Macros 1.0: What are carbohydrates and why do we need them? Or don’t we?

We need energy to survive. How much energy or how many kcalories you need, depends on your energy expenditure. We obtain our energy from 3 main macronutrients in food: protein, carbohydrates and fats. There is actually a fourth macronutrient which is alcohol, but I’ll talk more about that later. Each macro provides a different number of kcalories per gram. Protein and carbohydrates provide 4 kcals per gram, fats 9 and alcohol 7. This blog explores what carbohydrates are, what their use is and why they’ve seemingly earned themselves such a bad rep.

‘Carbs’ – it’s become a bit of a dirty word as of late. The low carb diet has never been more popular and we get a lot of requests at FFF from people who’d like to cut down on carbs in their diet because they’ve heard from somewhere or someone that these are going to make you fat.

Let’s challenge this a little shall we through simple science?

Carbohydrates provide the lowest number of kcalories per gram, only 4, and there’s no beating the Law of Thermodynamics when it comes to weight loss. If you consistently eat less kcalories than you burn, you will lose weight, no matter where these kcalories come from (as mentioned in our first myth-busting video). Carbohydrates have their place in a healthy balanced diet, and should not be so quickly shamed. They mainly serve as an energy source but do also have some other important functions. The structure of our DNA is made up of sugar and our brains prefer glucose as its source of energy. Some carbohydrates can also provide us with essential vitamins and minerals. Saying this, they do come in various different forms and some can be more useful to us than others.

What are carbohydrates and what happens when we eat them?

Carbohydrates are in pretty much everything, the obvious things like bread, pasta, sweets and chocolate, but also fruit, vegetables and many processed foods like sauces, soups and ready-made meals. All carbohydrates are chains of a combination of 3 simple sugars or monosaccharides: glucose, fructose and galactose. Fructose is sweeter than glucose and found in fruits, honey and some vegetables whereas galactose is only found in milk. Two monosaccharides linked together form a disaccharide: glucose and fructose form table sugar for example. Anything more than that is an oligosaccharide (3-10 monosaccharides, found in beans, peas and whole-wheat grains), or a polysaccharide (more than 10, found in grains, potatoes and cereal). Mono- and disaccharides are forms of simple or fast sugars and oligo- and polysaccharides are complex carbohydrates or starch.

All carbohydrates are broken down to the 3 monosaccharides: glucose, fructose and galactose because only these can cross the gut wall to be absorbed into the bloodstream. The Glycemic Index ranks foods based on how quickly this happens. Each food has a ranking from 1-100 where 100 is pure glucose and has the fastest absorption rate. Generally speaking high GI foods release glucose quickly and tend to be shorter chain carbohydrates. Low GI foods are often complex carbohydrates and release their glucose into the blood slowly, providing a steady supply of energy. Our body responds to glucose with the release of insulin which allows glucose to move into cells. The amount of glucose in the bloodstream is tightly regulated by the production of this hormone to avoid glucose levels varying too much.

All carbs are created equal but some provide more bang for your buck

Important to note is that all carbohydrates contribute the same to your energy balance. Carbohydrates in chocolate will not make you put on weight any quicker than carbohydrates in a sweet potato. If your goal is fat loss sweet potato might be the better choice of carbohydrate, but gram for gram their contribution to your calorie deficit or surplus is the same. The problem with sugary foods like chocolate for example is that they do not satiate. It’s really easy to eat 500 kcalories of chocolate (this is the average 100g chocolate bar) without feeling full, whereas eating the equivalent in sweet potato translates to over half a kg of sweet potato, which is a lot harder to eat without feeling full. Sweet potato is a better choice of carbohydrate for fat loss in the sense that it provides vitamins and minerals, fibre and adds volume to your meals. The last 2 also help to make you feel full for longer which is great if you’re in a kcalorie deficit.

I’m not saying you shouldn’t have chocolate if you are on a diet, because let’s be honest life without chocolate would be a sad one. The trick is simply to control your portions. The problem with sugar is not that the sugar itself makes you put on weight, but rather our eating behaviours associated with it. We tend to overeat it and therefore this puts you at risk of getting into an energy surplus. It is the energy surplus that makes you gain weight, not the foods that created the surplus. So, if the portion is controlled it is certainly possible to eat some chocolate and still lose weight.


Some carbohydrates cannot be metabolised, these are called fibre. Fibre is only found in plants. Even though we cannot break it down, fibre is an essential part of a healthy diet. It helps bowel movement and is food for our microbiome: the bacteria in our gut. These bacteria can produce useful compounds that help us digest our food but also some that improve our health such as short chain fatty acids. The exact mechanisms aren’t known but a high fibre intake is linked to a lower risk of bowel cancer, heart disease and type 2 diabetes.

Fibre is found in unrefined grains, fruit, vegetables, peas, beans and pulses, potatoes with skin, nuts and seeds. Fibre can either be soluble or insoluble but most vegetables and complex carbs will contain a bit of both. Insoluble fibre adds bulk to the stool which helps movement through the digestive tract, whilst soluble fibre forms a gel which slows down absorption of nutrients like glucose. In this way fibre helps you feeling full for longer.

Processed foods often contain no fibre at all because they are made with refined, rather than whole carbohydrates. Fibre, and a lot of other micronutrients are found in the outer shell of a grain and refining a grain involves removing this shell.

The recommended daily intake for fibre is 30g per day for adults, but on average we tend to eat much less. The fibre content varies per food, but by making simple changes you can ensure to get enough: always go for whole grain options and try to incorporate vegetables and fruit in every meal and snack.

How do our bodies use glucose?

As mentioned, the favourite fuel of all our cells, muscle and brain cells predominantly, is glucose. Our bodies tend to convert most of the galactose and fructose to glucose because they are less useful as an energy source. Some cells can only use glucose, red blood cells for example, but most tissues can use fats as well.

Our muscles always use a combination of both carbohydrate and fat for energy. Glucose can be used with or without oxygen but to use fat, oxygen is always needed. This is why during intense exercise, if your oxygen supply can’t keep up with your energy expenditure, for example when you are sprinting, our muscles switch to using mostly carbohydrate without oxygen. A side effect of burning carbohydrates without using oxygen is that it produces lactic acid as waste. This is the burn that you feel at the end of your sprint.

Our bodies can store glucose in the form of glycogen in our muscles and liver, however, compared to the almost endless capacity of our bodies to store fat, this is very limited, sitting at only about 500 grams. To store glucose water is needed, which can add a lot of weight and makes storing much of it impractical. This is why our bodies tend to store excess energy as fat, rather than glycogen as this is much more efficient. It also explains why anyone who goes on a low carb diet loses a lot of weight instantly, even though this is just water weight.

Why do carbohydrates have such a bad name?

Unlike fats and protein carbohydrates are what we call a “non-essential nutrient”: this means our bodies can synthesise glucose from protein and fats. However, this is a very narrow minded view on nutrition and completely ignores the other nutrients carbohydrates often pack in: vitamins, minerals and fibre. Food is more than macros and micros. It is true that we tend to eat too much sugar and refined grains, which is carbohydrate, but this has more to do with our food choices and feeding behaviour than carbohydrates per se. No nutrient is useless, not even sugar, because food is also about enjoying life sometimes. But to maintain health, both physically and mentally, balance is paramount.

Robin Swinkels

FFF Nutritionist