Here’s a closer look at carbohydrates, what they are, what foods can be defined as carbs, and why they may not be as terrible as you might think.
Carbohydrates have recently developed a poor name and have been criticised both in the press, and on social media. It can be difficult to decipher between fact and fiction, as well as scientific evidence and opinion.
The idea that carbohydrates are an unnecessary evil has seen a rise in fad diet crazes and the removal or drastic reduction of carbohydrates from the diet. Diets such as keto or paleo frown upon carbohydrate consumption, and in the case of the latter, even discourage whole grain and legume consumption.
There is also wide promotion by avid fitness enthusiasts regarding the merits of protein and energy with little regard to how carbohydrates are a necessary piece of the jigsaw. Perhaps one piece of information which has been lost along the way is that not all carbohydrates are the same, and not all of them are bad.
Carbohydrates are a vital source of energy, providing our body with the fuel it needs to complete the tasks we need it to. Here, we look at the facts and why not all carbohydrates can be tarred with the same (sugar-coated) brush.
Coming up in this article
- Simple vs complex carbohydrates: important differences
- Why you shouldn’t just cut sugar from your diet
- Your gut microbiome needs complex carbs to thrive
- The human brain is powered by glucose
- Watch out for refined, added, and free sugars
- How to build a healthy, balanced meal with carbs
What are carbs?
Carbohydrates are an essential macronutrient the body requires in large amounts to run smoothly, but not all carbs are created equal.
Sugars mostly make up carbohydrates. They get their name from their chemical composition: carbon, hydrogen, and oxygen (thus carbo-hydrate). Generally, the length of the sugar chain making up the carbohydrate can determine the rate of digestion and absorption.
Historically, different populations have thrived on varying amounts of carbohydrates in their diets depending on the geography and climate, which influences access to this macronutrient.
If we take a look at historic eating patterns, in Mediterranean climes, vegetables, legumes, and nuts have always featured heavily in local cuisine, whereas tribes in the Arctic have traditionally followed high-fat, high-protein diets because fresh plant-based foods were hard to grow and forage.
However nowadays, processed and refined dietary carbohydrates are commonplace, and herein lies some important differences for long-term health.
These fast-digesting sugars can be found in complex carbohydrates, but they are also an important ingredient in processed foods.
Simple carbohydrates include monosaccharides and disaccharides. Monosaccharides are often referred to as single sugars and are the building blocks for which larger, more complex carbohydrates can be made.
Sugars such as glucose and fructose are examples of simple sugars, and so too are disaccharides, which consist of two chemically joined sugar molecules like sucrose, a combination of glucose and fructose.
Sucrose is found in many foods, and provides the natural sweetness in honey, fruit, and maple syrup. Processed foods often include refined sugars that are extracted and purified from plants, like sugar beets, sugar cane, and corn.
Many popular foods contain added sugars that increase the risk of obesity, diabetes, and heart disease. In fact, in the UK, the National Diet and Nutrition survey estimates that added sugar makes up 14% of the daily calories consumed by 11-18 year-olds.
Top sources of added sugars (NHS)
|Soft drinks||Fruit juices||Alcohol|
|Fruit yoghurt||Ice cream||Flavoured milks|
|Ready meals||Salad cream||Crisps|
Refined sugars are digested faster than complex carbs, and are implicated in weight gain and metabolic diseases. Carbohydrates are confused with refined sugars, but as we’ll explain below, complex carbohydrates are important for health.
These sugars naturally occur in whole foods and take longer to digest. Many have prebiotic properties that nourish beneficial bacteria in the gut.
Complex carbohydrates are made up of more than two sugar molecules. They can be split into two categories: oligosaccharides and polysaccharides.
Oligosaccharides are short carbohydrate chains, usually between 3 and 10 sugar molecules long, whereas polysaccharides are long-chain carbohydrates which may contain hundreds, or even thousands, of monosaccharide units.
Polysaccharides can vary in structure and composition. The chains can be long, straight or branched, and may contain different types of molecules (monomers). These differences can make them either digestible (starch) or indigestible (fiber).
