Carbohydrates have been blamed as the main culprit for many modern diseases, such as obesity and type 2 diabetes. However, carbohydrates is a broad group that includes many different nutrients with varying properties. So, when talking about carbohydrates, it’s important to understand specifically which carbohydrates. Is it sugars from processed foods, from fruits, longer starches from vegetables or fibre from wholegrains? If it’s not clear how these differing carbohydrates may affect the body, read on to find out!
Carbohydrates are organic compounds that are made up of carbon, oxygen and hydrogen. One of the easiest ways to classify carbohydrates is based on their chain length.
Monosaccharide – the simplest form of carbohydrate and the basic unit that makes up all other carbohydrates[A1] . Examples include glucose and fructose. Glucose is used in a lot of energy and sport drinks because it’s a readily available form of energy that the body can access quickly. Fructose is the main sugar present in fruit.
Disaccharide – a carbohydrate that contains two monosaccharide units. Disaccharides include sucrose, consisting of a glucose and a fructose molecule, which is the form of sugar people are most familiar with as table sugar. Lactose is another example, otherwise known as milk sugar.
Oligosaccharide – a carbohydrate made up of around 3-9 monosaccharide units. This group is less well known, and the definition can vary. Oligosaccharides often fall under polysaccharides. Raffinose is present in beans while oligofructose, a subgroup of inulin, is commonly used in the food industry as a prebiotic.
Polysaccharide – a carbohydrate consisting of 10 or more monosaccharide units. Polysaccharides are the most diverse group of carbohydrates. They can be further divided into starches and fibres. Starches, like the other carbohydrate groups, contain units that are joined by alpha glycosidic bonds. This means the enzymes in the body can break these bonds creating monosaccharides and disaccharides that can be absorbed in the small intestine. Polysaccharides often act as energy stores; many plants, such as potatoes and wheat, are comprised of starches that vary in structure. In humans glycogen is an important storage molecule.
On the other hand, the units in fibres tend to be linked by beta glycosidic bonds. These bonds can’t be broken during digestion so pass through the small intestine without being absorbed into the large intestine. Fibre can be separated into two groups. Soluble fibre dissolves in water, and once in the large intestine can be broken down by the gut microbiota and serve as a food source. Insoluble fibre doesn’t dissolve in water; most can’t be digested by gut bacteria and so passes out of the body in almost the same state that it entered. Fruits and oats are high in soluble fibre while wholegrains and nuts are high in insoluble fibre.
Carbohydrate has several functions in the body. It is an effective source of immediate energy and an energy store. Carbohydrate can be used for the synthesis of molecules, for example DNA and glycoproteins, which are components of cell membranes. Finally, carbohydrate helps to spare protein and fat for other uses in the body[5, 6].
When talking about carbohydrates it’s crucial to understand that not all are the same and that their effects on the body and health vary. This is true for all macronutrients as they are broad categories. Humans also eat foods, not nutrients, so referring to carbohydrates in isolation and disregarding the other nutrients a high-carbohydrate food may contain reduces the applicability to real life.
Most of the calories in wholegrains, legumes and vegetables are provided by carbohydrates. These foods have a low glycaemic index (GI - discussed below), resulting in more stable metabolic changes[8, 9], and are significantly more filling than other carbohydrate-containing foods[10, 11]. This is because the carbohydrates in these foods are complex and incorporated within the matrix of the food. Additionally, these foods are high in fibre.
There are several positives to consuming fibre including keeping the digestive system healthy, preventing constipation and increasing how full a person is after a meal. These effects occur because fibre takes up space and slows digestion in the small intestine and once in the large intestine softens stools and increases their bulk. Because of fibre’s roles in the small intestine it can attenuate the rise in blood glucose and reduce the absorption of other compounds in the gut, which can have positives and negative effects.
As previously mentioned, some fibres can be fermented by the bacteria that reside in the large intestine, allowing bacteria to grow. Fibres that promote the growth of beneficial bacteria are called prebiotics. The main products of fermentation are short-chain fatty acids (SCFAs), which are fatty acids consisting of six carbons or less. Such compounds act as fuel for the cells of the colon and appear to maintain gut homeostasis. Looking at the body as a whole, SCFAs have wider anti-inflammatory properties.
When fibre intake is looked at in populations, higher fibre intakes correlate with a reduced risk of developing a wide variety of chronic diseases and with better health markers[3, 16-18]. While the properties of soluble and insoluble fibres differ, studies have yet to declare a greater health benefit towards either[3, 19]. Considering that the majority of people consume less than the recommended amounts of fibre, increasing fibre intakes, whatever the form, is desirable.
The foods referenced above also contain relatively high amounts of vitamins, minerals and phytonutrients[20-22]. Phytonutrients are chemicals from plants that while not essential may exert health benefits. There are thousands of different phytonutrients, and because of this there is still a lot we don’t know. What we do know is that the foods that contain them are repeatedly associated with a reduced risk of obesity, type 2 diabetes and many other diseases. The nutrients within them can be extracted and shown to have positive effects in cell cultures[24, 25], but in humans as isolated supplements the results are much less promising. Therefore, it’s important to get phytonutrients from wholefoods such as wholegrains, fruits and vegetables rather than a pill.
It can also explain why highly processed foods such as refined grains do not show these results, and in fact can have the opposite effects. Depending on the type and amount of processing, if the preference is palatability over nutritional quality, then nutrients can be degraded, removed or even replaced in favour of cheaper filler ingredients such as fats and added sugars. The final product can be far removed from the once-beneficial raw material. Processing is not necessarily a bad thing and is vital in modern-day society for many reasons from safety to sustainability. This can make food choice difficult. If you want to find out more about food processing, you can do so here.
