Weight Loss Essentials: Explaining the Roles of the Three Major Nutrients and How They Contribute to Weight Gain

The Three Major Nutrients:
Which is most likely to cause weight gain—
carbohydrates, fats, or proteins?

Humans require energy to sustain life, obtained through eating. Yet it may seem remarkable that some animals (such as cattle and horses) thrive solely on grass, whereas humans cannot.
Four substances in food provide energy: carbohydrates, proteins, fats, and alcohol. The first three are typically termed macronutrients, as they are essential for sustaining daily human activity.

Although alcohol also provides energy, it cannot be classified as a nutrient. We can live perfectly healthily without it, and its negative effects far outweigh any benefits. Therefore, we shall not discuss alcohol here.

Let me briefly outline the three major nutrients.

First, carbohydrates. Widely distributed and abundantly stored in nature, carbohydrates are arguably the most economical nutrient and serve as the body's rapid energy source, supplying the bulk of our daily energy requirements.

Indeed, the white sugar we commonly consume, staple foods, and even fruits contain substantial carbohydrates. Examples include bread, rice, rice noodles, wheat noodles, maize, sweet potatoes, ice cream, marshmallows, watermelon, cantaloupe, and even beverages and fruit juices. Essentially, one may understand carbohydrates as sugars; thus, foods like sweet potatoes, white sugar, and watermelon are fundamentally sugars.

As covered in secondary school biology, the core structure of sugars comprises carbon, hydrogen, and oxygen. Based on their degree of polymerisation, carbohydrates can be categorised into three types: monosaccharides, disaccharides, and polysaccharides. Let us briefly revisit this biological knowledge: glucose, fructose, and galactose are monosaccharides; sucrose, maltose, and lactose are disaccharides; while starch and dietary fibre are polysaccharides.

What practical use is this knowledge? Remember this simple principle: different sugars are digested and absorbed at varying rates. Monosaccharides and disaccharides are absorbed relatively quickly, while polysaccharides take longer. Consequently, monosaccharides and disaccharides cause blood sugar levels to rise rapidly. This is why, when we are ill and expending significant energy, hospitals administer glucose injections to provide a swift energy boost. Sports drinks also contain glucose. Polysaccharides, however, must first be broken down into disaccharides and monosaccharides before they can be effectively absorbed by the body.

Now, let's discuss protein. If we liken the human body to a building, protein serves as its primary construction material. Muscles, blood, nerves, and hair are all composed of protein. In fact, the lean meats we commonly consume (the fatty parts being fat), seafood, eggs, milk, and soy products are all rich in protein.

Proteins are composed of amino acids. Each protein is formed from a unique sequence of amino acids. As each amino acid possesses distinct functions, each protein performs specific roles. For the human body, nine amino acids are essential (with histidine being essential for infants), as we cannot synthesise them ourselves and must obtain them from food. Additionally, there are eleven non-essential amino acids that the human body can synthesise.

If the protein in our diet contains all essential amino acids, it is termed a complete protein. Meat, dairy, and eggs provide complete proteins. Proteins lacking essential amino acids are called incomplete proteins, and most plants provide incomplete proteins, such as maize, vegetables, and seeds. Only a very small number of plants provide complete proteins, such as soybeans. Therefore, strict vegetarians should consume a variety of legumes to ensure the body's requirements for essential amino acids are met.

Protein is not a primary contributor to energy production. However, when dietary carbohydrate intake is insufficient, the body will mobilise protein through gluconeogenesis to produce glucose for energy, thereby meeting its own demand for glucose.

Now, regarding fats. To be precise, fats are lipids in solid form, while oils are lipids in liquid form. For the sake of clarity for readers of this book, both are collectively referred to as fats.

Fats comprise fatty acids and glycerol. Sources include various fatty meats, cooking oils, and the oils found in nuts such as peanuts and cashews.

Essential fatty acids warrant mention here, as the human body cannot synthesise them and must obtain them from food. The two most crucial essential fatty acids are Omega-3 and Omega-6 fatty acids. Vegetable oils contain substantial amounts of Omega-6 fatty acids, while deep-sea fish such as salmon and cod are rich in Omega-3 fatty acids. Modern diets commonly lack Omega-3 fatty acids, as we consume considerable amounts of cooking oils but rarely eat deep-sea fish.

As previously discussed, weight gain occurs when energy intake exceeds energy expenditure, leading the body to store excess energy as fat.