Complex carbohydrates consist of long sugar chains that are harder to break down and take longer to digest. They are found in whole foods, which are also high in fiber and nutrients, meaning they have added nutritional benefits and can make us feel fuller for longer.
|Classification||Type of sugar||Food sources|
|Monosaccharides||Glucose, fructose, galactose||Fruit, vegetables|
|Disaccharides||Sucrose, lactose||Table sugar|
|Oligosaccharides||Raffinose||Beans, brussels sprouts, wholegrains|
|Fermentable polysaccharides||Amylose, amylopectin||Grains, legumes, potatoes|
|Non-fermentable polysaccharides||Cellulose, pectin, lignin||Cereal bran, whole grains, edible plants|
Don’t just cut carbs from your diet
Carbohydrates, along with fats and protein, are three essential macronutrients that the body needs to function.
Carbohydrates are the human body’s main source of energy, yet, they are also blamed for the rise in obesity, metabolic syndrome, and cardiovascular disease. But there are distinct differences between the different carbohydrates we consume.
In fact, it’s processed and refined carbs which have given all carbohydrates a bad reputation. Refined carbs and processed foods with high amounts of added sugar have had all their fiber and essential nutrients taken away.
Therefore, they can be broken down into glucose and released quickly into the bloodstream. The quick release means there is a spike in blood sugar levels, and you may even feel hungry again a short while after consuming them.
Carbohydrates are a broad category of macronutrients. Rather than just eliminating all of them from your diet, think about both the quality and quantity of the carbohydrates you consume.
There is no doubt that cutting or reducing added sugar from the diet is highly beneficial, but the same cannot be said for the fiber and nutrients some complex carbohydrates provide, like fiber, polyphenols, and essential vitamins and minerals.
Equally, replacing carbohydrates with other macronutrients, such as protein or fats, can negatively impact the function of your brain (something we’ll explain a bit later).
Complex carbohydrates that make up whole foods like grains, vegetables, legumes, fruit, seeds, and nuts have many important benefits for health because they contain complex sugars the body can’t digest. You can read more about it in our article on fiber.
☝️TIP☝️: We’ve included simple strategies to get more whole foods into your diet at the end of this article.
Your gut microbiome needs carbohydrates
Some carbohydrates can’t be digested by the body. Instead, they travel to the colon where they provide important sustenance for your gut bacteria.
Bifidobacterium and Lactobacillus are two examples of important probiotic bacteria found in the gut and in cultured foods. They feed on the complex sugars, which are often referred to as dietary fibers, or prebiotics.
Probiotic and beneficial bacteria that ferment carbohydrates have a range of benefits for digestive and overall health. They support a healthy immune system, deter pathogens, and produce vitamins and short-chain fatty acids that maintain the gut lining.
Interestingly, artificial sweeteners have long been promoted as healthier alternatives to natural sugar. However, a recent study indicates that artificial sugars, like sucralose, aspartame, and saccharin, are more likely to cause glucose intolerance (high blood sugar level) than pure glucose or sucralose.
The microbiome may play a role in this: artificial sweeteners can alter your gut microbiota by reducing Lactobacillus and increasing the abundance of Bacteroides. The effect these artificial sweeteners have on the gut microbiota is the opposite of the effect of natural sugars.
Human beings need to consume at least 30g of fiber per day to see and feel its benefits. Much of the fiber found in plant-based foods helps to feed the abundance of bacterial cells living in our gut, known as prebiotics.
High fiber diets aren’t complicated to implement. Whole foods are available in all supermarkets, think fruit and vegetables. Let’s face it, this aisle is probably the most colourful and enticing of them all.
You can use whole grains, legumes, pulses, and starches as a base for your meals and build upon these, adding lots of fruits and vegetables alongside protein and fats. Incorporating more fiber into your diet doesn’t need to be boring, nor do you need to be like Popeye and consume only spinach leaves.
☝️TIP☝️: levels of probiotic and beneficial bacteria, butyrate, and microbiome diversity are all measured by the Atlas Microbiome Test.
Carbohydrates and cognitive function
Our brains are complex organs which require energy to work. Without it, you can’t perform at your very best.
The brain mostly relies on glucose as its energy source, and so to work effectively, the glucose supply to the brain needs to be continually renewed, particularly as stores can be depleted within ten minutes.
In fact, the brain needs about 120 grams of glucose per day, and without it, cognitive function is impaired. Research has shown that both children and adults who have not eaten can see improvement in their episodic memory just by drinking a glucose drink, highlighting just how powerful the source of energy is.
Refined carbohydrates like bread, cakes, pastries, sweets, and sugary drinks may play a role in the development of metabolic diseases, but they can also have a major effect on our neurocognitive function.