Fruits are often avoided because they are thought to be high in sugar. While this is partly true, fruits are also high in vitamins, minerals and phytonutrients making them nutrient dense, and the sugar between fruits varies. As fruit is high in fibre, the digestion and absorption of this sugar is quite slow; it also explains the encouragement to consume fruits over fruit juices which have the fibre removed during processing. At worst, fruit has no association with weight gain or excessive energy intake.
The principal carbohydrates in all Huel products are provided by grains, oats and flaxseed. The grain in Huel Powder v3.0 and Huel Bar is oats while Huel Hot & Savoury contains brown rice and quinoa. This ensures the Huel range has a low glycaemic index of below 32 and is high in fibre and naturally occurring micronutrients. Huel Ready-to-drink also contains tapioca starch and brown rice flour because they’re readily soluble and contribute to the smooth texture. While the Hot and Savoury range includes lentils, black beans and vegetables (ingredients vary between flavours).
The carbohydrate in Huel Bars comes from a variety of ingredients including oats and brown rice syrup. Huel Bars are low in sugar for their product category but are higher in sugar than Huel Powder and Ready-to-drink to help bind the ingredients together and create a product with the correct texture and flavour.
Monosaccharides and disaccharides are known as simple carbohydrates, while most oligosaccharides and all polysaccharides are known as complex carbohydrates because of their structure. Simple carbohydrates are more rapidly digested and absorbed than complex carbohydrates. Simple carbohydrates tend to have a high glycaemic index (GI), which means they cause a large, rapid change in blood glucose. More information on the glycaemic index (GI) can be found here.
Glucose in the blood is important because the components of a carbohydrate must be transported to where they are needed and enter cells. One of the main hormones that is involved in this process is called insulin, which is produced and released by the beta cells of the pancreas into the blood. Insulin allows cells to increase the amount of glucose they can take up from the blood. It works alongside another hormone, glucagon, to tightly regulate blood glucose levels.
One of the main reasons for the focus on reducing carbohydrate consumption is that there are no carbohydrates that are essential and therefore required in the diet. An essential nutrient is one which is required for the body to function properly but cannot be synthesised in adequate amounts, so it must be obtained from the diet.
Contrary to carbohydrates, there are nine essential amino acids that make up proteins and two essential fatty acids that make up fats. For a 75kg (11.8 stone) adult approximately 60g of protein per day will provide a sufficient amount of all the essential amino acids. The daily protein requirement will depend on a person’s health status, activity levels and the quality of protein consumed. Fat should make up at least 10% of total calorie intake to meet the body’s essential fatty acid needs.
Protein and essential fatty acid deficiencies are rare in the Western world, especially on their own as they often co-occur with other health complications[36, 37]. After meeting these minimum requirements, based on a 75kg male with a daily calorie requirement of 2,500kcal, roughly 2,075kcal still needs to be consumed to hit 2,500kcal. So, the question is, what should be eaten to meet this calorie requirement and be healthy? Just because carbohydrates are not essential does not mean that carbohydrates do not, or cannot, form an important part of a healthy diet.
Insulin has several functions; it triggers cells to take up more glucose from the blood, but it also stops the breakdown of fat tissue. This mechanism has led to the idea that carbohydrates prevent weight loss because fat is no longer oxidised at a high rate. However, in the context of weight loss and weight gain calorie intake is far more important. It has been shown that a high-carbohydrate diet results in comparable weight loss to a low-carbohydrate diet and the people that were able to stick to their diet lost the most weight[38, 39]. Additionally, if carbohydrates caused fat gain through insulin being released, then protein would be too. This is because proteins can also result in insulin secretion, and this is comparable to carbohydrates.
One of the greatest illustrations of carbohydrates and weight comes from Cuba in the 1990s. Cuba went through an economic crisis that put severe limitations on access to food. Calorie consumption decreased, sugar cane and rice formed a significant part of the diet and as a result carbohydrate consumption as a percentage of calories increased. Nevertheless, Cubans lost weight over this period.
This is further supported by present-day hunter-gatherers who give an insight into what our ancestors were likely to have eaten. Depending on the environment and season, early Homo sapiens ate whatever was available, meaning a variety of different food sources and amounts. One such hunter-gatherer population are the Hadza of North Tanzania, who get 65% of their calories from carbohydrates. Looking at this population, the prevalence of obesity is less than 5% with a low-energy density diet consisting of largely tubers, fruits and honey[43, 44]. This points towards modern foods of a high-energy density, processing and palatability as one of the culprits for weight gain rather than all carbohydrates.
Looking at the calories provided per gram, carbohydrate contains 4kcal/g, the same as protein, and fat contains 9kcal/g. Fermentable fibres supply roughly 2kcal/g. More information on how the energy value of food is calculated can be found here. The idea that carbohydrates are fattening most likely comes from the carbohydrates that are most commonly consumed in modern diets, which are highly processed and/or simple carbohydrates. The issue with foods that are high in these types of carbohydrates is that they lack satiety and are easy to overconsume[46, 47]. Once you factor in that most of these foods are also high in fat but low in micronutrients, you have foods which supply energy, but not much else. In contrast, many studies have shown that a higher carbohydrate intake is associated with a lower body weight and risk of chronic disease especially when the focus is on more complex carbohydrates from whole foods[45, 49, 50].
For a person consuming a typical Western diet, a reduction in carbohydrate intake will naturally result in a lower consumption of processed foods high in both carbohydrate and fat. It can be a simple way for a person to move towards a more satiating whole-food diet. However, it’s important to note a reduction in fat intake will do the same and reducing or eliminating food groups does not automatically mean a diet will be of a higher nutritionally quality; on the contrary, the risk of nutrient deficiencies may increase if some thought is not put into what is eaten.
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