores the stool until it pushes it out of the body during a bowel movement.

So, now that you understand the process of digesting carbohydrates, you may understand the process of digesting the likes of an apple, a carrot, an orange and five strawberries.


What happens when you make a juice or smoothie with all the ingredients?

When it comes to how quickly something like fruit and vegetables are absorbed, it depends on a number of factors. For example, juice will be absorbed quicker into the body than smoothies due to the lack of fibre within juice. Juice is simply the sugar-containing water from the fruit, while smoothies are the whole fruit blended. So in this example the fruit and vegetables would add up to 177kcal but the juice would have minimal fibre, while the smoothie would contain 10g fibre.

Smoothies will be absorbed into the body faster than whole fruit because the mechanical breakdown of the food is already complete. The body simply has to chemically break down the food before it enters our bloodstream.

There are other factors too. For example, the glycaemic index (aka GI) of a carbohydrate describes how quickly the carbohydrate is broken down and released into our bloodstream. Carbohydrate-containing foods that are low-GI are released slower into the body; foods that are high-GI are released more rapidly.

Is how you eat them important?

The GI of a food only tells us part of the story. It doesn't actually indicate how high your blood sugar levels could go up when you eat the standard portion of the individual food.

For example, the glycaemic index for watermelon is high, at 80, but a serving of watermelon has only 6g of carbs within it, so the glycaemic load is actually low, at 5.

This is important, as it would be healthier for your blood sugar levels if you spread your carbohydrate intake, which includes fruit and vegetables, across the day rather than have them all in one sitting.

The GI also doesn't consider what you're eating with the food. The amount of the particular carbohydrate-rich food eaten is a major factor in the effect it has on your blood sugar levels. So too is what you eat it with, i.e. more fibre, more fat or more protein. Therefore, foods are more often considered by their glycaemic load (GL), which considers all these factors. It gives a more real-life example of the meal's impact on your blood sugar levels.

The effects of protein and fat on GL are quite pronounced. In one study, scientists looked at the impacts of different amounts of protein and fat on blood sugar levels after drinking down a drink containing 50 grammes of carbohydrate.

A drink with 50g of carbohydrate would be found in a typical homemade smoothie so this study is applicable to a real-life scenario. None of the people they included in the study were diabetics, which would alter the results significantly. They were tested after a 10-14-hour overnight fast, so similar to having a breakfast smoothie. Into the drink they added 0, 5, 10 or 30g fat and/or 0, 5, 10 or 30g protein. Each level of fat was tested with each level of protein. At home, this would be similar to adding the likes of avocado, nuts, seeds or nut butter, or else yoghurt, milk or Greek yoghurt. They showed that gramme per gramme, protein reduced blood sugar responses by around two times more than fat. Interestingly, protein had more of an effect the bigger your waist circumference and the higher your intake of dietary fibre.

The effect of fat was greater the lower your blood sugar levels were when you woke up in the morning. It's therefore a good idea to choose whole fruit over smoothies. However, if you are having a smoothie, it's preferable to bump up the protein content by using milk instead of fruit juice or water and perhaps adding more protein such as Greek yoghurt, cottage cheese, quark, fromage frais or yoghurt. Good news for teeth too, as higher intake of fruit juices increases the risk of tooth erosion, while higher intake of milk and yogurt reduces the risk.

You can't ignore the sugar content

When sugar is in the whole fruit, it's not considered to be harmful to health. When it is juiced, it is classified as a 'free sugar' and is considered detrimental to health. Drinking down 'free sugars' can lead to an increase in total sugar intake, thus leading to an unhealthy diet, weight gain and diseases. High-sugar drinks are also a major contributor to rotting teeth.

Research shows that adults vastly underestimate the sugar content of fruit juices and smoothies. Some go on a health kick and swap fizzy drinks for fruit juices. Although juices may be perceived to be healthier, they often have a similar sugar content as fizzy drinks and don't have the same nutritional benefit of the whole fruit.

A study looked at the sugar content per standardised 200ml portion of all fruit juices, juice drinks and smoothies sold by seven major supermarkets in the UK. The average sugar content of fruit juices was 21.4g per 200ml (more than 5 tsp of sugar) and 26g per 200ml for smoothies (6.5 tsp of sugar). To put it in perspective, cola has 21.2g of sugar per 200ml (over 5 tsp of sugar).

Would you put more than 5 tsp of sugar in your cup of tea? As the aim is to have less than 6 tsp of sugar per day, it's easy for a juice to send you over your limit.

So perhaps, all things considered, it may be better to eat your fruit whole throughout the day rather than drink it! By making juice, or a even a smoothie of it, you risk sending your blood sugar levels askew.

Foods are ranked on a scale of 0 to 100, with pure glucose (a.k.a. sugar) having a value of 100. The lower a food's GI (glycaemic index), the slower blood sugar rises after eating that food.

To understand a food's complete effect on blood sugar, you need to know both how quickly it makes glucose enter the bloodstream and how much glucose it can deliver. This is called the glycaemic load (GL)

A GL of 10 or below is considered low while 20 or above is considered high.

Food                   GIGL       Food (250ml)    GIGL

Apple x 1            345        Apple juice        4413

Carrot x 1          161         Carrot juice      4310

Orange x 1         476       Orange juice      5012

Strawberries x 8 401         Strawberry juice N/A

Smoothie containing: GIGL

Apple + Carrot + Orange + 8 Strawberries  3517

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