Weight Loss Key: Fat Is Most Likely to Cause Weight Gain – The Truth About Staple Foods and Low-Carb Diets

So, which of the three major nutrients is most likely to cause weight gain?
The answer is fat. There are two primary reasons for this:

First, in terms of energy density.
Although carbohydrates, proteins, and fats all provide energy, the amount of energy per unit varies significantly. One gram of carbohydrate and one gram of protein each supply the body with 4 kilocalories of energy, whereas one gram of fat provides 9 kilocalories – more than double that of the other two. Given its immense energy density, consuming fat in equivalent quantities naturally makes it easier to exceed daily energy requirements.

Secondly, consider the efficiency with which they are converted into body fat.
While the body can store any surplus of these nutrients as fat, the efficiency of this storage process varies significantly.
For instance, dietary fat converts into body fat almost instantaneously, requiring minimal additional energy expenditure for storage. This is readily understandable, as fats share similar molecular structures, making dietary fat readily adaptable for bodily fat reserves.

Following digestion and absorption, carbohydrates must first be broken down into simple sugars. To be converted into body fat for storage, they undergo a series of transformations, as sugars and fats belong to distinct chemical categories. This conversion process consumes energy, typically requiring an additional 20% energy expenditure. Converting protein into fat involves an even more complex intermediate process, consuming significantly more energy – approximately 50% energy loss occurs.

However, since sugars and fats share a basic structure of carbon, hydrogen, and oxygen, their composition is relatively similar. In contrast, proteins are composed of amino acids. Consequently, sugars are more readily stored as fat than proteins and consume less energy in the process.

This is somewhat analogous to withdrawing cash from a bank card at an out-of-town branch. While transactions within the same bank may incur no or minimal fees, cross-branch withdrawals often attract higher charges.

Consider another straightforward example: suppose my daily energy expenditure is 2000 kilocalories. After dinner, I've consumed precisely 2000 kilocalories, balancing intake and expenditure for the day, correct? Now suppose a friend invites me out for a late-night snack, and I consume an additional 100 kcal. If these 100 kcal are entirely from fat, over 90 kcal will likely be converted into body fat. If the snack is 100 kcal of carbohydrates, 70–80 kcal might be converted into fat. If it's 100 kcal of protein, perhaps only 50 kcal would be converted into body fat.

Thus, different nutrients convert to fat at varying efficiencies. In real life, those who favour high-fat foods tend to gain weight more easily, yet many shed pounds simply by altering their dietary structure.

Staple Foods:
Does avoiding staple foods lead to weight loss?

As mentioned earlier, among the three macronutrients, fat is most likely to cause weight gain due to its high energy density and efficiency in converting to body fat.

Given this, why has the low-carbohydrate diet approach—avoiding staple foods for weight loss—become so prevalent? Let us now examine whether eliminating staple foods is truly effective for weight management.

Firstly, avoiding or reducing staple foods constitutes a low-carbohydrate dietary approach, commonly known as the ‘Atkins Diet’ or sometimes termed the ‘meat-based weight loss method.’ This approach gained popularity in the United States during the 1970s and 1980s. This approach strictly limits daily carbohydrate intake, requiring the replacement of staple foods like rice, bread, rice noodles, and steamed buns in one's daily diet with meat, seafood, eggs, dairy, and soy products.

However, as mentioned earlier, among the three major nutrients, carbohydrates are the primary source of energy for humans. If one avoids staple foods, the body will mobilise more body fat or dietary fat to break down into fatty acids for energy. During this process, insufficient carbohydrate supply leads to inadequate oxaloacetic acid production, preventing complete oxidation of fatty acids. This results in the formation of intermediate metabolic byproducts known as ketone bodies. If ketone bodies accumulate excessively without timely oxidation, blood ketone levels rise, prompting the body to expedite their elimination. Excess ketones are primarily excreted via urine, hence the term ketosis.

As ketone bodies are metabolic byproducts of fat breakdown, they carry significant energy. Thus, bodily fat is broken down and expelled along with its stored energy, naturally reducing fat stores. Moreover, without consuming staple foods, bodily water is also expelled as sugar reserves diminish. Consequently, weight naturally drops rapidly. (You've surely heard of the “ketogenic diet”? It's another form of low-carbohydrate eating, though this weight-loss approach not only strictly limits carbohydrate intake but also regulates the ratio of fat and protein consumption.)