You will often hear that a calorie is a calorie and that it doesn’t matter whether you eat a chocolate bar or 4 buckets of broccoli, if they contain the same number of calories they will have the same effect on your weight. Have we become so focused on calories that we forgot about nutrients? It is true that all calories have the same amount of energy. One dietary calorie contains 4.184 kilojoules of energy and as such, from a numbers perspective, a calorie is a calorie. However when it comes to the human body, it is not that simple. The highly complex biochemical systems that make up the metabolism, showcase intricate processes that regulate energy balance. Varying foods undergo different biochemical pathways, of these; some are highly inefficient and allow energy in the form of calories, to be lost as heat. Different macronutrients, carbohydrates, proteins or fats, have varying impacts on hormones and hunger levels. As a result, it is important to understand and consider that the types of foods we eat. As the quality of the calories we consume can have a huge impact on when, what and how much we eat.


The body can differentiate between fructose and glucose, although they have a very similar chemical structure and formula and they weight exactly the same. Despite appearing so similar, the body metabolises these two sugars completely differently. Fructose can only be metabolised in the liver whilst glucose is metabolised in tissues throughout the body. The particular metabolism of each of these sugars has an effect on hunger and satiety levels. Fructose does not stimulate the satiety centres of the brain to the same extent as glucose and as a result does not encourage the same feelings of fullness. On top of this fact, fructose has been studied to increase ghrelin levels more than glucose. Ghrelin is known as “the hunger hormone” due to that fact that it increases before a meal and normalises after a meal. Therefore fructose has a greater impact on hunger levels than glucose. Evidence shows that excess consumption of fructose found in sugar sweetened beverages and other sweets can cause increases in abdominal fat, increase triglyceride levels and insulin resistance. Fructose found in its natural state, in the form of fresh fruit in a fibre matrix, does not have the same effect due to other factors such as fibre and water content which add bulk and increase satiety. Therefore, despite both molecules having similar structure they switch on different hormonal processes which have differing effects on metabolism.


Satiety plays a key role in controlling the portions of food eaten, which assists with optimal weight management. It is much easier to overeat on foods that are high in simple sugars and fats due to the palatability and the energy density of foods high in these macro-nutrients. Similarly, foods high in fibre and water are much harder to consume in excess due to the effect that these factors have on satiety levels. There are many factors that determine the satiety of different foods, which is measured on a scale called the satiety index. The satiety index is a measure of the ability of foods to reduce hunger, increase feelings of fullness and reduce energy intake for the next few hours. Therefore if foods eaten contain a low satiety index, one will feel hungry quickly after eating them and this will result in over-consumption of calories. The opposite is true for foods high on the satiety index. Potatoes rank as one of the foods highest on the satiety index and as a result, leave one feeling full and satiated and do not lead to excess calorie consumption.


The glycaemic index GI is a measure of how quickly a food raises the blood sugar level. Foods that cause a rapid spike in blood sugar levels cause an increase in insulin levels. Insulin is the hormone known as “the boss of fat” and at high levels, this hormone can increase fat storage and increase appetite. As a result, foods that have a high GI level, can increase appetite and increase fat storage. Refined carbohydrates tend to be low in fibre and they get digested and absorbed quickly, leading to rapid spikes in blood sugar. The fibre content, water content and sugar content of a food has a direct effect in the GI level of that food. Boiled baby potatoes have a lower GI due to their fibre and water content and as a result can be included in a healthy balanced diet. The type, quantity and distribution of carbohydrates eaten plays an integral role in the metabolic repercussions that result. Not all carbohydrates are equal, therefore the calories they contain, are not equal. It is important to choose carbohydrates that have a lower GI level to ensure better blood glucose control.

Different calorie sources can have vastly different effects on hunger levels and the hormones that control food intake. Calories play an important role in weight management and being conscious of the calories consumed in the diet is a key factor in optimising one’s weight. However, the quality of the calories and the effect that the foods eaten have on hunger and hormones must also be considered when making healthy food choices.

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