Carbs make you fat right?

Carbohydrates, or carbs as all hipsters and other cool people refer to this macronutrient, is a bit of a dirty word lately. The low carb diet has never been more popular.  The universal fear about this nutrient seems to be its capacity to cause fat gain. The ketogenic diet is the latest diet craze and if you haven’t tried it you’re losing out on some serious fat loss gains. Or so they say.

However, carbohydrates provide the lowest number of calories per gram, only 4, and there’s no beating the Law of Thermodynamics when it comes to weight loss. If you consistently eat less calories than you burn, you will lose weight, no matter where these calories come from. 

Carbohydrates can have their place in a healthy balanced diet. They mainly serve as an energy source as carbohydrates are the preferred, and only to some, fuel of our cells. Furthermore the structure of our DNA is made up of sugar and some carbohydrates pack important vitamins, minerals and fibre. Carbohydrates come in many different shapes and sizes and some are 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 in fruit and vegetables and many processed foods like sauces, soups and prepared meals. Anything that’s sweet will probably contain some sort of carbohydrate and plants are pretty much just carbohydrate.

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. Galactose is only found in milk. 2 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 whole wheat grains) or a polysaccharide (more than 10, found in grains, potatoes and cereal). Mono- and disaccharides are simple or fast sugars and oligo- and polysaccharides are complex carbohydrates or starch. All carbohydrates are broken down during digestion to their basic units, or monosaccharides: glucose, fructose and galactose, because only these can cross the gut wall and be absorbed in the blood stream. 

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 are shorter chain carbohydrates. Low GI foods are complex carbohydrates and release their glucose into the blood slowly, providing a steady supply. Our body responds 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 to vary too much.

All carbohydrates 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 kcal of chocolate (this is the average 100 g chocolate bar) without feeling full. Eating the equivalent in sweet potato translates to over half a kg 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 calorie deficit.

I’m not saying you shouldn’t have chocolate if you are on a diet. I think life without chocolate would be sad. The trick is to control your portions. The problem with sugar is not that the sugar itself makes you put on weight, but rather our eating behaviour. We tend to overeat 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 portion is controlled it is certainly possible to eat some chocolate and still lose weight.

The other thing carbohydrates provide best: fibre 

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 (yes that means better poo), soluble fibre forms a gel in the digestive tract which slows down absorption of nutrients like glucose, this 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. This is another reason why sweet potato is generally speaking a better choice of carbohydrate than chocolate. Chocolate contains no fibre. 

The recommended daily intake for fibre is 30 g 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 cells use carbohydrates?

As mentioned, the favourite fuel of all our cells, muscle and braincells 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 carbohydrate 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, only about 500 grams. To store glucose you also need water, 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, 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 water weight.

So is the bad rep of carbs deserved?

Unlike fats and protein carbohydrates are what we call a “nonessential nutrient”: this means our bodies can synthesise glucose from protein and fats. However, is a very narrow minded view on nutrition and completely ignores the other nutrients carbohydrates often pack: 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. To maintain health, balance is paramount.