In fact, deficits in our cognition may be noticed before any of the other effects associated with the consumption of refined carbohydrates such as obesity. Therefore, switching refined carbs for healthier ones, such as whole grains, nuts, and fruit, are good for the brain.
Why is sugar bad for you?
Added, refined sugars in readily available processed foods are a health risk, not fruit, vegetables, and grains.
It’s fair to say that when we mention carbohydrates, most people think of sugar. Although they may be partly correct, as this article shows, not all carbohydrates are bad. In fact, some are essential for the health of many of our body systems.
When we talk of “bad” sugar, we are mostly referring added sugar or free sugars that are used by manufacturers to flavour foods: these are the ones we need to become more conscious of when selecting foods to eat.
Sugars which occur naturally, like those in fruit, vegetables, and milk, are not harmful like free sugars, and we don’t need to reduce our intake of them. Nowadays, most individuals consume more added sugar than the recommended amounts.
For example, it’s easy to exceed the daily recommended limit for added sugars: a soft drink with lunch, a chocolate bar for your afternoon snack… When you add it all up, it’s easy to exceed the limit.
It’s these added sugars that can be detrimental to our health, especially when you look at the science. Studies highlight significant links between diets high in refined sugars and obesity, cardiovascular disease, and diabetes.
Diets high in sugar put stress on the body’s mechanism for regulating blood glucose levels. This is managed by insulin, a hormone that signals to the liver, muscles, and fat cells that it’s time to store sugar as energy.
Before, most of our sugars came from whole carbohydrates (like fruit and vegetables): they took time to be digested and were used quickly as fuel. Nowadays, we have more free sugars than our body needs, so it stores them in our fat cells.
Eventually, when we consume too much sugar regularly, the fat cells run out of space to store this excess energy. When there’s too much free sugar entering the bloodstream directly (because it digests quickly), the effectiveness of insulin progressively declines. This is called insulin resistance, and it’s a precursor of diabetes that is often detected in obese people.
When the body is insulin resistant, it means that too much glucose is circulating in the bloodstream (and not being stored as energy). This is bad because high levels of glucose causes damage to the blood vessels.
This is why having too much refined sugar is “bad”: it is associated with insulin resistance, obesity, diabetes type 2, and cardiovascular disease, all of which are preventable and serious diseases that are common in developed countries.
Make a healthy meal with carbs
You can easily reduce your "free sugar" intake by switching to a healthier, high-fiber diet.
We like to follow the dietary guidelines by the British Association for Nutrition and Lifestyle Medicine. They suggest we eat the rainbow, and incorporate at least five portions of vegetables and two fruit per day in many different hues and colours.
|Type of food||Examples||How much|
|Root vegetables, whole grains||Brown rice, whole oats, quinoa, parsnips, carrots, potatoes||25% of your meal|
|Leafy greens, salads||Broccoli, cabbage, spinach, kale, salad leaves||25% of your meal|
|Vegetables||Cauliflower, onions, courgette, sweetcorn, peppers||25% of your meal|
|Protein||Fish, poultry, eggs, pulses, red meat||25% of your meal. Limit your consumption of red and processed meat|
|Oil||Olive oil, avocado, nuts||Use olive oil for cooking and seasoning|
|Beverages||Water and tea||Hydrate with water. Avoid juices and soft drinks.|
|Fruit||Apples, strawberries, pears, oranges, grapes, cherries, blueberries, plums, peaches||1-3 palm-sized portions of fruit per day|
- Benton, D. (2018). Carbohydrates, Mood and Cognition. Abbot Nutrition Research Conference: Carbohydrates Through the Life Cycle and Across Tissues.
- Davani-Davari, D et al. Prebiotics: Definition, Types, Sources, Mechanisms and Clinical Applications. Foods: 8(3).
- Ludwig, D, S et al. (2018). Dietary Carbohydrates: Role of Quality and Quantity in Chronic Disease. BMJ: 361.
- National Health Service. (2019). Top Sources of Added Sugar in Our Diet.
- O’Callaghan, A and van Sinderen, D. (2016). Bifidobacteria and Their Role as Members of the Human Gut Microbiota. Front Microbiol: 7(925).
- Singh, R, K et al. (2017). Influence of Diet on the Gut Microbiome and Implications for Human Health. Journal of Translational Medicine: 15: 73.
- Swan, G, E et al. (2018). A Definition of Free Sugars for the UK. Public Health Nutrition: 21(9), pp 1636-1638.